Mécanismes responsables de la fermeture laryngée en ventilation en pression positive intermittente par masque nasal

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Membres

du jury

Dr Jean-Paul Praud: Directeur de recherche Dr Louis Gendron : Membre du programme Dr André Cantin : Membre extérieur du programme

Université de Sherbrooke

MÉCANISMES RESPONSABLES DE LA FERMETURE

LARYNGÉE EN VENTILATION EN PRESSION POSITIVE

INTERMITTENTE PAR MASQUE NASAL

par

Bianca Roy B.Sc.

Département de physiologie et biophysique

Mémoire présenté à la Faculté de médecine et des sciences de la santé

en vue de l'obtention du grade de

l+I

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TABLE DES MATIÈRES

LISTE DES ABRÉVIATIONS ... 4

RÉSUMÉ ... 5

INTRODUCTION ... 7

Mise en contexte ... 11

ARTICLE ... 14

Mechanisms of active /aryngea/ closure during non-invasive intermittent positive pressure ventilation in the non-sedated lamb DISCUSSION ... 48

Perspectives ... 53

CONCLUSION ... 55

REMERCIEMENTS ... 56

LISTE DES ABRÉVIATIONS

CT

EEG

EMG

EOG

EVC

FR

SC

TA

VAi

VAS

VPPI

vc

Ve

muscle cricothyroïdien électroencéphalogramme électromyogramme électrooculogramme éveil calme fréquence respiratoire sommeil calme muscle thyroaryténoïdien voies aériennes inférieures

voies aériennes supérieures

ventilation à pression positive intermittente

volume contrôlé volume courant

RÉSUMÉ

Une étude précédente au laboratoire a montré que l'augmentation progressive d'une

ventilation nasale conduit à la fermeture active du larynx lors des insufflations

mécaniques. En effet, cette ventilation nasale en pression positive intermittente (VPPln)

conduit

à

une diminution de l'activité électromyographique (EMG) d'un muscle dilatateur

(cricothyroïdien, CT) et à une augmentation de l'activité EMG d'un muscle constricteur

(thyroaryténoïdien, TA) de la glotte entraînant une diminution de la ventilation pulmonaire.

Le but de ce projet est de déterminer si ce réflexe de fermeture est modulé par les récepteurs bronchopulmonaires ou par les récepteurs des voies aériennes supérieures (VAS).

Deux modèles ovins nouveau-nés différents ont été mis au point pour étudier les récepteurs bronchopulmonaires ou les récepteurs des VAS. Chez les agneaux du premier groupe, une vagotomie bilatérale en 2 étapes a été réalisée par vidéothoracoscopie (groupe vagotomie bilatérale), tandis que les agneaux du second groupe ont subi une séparation chronique de la trachée et du larynx pour isoler les VAS (groupe VAS isolées). De plus, une instrumentation chirurgicale chronique a permis l'enregistrement polysomnographique des stades de conscience, de l'EMG des muscles constricteurs (TA) et dilatateurs (CT) de la glotte et des mouvements respiratoires lors

Chez le groupe vagotomie bilatérale, l'augmentation de l'EMG des muscles constricteurs (TA) du larynx en inspiration observée lors de l'augmentation de la VPPln avant vagotomie disparaît après vagotomie bilatérale. Par contre, la diminution de l'EMG des muscles dilatateurs (CT) du larynx n'est pas modifiée par la vagotomie. Chez le groupe VAS isolées, l'activité inspiratoire des constricteurs larynx augmente de façon significative lors de la ventilation par les VAi, mais cette augmentation est absente lors de la ventilation des VAS isolées. De plus, l'activité des dilatateurs diminue seulement lors de la ventilation des VAi, mais non lors de la ventilation des VAS.

La fermeture active du larynx lors des insufflations mécaniques en VPPln est donc un réflexe provenant des afférences bronchopulmonaires pour l'activité des constricteurs seulement, les récepteurs des VAS ne semblant pas impliqués.

Mots clés : récepteurs bronchopulmonaires, VPPln, muscles laryngés, vagotomie bilatérale.

INTRODUCTION

Le larynx est un organe d'une composition très complexe impliqué dans plusieurs fonctions de l'organisme tel la phonation, la respiration, les manœuvres expulsives (défécation, parturition, miction) ainsi que la protection des voies aériennes inférieures. Il est situé entre le pharynx et la trachée et soutenu par l'os hyoïde. Afin d'assurer ces fonctions vitales, il est formé de neuf cartilages, dont les deux plus importants sont les cartilages cricoïde, premier anneau complet de la trachée, et le cartilage thyroïde, permettant la protection des cordes vocales. Voir figure 1.

Os hyoïde

Ligament crico-thyroïdien

Figure 1. Vue antérieure du larynx

Ëpiglotte Cartilage thyroïde Muscle cricothyroïdien Cartilage cricoïde Trachée source : http://www.gbmc.org/voice/imaqes/bluetree/Larvnx%20front. jpg

directement dans la ventilation par leur contrôle des mouvements des cordes vocales. Certains seront des dilatateurs puisqu'ils permettent l'ouverture de la glotte (espace limité par les cordes vocales) tel les cricoaryténoïdiens postérieurs et les cricothyroïdiens (CT), d'autres seront constricteurs, les thyroaryténoïdiens (TA), diminuant ainsi la surface de la glotte (Voir figure 2). Lors de la respiration spontanée, l'activité des muscles dilatateurs est observée en inspiration, ce qui diminue la résistance laryngée et le travail des muscles thoraciques inspiratoires, permettant le passage de l'air plus facilement vers les poumons (Samson, N. et al. , 2007). Au contraire, l'activité des muscles constricteurs du larynx est observée plutôt en début d'expiration ; dans ces circonstances, l'ouverture glottique diminuée agit comme un frein

à la vidange pulmonaire et maintient un volume de fin d'expiration (capacité résiduelle

fonctionnelle) plus élevé (Bartlett, D.,Jr, 1989) (Diaz, V. et al. , 2000) (Harding, R. et al. , 1986).

Figure 2. Vue supeneure des muscles intrinsèques constricteurs thyroaryténoïdiens (TA) et des dilatateurs cricothyroïdiens (CT).

source : Frank H. Netter MD, At/as d'anatomie humaine, 2e édition, Éditions Maloine, New Jersey, 1997, p.73.

mécanorécepteurs sensibles à des variations de température, de pression ou aux mouvements ; 2) des chémorécepteurs et des osmorécepteurs sensibles aux irritants,

telle la fumée de cigarette, ou à des variations d'osmolarité ; et 3) les terminaisons

nerveuses des fibres C (canaux TASK-1) sensibles aux irritants et à l'acidité et

responsables des sensations de douleur (Sant'Ambrogio, G. et al. , 1995). Par ces récepteurs, le larynx assure son rôle important de protection des voies aériennes inférieures en acheminant par la branche interne du nerf laryngé supérieur ces sensations perçues jusqu'au tronc cérébral (noyau du faisceau solitaire), qui les intègre et les relaie vers différents centres (respiratoire, cardiaque vagal, déglutiteur). Les messages efférents issus du noyau ambigu peuvent revenir au larynx soit par la branche externe du nerf laryngé supérieur pour innerver les muscles dilatateurs cricothyroïdiens, soit par le nerf récurrent laryngé, principal nerf moteur du larynx,

Nerf laryngé supérieur branche interne branche externe Anse de Galien Nerf récurrent laryngé

Figure 3. Innervation du larynx

assurant l'innervation de tous les autres muscles intrinsèques du larynx, dont le

constricteur thyroa ryténoïd ien. Les nerfs

laryngés supérieurs et les nerfs récurrents laryngés sont des branches du nerf vague.

Récepteurs bronchopulmonaires

Au niveau des voies aériennes inférieures (sous-laryngées), les messages afférents naissent des différents récepteurs bronchopulmonaires. Trois types de récepteurs bronchopulmonaires sont décrits : 1) les récepteurs à l'étirement ou récepteurs bronchopulmonaires à adaptation lente, situés dans la couche musculaire de la trachée et des bronches ; 2) les récepteurs à l'irritation ou récepteurs bronchopulmonaires à adaptation rapide, situés dans la muqueuse trachéobronchique et sensibles aux irritants mécaniques ou chimiques ; 3) les terminaisons nerveuses des fibres C situées au niveau de la muqueuse bronchique et sensibles aux irritants, ou au niveau pulmonaire Uuxta-alvéolaire) et sensibles à la congestion pulmonaire et à l'œdème interstitiel. Les récepteurs bronchopulmonaires acheminent leurs afférences par les nerfs vagues jusqu'au noyau du faisceau solitaire, qui sert de relais jusqu'aux centres de contrôle cardiorespiratoires. Les messages efférents cheminent par le nerf vague et sont entre autres responsables de mécanismes de défense telle la toux et la bronchoconstriction.

Mise en contexte

Des études antérieures ont démontré que l'application d'une ventilation nasale peut s'accompagner d'une diminution de l'ouverture glottique (Jounieaux, V. et al., 1995b) (Jounieaux, V. et al., 1995a) et d'une augmentation d'activité du muscle constricteur glottique TA chez l'homme adulte (Kuna, S.T. et al., 1993). Récemment, nous avons montré (Moreau-Bussiere, F. et al., 2007) que la ventilation nasale en pression positive

intermittente (VPPln) particulièrement en mode volume contrôlé, conduit à une

fermeture active du larynx chez l'agneau nouveau-né non sédationné à l'éveil et au

cours du sommeil. En fait, ce rétrécissement glottique observé au moment des insufflations du ventilateur apparaît avec l'augmentation de la VPPln et est induit par la

diminution de l'activité EMG du dilatateur CT associé à une augmentation de l'activité

EMG du constricteur TA. Il est observé en mode aide inspiratoire et en mode volume contrôlé (figure 4). TA f TA Cl JCT Pressure support ' '. ' 1

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De plus l'augmentation de la résistance laryngée inspiratoire est proportionnelle à l'amplitude de l'EMG du muscle constricteur du larynx TA et est responsable d'une diminution de la transmission des pressions à l'étage sous-glottique (figure 5), c'est à dire d'une diminution de la ventilation pulmonaire.

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Vig. 4. lncrcase in uppcr ;Ùfl.l'll..)' œ&Ïsbmt:C' dur:Î.llJl nn>PV :in thC'. VC rucde. A: tl:c ielaiions:hip bct!i'~cn t1uns-uppcr: airway f.UIC''ilUl'.I:· ('TIJAP. cml-hO) and TA muscle dcctrkW activity (TA Eli.1G, arbitrnry unil'!:i) in 7 IB.mbs during. nlPPV in the VC moJc (VC-3) during waiœful.ncs.\. N~ lhat the bclf<.'lfn lefr gru.ph has

a ditfcrent y-a.xis scale, Tb~. bortan müklle-~ra.ph _reprc.i;crrts the 95% co.nfidem .. -e inlerv:1J tQunrion (a,.. and -\'T'll'S: SU of the !>lope and ink'roept witb x-a&is) fur

the 6 ln:mb.s dcpjc:ted. in the top 6 graphs (the la.st lamb W!lS c~ludcd becau:sl!. of signllicant diff«eflc~ from the ct.her lum~). The i11Crct1se in TUAP with TA

EMG 111 ton.<ttant airfli:.1_w (VC-3) indic.ote1 tbat upric:r airway J'C.!li1au:nœ incrc:ain:s whc:n TA EMG increaFC-io, _~UG&"C~ling that an ill;.:tivc g.11. ... uaJ t:k"stl.lt'= _œcur.!I in

rc-spons:ero p.dmi.>:nmy inflations. Scc.text for furth« apkuu:uion, B: the obovehyroth:.'iÎ.~ i!t furtheuuppottcd by the sjgnificant rclruit.i:n.ship b:i'lvccn trm1-~gfot1:d

rcsistn.nœ (TGR) und TA EMG in ooo lamb durin,g nlPPV in th: VC mu-de- du ring w:a:kcfolnc-ss (top gmpli), BottOJfl 1·lg/Jr. lnc:rcns.:. in trons--g.lotta.1 pressure. (TGP, cmH20) durin.g ~ak. TA EMG activity ·($') w.ilh constnnl nidfow Ols). Duhed. lines deli.mlt khe i.ospir.atory (Ï) ard e><piratoiy (eJ phases of the reb,piratOI}' cycle.

Figure 5. Résistance laryngée inspiratoire en fonction de l'amplitude de l'EMG du muscle constricteur du larynx TA. Extrait de Moreau-Bussière, Samson, et al,

2007.

Toutefois, le(s) mécanisme(s) par lequel ce rétrécissement glottique est induit pendant la ventilation nasale n'est pas connu. La seule information obtenue à l'issue de notre

première étude est que les stimuli chimiques ne semblent pas impliqués, car nous n'avons pas observé de variation significative des gaz du sang entre les valeurs de base en ventilation spontanée et les valeurs mesurées en VPPln lorsque l'EMG du TA était présent et l'EMG du CT très diminué à l'inspiration.

Notre hypothèse est que le réflexe de fermeture glottique constaté lors de la VPPln provient des récepteurs situés au niveau des voies aériennes supérieures ou au niveau des récepteurs bronchopulmonaires. Le but de mon projet de maîtrise est de déterminer si le rétrécissement glottique inspiratoire actif observé durant la VPPln provient des voies aériennes inférieures (sous-glottiques) et/ou des voies aériennes supérieures (incluant des narines jusqu'à l'extrémité caudale du larynx).

ARTICLE

Mechanisms of active laryngeal closure during non-invasive

intermittent positive pressure ventilation in non-sedated lambs

Bianca Roy, Nathalie Samson, François Moreau-Bussière, Alain Ouimet, Dominique

RÉSUMÉ DE L'ARTICLE

L'origine de cette étude provient d'une de nos découvertes récentes dans laquelle nous avons démontré que l'augmentation progressive de la ventilation nasale en pression

positive intermittente (VPPln) conduit à une fermeture active du larynx chez l'agneau

nouveau-né non-sédationné (9). Le but de cette présente étude était donc de déterminer si les mécanismes impliqués dans ce rétrécissement glottique pendant la VPPln origines des récepteurs des voies aériennes supérieures et/ou des récepteurs bronchopulmonaires. Deux groupes d'agneaux nouveau-nés ont eu une instrumentation

chirurgicale chronique afin de procéder à des enregistrements polysomnographiques

par la suite. De plus, une chirurgie par vidéothoracoscopie à été réalisée chez 5

agneaux afin de procéder à une vagotomie thoracique bilatérale différée (groupe

vagotomie bilatérale) puis une séparation laryngo-trachéale chronique a été réalisée chez 6 autres agneaux (groupe voies aériennes supérieures isolées). Quelques jours plus tard, des enregistrements polysomnographiques avaient lieu afin d'évaluer l'activité EMG des muscles de la glotte lors de l'augmentation de la VPPln (mode volume contrôlé). Les résultats démontrent que le rétrécissement actif de la glotte n'apparaît pas lors que la VPPln est appliquée que sur les voies aériennes supérieures, et qu'elle est empêchée par la vagotomie bilatérale lorsque la VPPln est appliquée sur les voies aériennes intactes. En conclusion, l'apparition active du rétrécissement de la glotte lors de la VPPln origine des récepteurs bronchopulmonaires.

Mechanisms of active laryngeal closure · during non-invasive

intermittent positive pressure ventilation in non-sedated lambs

Roy Bianca 1, Samson Nathalie 1, Moreau-Bussière François 2, Ouimet Alain 3, Darion

Dominique 3, Mayer Sandeep 3, Praud Jean-Paul 1•3

1: Neonatal Respiratory Research Unit, Departments of Pediatrics and Physiology; 2: Department of Surgery; 3: ENT Division, Université de Sherbrooke.

Short title: Mechanis~s of glottal closure during nasal ventilation

Address for correspondence

Jean-Paul Praud MD PhD

Departments of Pediatrics and Physiology Université de Sherbrooke

J 1 H 5N4 - Quebec, Canada

Email: [email protected] Phone: 1 819 346 1110, ext 14851

ABSTRACT

The present study stems from our recent demonstration that a progressive increase in nasal intermittent positive-pressure ventilation (nlPPV) leads to an active glottal closure in non-sedated, newborn lambs (9). The aim of the present study was to determine if the mechanisms involved in that glottal narrowing during nlPPV originate from upper airway receptors and/or from bronchopulmonary receptors. Two groups of newborn lambs underwent a surgical chronic instrumentation for polysomnographic recording. ln addition, while video-assisted thoracoscopic surgery was used in the first 5 lambs to perform a two-step, bilateral thoracic vagotomy (bilateral vagotomy group), a chronic laryngo-tracheal separation was performed in the remaining 6 lambs (isolated upper airway group). A few days later, polysomnographic recordings were performed to assess glottal muscle EMG during step-increase in nlPPV (volume contrai mode). Results show that active glottal narrowing does not develop when nlPPV is applied on the upper airways only, and that it is prevented by bilateral vagotomy when nlPPV is applied on intact airways. ln conclusion, active glottal narrowing developing when increasing nlPPV originates from bronchopulmonary receptors.

Kevwords: bronchopulmonary receptors, volume contrai ventilation, video-assisted

INTRODUCTION

Nasal intermittent positive pressure ventilation (nlPPV) is more and more often used to treat acute and chronic respiratory insufficiency, including in the neonatal period, in an effort to decrease the complications related to endotracheal tube ventilation (8). However, a major difference regarding IPPV via the nasal vs. endotracheal route, the presence of the larynx, a closing valve, which can prevent nlPPV to reaching the lungs, is generally overlooked. A few studies have shown that increasing nlPPV in either the volume control or pressure support mode induces an active glottal closure in both adult humans and newborn lambs (4)(9). We further showed in lambs that this active glottal narrowing was related to both a decrease in glottal dilator EMG activity (cricothyroid, CT) and an increase in glottal constrictor EMG activity (thyroarytenoid muscle TA) (9). However, the mechanisms by which the active glottal narrowing is induced during nlPPV are totally unknown. Results from our previous study strongly suggest that afferent messages from either central of peripheral chemoreceptors are not involved. Theoretically, the responsible reflex mechanism could originate from the upper airways receptors, which include pressure, temperature (flow) and drive receptors (12) or from bronchopulmonary receptors, which include the slow adapting (stretch) receptors, the rapidly adapting pulmonary (or irritant) receptors and the bronchopulmonary C-fiber endings (17). Finally, the parietal, rib cage mechanoreceptors, including the neuromuscular spindles, Golgi tendon organs and articulation receptors may also bear some responsibility. The aim of the present study conducted in lambs is to determinate if the mechanisms involved in the active glottal narrowing developing with increasing nlPPV originates from upper airway receptors and/or bronchopulmonary receptors.

MATERIALS AND METHODS

Experiments were conducted in 14 mixed-bred lambs aged from 2 to 6 days and weighing 4.1 kg (SD 0.8; range 2.9 from 5.4) on the day of the experiment. Ali lambs were born at term by spontaneous vaginal delivery at the sheepfold of our usual provider. The protocol of the study was approved by the ethics committee for animal care and experimentation of Sherbrooke University.

Surgical preparation

The lambs were separated in 2 groups before surgery, including 8 lambs instrumented for bilateral vagotomy and 6 lambs with isolated upper airways. Surgical implantation of electrodes for subsequent polysomnographic recording was identical in all lambs (see Common instrumentation below). However, the remaining surgery was different, depending on the experimental group.

Common instrumentation. Aseptic surgery was performed at 1-2 days of life under

general anesthesia (2 % isoflurane + 30 % N20 + 68 % 02). Endotracheal intubation was preceded by an intramuscular injection of atropine sulphate (0.1 mg/kg), ketamine (10 mg/kg) and antibiotics (5 mg/kg gentamicin and 7,500 IU/kg Duplocillin). One dose of ketoprofen (3 mg/kg IM) was given immediately before surgery for analgesia and repeated if needed on the next day. An intravenous injection of Ringer lactate (10 ml/Kg) was administered before surgery and a mixture of 5% dextrose in NaCI 0.9%

electrodes were inserted into the two thyroarytenoid muscles (TA, a glottal adductor), and bipolar enameled chrome wires were sewn into the two cricothyroid muscles (CT, a glottal dilater) for recording electromyographic activity (EMG). Two right-angled, platinum needle-electrodes were inserted into the parietal cortex through the skull, for electrocorticogram (EEG) recording. One platinum needle-electrode was also inserted under the scalp as a ground. Leads from all electrodes were subcutaneously tunnelled to exit on the back of the lamb and housed in a pocket on a vest. Finally, a catheter was

placed into the brachial artery for measuring pH, P02, PC02, HC03- and hemoglobin

saturation throughout surgery and on the subsequent days. Heart rate, rectal temperature, pulse oximetry, end tidal C02 and blood pH were continuously monitored throughout surgery. Post-operative care included daily intramuscular injection of 5 mg/kg gentamicin and 0.05 ml/kg duplocilline until the end of the experimentation; in addition, the arterial catheter was flushed twice a day with a heparinized solution.

Surgical instrumentation for bilateral vagotomy. Ali 8 lambs underwent a 2 step, intrathoracic bilateral vagotomy, which first involved a Video-Assisted Thoracoscopic Surgery (VATS) (KARL STORZ GmbH & Co. KG, Tuttlingen, Germany). After creation of a right pneumothorax by C02 insufflation, the endoscope and surgical instruments were introduced into the pleural space through 2 small (5-10 mm) parietal incisions. The bare portion of an enameled chrome wire (0.12 mm diameter, Leico Industries lnc., New York, NY, USA) was positioned around the vagus nerve, just caudally to the origin of the recurrent laryngeal nerve. The rest of the enameled wire was glued in polyethylene tubing, whose two ends exited through the skin. Once completed on the right, the same procedure was repeated on the left. Finally, 2 to 5 days after surgery, a bilateral

vagotomy was performed as previously described for cutting the superior laryngeal nerve (3). The two bared ends of chrome wire protruding from the right thorax with the polyethylene tubing were attached to an electrocauter (Electrosectilis, Model 770, Britcher Corp., CA, USA). Traction was then applied to the wire during electrocautery, thus sectioning the vagus nerve. The procedure was completed in less than 5 sec and resulted in minimal discomfort for the lamb (startle at most). The procedure was repeated on the left side. Bilateral vagotomy was confirmed in multiple ways, including by pulling off the unbroken wires from the thorax right after electrocautery, by immediately observing both a decrease in respiratory rate and an increase in tidal volume, and by a systematic verification at necropsy. This unique model allowed studying the same lambs before and after bilateral vagotomy, each lamb being its own control.

Surgery for the isolated upper airway group. Ali lambs in this group underwent a chronic separation of their upper airways from lower airways. The separation was performed right under the larynx, just above the first tracheal ring. The caudal end of the larynx was attached to a 2 cm-long Dacron aortic prosthesis, whose caudal end was attached to a neck stoma. ln addition, a tracheostomy was performed between the fifth and sixth rings of the trachea, and a 2 cm-long endotracheal tube sutured and glued externally around the tracheostomy, in such a way that there was no permanent endotracheal tube. Finally, the rostral end of the trachea was sutured. This unique model allowed either to perform nasal mask ventilation to the isolated upper airways, while the lamb was spontaneously breathing through the tracheostomy, or to perform mechanical

note, to our knowledge, this chronic animal model with isolated upper airways, which has taken several months to design with the help of an experienced ENT surgeon (DO), is unique.

Experimental eguipment

Ventilatory equipment. Intermittent positive pressure ventilation was performed using a

Siemens Servo 300 ventilator and Servo Screen (Siemens Corporation, New York, NY) with heated (32°C) and humidified air. Nasal ventilation was performed through a custom-made nasal mask, as previously described (9). Briefly, the mask was built from a plaster shell, which had a double nasal canula, a naso-gastric tube and a plastic catheter for mask pressure recording and was filled with dental paste to best

fit

the muzzle of each lamb. A small, non-diffusing gas bag (200 ml) was attached to the external end of the Dacron tube, as a surrogate for the lamb's lungs.

Recording equipment. Just prior to polysomnographic recordings, 2 needle electrodes

were inserted subcutaneously on each side of one eye for electrooculogram (EOG) recording and a pulse oximeter (Sp02) probe was attached at the base of the tail. ln

addition, elastic bands for respiratory inductance plethysmography (Respitrace, NIMS, Miami Beach, FL) were installed on the thorax and the abdomen to monitor respiratory movements and assess lung volume variations qualitatively. Mask pressure was monitored by using calibrated pressure transducers (MP 45-30-871, Validyne, Northridge, CA). Ali recordings were carried out in non-sedated lambs, using our custom-designed radiotelemetry system. The transmitter used for this study was composed of differential channels (EEG, EOG, ECG and 4 EMGs) as previously

described (6) (7). Ali transmitted signais were fed from the receiver to the acquisition system. The raw EMG signais were sampled at 500 Hz, rectified, integrated and

averaged (moving time average = 1 OO ms). The telemetry transmitter was connected to

the electrode leads and housed in the pocket of a vest worn by the lamb. Polysomnographic signais were recorded on a PC, using Acknowledge software (version 3.7.3, BioPac Systems, lnc., Santa Barbara, CA, USA).

Design of the study

On arrivai in our animal quarter, only lambs of the bilateral vagotomy group were housed with their mother. Lambs from the isolated upper airway group were housed in a

Plexiglas chamber (1.2 m3, in agreement with recommendations by the Canadian

Council for Animal Care for sheep housing) through with water-saturated air was continuously flowed (10L/min) using an Allegiance Airlife™ Nebulizer (no 5207) and a home humidifier. Tracheal secretions were systematically suctioned at least three times a day, according to American Thoracic Society recommendations (15). Lambs from that

group were also fed ad libitum three times a day with ewe's milk at 8:00 am, 12:00 pm

and 4:00 pm. The study was performed without sedation at least 48 h after surgery. The study was designed to allow simultaneous recording of EEG, EOG, and EMG activity, variations of mask pressure, respiratory movements and Sp02 while using incresing levels of ventilation in wakefulness and quiet sleep. The lambs were comfortably positioned in a sling with loose restraints. Two experimenters were present throughout all recordings to note lamb's behavior, set ventilator parameters and prevent

Bilatera/ vagotomy group. A first polysomnographic recording was performed during

nasal ventilation while the vagi were intact(= instrumented but not eut). On the following day, the same experiment was repeated during polysomnographic recording after performance of the bilateral vagotomy (see above). The protocol design for nasal ventilation has been previously described (9). Following an initial recording with no CPAP (continuous positive airway pressure), i.e., with the nasal mask on but without any mechanical ventilatory support, "baseline" tidal volume (Vt) and respiratory rate (RR) were obtained with a CPAP of 4 cmH20 applied via the nasal mask. Three levels of ventilation were tested in the volume contrai mode (VC), while maintaining a positive end-expiratory pressure (PEEP) at 4 cmH20. For the first level of volume contrai ventilation (VC#1 ), tidal volume and respiratory rate were set at the same values as when the lamb was breathing spontaneously with CPAP 4 cmH20. Thereafter, tidal volume was increased in a stepwise fashion to 10 ml/ Kg (VC#2), 15 ml/ Kg (VC#3) and 20 ml/Kg (VC#4). Every effort was made to record approximately 1 OO respiratory cycles in wakefulness and in quiet sleep each, at each level of ventilation. At any given time during experiment, ventilation was stopped if lamb displayed discomfort or agitation and/or there was an obvious abdominal distension or presence of liquid reflux via the nasogastric tube. While both the VC mode and pressure support IPPV were tested in our previous study (9), only the VC mode was tested in the present study, for pressure support was not doable on isolated upper airways (no inspiratory trigger from the lamb to the ventilator).

lsolated upper airways group. Two polysomnographic recordings were performed on

level of IPPV (VC mode) was sequentially tested as described above for the bivagotomy group. After completion of the first round of ventilation via the nasal or tracheostomy route, the lambs were allowed 30 min of rest before the same protocol was repeated on the other portion of the airways.

Data analysis

States of alertness. Standard electrophysiological and behavioral criteria were used to define W,

as

and AS from EEG, EOG and continuous observation (13). Amusai from

as

was characterized by sudden disappearance of high-amplitude, low-frequency

waves on the EEG trace whereas amusai from AS was recognized by direct observation of the lamb and disappearance of intense EOG activity.

Respiratory parameters. Twenty consecutive breaths, which had to be preceded and followed by 20 seconds of stable respiratory pattern, were selected for analysis in each lamb at every ventilatory level in W and

as.

lnspiratory duration was defined for analysis of the glottal muscle EMG as the insufflation time by the mechanical ventilator, excepted when IPPV was applied on the isolated upper airways (see below). Amplitude of the inspiratory TA and CT EMGs were analyzed and averaged, together with the inspiratory mask pressure to recognize mechanical insufflation, using Acknowledge (version 3.7.0 Biopac Systems) and Microsoft Excel software. The maximal amplitude of the phasic inspiratory CT EMG measured in W and in the no CPAP condition was averaged and used as a reference value (100%) for subsequent measurements of CT EMG in the various ventilatory modes and states of alertness in each lamb. Since typically, no

TA EMG was averaged from 4 swallowing activities in the no CPAP condition and used as the reference value (100%) for subsequent measurements of TA EMG. Of note, for lambs, in which IPPV was applied on the isolated upper airways, regular phasic inspiratory CT EMG and expiratory TA EMG were still present with spontaneous breathing via the open tracheostomy, which occurred irrespective of the timing of mechanical insufflations. A different analysis was then necessary on the 20 breaths selected as above during stable respiration via the tracheostomy. First, we counted the number of mechanical insufflations with inspiratory CT or TA EMG. Then, we discarded the cycles with phasic CT or TA EMG obviously occurring respectively with spontaneous inspiration or expiration. When in doubt, the cycles were not discarded. Finally, the number of mechanical insufflations with phasic inspiratory CT or TA EMG was expressed as a percentage of the total number of mechanical insufflations in each condition.

Statistical analysis. Amplitude of TA and CT EMG were first averaged in each lamb for

each ventilation step, each experimental condition and W or QS, then in all lambs as a whole. Results were finally expressed as a mean with standard deviation (SD). Statistical analyses were conducted using generalized estimating equations (GENMOD procedure of SAS software, version 8) for repeated measures and Poisson distribution. The working correlation matrix was of the exchangeable type. A difference was deemed statistically significant if p value was lower than 0.05.

RESULTS

As results for inspiratory TA and CT EMGs were not significantly different between W and QS both in the present and our previous study (9), results obtained in both states of alertness are reported together (W vs. QS: inspiratory TA EMG, p = 0.83; inspiratory CT EMG, p= 0.51 ).

Lambs with bilateral vagotomy

From a total of 8 lambs, which underwent surgery, the study was completed in 5 lambs, due to technical problems with chronic electrodes or the vagotomy, which was not complete on one side. Total duration of polysomnographic recordings was 392 min. With intact vagi, and while breathing with the nasal mask on, but without CPAP, regular phasic inspiratory CT EMG was consistently observed in all 5 lambs. On the contrary, phasic TA EMG was observed during expiration only for most respirations in 2 lambs, but more irregularly in the remaining 3 lambs. Moreover, no phasic inspiratory TA EMG was observed in any lamb. Overall, CT and TA EMG were identical after bilateral vagotomy (See table 1).

While no significant changes in inspiratory TA EMG were observed from no CPAP to CPAP 4 breathing (p = 0.44) before bilateral vagotomy, a significant decrease in inspiratory CT EMG followed the application of nasal CPAP 4 (p = 0.003). However, the inspiratory CT EMG activity was always present when breathing with CPAP 4. Moreover, the expiratory TA EMG was only present in one lambin the two phases of the expiration. Similar changes were observed when switching from nasal CPAP O to 4 after bilateral

vagotomy, i.e,, no significant difference in inspiratory TA EMG (p = 0.76), but a significant decrease in inspiratory CT EMG (p

=

0.009) (Table 1 ).

The progressive increase in nasal ventilation before bilateral vagotomy was paralleled by an increase in inspiratory TA EMG, in phase with mechanical insufflations. Overall, this increase in TA inspiratory EMG was significant at VC#3 level compared to ail the others VC levels (p = 0.0001) (figure 2). On the contrary, inspiratory CT EMG progressively decreased with increasing nasal ventilation (p ~ 0.0001) (Table 2).

Following bilateral vagotomy, the increase in inspiratory TA EMG previously observed with increasing nasal ventilation was inhibited (VC#3, p > 0.1) (Table 2). However, the decrease in inspiratory CT EMG was still present (VC#3, p < 0.0001 ).

Lambs with isolated upper airways

Total duration of polysomnographic recordings was 586 min in 6 lambs. Baseline recording was performed with lambs breathing through their tracheostomy, with a nasal mask in place but no CPAP. As expected, regular phasic inspiratory CT EMG as well as regular phasic expiratory TA EMG were observed in 5 lambs. However, no inspiratory TA EMG or expiratory CT EMG was observed.

Mechanical ventilation applied

on

the /ower airways (via tracheostomy). While the addition of CPAP 4 via the tracheostomy induced no changes in inspiratory TA (p

=

0.96), a statistically significant decrease in inspiratory CT EMG was observed (p

=

0.0001). Both the expiratory TA EMG and the inspiratory CT EMG were still present in the same 5 lambs.

The step-increase in IPPV via the tracheostomy induced a significant increase in

inspiratory TA EMG (VC#2 vs. no CPAP, p < 0.0001) (table 2). Simultaneously,

inspiratory CT EMG significantly decreased (VC#2 vs. no CPAP, p < 0.0001).

Mechanical ventilation applied on the isolated upper airways (via the nasal mask).

Application of nlPPV on the isolated upper airways did not induce any increase in

inspiratory TA EMG activity, as compared to the no CPAP condition (1.2 % vs. 0.4%, p

=

0.5). ln addition, inspiratory TA EMG was significantly lower when IPPV was applied onto the isolated upper airways than on the lower airways via the tracheostomy (1.2 %

vs. 55%, p < 0.0001) (figure 38). ln addition, no decrease in inspiratory CT EMG activity

was noted when IPPV was applied on the isolated upper airways, as compared to no

CPAP (100 % vs. 91%, p = 0.3). Finally, the percentage of respiratory cycles with

inspiratory CT EMG was significantly higher when IPPV was applied onto the isolated

DISCUSSION

The present study provides new insight on the mechanisms, which are involved in the active laryngeal closure during non-invasive intermittent positive pressure ventilation. lndeed, the present results strongly suggest that the increase in glottal constrictor muscle EMG, which develops in lambs during wakefulness and quiet sleep when increasing nlPPV in volume contrai mode, originates mainly from bronchopulmonary receptors, with no role for upper airway receptors. ln addition, results show that the simultaneous decrease in glottal dilater muscle EMG does not originate from upper airway or bonchopulmonary receptors. Such unique results obtained in newly developed ovine models further illustrate the influence lower airway receptors can have on upper airway function.

lncrease in thyroarytenoid muscle inspiratory EMG activity

The involvement of bronchopulmonary receptors in the increase in inspiratory TA EMG during nlPPV is shown by 1) the absence of any increase in inspiratory TA EMG when nlPPV is applied on the isolated upper airways, in contrast with 2) the increase in inspiratory TA EMG when IPPV is applied via a tracheostomy and 3) prevention of this increase by bilateral vagotomy, which prevents vagal afferent messages from bronchopulmonary origin from reaching the brainstem respiratory centers. ln addition, the absence of any increase in inspiratory TA EMG activity when nlPPV is applied on the isolated upper airways strongly argues against the involvement of any type of upper airway receptor.

Our study was not aimed at determining which type of bronchopulmonary receptor(s) is involved in the increase in inspiratory TA EMG with nlPPV. Bath the slowly and rapidly adapting receptors are stimulated by an increase in tidal volume (14). Stimulation of the rapidly adapting receptors is further suggested by the observation of frequent swallows at the highest volumes (VC #3) tested in the present study (14). Further partitioning the

responsibility of slowly

vs.

rapidly adapting bronchopulmonary receptors would not be an

easy task; attempts could be made with 802 inhalation (via a tracheostomy), after verification that S02 is capable to inhibit slowly adapting receptors in lambs, as reported in rabbits (10). Finally, we propose that the involvement of C fiber endings is not likely, for we previously showed that stimulation of pulmonary C fiber endings in lambs leads instead to an increase in expiratory TA EMG (2). That hypothesis could be easily tested using our neonatal ovine model with blocked C fibers (2).

Decrease in cricothyroid muscle inspiratory EMG activity

Similarly to TA EMG, no significant variation in inspiratory CT EMG was observed when nlPPV was administered directly on the upper airways, suggesting that the decrease in CT inspiratory EMG observed when increasing nlPPV onto intact airways does not originate from upper airway receptors. Contrarily to the increase in inspiratory TA EMG however, bilateral vagotomy did not prevent the decrease in inspiratory EMG, suggesting that bronchopulmonary receptors are not involved in the inhibition of CT EMG with nlPPV. Results in our previous study showed that arterial blood gases were not modified when the decrease in inspiratory CT EMG was observed with increasing

receptors of the chest wall, such as the neuromuscular spindles or Golgi tendon organs of the intercostal muscles, could be involved in the decrease in CT activity, this is yet speculative.

Validation of two new neonatal ovine models

A recent review on bronchopulmonary receptors/reflexes has highlighted the importance to gain further knowledge on the modifications of upper airway function induced by mechanisms originating from the intrathoracic airways and the lungs (1). This is likely to be especially relevant in the neonatal period, where vagal afferent messages originating from bronchopulmonary receptors seem preponderant, as compared to later in life (5). Two unique, animal models were developed for tackling those issues and validated in the present study. A 2-step bilateral vagotomy, enabling to use each lamb as its own contrai, was developed with a pediatric surgeon (AO) with extensive expertise in video-assisted thoracic surgery in children. Among several advantages this mode! offers over previous bivagotomized lamb models (18) (11 ), the use of video-assisted surgery is especially attractive, for it is far less invasive and painful than a standard thoracotomy. Hence, the overall experiment is performed in bath more physiological and ethical conditions. Secondly, a chronically isolated upper airway lamb preparation was developed with the help of an ENT surgeon (DO) with extensive experience in upper airway reconstruction. With careful postoperative care, lambs in this group appeared to display a normal activity and no breathing problems.

Overall, the development of these two unique animal models was an important part of the present study and it paves the way for further studies on the interrelationships

ln conclusion, using 2 unique, specifically designed lamb models of bilateral vagotomy or chronically isolated upper airways, we have shown that the active glottal closure, which develops when nasal IPPV is increased, originates from bronchopulmonary receptors. Beyond the overall clinical relevance of this knowledge for the care of newborn infants treated with nlPPV, the demonstration of further interrelationships between the lower and upper airways is of significant physiological importance.

ACKNOWLEDGMENTS

The authors would like to express their profound gratitude to Jean-Philippe Gagné for expert assistance and technical help, to Marie-Pierre Garant for statistical analyses, and to the Storz Cie for the loan of the equipment used for Video-Assisted Thoracoscopic Surgery.

GRANTS

The research is supported by grants from the Canadian lnstitute for Health Research (MOP 15558) and the Foundation of Stars. Jean-Paul Praud is a member of the

FRSQ-funded Centre de recherche clinique Étienne-Le Bel and a national scholar, Fonds de

recherche en santé du Québec. Nathalie Samson is a recipient of a Canada Graduate

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bronchopulmonary afferents. J.Appl.Physiol. 101: 2: 609-617, 2006.

2. Diaz V, Arsenault J and Praud J-P. Consequences of capsaicin treatment on

pulmonary vagal reflexes and chemoreceptor activity in lambs. J.Appl.Physiol. 89: 5: 1709-1718, 2000.

3. Fortier PH, Reix P, Arsenault J, Dorion D and Praud J-P. Active upper airway

closure during induced central apneas in lambs is complete at the laryngeal level only. J.Appl.Physiol. 95: 1: 97-103, 2003.

4. Kuna ST, McCarthy MP and Smickley JS. Laryngeal response to passively induced

hypocapnia du ring NREM sleep in normal adult humans. J.Appl.Physiol. 75: 3: 1088-1096, 1993.

5. Lalani S, Remmers JE, Green FH, Bukhari A, Ford GT and Hasan SU. Effects of

vagal denervation on cardiorespiratory and behavioral responses in the newborn lamb. J.Appl.Physiol. 91: 5: 2301-2313, 2001.

6. Letourneau P, Dumont S, Kianicka I, Diaz V, Dorion D, Drolet Rand Praud J-P.

Radiotelemetry system for apnea study in lambs. Respir.Physiol. 116: 1: 85-93, 1999.

7. Letourneau P and Praud J-P. A radiotelemetry system for polysomnographic

8. Manzar S, Nair AK, Pai MG, Paul J, Manikoth P, Georage M and Al-Khusaiby SM. Use of nasal intermittent positive pressure ventilation to avoid intubation in neonates.

Saudi Med.J. 25: 10: 1464-1467, 2004.

9. Moreau-Bussiere F, Samson N, St-Hilaire M, Reix P, Lafond JR, Nsegbe E and

Praud J-P. Laryngeal response to nasal ventilation in nonsedated newborn lambs.

J.Appl.Physiol. 102: 6: 2149-2157, 2007.

1 O. Mortola JP, Fisher JT and Sant'Ambrogio G. Vagal contrai of the breathing

pattern and respiratory mechanics in the adult and newborn rabbit. Pflugers Arch. 401:

3: 281-286, 1984.

11. Praud J-P, Canet E and Bureau MA. Chemoreceptor and vagal influences on

thyroarytenoid muscle activity in awake lambs during hypoxia. J.Appl.Physiol. 72: 3:

962-969, 1992.

12. Reix P, St-Hilaire M and Praud J-P. Laryngeal sensitivity in the neonatal period:

from bench to bedside. Pediatr.Pulmono/. 42: 8: 674-682, 2007.

13. Renolleau S, Letourneau P, Niyonsenga T, Praud J-P and Gagne B.

Thyroarytenoid muscle electrical activity during spontaneous apneas in preterm lambs.

Am.J.Respir.Crit.Care Med. 159: 5

Pt

1: 1396-1404, 1999.

14. Sant'Ambrogio Gand Widdicombe J. Reflexes from airway rapidly adapting

receptors. Respir.Physiol. 125: 1-2: 33-45, 2001.

Zinman R. Gare of the child with a chronic tracheostomy. Am.J.Respir.Crit.Care Med.

161: 1: 297-308, 2000.

16. St-Hilaire M, Samson N, Nsegbe E, Duvareille C, Moreau-Bussière F, Micheau

P, Lebon J and Praud J-P. Postnatal maturation of laryngeal chemoreflexes in the

preterm lamb. J.Appl.Physiol. 102: 4: 1429-1438, 2007.

17. Widdicombe J. Airway receptors. Respir.Physiol. 125: 1-2: 3-15, 2001.

18. Wong KA, Bano A, Rigaux A, Wang B, Bharadwaj B, Schurch S, Green F,

Remmers JE and Hasan SU. Pulmonary vagal innervation is required to establish

TABLES

Table 1: Mean values of TA (laryngeal constrictor) and CT (laryngeal dilater) EMG activity and respiratory parameters during no CPAP, CPAP 4 cmH20 and nasal volume-controlled ventilation in the bilateral vagotomy group and isolated upper airway group.

BILATERAL VAGOTOMY GROUP ISOLATED UPPER

AIRWAY GROUP

BEFORE AFTER _VAi

BILATERAL VAGOTOMY BILATERAL VAGOTOMY

TA CT Vt RR TA CT Vt RR TA CT Vt RR

(%) (%) (ml) (min"1) _{(%) (%)} (ml) (min"1) _{(%) (%)} (ml) (min"1)

No _{7 (2)" 10b~c.~~3) 57 9 (3)}0 104 (32) _{56 6 (1) d,e} 100 (13) ₅₃

CPAP b,d,e b,d,e

CPAP _{6 (1)}0 _{66 (36)}0_{·d 49 51 9 (5) 62 (20) d,e 47 48 5 (1) d,e 63 (23) d,e 33 57}

4

VC#1 8 (4) d,e 49 (22)d 49 51 7 (1)d 60 (43) d,e 47 48 6 (1) d,e 85 (77) d,e 33 57

VC#2 13 (12) e 26 (7) 93 51 8 (3) 31 (22) 92 48 9 (4) 32 (22) 70 57

VC#3 16 (13) 42 (23) 114 51 7 (4) 33 (24) 114 48 11 (4) 29 (21) 88 57

TA, CT EMG: thyroarytenoid, cricothyroid inspiratory electrical activity, expressed as percentage of baseline EMG; Vt: tidal volume; RR: respiratory rate; CPAP: continuous positive airway pressure; VC: volume control, intermittent positive pressure ventilation.

Table 2: Statistical differences (p values) between each ventilation level in bilateral vagotomy and isolated upper airway group.

ISOLATED

BILATERAL VAGOTOMY GROUP UPPER AIRWAY

GROUP

BEFORE AFTER _VAi

BILATERAL VAGOTOMY BILATERAL VAGOTOMY

TA CT TA CT TA CT CPAP 4 vs. No CPAP 0.45 0.003 0.76 0.009 0.95 0.0001 VC#1 vs. No CPAP 0.52 0.0001 0.01 0.10 0.60 0.54 VC#2 vs. No CPAP 0.14 0.0001 0.59 0.001 0.003 0.0001 VC#3 vs. No CPAP 0.045 0.0004 0.86 0.002 0.0001 0.0001 VC#1 vs. CPAP 4 0.25 0.04 0.23 0.86 0.59 0.29 VC#2 vs. CPAP 4 0.054 0.0001 0.89 0.003 0.002 0.005 VC#3 vs. CPAP 4 0.01 0.18 0.95 0.002 0.0001 0.004 VC#2 vs. VC#1 0.006 0.002 0.02 0.0001 0.001 0.04 VC#3 vs. VC#1 0.0001 0.62 0.11 0.003 0.96 0.03 VC#3 vs. VC#2 0.0001 0.06 0.76 0.93 0.60 0.14

FIGURE LEGENDS

Figure 1: Electrical activity (EMG) of thyroarytenoid (a laryngeal constrictor) and cricothyroid (a laryngeal dilater) muscles in one lamb during baseline breathing (no CPAP, left) and nasal intermittent positive pressure ventilation (nlPPV), before (middle) and after (right) bilateral vagotomy.

Recordings were obtained in quiet sleep. Note: 1) the increase in thyroarytenoid muscle (TA) EMG during inspiration (1) from no CPAP to nlPPV before bilateral vagotomy; 2) the absence of increase in TA EMG after bilateral vagotomy; 3) the disappearance of inspiratory cricothyroid muscle EMG in nlPPV, which is not affected by bilateral vagotomy; 4) the decrease in respiratory rate after bilateral vagotomy. Abbreviations: TA: thyroarytenoid muscle EMG; fTA: moving time averaged TA; CT: cricothyroid

muscle EMG;

f

CT: moving time averaged CT; SUM: sum signal of the respiratory

inductance plethysmograph, illustrating the variations of lung volumes with respiration (inspiration upwards); EEG: electroencephalogram; EOG: electrooculogram.

Figure 2: Variations of inspiratory TA and CT EMG with increasing intermittent positive

pressure ventilation (n = 5 lambs)

No CPAP: baseline breathing; CPAP 4: continuous positive airway pressure, 4 cmH20; VC

#1, 2

and 3: progressively increasing intermittent positive pressure ventilation in the volume control mode. Voltage amplitude of inspiratory TA EMG is expressed as a percentage of the mean amplitude observed with swallows during baseline recording.

Voltage amplitude of inspiratory CT EMG is expressed as a percentage of the mean

amplitude observed during baseline recording. *: p < 0.05.

Figure 3: The increase in inspiratory thyroarytenoid muscle (TA) EMG observed with

intermittent positive pressure ventilation (IPPV) originates from bronchopulmonary receptors, and not from the upper airways.

A, effects of vagotomy: the significant increase in mean inspiratory TA EMG observed

when ventilating intact lambs via a nasal mask (left) (p = 0.0008 vs. baseline breathing)

is inhibited by bilateral vagotomy (right) (p = 0.4). B, lambs with isolated upper

airways: the significant increase in inspiratory TA EMG observed when IPPV is applied

on the lower airways only via a tracheotomy (p < 0.0001 vs. baseline breathing) (middle)

is absent when ventilating the isolated upper airways (right) (p

=

0.5). * : p < 0.05. VC:

IPPV, volume contrai mode. Abbreviations: no CPAP: baseline breathing; LA-VC: ventilation in volume contrai on the lower airway; UA-VC: ventilation in volume contrai on the upper airway.

Figure 4: Recordings obtained in one lamb with chronic laryngo-tracheal separation.

ln contrai conditions (left), both expiratory thyroarytenoid muscle (TA) EMG and inspiratory cricothyroid muscle (CT) EMG are present. During intermittent positive pressure ventilation (IPPV) applied on the isolated upper airways, similar TA and CT EMG patterns are observed. On the contrary, during IPPV applied via the tracheostomy,

the mask for baseline conditions and IPPV on the upper airways and at tracheostomy site for IPPV applied via tracheostomy.

Figure 5: The decrease in inspiratory cricothyroid muscle (CT) EMG from baseline

breathing to intermittent positive pressure ventilation (IPPV).

The results suggest that the inhibiting effect of IPPV on inspiratory CT EMG originates neither from the bronchopulmonary receptors (see A, upper graphs, no effect of vagotomy), or from the upper airway receptors (see B, lower graphs, effects are identical when IPPV is applied on the isolated upper airways (right) and without CPAP (left). Amplitude of the inspiratory CT EMG is expressed as a percentage of average inspiratory CT EMG observed at no CPAP. * p < 0.05. Abbreviations: no CPAP: baseline breathing; LA-VC: ventilation in volume contrai on the lower airway; UA-VC: ventilation in volume contrai on the upper airway.

TA fTA CT fCT SUM EEG EOG Figure 1: No CPAP .----i---- ---i---1 1 1 1 1 1 1 1

--~~

1 1 1 1

...

1 1 1 1 1 1 1 1 1 .... ~~~~._,Jt~ 1 1 1 1 1 1 1 l 1 ---1 1 ' l 1 1 1 1 1 1

ir-'""''l~;,~~ '11·~1·~111

_{1 1 1 1}

'* '"'"

~~'

_{1 1}

1•#·1•

111 1 1 1 1 1 1 ' ' 1

W1Wij'vf~rvhjt~rvf~~

1 1 1 1 1 1 1 1 1 1 1 1

A:

À /'"· :J!'-. A :J.'\ A /'-di' .. v v;"-1 ~i'V "'-• 1 1 1 t 1

Before bilateral vagotomy After bilateral vagotomy

--~~!~~-·

1 1 ---.--1

---~,---

1 1 1 1 1 1

•.

1 1 1 • • • • ' • • • 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

}\ :: :: iÂ

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DISCUSSION

La ventilation nasale en pression positive intermittente (VPPln) est un mode ventilatoire non invasif qui est de plus en plus utilisé en période néonatale comme traitement dans les cas de détresse respiratoire, d'apnée du prématuré et peut être un pont entre la ventilation endotrachéale et la respiration spontanée (Moreau-Bussiere, F. et al., 2007). En effet, la VPPln est d'un recours bénéfique puisqu'elle évite, par sa nature non-invasive, des blessures causées par l'intubation ainsi que les traumatismes causés par la ventilation invasive. Cependant, l'une des différences majeure entre la ventilation mécanique via un tube endotrachéal et un masque nasal est l'interposition dans ce dernier cas du larynx qui peut jouer le rôle de valve se fermant activement sous l'action des muscles constricteurs. Étonnamment, en dépit du succès grandissant de la VPPln, les connaissances sur la dynamique des voies aériennes supérieures au cours de la VPPln sont quasi-inexistantes. À notre connaissance, un seul groupe s'est intéressé au comportement du larynx en VPPln chez l'adulte et a montré par observation laryngoscopique que les effets bénéfiques de la VPPln peut s'accompagner d'un phénomène inattendu, la fermeture du larynx lors des insufflations du ventilateur mécanique (Delguste, P. et al., 1991). (Jounieaux, V. et al., 1995b) (Jounieaux, V. et al., 1995a). Récemment, nous avons vérifié que ce phénomène était aussi présent en période néonatale et démontré que la fermeture du larynx en VPPln était non seulement passive, par diminution de la contraction inspiratoire normale des dilatateurs du larynx, mais aussi active, avec apparition d'une activité électrique du muscle thyroaryténoïdien, constricteur du larynx (Moreau-Bussiere, F. et al., 2007). Au cours de cette même étude, nous avons aussi montré que la résistance glottique augmentait simultanément, avec diminution de la ventilation pulmonaire.

Ces résultats originaux nous ont incités à rechercher le réflexe responsable du rétrécissement glottique en VPPln, et d'enrichir par la même occasion les connaissances générales fort incomplètes sur le contrôle de la dynamique du larynx. Les résultats obtenus au cours de mes études de maîtrise et présentés dans ce mémoire apportent des informations uniques sur les relations entre récepteurs bronchopulmonaires et contrôle des muscles constricteurs du larynx au cours de la VPPln.

Activité inspiratoire des muscles laryngés

L'utilisation de deux modèles ovins originaux et ambitieux permettant d'étudier séparément les VAS et les VAi nous a permis d'obtenir des résultats qui n'auraient pu être acquis autrement. Grâce au modèle de vagotomie bilatérale, nous avons pu montrer que la stimulation des récepteurs bronchopulmonaires était responsables de l'activité EMG du muscle constricteur (TA) du larynx. En effet, la réponse du muscle constricteur était complètement abolie après vagotomie bilatérale. Par contre, l'activité EMG du muscle dilatateur du larynx (CT) restait inchangée après la vagotomie, un résultat qui reste sans explication pour le moment. Malgré que ce muscle ne soit pas innervé par le même nerf laryngé, on croyait au départ que son activité serait également affectée par la vagotomie. Ce qui signifie, que le muscle dilatateur du larynx (CT) n'est pas sous l'influence des récepteurs bronchopulmonaires.

Grâce au deuxième modèle ovin avec VAS isolées, nous avons pu confirmer que les récepteurs des VAS ne sont pas impliqués dans l'activité EMG du TA et du CT lors de la VPPln. La faible densité de récepteurs à pression positive dans les voies

aériennes supérieures (Reix, P. et al., 2007) explique peut-être en partie cette absence d'implication.

Quels types de récepteurs bronchopulmonaires sont impliqués ?

Mon étude n'avait pas comme but de déterminer quel(s) type(s) de récepteurs bronchopulmonaires étai(en)t impliqué(s) dans l'augmentation de l'activité inspiratoire du TA lors de la VPPln. Cependant, comme l'activité du TA en VPPln est brève et simultanée au pic de pression positive, nous croyons que les récepteurs à adaptation rapide (connus aussi sous le nom de récepteurs à l'irritation) sont impliqués. L'observation pendant les expérimentations de déglutitions fréquentes à haut volume courant en VPPln va dans ce sens.

Contrairement à l'activité du TA, la diminution de l'activité EMG du muscle CT n'est pas médiée par l'activité des récepteurs bronchopulmonaires. De plus les résultats de travaux précédents dans notre laboratoire (Moreau-Bussiere, F. et al., 2007) suggèrent fortement que les chémorécepteurs centraux et périphériques ne sont pas impliqués. En effet, les gaz sanguins restaient inchangés lors de la VPPln. Puisque les récepteurs des VAS, les récepteurs bronchopulmonaires, ainsi que les chémorécepteurs ne semblent pas impliqués dans la diminution de l'activité EMG du muscle dilatateur lors de la VPPln, nous émettons l'hypothèse, sans pouvoir cependant la vérifier pour le moment, que les afférences provenant de la paroi thoracique pourraient être impliqués. Selon cette hypothèse, les messages afférents pourraient provenir des fuseaux neuro-musculaires (ou organes tendineux de Golgi) présents dans les muscles respiratoires thoraciques, que ce soit les muscles intercostaux, abdominaux ou le diaphragme. Il est tout de même trop tôt pour affirmer qu'ils sont les récepteurs responsables de l'activité inspiratoire de ces deux