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Introduction
In athletic (e.g. rowing, yachting) or occupational (e.g. naval) perspective, any accidental fall in cold water, may be fatal for the immersed individual. Long-term immersion in cold water induces hypothermia, which is believed to be the major danger for the cause of death. Previous studies have shown that several factors can affect the rate of body cooling, such as body fat (McArdle et al, 1984), age, or gender (Wagner & Horvath, 1985), level of physical fitness (Fortney & Vroman, 1985), clothing (Tipton, 1992). and alcohol consumption (Roeggla et al, 1995).
While the possibility of injurious hypothermia does not usually occur within the first 15 minutes of immersion, the immersed individual must first survive the initial minutes of exposure, especially in ice water (Tipton, 1989). Initial responses in cold water immersion include a reflex respiratory gasp followed by a short period of uncontrollable hyperventilation and tachycardia (Tipton, 1989). According to Golden et al, (1986), uncontrollable hyperventilation can lead to a lack of coordination between swim stoke and respiration, and that might lead to inability to swim, and drawing may occur.
The experiment included 15min of rest or exercise period and 60min immersion in cold water (18o C). This report examined the initial responses in cold water immersion following two different pre-immersion conditions. First condition included 15min of rowing at 70% HRR, and the second condition included 15min of rest period. Experimental output was focused on: i) Skin temperature (Tsk); ii) Ventilation (VE); iii) Tidal volume (VT); iv) Respiratory frequency (FR); and v) Heart rate (HR).
Method
Subjects:
Two young, fit, healthy male subjects participated in this experiment. Subjects were fully informed about the experimental investigation before they gave written informed consent to participate (appendix 1, 2). Their physical characteristics (means) were the following: age, 21 yr; height, 175 cm; body weight, 75 kg; and percentage of body fat, 14.6%.
Preliminary Measures:
Body fat and mean skinfold thickness was calculated from 4 sites (biceps, triceps, subscapular and suprailliac) according to Durnin & Wormslely (1974). In addition Heart rate (HR) measurements were taken for determination of 70% of exercise intensity, using the equation: Target heart rate = (HRR fraction) (HRmax HR rest) + HR rest.
Protocol:
Subjects were assisted into a water tank and immersed up to the shoulder level in water at 18o C for 60min, under two different pre-immersion conditions:
Exercise trial (ET): In an ambient temperature of 20o C, subjects changed into shorts, socks and trainers, and performed exercise in a rowing ergometer at 70% of their relative HRR for 15min. At the end of the exercise phase, subjects were assisted from the rowing ergometer, and immersed up to the shoulder level into water (18o C) for 60min.
Rest trial (RT): In an ambient temperature of 20o C, subject wearing shorts, socks and trainers stayed rest for 15min. Subjects then following the same procedure as above immersed into water tank.
Re-warming phase
After the end of cold water immersion phases, subjects immersed in warm water (~ 37o C) until the point of time that they felt warm and comfortable.
Measurements:
Gases collection: VE, VCO2, VO2, and breath frequency during the 15min of intervention phase, and for the 60min of immersion phase were measured every 30sec using an automatic respiratory system.
Thermoregulation: Deep body temperature was measured with a rectal probe (Grants instruments, Cambridge), inserted by the subjects 15cm beyond the anal sphincter. Five skin thermistors (chest, forearm, fingertip, thigh, calf) and four heat flux transducers (chest, forearm, thigh, calf) were also attached to the skin with waterproof tape. Rectal temperature (Trec), heat flux, and skin temperature (Tsk) were measured continuously every 30sec with a data logger (1200 series, Grants Instruments, Cambridge).
Heart rate: A three lead ECG (lead II) displayed continuously (HRM, Life Pulse, HERTS) with heart rate recorded every 5min during the intervention phase, and every 30sec during the first 5min of cold water immersion, and then every 5 min until the completion of the immersion phase via a data acquisition system (ADI Instruments).
Thermal sensation and thermal comfort were measured every 5min during the intervention phases, every 1min for the first 5min of water immersion, and then every 5 min until the completion of the immersion phase.
Withdraw criteria
i) Core temperature less than 35.5o C.
ii) ECG abnormalities.
iii) Subjects decision.
iv) Experimenter decision.
Results
At this point you must put your results (VE, Skin temp, Tidal volume, breathing frequency, and heart rate)
Discussion
To start with, it will be valuable to divide the experiment into three phases. During the first phase subjects performed 15 minute exercise on a rowing ergometer at their 70% HRR, or stayed rest for 15 minutes. At the second phase of the experiment, subjects immersed in cold water (18o C) up to their shoulder level for 60 minute. The final phase of the experiment included the re-warming procedure, where the subject immersed in warm water (~ 37o C) until the point of time that they felt warm and comfortable. Despite the 60min immersion in cold water (18o C); this report examined the initial responses (5min) in cold water immersion, with prior rest or exercise conditions.
Sudden immersion in cold water stimulates peripheral cutaneous cold receptors, which initiates the hazardous physiological responses collectively known as the cold shock (Tipton, 1989). Previous studies showed that the cold shock response begins at water temperatures below 25ºC (Keatinge & Nadel, 1965) and peak at a temperature between 10-15ºC. (Tipton et al, 1991). Cold shock comprises a reflex respiratory gasp, followed by short period of uncontrollable hyperventilation and tachycardia. Based on previous studies (Tipton, 1989; Tipton et al, 1998) initial responses (within the first 30s) in cold water immersion included an elevation in: i) respiratory frequency, ii) heart rate iii) blood pressure, iv) inspiratory minute volume, and v) tidal volume. This elevation in responses of cardio-respiratory system reduced over the next 2-5min of immersion, but still remained above pre-immersion values. Based on previous study the respiratory frequency, inspiratory volume, and heart rate responses in the first 3min of cold water immersion increase with degreasing water temperature (Tipton et al, 1999). For individuals with heart problems, the increased cardiac workload associated with the tachycardia and cold-induced vasoconstriction can result in a cardiovascular accident (Tipton et al, 1989). Moreover, immersion in cold water might be hazardous not only for unhealthy (heart or circulating pathology) individuals, but also for fit, healthy individuals, since sudden cold water immersion associated with the reduction in maximal breath hold time (Tipton, 1989). According to Tipton (1989) a reduction in breath hold time and the loss of voluntary control of breathing during the first minutes of immersion increase the changes of aspirating water and thus drowning. Cold exposure stimulated peripheral vasoconstriction, due to increase in sympathetic tone (Marsh & Sleivert, 1999). An increase of sympathetic tone initiated rapid elevation of plasma noradrenalin
levels within the first few minutes of entering the cold water (Johnson et al, 1977). Additionally, sympathetic impulse to adrenal medulla increased secretion of adrenalin hormone. Noradrenalin in particular is responsible for blood vessels constriction, where adrenalin is responsible for the increase in metabolic rate. However, despite the elevation in medullary hormones, the rapidity with which the responses occur on immersion suggests that they are initiated by neurogenic pathways rather than circulation hormones (Tipton et al, 1998).
Exercise for 15min in a rowing ergometer increased skin temperature by ~5o C, compared to rest trial. However, despite the elevation in Tsk during exercise, Tsk for both trials (ET, RT) decreased rapidly at the onset of cold water immersion. Skin temperature dropped and remained constant at ~18o C, and thus relative close to water temperature (Fig 1). This indicates that despite the degree of elevated in Tsk during exercise before the immersion, cold water immersion led to similar significant decrease in Tsk for both trials. The reason for this is that water has a specific heat 1000 times that of air and a thermal conductivity of about 25 times that of air. Decrease in Tsk expected to reduce intramuscular temperature (Tim), and according to Johnson et al (1979) the decline in Tim can reach approximately 1.2o C after 5min cold water (10oC) bath.
After 15min of rest period, cold water immersion produced a rapid elevation in cardio-respiratory responses. During rest, minute ventilation was ~11L/min, and when the subjects immersed in cold water, VE rabidly increased at 67L/min (fig 2). In addition, at the onset of cold water immersion tidal volume in RT increased rapidly from 0.75 L to 1.99 L (Fig 3). Moreover, cold water immersion in RT produced a great impact in breathing frequency and heart rate. At the onset of immersion, breathing frequency increased by 35 breaths per minute (Fig 4), where heart rate increased by 50 beats per minute (Fig 5), compared to rest values. Conversely, after 15min of exercise, cold water immersion had no effect in cardio-respiratory responses. Exercise for 15min, at 70% HRR in a rowing ergometer produced elevation in cardio-respiratory function. More specific, during the intervention phase, VE (Fig 2), tidal volume (Fig 3), breathing frequency (Fig 4), and heart rate (Fig 5) were higher in ET compared to RT. This indicated that cardio-respiratory responses were higher in ET compared to RT at the point that subjects were prepared to immerse in cold water. Minute ventilation in ET just before the immersion was 75.3 L/min, and when the subjects immersed in cold water VE dropped at 58.2L/min (Fig 2). In addition, just before immersion tidal volume in ET was 2.17L and at the initial stage of immersion dropped to1.99L (Fig 3). Heart rate during the exercise period was ~144 bpm, and when the subjects immersed in the cold water, HR dropped to 115bpm (Fig 5). The only elevation in ET during cold water immersions was found in breathing frequency. During exercise, breathing frequency was 37 breaths per minute, but when the subjects immersed in the cold water, breathing frequency elevated at 52 breaths per minute (Fig 4). Similarly to previous studies (Tipton 1989; Tipton et al, 1999) in this experiment, elevation in responses of cardio-respiratory system in RT reduced over the next 2-5min of immersion, but still remained above pre-immersion values. Similarly there was a reduction in responses of cardio-respiratory system in ET, but conversely to RT, reduction in ET remained below pre-immersion values. Degrease in VE during immersion was similar for both conditions, leveling after 3min at 14.6L/min (Fig 2). The decline in tidal volume and heart rate was slower, and at the 5th min of immersion both tidal volume and heart rate were higher in ET compared to RT (Fig 3,5). Decline in breathing frequency was faster in RT compared to ET, but after 5min of immersion, breathing frequency was similar for both conditions. Despite the differentiation in the rate that cardio-respiratory responses were declined in ET and RT, the most important element of this experiment was that cardio-respiratory responses in cold water were higher with prior resting period, compared to prior exercise period.
Evidently, the magnitude of cardio-respiratory responses during the first minutes of cold water immersion is highly depended on pre-immersion physiological (exercise, rest) conditions. According to the experimental results, hazardous physiological responses in cold water immersion, collectively known as the cold shock were greater with prior rest condition, compared to prior exercise condition. From the above, it can be assumed that for individuals who performed exercise before any accidental fall in cold water the magnitude of cold shock will be smaller compared to individuals who were sitting rest before falling in cold water.
Despite the pre-immersion physiological condition (rest or exercise), sudden cold expose under any circumstances may be fatal for the immersed individual. As a conclusion it will be valuable to briefly refer to the role of protection that must be taken for a possible fall in cold water. As it was mention before in the discussion, during the initial stages of cold water expose, the risk for cardiovascular accident is high. In addition, the loss of voluntary control of breathing may increase the changes of aspirating water and thus drowning. Is situations where the risk of fall in cold water is high, several rules must be taken into consideration in order to minimize the risk of sudden death or drowning during the first minutes of the immersion. The role of clothing is important, since the use of appropriate clothes can minimize the initial cardio-respiratory responses in cold water, and according to Martin et al (1978) the use of appropriate clothing may prove beneficial during the first few minutes of a cold water immersion by degreasing the powerful drive to increased cardio-respiratory responses.
References
Durnin, J.V.G.A. and Womersley, J. (1974). Body fat assessed from total body density and its estimation from skinfold thickness: measurement on 481 men and women aged from 16-72 years. British Journal of Nutrition, 32, 77-97
Fortney, S.M. and Voman, N.B. (1985). Exercise performance and temperature control: temperature regulation during exercise and implications for sports performance and training. Medicine of Sciences and Sports and Exercise. 28, 20-28
Golden F.S.t.C, Hardcastle, P.T, Pollard, C.E. and Tipton, M.J. (1986). Hyperventilation and swimming failure in man in cold water. Journal of physiology. 378, 94
Johnson, D. G., Hayward, J.S., Jacobs, T.P., Collis, M.L., Eckerson, J.D. and Williams, R.H. (1977). Plasma norepinephrine responses of man in cold water. Journal of Applied Physiology. 43 (2), 216-220.
Johnson, D,J., Moore, S., Moore, J. and Oliver, A.R. (1979). Effect of cold submersion on intramuscular temperature of the gastrocnemius muscle. Physical Therapy. 59 (10), 1238-1242
Keatinge, W.R., Nadel, J.A. (1965). Immediate Respiratory Response to Sudden Cooling of the Skin. Journal of Applied Physiology. 20, 65-69
Marsh, D. and Sleivert, G. (1999). Effect of precooling on high intensity cycling performance. British Journal of Sports Medicine. 33, 393-397.
Martin, S., Diewold, R.J. and Cooper, K.E. (1978). The effect of clothing on the initial ventilatory responses during cold-water immersion. Canadian Journal of Physiology and Pharmacology. 56 (5), 886-888.
McArdle, W. D., Magel, J.R., Spina, R.J., Gergley, T.J. and Toner M.M. (1984). Thermal adjustment to cold water expose in resting men and women. Journal of Applied Physiology. 56, 1565-1571.
Roeggla, G., Roeggla, M., Binder, M., Roeggla, H., Muellner, M. and Wagner, A. (1995). Effect of alchochol on body core temperature during cold-water immersion. British Journal of Clinical Practice. 49 (5), 239-240
Tipton, M.J. (1989). The initial responses to cold water immersion in man. Clinical Science. 77, 581-588.
Tipton, M.J., Stubbs, D.A, Elliott, D.H. (1991). Human Initial Responses to Immersion in Cold Water at Three Temperatures and after Hyperventilation. Journal of Applied Physiology. 70(1), 317-322.
Tipton, M.J. (1992). The concept of an 'Integrated Survival System' for protection against the responses associated with immersion in cold water. Journal of Royal Navy Medicine Service. 79(1), 11-4.
Tipton, J.M., Eglin, C.M. and Golden, F.St.C. (1998). Habituation of the initial responses to cold water immersion in humans: a central or peripheral mechanism? Journal of Physiology. 512 (2), 621-628.
Tipton, J.M., Eglin, C.M., Gennser, M. and Golden, F. (1999). Immersion deaths and deterioration in swimming performance in cold water. The Lancet. 354 (21), 626-629.
Wagner, J.A. and Horvath, S.M. (1985). Cardiovascular reactions to cold exposure differ with age and gender. Journal of Applied Physiology. 58, 187-192
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