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A study of the physiological and subjective responses to repeated cold water immersion in a group of year olds Flora L Bird

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A study of the physiological and subjective responses to repeated cold water immersion in a group of year olds Flora L Bird A thesis submitted for the award of the degree of Master of Philosophy
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A study of the physiological and subjective responses to repeated cold water immersion in a group of year olds Flora L Bird A thesis submitted for the award of the degree of Master of Philosophy of the University of Portsmouth July 2011 ABSTRACT Swimming is the most popular participation sport in the UK with open water swimming seeing a rise in popularity over the last decade. However, cold water immersion is not without significant risks. Drowning represents the third leading cause of accidental death worldwide and in those aged 1 to 14 years it represents the leading cause of accidental death in some countries. Given the physical, physiological and psychological differences between adults and children, the latter are considered particularly at risk of cold-related illness and hypothermia. The cold shock response on initial immersion, and the insidious onset of hypothermia and swim failure that accompanies prolonged exposure and swimming, are recognised to be potentially fatal. This has been well documented in adults, and whilst it is assumed that similar responses occur in children there is little quantitative evidence of this to date. Furthermore, adults show an habituation of their cold shock response and change in their cooling rates following repeated exposure to cold water, however there are no data that show similar changes in children. This study examined the physiological and subjective responses of children to cold water on initial immersion and on prolonged immersion whilst swimming, and assessed for any adaptation in these responses following a year of repeated swim training in cold water. It was hypothesised that: children would demonstrate a cold shock response on initial immersion that would habituate following a period of acclimatisation; children would demonstrate faster cooling rates than those seen in adults whilst swimming in cold water, and their rate of cooling would adapt over a year of cold water swim training. METHOD 17 children aged 10 and 11 years old were recruited from applicants to the Bristol English Channel Swim Team (an attempt by a group of children to be the youngest relay team to swim the Channel). They underwent a five-minute static immersion in 15 C water, during which their cardiovascular, respiratory and metabolic responses were recorded. Ten of these participants went on to swim for up to 40 minutes in 15 C water, during which their heart rates, gastrointestinal temperatures and oxygen consumption were measured. The gastrointestinal temperatures of participants during the rewarming phase (post immersion) was also monitored and recorded. Subjective thermal sensation and comfort were recorded prior to immersion, after five minutes static immersion, and at the end of the swims. Following a year of regular cold water swim training, eight participants returned to complete the five-minute static immersion and five of the original ten swimmers completed a swim of up to 40 minutes in 15 C water. This allowed us to identify any evidence of adaptation in their 1 initial responses to immersion in cold water and cooling rates whilst swimming. The data gathered were compared to adult data collected in the same laboratory during a different experiment. RESULTS An increase in heart rate, respiratory frequency and inspiratory volume was seen in all participants in the first few minutes of immersion. However, responses were found to be smaller in children compared to adults (P 0.05), and no significant attenuation was seen in these after a year of regular exposure to cold water. Children did however feel warmer (P 0.01) and more comfortable (P 0.05) following five minutes of static immersion after a year of cold water swim training. There was great variability in the rate of cooling between children, likely due to differences in their anthropometric profiles. Sum of skinfolds was found to hold the greatest correlation with rate of deep body cooling (R 2 = ). The mean (SD) cooling rate of the children whilst swimming was 2.5 (3.06) C.h -1. No statistical difference was found in the cooling rates of five children following a year of cold water swim training. No difference was found between children and adults in their cooling rates whilst swimming, however the trend in both groups of a slower rate of cooling following acclimatisation became significant (P = 0.026) once the child and adult data were pooled. DISCUSSION This study provides evidence that the cold shock response exists in children, but is possibly smaller than that seen in adults. The lack of attenuation in this response following acclimatisation is a surprising finding that warrants further investigation, although it may be that the children were pre-acclimatised prior to their initial immersion, or due to a small sample size. This study provides quantitative data on cooling rates of children swimming in cold water. It finds that children maintain their deep body temperature as effectively as adults, which is likely partly explained by a greater percentage body fat (P 0.05) and higher relative heat production, as measured by oxygen consumption (P 0.05), seen in the children. The data support an habituation of children s subjective thermal awareness and goes some way to suggest that children aged years old exhibit an insulative adaptation following regular swimming in cold water. It is hoped that this study provides a better understanding of children s physiological responses to accidental and nonaccidental immersion, and will aid risk assessments in any projects involving paediatric immersion in cold water. 2 DECLARATION Whilst registered as a candidate for the above degree, I have not been registered for any other research award. The results and conclusions embodied in this thesis are the work of the named candidate and have not been submitted for any other academic award. DR FLORA BIRD 3 ACKNOWLEDGEMENTS I would like to acknowledge the following people and thank them for the help, advice and guidance they have given me with this project: The BEST children and their parents University of Portsmouth Supervisors: Professor Mike Tipton Dr Jim House University of Portsmouth staff: Mr Geoff Long Dr Heather Lunt Miss Penny Porter for her help with data collection Dr Sakura Hingley for her unpublished adult data The IMOs: Dr Paddy Morgan Dr Simon Guest Dr Rebecca Dale Dr John Brewin Dr Dan Roiz de Sa I would like to thank the following for their contribution of funding towards this project: University of Portsmouth Amateur Swimming Association Royal Life Saving Society Sackler Foundation Trust 4 TABLE OF CONTENTS LIST OF FIGURES... 6 LIST OF TABLES CONFERENCE PROCEEDINGS INTRODUCTION... 9 REVIEW OF THE LITERATURE HYPOTHESES METHODS RESULTS 43 DISCUSSION CONCULSIONS & FUTURE RECOMMENDATIONS LIMITATIONS, DELIMITATIONS & ASSUMPTIONS REFERENCES 74 LIST OF APPENDICES LIST OF FIGURES Figure 1: Visual Analogue Scales measuring Thermal Sensation and Thermal Comfort. Figure 2: Group mean (SD) respiratory frequency during immersion in 15 C water (n = 17). Figure 3: Group mean (SD) heart rate plots during immersion in 15 C water (n = 17). Figure 4: Group mean (SD) inspiratory volume plots during immersion in 15 C water (n = 17). Figure 5: Group mean (SD) thermal sensation in children after a five-minute static immersion in 15 C water, pre and post a year of cold water swim training (n = 8). Figure 6: Group mean (SD) thermal comfort in children after a five-minute static immersion in water 15 C water, pre and post a year of cold water swim training (n = 8). Figure 7: Group mean relative oxygen uptake (V O 2 ml.kg -1.min -1 ) taken for one minute every 10 minutes of the swim period, water temperature 15 C. Figure 8: Individual plots of T GI over the course of the swim in water temperature 15 C. Figure 9: Individual plots of T GI ( C) taken from the latter part of participants swims (minutes -20 to 0) and from entering the re-warming bath (minutes 0 to 30). Figure 10: Group mean rate of cooling in children swimming in 15 C water, pre and post a year of cold water swim training. Figure 11: Group mean rate of cooling in children versus adults during steady states of swimming in cold water, non-acclimatised (children: pre; adults: non-acclimatised (NA)) versus acclimatised (children: post; adults: acclimatised (A)). Figure 12: Group mean rate of cooling in adults and children swimming in cold water; Nonacclimatised and Acclimatised. 6 LIST OF TABLES Table 1: Group mean (SE) height, body mass and body mass index (BMI) of children who took part in this study (n = 17) compared to age and sex matched children from UK Reference Data (n = 3950 for children aged 2-15 years) (National Health Service [NHS], 2010). Table 2: Group mean (SD) anthropometric characteristics in participants pre and post a year of cold water swim training (n = 8). Table 3: Group mean (SD) heart rates, respiratory frequencies and relative oxygen uptake ( V O 2 ml.kg -1.min -1 ) on initial immersion in 15 C water pre and post a year of cold water swim training (n = 8). Table 4: Group mean (SD) body fat, minute heart rates, respiratory frequencies and minute ventilations for non-acclimatised (NA) adults and children pre a year of cold water swim training on static immersion in cold water (12 C with adults, 15 C with children). Table 5: Group mean (SE) height, body mass and BMI of children who took part and swam in this study (n = 10) compared to age and sex matched children from UK Reference Data (n = 3950 for children aged 2 15 years) (NHS, 2010). Table 6: Individual cooling rates, heat balance (once in a steady state towards the end of swim), and factors considered important to heat production and preservation whilst swimming in 15 C water (n = 10). Table 7: Group mean rate of cooling, energy change, heat produced and overall heat lost to the water in children swimming in 15 C water, pre and post a year of cold water swim training (n = 5). Table 8: Group mean (SD) body fat of children pre a year of cold water swim training and adults, and their cooling rates, absolute oxygen uptake ( V O 2 L.min -1 ) and relative oxygen uptake ( V O 2 ml.kg -1.min -1 ) whilst in a steady state of swimming in cold water (12 C with adults, 15 C with children). 7 CONFERENCE PROCEEDINGS These data were presented at the World Conference on Drowning Prevention, International Life Saving (ILS), Vietnam 2011: Bird F, House J, Tipton M (2011) The responses of a group of 10 to 11 year old children swimming in cold water. World Conference on Drowning Prevention, Vietnam. ID: 886, Paper: 253. It is hoped that these data will be presented to the Amateur Swimming Association (ASA) and Royal Life Saving Society (RLSS) in the future. 8 INTRODUCTION Swimming is the most popular participation sport in the UK with almost 12 million people of all ages and abilities taking part regularly both competitively and non-competitively (ASA, 2010). It is part of the National Curriculum and the Amateur Swimming Association aims to ensure 85 % of children can swim 25 metres as part of school swimming by 2012 / 13 (ASA, 2010). The marked increase in successful solo and relay-team crossings of the English Channel in the last decade reflects the increasing popularity of open water swimming in the UK (ASA, 2010; CS&PF, 2011), and its inclusion in the London Olympics 2012 may see its popularity continue to rise. However, swimming and particularly that involving cold open water, is not without its risks. Drowning represents the third leading cause of accidental death worldwide. In 2004, an estimated people died from drowning (World Health Organisation [WHO], 2004). Children are recognised to be particularly at risk; in those aged 1 to 14 years it represents the leading cause of accidental death in some countries, and those aged under 5 years have the highest drowning mortality rates worldwide (with the exception of Canada and New Zealand) (WHO, 2004). The human physiological response to acute cold exposure has been well documented, and substantial research has been conducted into adult thermoregulatory responses to initial and prolonged immersion in cold water (Golden & Tipton, 2002; Stocks, Taylor, Tipton, & Greenleaf, 2004; Tipton, Pandolf, Sawka, Werner, & Taylor, 2008). It is well recognised that the initial cold shock response seen in adults on immersion in cold water, and the risk of swim failure and hypothermia that can develop with prolonged exposure to cold, are critical to a person s chances of survival (Tipton, Eglin, Gennser, & Golden, 1999; Tipton, 1989). This will be discussed in greater detail in the literature review. Children differ from adults physically, physiologically and psychologically. They are deemed poor subjective judges of the cold, and with a larger surface area to mass ratio (SA: M), less subcutaneous fat, and less efficient thermoregulation, they are considered more susceptible to hypothermia (Klein & Kennedy, 2001). However, there is little quantitative evidence to support these considerations. From what research has been performed, boys have been found to have lower skin temperatures and to demonstrate greater relative metabolic heat production than men, both at rest and during cycling exercise in the cold (Falk, 1998). A seminal paper published in 1973 (Sloan & Keatinge, 1973) observed the response to hypothermia in children swimming in cold water, and found that subcutaneous fat and SA: M ratio were most strongly correlated to body temperature. 9 Since then, experiments have been conducted with children cycling in a cold environment of 5 C (Smolander, Bar-Or, Korhonen, & Ilmarinen, 1992), but there is little quantitative data on children s physiological responses to initial immersion and swimming in cold water. It has also been shown that adults show a thermoregulatory and sympathoadrenal adaptation to cold immersion with a number of exposures (Golden & Tipton, 1988; Huttunen, Rintamäki, & Hirvonen, 2001; Keatinge & Evans, 1961), and whilst it has been suggested that training children in a cold environment may improve their thermoregulation (Falk, 1998), this remains untested. Given the high level of risk associated with children and cold water, and the recognition of fundamental physiological differences between adults and children, it seems inadequate that the current understanding, management, and safety guidelines associated with paediatric immersion and cold water induced hypothermia remain largely theoretical or extrapolated from adult studies. As a medical doctor whose interest lies in pre hospital and wilderness medicine I was delighted to be one half of the medical team for BEST (Bristol Junior English Channel Swim Team); a group of children attempting to break the World record and become the youngest team to swim the Channel. The governing bodies of the Channel Swimming Association and Channel Swimming and Piloting Federation, require swimmers to be a minimum of 16 years old to attempt a solo crossing and 12 years old to partake in a relay team. Selection for BEST took place in February 2009 and following an 18-month training programme the children successfully completed the 21-mile swim from Dover to Cap Gris Nez in 13.5 hours on September 4 th With an average age of 12 years and 118 days, they became the youngest relay team to swim the English Channel. With a cohort of children volunteering to train for a cross-channel swim, this project provided the unique opportunity for research into the responses of children on immersion and swimming in cold water, and the effect of repeated cold water exposure. Overview of the thesis This thesis reviews the current understanding of adult s initial and prolonged responses to immersion in cold water, and presents the research and theories on this subject in children. It reviews the current literature on thermoregulatory adaptation on initial and prolonged immersion in cold water in adults, and the theoretical basis for similar processes in children. 10 General hypotheses Substantial data have been collected in adults during initial and prolonged immersion in cold water, whilst static and swimming. However, there are little data in children despite the significant risks associated with accidental immersion, likely due to the difficulties faced in working with this age group in a risky environment. It was hypothesised that similar physiological responses would occur in children as those seen in adults on initial immersion in cold water; whilst swimming; and following repeated training in this environment. 11 REVIEW OF THE LITERATURE Initial responses to immersion in cold water The large number of deaths per year associated with accidental immersion, representing the 3 rd leading cause of unintentional injury death worldwide (WHO, 2004), has been partly responsible for the extensive research conducted in adults, in an attempt to better understand the physiology of acute cold exposure and immersion in cold water. Whilst hypothermia, a fall in core temperature below 35 C, was long considered the most likely primary cause of death, it has since been recognised that there are other more immediate reflex physiological responses that may be held responsible. Golden and Hervey (Golden & Hervey, 1981) identified four stages of immersion that pose potential risk: the initial responses (0 3 minutes), short term responses (3 15 minutes), long term responses ( 30 minutes), and post immersion responses. The initial responses include the cold shock response and diving reflex. The latter is seen in individuals who experience submersion (face-in or head-under) and is thought to be a protective mechanism with prehistoric origin, seen in diving mammals where it has most extensively been investigated. It involves a reflex apnoea (cessation of breathing), bradycardia (slow heart rate) and selective vasoconstriction (Foster & Sheel, 2005). This in turn reduces oxygen demand in tissues most susceptible to hypoxia (insufficient levels of oxygen) and extends the viable underwater time for that mammal. In contrast, the cold shock response does not appear to serve any beneficial purpose and is increasingly recognised to pose the most immediate, and potentially the greatest threat to an individual immersed in cold water (Tipton, 1989). The cold shock response in adults and its associated risks The cold shock response in adults is considered an immediate physiological response comprising of cardiovascular, respiratory and metabolic components. These responses, their underlying mechanisms, and associated risks are detailed below. Cardiovascular On immersion, stimulation of the cardiovascular system results in a profound tachycardia (rapid heart rate) (Keatinge & Evans, 1961). Significant peripheral vasoconstriction, and therefore reductions in peripheral blood flow are seen (Barcroft & Edholm, 1946), and will result in an increase in peripheral resistance and subsequently an increase in cardiac afterload, in keeping with 12 Starling s Law. In combination with hydrostatic effects on immersion, there is a displacement of peripheral blood into the central venous system, resulting in an increase in diastolic filling (Arborelius Jr, Ballidin, Lilja, & Lundgren, 1972). Together, these cardiac and vascular effects result in an increase in systolic and diastolic blood pressure and significant increases in cardiac output. This was demonstrated in two subjects whose baseline cardiac outputs increased by 59 % and 100 % when exposed to ice cold showers (water temperature between 0 C and 2.5 C) (Keatinge, McIlroy, & Goldfien, 1964). It is recognised that cold water acts as the stimulus to peripheral thermoreceptors (sensory receptors that respond to heat and cold), mechanoreceptors (sensory receptors that respond to mechanical stimuli) and nociceptors (sensory receptors that respond to potentially painful stimuli) located superficially in the skin (Schepersa & Ringkamp, 2009). This resu
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