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The Evaluation of Human Thermo Regulatory Responses in Varying Weather States
Power, J.; Simões Ré, A.; Tipton, M.
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National Research Council Canada Institute for Ocean Technology Conseil national de recherches Canada Institut des technologies oc ´eaniques
TR-2009-18
Technical Report
The Evaluation of Human Thermo Regulatory Responses
in Varying Weather States.
Power, J.; Simões Ré, A.; Tipton, M.
Power, J.; Simões Ré, A.; Tipton, M., 2009. The Evaluation of Human Thermo Regulatory Responses in Varying Weather States. St. John's, NL : NRC Institute for Ocean Technology. Technical Report, TR-2009-18.
Documentation Page REPORT NUMBER
TR-2009-18
NRC REPORT NUMBER DATE
October 2009
REPORT SECURITY CLASSIFICATION
Unclassified
DISTRIBUTION
Unlimited
TITLE
THE EVALUATION OF HUMAN THERMO REGULATORY RESPONSES IN VARYING WEATHER STATES
AUTHOR(S)
J. Power1, A. Simões Ré1, and M. Tipton2
CORPORATE AUTHOR(S)/PERFORMING AGENCY(S) 1
National Research Council of Canada – Institute for Ocean Technology, Canada
2
University of Portsmouth, United Kingdom
PUBLICATION
SPONSORING AGENCY(S)
Transport Canada
Program for Energy Research and Development
IOT PROJECT NUMBER
42_2264_16
NRC FILE NUMBER
KEY WORDS
Immersion suit, immersion, deep body temperature, heat flow, skin temperature, wind, waves.
PAGES ix, 31 FIGS. 20 TABLES 3 SUMMARY
The thermal responses to environmental conditions consisting of varying wind speeds and wave heights were measured using volunteers at the National Research Council of Canada’s Institute for Ocean Technology. Twelve healthy males performed three, three hour immersions in Calm Water, Weather 1 (wind speed = 3.5 m·s-1, max wave height = 0.34m), and Weather 2 (wind speed = 4.6 m·s-1, max wave height = 0.64m) in a commercially available immersion suit. The two weather conditions produced significantly greater heat flow in the participants compared to the Calm condition. There was no significant difference in deep body temperature across all immersion conditions; however Weather 2 produced a significantly greater drop in mean body temperature (-1.51°C) compared to the Calm condition (-1.10°C). Small changes in cutaneous blood flow and increased metabolic heat production allowed the participants to successfully thermoregulate in the environmental conditions tested. It is recommended that future testing of humans in immersion suits incorporate the increased heat loss due to wind and waves.
ADDRESS National Research Council
Institute for Ocean Technology Arctic Avenue, P. O. Box 12093 St. John's, NL A1B 3T5
National Research Council Conseil national de recherches Canada Canada Institute for Ocean Institut des technologies Technology océaniques
THE EVALUATION OF HUMAN THERMO-REGULATORY RESPONSES TO VARYING WEATHER STATES
TR-2009-18
Prepared for: Transport Canada
Program for Energy Research and Development By:
Jonathan Power1 António Simões Ré 1
Michael Tipton2 1
National Research Council of Canada – Institute for Ocean Technology, Canada
2
University of Portsmouth, United Kingdom
iii
Acknowledgements
The research team would like to thank Transport Canada and the Program for Energy Research and Development for the continued financial support and interest in this work. The research team would also like to extend their thanks to White Diving for their interest and support in this work. We would also like to thank all the exceptionally talented staff at NRC-IOT who worked on this project for their hard work and effort. The project would never have been completed if it were not for their creative, insightful input and dedicated support.
Last, but certainly not least, the research team would like to extend a very big thank you to all the participants who volunteered for this study. All the participants were a pleasure to work with thanks to the positive, accommodating attitude they had during the
Table of Contents
Documentation Page ... ii
Acknowledgements... iii
Table of Contents... iv
List of Figures ... vi
List of Tables ... viii
Glossary ... ix 1.0 Introduction... 1 1.1 Experiment Hypothesis... 2 2.0 Test Setup... 3 2.1 Environmental Conditions ... 5 3.0 Participants... 6 3.1 Immersion Suits ... 6 3.2 External Bladders... 7 4.0 Instrumentation ... 8
4.1 Heat Flow Sensors ... 8
4.2 Gastrointestinal Pills ... 10
4.3 Heart Rate Monitor ... 11
4.4 Wireless Thermocouple System ... 11
4.5 Metabolic Measurements ... 12
4.6 Body Composition Measurements... 13
5.0 Procedure ... 15
5.1 Calculations... 16
5.1.1 Mean Skin Temperature and Mean Body Temperature... 16
5.1.2 Mean Body Heat Flow ... 17
5.1.3 VO2... 17
5.1.4 Statistical Analysis... 17
6.0 Results... 18
6.1 Environmental Conditions ... 18
6.2 Mean Skin Temperature Change ... 18
6.3 Deep Body Temperature Change... 19
6.4 Mean Body Temperature Change ... 20
6.5 Mean Body Heat Flow ... 21
6.7 Measured vs. Calculated MBT Change. ... 22
7.0 Discussion ... 24
8.0 Recommendations... 27
9.0 References... 28
List of Figures
Figure 2.1: OEB located at the NRC-IOT. ... 3
Figure 2.2: Concept drawing of OEB setup... 4
Figure 2.3: Actual test setup. ... 4
Figure 3.1: White’s Marine Abandonment Suit... 6
Figure 3.2: External bladder assembly... 7
Figure 4.1: Heat flow sensor... 8
Figure 4.2: Self contained data loggers connected to heat flow sensors (second logger is magnetically attached behind logger “Skin Temp A2” pictured in photo.)... 9
Figure 4.3: Logger package in the vest worn by a participant... 9
Figure 4.4: CorTemp Ingestible Sensor pill... 10
Figure 4.5: CorTemp Data Recorder. ... 10
Figure 4.6: Polar Heart Rate monitor... 11
Figure 4.7: Wireless thermocouple system... 12
Figure 4.8: Cardio Coach CO2... 12
Figure 4.9: Tanita Body Composition Analyzer... 13
Figure 4.10: Beta Technology Skin Fold Callipers. ... 14
Figure 5.1: Heat flow sensor placement. ... 15
Figure 6.1: Change in mean skin temperature over the course of the 3 hour immersions (Mean ± SD. ** = P = 0.001. n = 12). ... 18
Figure 6.2: Change in deep body temperature over the course of the 3 hour immersions. (Mean + SD. * = P < 0.05. n=12). ... 19
Figure 6.3: Change in mean body temperature during the three hour immersions. (Mean + SD. * = P <0.05. n=12). ... 20
Figure 6.4: Mean Body Heat Flow at the end of the 3 hour immersions. (Mean + SD. * = P < 0.05. n = 12). ... 21
Figure 6.5: Mean VO2 during the last 30 minutes of the 3 hour immersion. (Mean + SD. *
= P < 0.05. n =12). ... 22 Figure 6.6: Predicted and measured change in MBT after 3 hour immersions. (Mean ± SD. * = P < 0.05. n = 12)... 23
List of Tables
Table 2.1: Environmental characteristics of each immersion condition:... 5 Table 3.1: Participant anthropometric data... 6 Table 5.1: Skin temperature and heat flow measurement site weighting values (4). ... 16
Glossary
NRC National Research Council of Canada IOT Institute for Ocean Technology OEB Offshore Engineering Basin
TC Transport Canada
PERD Program for Energy Research and Development REB Research Ethics Board
PFD Personal Flotation Device CSR Cold Shock Response LSA Life Saving Appliances
JONSWAP Joint North Sea Wave Analysis Project SD Standard Deviation
MST Mean Skin Temperature MBT Mean Body Temperature MBHF Mean Body Heat Flow
1.0 Introduction
A large number of individuals work or travel over the cold ocean waters every day. Immersion in cold water represents a significant risk to those both at leisure and work in Canada. If an unprotected human is suddenly immersed in cold water, a series of
physiological responses termed the “Cold Shock Response” (CSR) occur that is
responsible for the majority of drowning deaths in cold water within the first few minutes of immersion. Even in unprotected individuals, hypothermia (a drop in deep body
temperature of 2ºC or more) does not usually occur before 30 minutes of immersion. Life Saving Appliances (LSA), such as Personal Flotation Devices (PFD), liferafts and lifeboats, are required on board any sea-faring vessel in order to improve the survival chances of the people on board; the best approach to protecting people from the cold water is to keep them out of it. In an emergency situation however, there is always a chance that the people will be immersed in the water. In these situations, immersion suits can greatly increase the chance of a person being able to avoid the CSR and prolong their survival time before succumbing to hypothermia.
Current Transport Canada (TC) regulations require immersion suits to be carried on board all class 9 ships and higher in a sufficient quantity so that every person has one. Offshore oil installations follow a similar policy. The immersion suits are usually a one-piece suit system that provides thermal protection and may provide buoyancy to the wearer (9).
The Canadian General Standards Board (CGSB) requires that immersion suits be tested for material strength, flame resistance, and thermal protective properties. The thermal protective properties can be tested using either thermal manikins or human participants. For human participant tests (9), a rectal thermometer measures the deep body temperature; the skin temperatures of the index finger and large toe are also measured. The participant is immersed in calm, circulating water with a temperature between 0-2ºC for up to 6 hours. The test is terminated if the participant’s deep body temperature drops 2ºC lower than baseline conditions, if the finger or toe skin
temperature drops below 5ºC, or if the attending physician determines the participant should not continue.
A knowledge gap currently exists between the calm testing conditions used to determine human’s thermal responses in immersion suits, and a real world scenario where an immersed person could experience high wind speeds and waves. Previous work conducted by Hayes et al. found that wave motion did not significantly increase the rate of body cooling when compared to calm conditions across of variety of clothing
ensembles, ranging from swimming trunks to flight suits with long underwear underneath (5). More extensive work carried out by Steinman et al. examined the effects of rough seas on thermal performance of anti-exposure garments (7). Mean rectal temperature, and back skin temperature decreased significantly in this study with loose fitting wet suit garments in rough compared to calm water. Two different dry immersion suit systems were tested in the same study. There was a significant difference reported in the rectal temperature cooling rate for only one of the dry immersion suit systems between the
rough and calm conditions (7). Steinman et al. concluded that immersions in rough seas may be associated with much lower survival times than those expected with calm water (7).
Further work by Tipton also examined the effect of increasing weather conditions on survival time. Participants who wore a well fitting, uninsulated dry suit experienced a 30% reduction in predicted survival time when in relatively mild weather conditions compared to calm water (8). While in an environmental condition that consisted of 4°C water, 15cm waves, periodic surface spraying, a 6 knot wind, with an initial submersion of 15 seconds, the participant’s suits experienced an average leakage of 1.144 litres of water, reducing their estimated survival time from 6.8 hours, to 4.8 (8).
Ducharme and Brooks examined the effects of varying wave heights on dry suit insulation (2). The participants in the experiment were dressed in uninsulated dry immersion suits with a one piece undergarment. The study found that rectal temperature was not affected by the wave conditions, and mean skin temperature was only affected when the participants performed immersions up to their neck in a vertical position. Skin heat flow did show a significant increase with increasing wave height (2).
The current ambiguity in the literature of the effects of wind and waves on the thermal responses during immersion was the basis for the research team’s earlier experiment. Our previous work examined the effects of four separate environmental conditions on human thermal responses (6). Volunteer performed four separate, one hour immersions in the following conditions: calm water, wind only, waves only, and wind + waves. Our previous work showed that the wind + wave immersion condition resulted in a ~37% increase in heat flow compared to calm conditions (6). Mean Body Temperature (MBT) also significantly decreased in the wind + wave condition compared to calm (6). Building upon the findings of our previous work, the present experiment investigated the effects of varying wind and wave heights on the thermal responses of volunteers during 3-hour immersions.
1.1 Experiment Hypothesis
Our hypothesis for the current experiment was that an environment consisting of higher wind speeds and wave heights will cause a significantly greater decrease in deep body temperature conditions with lower wind speeds and wave heights during 3 hour immersions.
2.0 Test Setup
All experimental trials were conducted in the Offshore Engineering Basin (OEB), located at the National Research Council of Canada’s Institute for Ocean Technology (NRC-IOT), in St. John’s, Newfoundland, Canada. The OEB is a large basin of water measuring 65m long, 26m wide, with a water depth of 2.8m. On the West and South sides of the OEB are hydraulically powered wave makers (168 in total), with passive wave absorbers fitted on the East and North sides of the tank. The waves ran uni-directional from the west bank of wave makers, and travelled east.
Figure 2.1: OEB located at the NRC-IOT.
For the current round of experimental trials, the setup of the OEB was altered to allow for a suitable, safe testing area for the participants as well as the installation of a bank of 11 analog controlled wind fans.
A scaffolding system ran approximately 10m south from the north side of the OEB and terminated onto a 4m by 4m platform. At the beginning of the scaffolding system, a set of stairs was attached to allow the participants to walk from the scaffolding into the water with little physical exertion. Prior to entering the water, a loop of Taigon tubing was secured around the participant’s feet. The Taigon tubing was attached to a tether by a break away clip that was controlled by the participants. The tether was connected to a pulley system that allowed the research team to manoeuvre the participants into the correct test location (6m east of the wind fans), with no physical effort required by the volunteers. A safety line connected to the stairway was secured to the buddy line of the participant’s immersion suit.
Figure 2.2: Concept drawing of OEB setup.
Figure 2.3: Actual test setup.
2.1 Environmental Conditions
Table 2.1 provides the wind speeds, maximum wave heights, water temperature, and air temperature of each immersion condition. A single irregular, 20-minute
JONSWAP wave spectrum was used throughout the test program. The spectrum was generated from data collected from a wave buoy deployed on the Southwest edge of the Grand Banks off the east coast of Newfoundland, Canada. Once the spectrum was generated, the portion that contained waves of a maximum height of 0.67m and lower was used for the test program. The reason for this was two fold: the first was to use a portion of the spectrum that contained waves that the OEB was capable of generating. Secondly, once the wave period reaches a certain value, the wave length is long enough that the human participant experiences the wave as a swell, and simply becomes a particle riding on the surface of the water.
Table 2.1: Environmental characteristics of each immersion condition:
Condition Max Wave Height (m) Mean Wind Speed (m·s-1) Mean Water Temperature (SD) (°C) Mean Air Temperature (SD) (°C) Calm 0 0 11.14 (0.24) 17.17 (0.51) Weather 1 0.34 3.5 10.93 (0.41) 17.36 (0.40) Weather 2 0.67 4.6 10.85 (0.32) 17.34 (0.42) In order to reduce the risk of injury to the participant, the wind field was
calibrated prior to any human immersions. A wind anemometer was placed in the location where the participant would be during the trial (6m east of the wind machines), with a second mounted on the underside of the scaffolding section directly behind the participant’s location. The wind field was calibrated with the two anemometers in place, and then the participant’s location anemometer was removed for all the immersions. The same drive signal voltage that provided the correct wind speeds for each condition was used throughout the immersions; with the wind speeds verified by the second
anemometer.
During this round of experimental trials, the OEB contained approximately 4732 m3 of fresh water. The OEB does not contain a refrigeration system and therefore has no active way to maintain a set water temperature. The only way the research team was able to keep the water temperature below 15°C (current TC criteria for cold water), was for the OEB to be periodically drained and refilled with water from a municipal source. The procedure proved to be extremely effective in maintaining a water temperature between ~ 10.85 – 11.14 °C, and the air temperature was ~ 17°C during the test program.
3.0 Participants
A required sample size of 11 participants was determined using a power calculation (95% confidence interval, σ = 0.5, β = 0.3), however 12 healthy males completed all the immersion conditions. All participants gave their written informed consent to participate, and NRC’s Research Ethics Board (REB) approved the protocol (REB#: 2008-68). Before starting any of the experimental trials, the participants underwent a screening by a certified medical doctor to determine if they were physically fit to participate. Table 3.1 provides the anthropometric data on the participants:
Table 3.1: Participant anthropometric data
n = 12 Age Height (cm) Weight (kg) Body Fat % Surface
Area (m2)
Mean 23.90 181.0 83.2 16.78 2.0
SD 3.32 4.91 4.91 4.05 0.13
3.1 Immersion Suits
White’s Marine Abandonment Suit was selected for use during this round of experimental trials, pictured in Figure 3.1 The suits kept the majority of the participants completely dry throughout the test program. On a few occasions, a thermocouple that ran underneath the latex wrist cuff to the hand created a narrow channel that a small amount of water entered through. Once this was discovered, the thermocouple was moved to the anterior surface of the wrist, which ensured the channel was above the water surface, preventing a further ingress of water.
Figure 3.1: White’s Marine Abandonment Suit. 6
3.2 External Bladders
In order to allow the participants to urinate throughout the 3 hour immersion, an external bladder assembly was constructed. The external bladder assembly consisted of an external catheter, a length of surgical tubing, and a Travel John disposable urinal (Reach Global Industries, Irvine, CA, USA). The external bladder assembly was worn by the participants underneath their clothing, and allowed them to urinate throughout the immersion. An unattached external bladder assembly is shown in Figure 3.2
4.0 Instrumentation
4.1 Heat Flow Sensors
Heat flow sensors manufactured by Concept Engineering (Old Saybrook, CT, USA) were used to measure both heat flow and skin temperature at 12 different sites on the body based on the Hardy and DuBois weighting formula (4), with a slight
modification as no measurements were taken from the hand. The sites used were the right foot, left shin, right calve, right quadriceps, left hamstring, left abdominal, right lower back, left scapula, right pectoral, underside of the right forearm, top of left forearm, and the forehead.
Figure 4.1: Heat flow sensor.
The heat flow sensors were connected to self contained data loggers manufactured by ACR data systems (Surrey, BC, Canada). Two separate ACR data loggers were used: a logger that could measure the heat flow, and a second that was able to measure skin temperature. The loggers were self-contained and the data collected during the immersion was stored and subsequently downloaded immediately after the trial was completed. Heat flow and skin temperature were measured once every 8 seconds.
Figure 4.2: Self contained data loggers connected to heat flow sensors (second logger is magnetically attached behind logger “Skin Temp A2” pictured in photo.)
The logger and heat flow sensor system were protected from mechanical stress during the immersion by being attached to a plastic guard by Velcro, and then sealed inside a splash proof bag. The logger packages were then placed inside a vest worn by the participants over their test clothing, seen in Figure 4.3.
4.2 Gastrointestinal Pills
Deep body temperature was measured using CorTemp Ingestible Sensor pills manufactured by HQ Inc (Palmetto, FL, USA). The pills measure 22.35mm long with a diameter of 10.9mm, and contain a temperature sensor.
Figure 4.4: CorTemp Ingestible Sensor pill.
The pills transmitted the readings wirelessly to the CorTemp Data Recorder (also manufactured by HQ Inc.) that was housed inside the vest worn by the participants. This was the same vest that contained the data loggers packages.
Figure 4.5: CorTemp Data Recorder.
In turn, the data recorder recorded the measurements from the pills and
transmitted the values wirelessly in real time to a base station computer. This allowed the research team to monitor the participant’s deep body temperature in real time to ensure that no one experienced a drop of more than 2°C. Deep body temperature was measured once every 20 seconds through the use of the pills.
4.3 Heart Rate Monitor
Heart rate was measured using a Polar Heart Rate monitor manufactured by Polar Inc. (Lake Success, NY, USA). The heart rate monitor consists of a band worn around the chest, with conducting gel applied to the back of the band.
Figure 4.6: Polar Heart Rate monitor.
The polar heart rate monitor measured the heart rates of the participants and was recorded (wirelessly) by the CorTemp Data Recorder. The CorTemp Data Recorder then transmitted the heart rate data wirelessly, in real time, to a shore-based computer where the research team could monitor it. The heart rate was measured and recorded once every 20 seconds.
4.4 Wireless Thermocouple System
A wireless thermocouple system manufactured by Microstrain Inc. (Williston, VT, USA) was used to measure and transmit the skin temperature of the right index finger, and large toe in real time. The wireless thermocouple was used to ensure that the participants did not suffer a non-freezing cold injury (skin temperature falling below 8°C for more than 15 minutes) during the immersion.
Figure 4.7: Wireless thermocouple system 4.5 Metabolic Measurements
VE, VO2, and VCO2 measurements were made by the Cardio Coach CO2,
manufactured by KORR Medical Technologies (Salt Lake City, UT, USA.) Participants wore disposable latex face masks that allowed their exhaled gases to travel through a ~12m tube to the Cardio Coach CO2 located on the shore. VE, VO2, and VCO2 were
measured once every 15 seconds.
Figure 4.8: Cardio Coach CO2
Table 4.1 summarizes the different measuring devices, respective sample rates, and units of measure.
Table 4.1: Measurements acquired from the participants during the immersions
Measurement Units Sample Rate
Heat Flow W·m-2 0.125 Hz
Skin Temperature °C 0.125 Hz
Deep body temperature °C 0.05 Hz
Finger and toe temperature °C 1 Hz
Heart Rate BPM 0.05 Hz
Ve l·min-1 0.06 Hz
VO2/VCO2 l·min-1 0.06 Hz
4.6 Body Composition Measurements
Participant’s body fat percentage was collected using two separate methods: Method 1: A body composition analyzer manufactured by Tanita Corporation of America Inc. (Arlington Heights, IL, USA). Before each immersion, the participants had two measurements taken using the body composition analyzer: the first measurement was using the scale with the person’s profile set to “normal”, the second with the profile set to “athlete”. Given the rather broad description of “athlete” by the manufacturer, the
research team recorded both readings for body fat percentage from the analyzer.
Figure 4.9: Tanita Body Composition Analyzer
Method 2. Skinfold thickness measurements were also taken on each participant. Skin fold thickness was measured using skin fold callipers manufactured by Beta
Technology (Santa Cruz, CA, USA). After the participants performed their last
immersion, skin fold thickness was measured at the locations according to the Durnin and Womersly (3) method for estimating body fat percentage.
Figure 4.10: Beta Technology Skin Fold Callipers.
5.0 Procedure
Participants were instructed to refrain from consuming alcohol the night before a trial, and not to consume caffeine at least 3 hours arriving at the facility. Participants arrived at NRC-IOT at their scheduled time and were escorted to the testing area. The first step in the protocol was to determine if the participants had a CorTemp Ingestible Sensor pill present in their body from a previous trial. If the participant did not have a pill present in their body they ingested a pill with a small amount of tepid water. This was the first step in the protocol to allow the pill a sufficient amount of time to acclimate to the participant’s deep body temperature. If a pill was already present in the participant’s body, they did not consume a second would continue on with the protocol.
The participants would put on a pair of swim trunks, and then attached the external catheter and tubing themselves. The 12 heat flow sensors were attached to the participant as illustrated in Figure 5.1.
Figure 5.1: Heat flow sensor placement.
Once the heat flow sensors were applied, the participants changed into a clothing ensemble based on CGSB testing standards. The ensemble consisted of wool socks, cotton sweat pants, cotton under shirt, swim trunks, and a long sleeved cotton shirt. Participants first put on the swim trunks and external bladder assembly, then a research assistant would apply the instrumentation to them. Once the instrumentation was attached, the participant would put on the remainder of the clothing ensemble.
Participants would then don a White’s Marine Abandonment Suit, which is a TC certified immersion suit, and proceed to the entrance of the OEB.
Once at the entrance of the OEB, 5 minutes of baseline data was collected from the participants while they sat quietly on a chair on the deck area. Once baseline data
collection was complete, the participants proceeded to the scaffolding assembly that was constructed in the OEB. The tether comprised of Taigon tubing was looped around the participant’s feet, and a safety line was connected to the buddy strap on their suit. Once connected, the participants walked down a set of stairs into the water, and assumed a floating, supine position. The research team used the ankle tether to manoeuvre the participant into the correct test location, and secure them there. Once in position, the three-hour trial would begin.
Upon completion of the three hour trial, the research team would retrieve the participant from the water and download the data contained on the data loggers. After downloading the data, the participants were escorted to a change area where they removed the immersion suit, clothing ensemble, external bladder, and instrumentation. Participants then immersed themselves up the neck in a circulating water bath with a water temperature of 40°C to rewarm. Once participants reached pre-immersion values, they exited the bath and changed back into their street clothing. After changing into their clothing, the participants were offered hot beverages and snacks while they completed the exit questionnaire.
5.1 Calculations
5.1.1 Mean Skin Temperature and Mean Body Temperature
Mean Skin Temperature (MST) and Mean Body Temperature were calculated by weighting the measurements obtained from the 12 heat flow sensors by the values based on the work by Hardy and DuBois (4). The weighting values used in this report are given in Table 5.1
Table 5.1: Skin temperature and heat flow measurement site weighting values (4).
Measurement Site Weighting Value
Right Foot 0.07 Left Shin 0.065 Right Quadricep 0.095 Left Abdominal 0.0875 Right Pectoral 0.0875 Right Underarm 0.07 Forehead 0.07 Right Calve 0.065 Left Hamstring 0.095
Right Lower Back 0.0875
Left Shoulder 0.0875
Left Overarm 0.07
Due to the lack of the hand measurements, the final collapsed Mean Skin
Temperature (MST) value was divided by 0.95. The formulae for calculating MST is as follows:
(∑ (Measurement Site * Weighting Value))/0.95 = MST
Previous work by Burton (1) has shown that Mean Body Temperature (MBT) is a combination of both deep body temperature and MST. MBT is calculated as the
following:
64% (Deep Body Temperature)°C + 36% (MST)°C
The change in MBT was determine by averaging the values from a 5 minute segment at the beginning of the 3 hour immersion, and then subtracting from that value the calculated MBT during a 5 minute segment at the end of the 3 hour immersion.
5.1.2 Mean Body Heat Flow
Mean Body Heat Flow (MBHF) was calculated using the same methods described in section 5.1.1 for MST.
5.1.3 VO2
VO2 for each condition was calculated by averaging the values measured during
last 30 minutes of the immersion. VO2 was used to calculate the metabolic rate (M) for
the participants using the following formulae:
M (w·m-2) = ( (VO2 * 21.1 *1000)/(60 * (AD)).
Where AD = surface area of the participants in m2.
5.1.4 Statistical Analysis
Analysis of variance (ANOVAS) was performed on all collected results.
Tamahrene T2 post hoc tests were performed to determine significance, with a P value of less than 0.05 considered as significant.
6.0 Results
6.1 Environmental Conditions
The mean water temperature ranged from 10.85-11.14°C across all immersion conditions, and there were no significant differences between conditions. The mean air temperature ranged from 17.17-17.34°C, and there were no significant differences in air temperature between immersion conditions.
6.2 Mean Skin Temperature Change
Change in mean skin temperature is given in Figure 6.1.
-5.00 -4.50 -4.00 -3.50 -3.00 -2.50 -2.00 -1.50 -1.00 -0.50 0.00
Calm Weather 1 Weather 2
Weather Condition
MST Change (°C)
**
Figure 6.1: Change in mean skin temperature over the course of the 3 hour immersions (Mean ± SD. ** = P = 0.001. n = 12).
The decrease in mean skin temperature was significantly greater in the Weather 2 (-3.95 °C) immersion compared to Calm (-2.96 °C). There was no significant difference in the change in Weather 1 immersions (-3.46 °C) and the other two weather conditions.
6.3 Deep Body Temperature Change
Change in deep body temperature, measured by the gastro-intestinal pill, is given in Figure 6.2. -0.70 -0.60 -0.50 -0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.30
Calm Weather 1 Weather 2
Immersion Condition Cha nge in De e p Body Te mpe ra ture (°C)
Figure 6.2: Change in deep body temperature over the course of the 3 hour immersions. (Mean ± SD. * = P < 0.05. n = 12).
There were no significant differences in the change in deep body temperature over the 3 hour immersion across weather conditions. The Calm water immersion produced a mean drop in deep body temperature of 0.10°C, Weather 1’s mean drop was 0.29°C, and Weather 2’s mean drop was 0.20°C.
6.4 Mean Body Temperature Change
The changes in MBT over the 3 hour immersion are presented in Figure 6.3.
Figure 6.3: Change in mean body temperature during the three hour immersions. (Mean ±
The weather 2 immersion condition produced a significantly greater drop in mean body te -2.00 -1.80 -1.60 -1.40 -1.20 -1.00 -0.80 -0.60 -0.40 -0.20 0.00
Calm Weather 1 Weather 2
Immersion Condition
MBT Change (°C)
*
SD. * = P <0.05. n = 12).
mperature (-1.51°C) over the three-hour immersion compared to the Calm water condition (-1.10°C). The weather 1 condition did not produce a significantly greater drop in mean body temperature (-1.40°) compared to the other two immersion conditions.
6.5 Mean Body Heat Flow
The effects of the immersion conditions on Mean Body Heat Flow (MBHF) at the end of the 3 hour immersion are given in Figure 6.4.
0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00
Calm Weather 1 Weather 2
Immersion Condition Me a n Body He a t Flow (W.m-2 ) * *
Figure 6.4: Mean Body Heat Flow at the end of the 3 hour immersions. (Mean ± SD. * = P < 0.05. n = 12).
Both the Weather 1 and Weather 2 condition produced significantly greater increases in MBHF compared to the Calm condition. The Calm condition produced a MBHF of 62.96 W·m-2 compared to Weather 1 that produced 76.75 W·m-2, and Weather 2 that had 79.53 W·m-2. There was no significant difference in MBHF between Weather 1 and Weather 2.
6.6 Mean VO2
The effects of the immersion conditions on VO2 during the last 30 minutes of the
3 hour immersion is given in figure 6.5.
0 50 100 150 200 250 300 350 400 450 500
Calm Weather 1 Weather 2
Immersion Condition
VO2 (mL.min-1)
Figure 6.5: Mean VO2 during the last 30 minutes of the 3 hour immersion. (Mean ± SD. *
= P < 0.05. n =12).
There were no significant differences in oxygen consumption during the last 30 minutes of the immersions across all weather conditions. Mean VO2 during the last 30
minutes of the Calm water immersion was 325.41 ml·min-1, 332.74 ml·min-1 in Weather 1, and 365.83 ml·min-1 in Weather 2.
6.7 Measured vs. Calculated MBT Change.
Subtracting MBHF from M will give us a predicted change in MBT. If the heat lost from the participants to the environment has been greater than their own metabolic heat production (MBHF > M), then we would expect a decrease in MBT. However, if the participant’s metabolic heat production was greater than the heat flow to the environment (M > MBHF), then we would expect an increase in MBT. Figure 6.6 shows the
comparison between the measured MBT change (based on the calculations from section 5.1.1.), and the predicted MBT based on the difference between MBHF and M.
-3.00 -2.50 -2.00 -1.50 -1.00 -0.50 0.00 0.50
Calm Weather 1 Weather 2
Immersion Condition
Change in MBT (°C)
Measured
Predicted
Figure 6.6: Predicted and measured change in MBT after 3 hour immersions. (Mean ± SD. * = P < 0.05. n = 12).
There were no significant differences between the measured change in MBT, and the predicted values across all immersion conditions. For the Calm immersion condition, there was a 0.54°C difference between the predicted and measured values, 0.02°C difference for the Weather 1 condition, and 0.20°C for the Weather 2 condition.
7.0 Discussion
The results collected from this stage of experimental work do not support the original hypothesis that weather conditions with greater wave heights and wind speeds will cause a greater decrease in deep body temperature.
Our previous work examined the effects of wind and waves on the thermal responses of humans (6). The results showed that the environmental condition consisting of wind and waves caused a significantly greater increase in heat flow from the skin compared to calm conditions, without a significant change in air or water temperature (6). The current work supports our previous findings; as the Weather 1 and Weather 2
condition produced a significantly greater increase in mean body heat flow compared to the Calm condition. This is in agreement with Ducharme and Brooks’s earlier work that showed increasing wave heights produce a significantly greater increase in heat flow compared to calm conditions (2). However, in the current study, there was no significant difference in MBHF between Weather 1 and Weather 2, with the latter condition having greater wave heights and wind speed compared to the former.
With the significantly greater increase in MBHF flow in the Weather 1 and 2 conditions compared to the Calm water immersion (Figure 6.4), we might expect a
significant change in deep body and skin temperature between the weather conditions and the Calm condition. While Weather 2 did cause a significantly greater decrease in MST compared to the Calm condition (Figure 6.1), there were no significant differences in deep body change over the course of the immersions across all immersion conditions (Figure 6.2). The Calm water condition caused a mean drop in deep body temperature of 0.10°C, Weather 1 produced a 0.29°C mean drop, and Weather 2 caused a mean drop of 0.20°C. Even though there was a significant greater increase in MBHF in the Weather 2 condition compared to Calm, there was no significant difference in drop in deep body temperature. Compared to the Calm condition, Weather 2 only produced a 0.1°C greater drop in deep body temperature which was not statistically significant. Our findings are in agreement with Hayes et al’s. earlier work that found that wave motion did not
significantly increase the rate of body cooling when compared to calm conditions (5). The current work is also in partial agreement with Steinman et al’s work (7) that reported a significant decrease in rectal temperature in only one out of the two immersion suits test in rough water and clam conditions.
While there was no significant drop in deep body temperature measured in the current study, there was a significant drop in MBT (Figure 6.3). A significantly greater decrease in MBT of 1.51°C was measured in Weather 2, compared to the 1.10°C observed in the Calm condition. While the difference in the decrease of MBT between the two conditions was statistically significant, this difference was only 0.41°C.
Even though there were no significant differences in the fall in deep body temperature observed between immersion conditions, and only a small significant decrease in MBT, it is possible that the participant’s may have been able to produce sufficient amounts of heat through shivering to offset that lost to the immersion
conditions with weather as well as increase tissue insulation with small changes in peripheral blood flow.
Heat production through shivering results in an increase in metabolic rate, which can be inferred from the rate of oxygen consumption (VO2). There was very little
difference between the predicted and measured change in MBT (Figure 6.6) in the two weather conditions. MBHF was significantly greater in the two weather conditions (Figure 6.4), indicating that a greater amount of heat was flowing from the participants to the environment. If the participant’s metabolic heat production had not increased in response to the greater cooling effects of the weather conditions, then the change in MBT would have been greater. From this we can infer that small and statistically insignificant differences in the participant’s metabolic rate did reduce the differences seen in MBT between conditions.
The current body of work is in agreement with some previous studies, and contradicts others. Previous studies (2,5) have shown that weather conditions will have no effect on deep body temperature, compared to calm immersions, which is supported by this current study. However, other studies have shown that weather conditions can indeed cause a drop in deep body temperature (7) and Tipton (8) have shown that predicted survival times can be reduced by as much as 30% in simulated weather conditions, compared to calm water.
Several factors in the current study may have limited the extent of the thermal responses seen by the participant. The temperature of the water in the North Atlantic can drop below 0°C, and the air temperature can drop below –10°C as well. Our water temperature ranged between 10-11°C and our air temperature was approximately 17°C, both of which can be considered very warm compared to the North Atlantic. This is a limitation of the facility the experiment was conducted in; the OEB does not have an active refrigeration system, and the temperature of the water and air cannot be specified. Additionally, the suits worn by the participants were of a very high quality, prevented water leakage, and have an immersed clothing insulation value of 1.0 in similar tests (6).
Our findings do not fully support our initial hypothesis. While there was no significant change in deep body temperature across all immersion conditions, it is obvious that an environment consisting of wind and waves will have a greater cooling capacity than calm water (Figure 6.4), and that a human’s thermal responses will change in the rougher immersion conditions (Figure 6.6). In our experimental setup, the thermal gradient and immersed clothing insulation value of the immersion suits allowed our participants to thermoregulate. Through changes in metabolic heat production and sub-cutaneous blood flow, the participants were able to maintain a relatively stable deep body temperature in the wind and wave conditions produced here. Future work should examine immersions with colder water and air temperatures, creating a larger thermal gradient, and suits with reduced immersed clothing insulation values to determine the threshold for the ability to thermoregulate. A change in either the thermal gradient or immersed
clothing insulation value may cross that threshold and result in a situation where a person is at risk of eventually developing hypothermia. It is concluded, that in conditions where the body can thermoregulate, little difference will be seen in body temperature with and without wind or waves. However, the addition of wind and waves increased heat loss
from the body, and if the thermoregulatory system is unable to compensate for this increase, body temperature would be expected to fall at a faster rate and to lower temperatures. The environmental conditions and levels of clothing insulation at which this occurs remain to be determined; they will very between clothing conditions and individuals.
8.0 Recommendations
The following recommendations are based on the results collected from this set of experimental trials. :
1. When conducting assessments with humans (active thermoregulatory system) it is important to assess each side of the thermal balance equation, i.e. heat loss and heat production. An active thermoregulatory system may mean that in two different conditions (e.g. water temperature; level of clothing insulation) very similar regulated body temperatures are observed. In this case the difference will be in the demand place on the body to achieve this regulated change in body temperature in terms of the intensity of vasoconstriction or shivering evoked and consequent levels of discomfort. Thus, in circumstances where the body can thermoregulate, the definitive variable may not be body temperature.
2. In theory, in more severe conditions than those used in the present tests, wind and waves can increase the severity of an environment beyond the point where it is possible to thermoregulate (maintain a stable deep body temperature). In such situations it is important to consider the added effects of wind and wave
conditions when predicting survival time.
3. It follows that future work should examine the effect of varying clothing insulation by changing the immersion suit used, or by simulating water leakage. In the environments used in this study, reduced immersed clothing insulation value may push immersed participants past the point of being able to successfully thermoregulate and maintain a stable deep body temperature, wind and waves may then have a more significant impact on body temperature.
4. For the same reason, future work should also examine the effects of colder water and air temperatures. A higher thermal gradient between the immersed participants and the environmental conditions may result in them not being able to successfully thermoregulate and maintain a stable deep body temperature.
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9.0 References
1.) Burton, A.C. Human Calorimetry: The average temperature of the tissues of the body. Journal of Nutrition, 1935; 9: 261-80.
2.) Ducharme, M.B., and Brooks, C.J. The effect of wave motion on dry suit insulation and the responses to cold water immersion. Aviation, Space, and Environmental Medicine, 1998; 69: 957-64.
3.) Durnin, J.V.G.A., and Womersley, J. Body fat assessed from total body density and its estimation from skinfold thickness: measurements on 481 men and women aged from 16 to 72 years. Brit. J. Nutr. 1974: 32: 77-97.
4.) Hardy, J.D., and DuBois, E.F. The technic of measuring radiation and convection. Journal of Nutrition, 1938; 15: 461-75.
5.) Hayes, P.A., Sowood, P.J., and Cracknell, R. Reactions to cold water immersion with and without waves. Royal Air Force Institute of Aviation Medicine Report, 1985.
6.) Power, J., Simões Ré, A., MacKinnon, S., Brooks, C., and Tipton, M. The evaluation of human thermal responses in wind and waves. TR-2008-10. Institute For Ocean Technology, 2008. 38p
7.) Steinman, A.M., Hayward, J.S., Nemiroff, M.J., and Kubilis, P.S. Immersion hypothermia: comparative protection of anti-exposure garments in calm versus rough seas. Aviation, Space, and Environmental Medicine, 1987; 58:550-8.
8.) Tipton, M.J. Immersion fatalities: Hazardous responses and dangerous discrepancies. Journal of Royal Naval Medical Service, 1995; 81:101-107. 9.) Canadian General Standards Board. Immersion suit systems.
