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Biomedical subjects

G K Bristow

Publications and source records attributed to G K Bristow.

At least 19 recordsLinked to original sources
PubMed1998

Recovery of a 62-year-old man from prolonged cold water submersion.

Recovery from prolonged cold water submersion is well documented in children but rare in adults. In the few adult cases reported, significant body cooling occurred (rectal temperature ranging from 22 degrees to 32 degrees C) and the victims were relatively young (< 40 years). We report a case of a 62-year-old man who was submersed in 2 degrees to 3 degrees C water for 15 minutes (time from initial submersion to intubation = 22 minutes). At the time of rescue, he had no vital signs, received prehospital Advanced Life Support, and was transported to hospital. On arrival at hospital, the patient remained in full cardiopulmonary arrest with an agonal ECG rhythm and had an initial pH of 6.77. Initial rectal temperature was near normal (36 degrees C) but subsequently dropped to 33 degrees C. The patient was resuscitated, rewarmed by forced-air warming, and treated for acute myocardial infarction, pulmonary edema, and generalized seizures. He was discharged after 27 days with minor neurologic abnormalities. Given the near-normal initial rectal temperature, preferential brain cooling may have been at least partially responsible for the positive neurologic outcome.

Body Temperature↗
PubMed1998

The convective afterdrop component during hypothermic exercise decreases with delayed exercise onset.

HYPOTHESIS: Following cold water immersion, the post-cooling decrease in esophageal temperature (Tes) (i.e., afterdrop) is 3 times greater during exercise than during shivering, presumably due to increased muscular blood flow and convective core-to-periphery heat loss with exercise (J. Appl. Physiol. 63:2375, 1987). We felt that if exercise were to commence once the afterdrop period during shivering is complete, the threat of a further decrease in Tes (i.e., a second afterdrop) during the subsequent exercise would be minimized because much of the convective capacity for core cooling would already be dissipated. METHODS: Six subjects were each cooled three times in 8 degrees C water, until Tes decreased to 35.3 +/- 0.7 degrees C, and rewarmed by either shivering alone, exercise, or exercise commencing once a shivering afterdrop period was complete. RESULTS: The initial afterdrop was greater during Exercise only (1.1 +/- 0.4 degrees C) than Shivering only (0.35 +/- 0.3 degrees C) and Shivering-Exercise (0.45 +/- 0.2 degrees C) (p < 0.05). In contrast, exercise caused a secondary afterdrop of only 0.38 +/- 0.3 degrees C during Shivering-Exercise (p < 0.05). The initial rewarming rate during Exercise only (3.45 degrees C.h-1) was greater than the initial (2.7 degrees C.h-1) and second (2.4 degrees C.h-1) rewarming rates during Shivering-Exercise (p < 0.05), but not significantly greater than during Shivering only (2.99 degrees C.h-1) (p < 0.1). DISCUSSION: It is likely that during the Shivering-Exercise protocol, continued blood flow to shivering muscles: a) contributes to the initial afterdrop, and thus b) diminishes the convective capacity (or heat sink) available for further cooling during subsequent exercise.

Adult↗
PubMed1998

Ethanol ingestion prolongs orthostatic intolerance in hyperthermic humans.

BACKGROUND: Both ethanol ingestion and hyperthermia contribute to orthostatic intolerance (OI). HYPOTHESIS: Since ethanol has been cited as a major risk factor for hyperthermia-related deaths, we hypothesized that ethanol exacerbates OI induced by hyperthermia. METHODS: There were seven subjects (four males, three females) rendered hyperthermic (esophageal temperature = 39 degrees C) in a 40 degrees C water bath on two separate days: Condition 1) Control (juice ingestion); and Condition 2) Ethanol [ethanol (1 ml x kg(-1) body mass) and juice ingestion]. To test for OI, 5-min supine periods were followed by 5-min 63 degrees head-up tilts prior to and following immersion. BPs, heart rate and esophageal temperatures were monitored throughout the experiments. RESULTS: For first and second post-immersion tilts, mean arterial BP (MAP) during tilting increased by 5.9 +/- 3.6 (SE) and 9.8 +/- 2.6 mm Hg in the control condition, while it decreased by 7.9 +/- 5.8 and 0.6 +/- 4.3 mm Hg in the ethanol condition. This gave significantly lower MAP (ethanol vs. control) of 63.6 +/- 3.1 vs. 71.8 +/- 4.5 mm Hg (p < 0.05) for the first and 79.6 +/- 2.3 vs. 86.7 +/- 4.4 mm Hg (p < 0.05) for the second post-immersion tilts. These values were all significantly less (p < 0.05) than normothermic tilted values of 94.7 +/- 4.7 mm Hg in the ethanol and 93.6 +/- 2.9 mm Hg in the control condition. Prior to warm water immersion, subjects tolerated all head-up tilts. In the control condition, only one subject experienced orthostatic intolerance following the first post-heating tilt and no intolerance was experienced following 30 min post-heating. However, during the ethanol condition, 4 subjects experienced orthostatic intolerance following the first tilt with episodes of intolerance lasting as long as 80 min (8 supine/tilt cycles). CONCLUSION: Ethanol ingestion prolonged and increased the magnitude of OI in hyperthermic subjects. This may at least partly explain why ethanol is a major risk factor in hyperthermia-related deaths.

Adult↗
PubMed1997

Clonidine decreases vasoconstriction and shivering thresholds, without affecting the sweating threshold.

PURPOSE: This study was conducted to test the hypothesis that clonidine produces a dose-dependent increase in the sweating threshold and dose-dependent decreases in vasoconstriction and shivering thresholds. METHODS: Six healthy subjects (two female) were studied on four days after taking clonidine in oral doses of either 0 (control), 3, 6 or 9 micrograms.kg-1. The order followed a balanced design in a double-blind fashion. Oesophageal temperature and mean skin temperature (from 12 sites) were measured. Subjects were seated in 37 degrees C water which was gradually warmed until sweating occurred (sweat rate increased above 50 g.m-2.h-1). The water was then cooled gradually until thresholds for vasoconstriction (onset of sustained decrease in fingertip blood flow) and shivering (sustained elevation in metabolism) were determined. Thresholds were then referred to as the core temperature, adjusted to a designated mean skin temperature of 33 degrees C. RESULTS: High dose clonidine similarly decreased the adjusted core temperature thresholds for vasoconstriction by 1.16 +/- 0.30 degrees C and for shivering by 1.63 +/- 0.23 degrees C (P < 0.01). The dose response effects were linear for both cold responses with vasoconstriction and shivering thresholds decreasing by 0.13 +/- 0.05 and 0.19 +/- 0.09 degree C.microgram-1 respectively (P < 0.0001). The sweating threshold was unaffected by clonidine, however the interthreshold range between sweating and vasoconstriction thresholds increased from control (0.19 +/- 0.48 degree C) to high dose clonidine (1.31 +/- 0.54 degrees C). CONCLUSION: The decreases in core temperature thresholds for cold responses and increased interthreshold range are consistent with the effects of several anaesthetic agents and opioids and is indicative of central thermoregulatory inhibition.

Adrenergic alpha-Agonists↗
PubMed1997

Inhibition of shivering increases core temperature afterdrop and attenuates rewarming in hypothermic humans.

During severe hypothermia, shivering is absent. To simulate severe hypothermia, shivering in eight mildly hypothermic subjects was inhibited with meperidine (1.5 mg/kg). Subjects were cooled twice (meperidine and control trials) in 8 degrees C water to a core temperature of 35.9 +/- 0.5 (SD) degrees C, dried, and then placed in sleeping bags. Meperidine caused a 3.2-fold increase in core temperature afterdrop (1.1 +/- 0.6 vs. 0.4 +/- 0.2 degree C), a 4.3-fold increase in afterdrop duration (89.4 +/- 31.4 vs. 20.9 +/- 5.7 min), and a 37% decrease in rewarming rate (1.2 +/- 0.5 vs. 1.9 +/- 0.9 degrees C/h). Meperidine inhibited overt shivering. Oxygen consumption, minute ventilation, and heart rate decreased after meperidine injection but subsequently returned toward preinjection values after 45 min postimmersion. This was likely due to the increased thermoregulatory drive with the greater afterdrop and the short half-life of meperidine. These results demonstrate the effectiveness of shivering heat production in attenuating the postcooling afterdrop of core temperature and potentiating core rewarming. The meperidine protocol may be valuable for comparing the efficacy of various hypothermia rewarming methods in the absence of shivering.

Adult↗
PubMed1997

Efficacy of forced-air and inhalation rewarming by using a human model for severe hypothermia.

We recently developed a nonshivering human model for severe hypothermia by using meperidine to inhibit shivering in mildly hypothermic subjects. This thermal model was used to evaluate warming techniques. On three occasions, eight subjects were immersed for approximately 25 min in 9 degrees C water. Meperidine (1.5 mg/kg) was injected before the subjects exited the water. Subjects were then removed, insulated, and rewarmed in an ambient temperature of -20 degrees C with either 1) spontaneous rewarming (control), 2) inhalation rewarming with saturated air at approximately 43 degrees C, or 3) forced-air warming. Additional meperidine (to a maximum cumulative dose of 2.5 mg/kg) was given to maintain shivering inhibition. The core temperature afterdrop was 30-40% less during forced-air warming (0.9 degree C) than during control (1.4 degrees C) and inhalation rewarming (1.2 degrees C) (P < 0.05). Rewarming rate was 6- to 10-fold greater during forced-air warming (2.40 degrees C/h) than during control (0.41 degree C/h) and inhalation rewarming (0.23 degree C/h) (P < 0.05). In nonshivering hypothermic subjects, forced-air warming provided a rewarming advantage, but inhalation rewarming did not.

Adult↗
PubMed1996

Alcohol lowers the vasoconstriction threshold in humans without affecting core cooling rate during mild cold exposure.

Elevated blood alcohol levels are often seen in hypothermia and hyperthermia related deaths, leading to the belief that alcohol renders humans poikilothermic. We examined the core temperature (Tco) thresholds for sweating, vasoconstriction and shivering as well as core cooling rates of seven subjects immersed in 28 degrees C water. On two separate days, subjects exercised on an underwater cycle ergometer to elevate Tco above the sweating threshold. They then rested and cooled until they shivered vigorously. Subjects drank orange juice (7 ml.kg-1) prior to immersion during the control trial and 1 ml.kg-1 absolute ethanol, added to orange juice in a 1:6 ratio, during the alcohol trial. Mean blood alcohol concentration (breath analysis) was 0.097 +/- 0.010 g% at the start of cooling and 0.077 +/- 0.008 g% at the end of the cooling period. Alcohol lowered the vasoconstriction threshold by 0.32 +/- 0.2 degrees C and elevated finger tip blood flow, but had no effect on thresholds for sweating and shivering or core cooling rate. Considering these minor effects it is unlikely that moderate alcohol consumption predisposes individuals to hypothermia or hyperthermia via impaired thermoregulation, but rather likely due to behavioral factors.

Adult↗
PubMed1996

Eucapnic hypoxia lowers human cold thermoregulatory response thresholds and accelerates core cooling.

Hypoxia lowers the basic thermoregulatory responses of animals and humans. In cold-exposed animals, hypoxia increases core temperature (Tco) cooling rate and suppresses shivering thermogenesis. In humans, the experimental effects of hypoxia on thermoregulation are equivocal. Also, the effect of hypoxia has not been separated from that of hypocapnia consequent to hypoxic hyperventilation. To determine the isolated effects of hypoxia on warm and cold thermoregulatory responses and core cooling during mild cold stress, we examined the Tco thresholds for sweating, vasoconstriction, and shivering as well as the core cooling rates of eight subjects immersed in 28 degrees C water under eucapnic conditions. On 2 separate days, subjects exercised on an underwater cycle ergometer to elevate Tco above the sweating threshold. They then rested and cooled until they shivered vigorously. Subjects inspired humidified room air during the control trial. For the eucapnic hypoxia trial, they inspired 12% O2-balance N2 with CO2 added to maintain eucapnia. Eucapnic hypoxia lowered the Tco thresholds for vasoconstriction and shivering by 0.14 and 0.19 degrees C, respectively, and increased core cooling rate by 33% (1.83 vs. 1.38 degrees C/h). These results demonstrate that eucapnic hypoxia enhances the core cooling rate in humans during mild cold stress. This may be attributed in part to a delay in the onset of vasoconstriction and shivering as well as increased respiratory heat loss during hypoxic hyperventilation.

Adult↗
PubMed1995

Isolated effects of peripheral arm and central body cooling on arm performance.

BACKGROUND: Whole body cooling impairs manual arm performance. The independent contributions of local (peripheral) and/or whole body (central) cooling are not known. Therefore, a protocol was developed in which the arm and the rest of the body could be independently cooled. METHODS: Biceps temperature (Tmus), at a depth of 20 mm, and esophageal temperature (Tes) were measured. Six subjects were immersed to the clavicles in a tank (body tank) of water under 3 conditions: 1) cold body-cold arm (CB-CA); 2) warm body-cold arm (WB-CA); and 3) cold body-warm arm (CB-WA). In the latter two conditions, subjects placed their dominant arm in a separate (arm) tank. Water temperature (Tw) in each tank was independently controlled. In conditions requiring cold body and/or cold arm, Tw in the appropriate tanks was 8 degrees C. In conditions requiring warm body and/or warm arm, Tw in the appropriate tanks was adjusted between 29 and 38 degrees C to maintain body/arm temperature at baseline values. A battery of 6 tests, requiring fine or gross motor movements, were performed immediately before immersion and after 15, 45, and 70 minutes of immersion. RESULTS: In CB-CA, Tes decreased from an average of 37.2 to 35.6 degrees C and Tmus decreased from 34.6 to 22.0 degrees C. In WB-CA, Tmus decreased to 18.1 degrees C (Tes = 37.1 degrees C), and in CB-WA, Tes decreased to 35.8 degrees C (Tmus = 34.5 degrees C). By the end of immersion, there were significant decrements (43-85%) in the performance of all tests in CB-CA and WB-CA (p < 0.0002); scores for each test were similar in these two conditions. There was no significant change in scores throughout the CB-WA condition. In both conditions with arm cooling (i.e., WB-CA and CB-CA), Tmus accounted for 85-98% of the variance in all tests. When the core was cooled in the CB-WA condition, Tes was significantly correlated to scores in only two tests (accounted for 90 and 93% of the variance) although the actual effect was small. In the CB-CA condition, partial correlations indicated that Tes accounted for 4-10% of the variance in scores of 4 tests. CONCLUSIONS: We conclude that cooling of the body and/or the arm elicits large decrements in finger, hand and arm performance. The decrements are due almost entirely to the local effects of arm tissue cooling.

Adult↗
PubMed1995

Influence of body composition on rewarming from immersion hypothermia.

BACKGROUND: This study was conducted to determine if the differences between efficacies of three treatments for immersion hypothermia are affected by body composition. METHODS: Twelve subjects were divided into equally sized low (LF) and high (HF) fat groups. On three occasions subjects were each immersed in cold water until esophageal temperatures (Tes) decreased to approximately 33.2 degrees C (LF) and approximately 35.8 degrees C (HF). They were then rewarmed by: 1) shivering; 2) application of external heat; or 3) treadmill exercise in a balanced design. RESULTS: For HF, the afterdrop during exercise (1.04 +/- 0.2 degrees C) was greater than during shivering (0.35 +/- 0.3 degrees C) and external heat (0.36 +/- 0.1 degree C) (p < 0.01). In LF, however, the exercise afterdrop (0.75 +/- 0.2 degree C) was greater than only external heat (0.35 +/- 0.2 degree C) (p < 0.05) but not shivering (0.58 +/- 0.4 degree C). There was a positive relationship between % fat and afterdrop for the exercise condition with a slope (95% C.I.) of 0.03 (0.01 to 0.05) degree C.% fat-1 (r2 = 0.37, p < 0.05). The exercise rewarming rate (3.48 +/- 1.1 degrees C.h-1) was greater (p < 0.01) than during both shivering (1.80 +/- 0.7 degrees C.h-1) and external heat (2.22 +/- 0.7 degrees C.h-1) in HF while no difference was seen between the three treatments (5.28 +/- 0.4, 4.86 +/- 1.1 and 5.16 +/- 0.7 degrees C.h-1, respectively) in LF. There were inverse relationships between % fat and rewarming rate in the exercise -0.12 (-0.23 to -0.01) degree C.h-1.% fat-1, (r2 = 0.38), shivering -0.27 (-0.38 to -0.16) degrees C.h-1.% fat-1, (r2 = 0.76) and external heat -0.26 (-0.35 to -0.17) degree C.h-1.% fat-1, (r2 = 0.83) conditions (p < 0.05). CONCLUSIONS: The inter-treatment differences between these techniques are accentuated in the HF, and attenuated (afterdrop) or even eliminated (rewarming rate) in the LF subgroup.

Adult↗
PubMed1994

Treatment of mild immersion hypothermia by direct body-to-body contact.

Body-to-body contact is often recommended for rewarming mildly hypothermic victims in the field. This procedure involves a euthermic individual donating heat to the recipient by direct contact in an insulated bag. However, this technique has not been critically evaluated and may not be beneficial because there is limited direct contact between recipient and donor, peripheral vasoconstriction may impair heat transfer to the core, skin warming may blunt the recipient's shivering response, and cold stress to the donor may be excessive. The present study was designed to evaluate whether donation of heat by a donor would be sufficient to enhance rewarming of a hypothermic subject (recipient). Six pairs of recipients (5 men, 1 woman) and donors (2 men, 4 women) participated in the study. Esophageal and skin temperatures, cutaneous heat flux, and oxygen consumption were measured. Recipients were immersed in 8 degrees C water until esophageal temperature decreased to a mean of 34.6 +/- 0.7 degrees C (SD). They then were rewarmed by one of three methods: rewarming by the endogenous heat generated by shivering only (SH), body-to-body rewarming (BB), or rewarming with a constant-heat source manikin (MAN). Mean afterdrop for the three conditions was 0.54 +/- 0.2, 0.54 +/- 0.2, and 0.57 +/- 0.2 degrees C for SH, BB, and MAN, respectively (NS), and the rate of rewarming was 2.40 +/- 0.8, 2.46 +/- 1.1 and 2.55 +/- 0.9 degrees C/h for SH, BB, and MAN, respectively (NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Treatment of mild immersion hypothermia by forced-air warming.

Forced-air warming is used for prevention or reversal of hypothermia in surgical patients. In the present study, the efficacy of this system for treatment of immersion hypothermia was evaluated. Six men and two women were twice immersed in 8 degrees C water until hypothermic. They were then rewarmed by either: 1) shivering-only inside a sleeping bag; or 2) forced-air warming. Esophageal and skin temperature, cutaneous heat flux and metabolism were measured. Afterdrop (+/- SD) during forced-air warming (0.43 +/- 0.26 degrees C) was approximately 30% less than during shivering (0.61 +/- 0.26 degrees C) (p < 0.001). Rewarming rate during forced-air warming (3.26 +/- 1.8 degrees C.h-1) was not significantly different from shivering (3.02 +/- 1.2 degrees C.h-1). Skin temperature was higher during forced-air warming by 3.7 degrees C early and 4.5 degrees C after 35 min of warming. Heat production increased by 77 W over the initial 20 min of shivering, and subsequently declined, compared to an immediate decrease with forced-air warming. During shivering heat flux ranged from 30 W early in rewarming, to 50 W after 35 min, compared to -237 W and -163 W respectively, for forced-air warming. Forced-air warming attenuated afterdrop and the metabolic stress of shivering while maintaining an average rate of rewarming comparable to shivering. Forced-air warming is a safe, simple, noninvasive treatment and could be used effectively in an emergency medical facility, and possibly in some rescue/emergency vehicles or marine vessels.

Adult↗
PubMed1994

Leg temperature and heat content in humans during immersion hypothermia and rewarming.

Core temperature afterdrop following cold water immersion has previously been shown to be greater during treadmill exercise than shivering (J. Appl. Physiol. 1987; 63:2375-9). To test the hypothesis that this results from increased transfer of heat from the core to exercising muscles, we quantified the changes in leg temperature and heat content during cooling and exercise/shivering protocols. Upper and lower leg muscle temperatures were measured at multiple depths in five thin healthy male subjects immersed in 8 degrees C water until core temperatures reached 32.8-34.9 degrees C. In these thin subjects there was a significant but small difference between exercise and shivering afterdrop (approximately 0.2 degrees C), and total leg heat content was unchanged during this period with both protocols. Subsequent heat gain was similar in both treatments but, in the lower leg, was greater during exercise than shivering, suggesting that shivering is less effective than exercise in increasing lower leg heat content.

Adult↗
PubMed1993

Effect of task complexity on mental performance during immersion hypothermia.

The effect of task complexity on the decrement in mental performance during immersion hypothermia was studied. Psychometric tests of varying length and complexity were administered: 1) prior to cold water immersion (baseline); 2) soon after immersion to the neck in cold (8 degrees C) water but prior to any decrease in core temperature; and 3) after 55 to 80 min of immersion when core temperature had decreased 2-4 degrees C. Results indicated that tests placing relatively minimal cognitive demands on individuals, such as auditory attention, the Benton visual recognition test and forward digit span, were unaffected by either initial cold water immersion or central cooling. On the other hand, tests requiring relatively greater mental manipulation and short term memory (i.e., backward digit span) or processing and analysis (i.e., Stroop test) showed a slight improvement upon cold water immersion (perhaps related to increased arousal and/or learning) but a significant decrement following central cooling of 2-4 degrees C. Thus, relatively simple tasks were unaffected by central cooling, whereas more complex tasks were adversely affected. Cold water immersion itself did not interfere with performance of any tasks. Central nervous system cooling probably interferes with mental processing although discomfort and/or the physiological and physical effects of cold on the neuromuscular aspects of speech, required for responses to some of the tasks, may also affect performance.

Adult↗
PubMed1992

A second postcooling afterdrop: more evidence for a convective mechanism.

An attempt was made to demonstrate the importance of increased perfusion of cold tissue in core temperature afterdrop. Five male subjects were cooled twice in water (8 degrees C) for 53-80 min. They were then rewarmed by one of two methods (shivering thermogenesis or treadmill exercise) for another 40-65 min, after which they entered a warm bath (40 degrees C). Esophageal temperature (Tes) as well as thigh and calf muscle temperatures at three depths (1.5, 3.0, and 4.5 cm) were measured. Cold water immersion was terminated at Tes varying between 33.0 and 34.5 degrees C. For each subject this temperature was similar in both trials. The initial core temperature afterdrop was 58% greater during exercise (mean +/- SE, 0.65 +/- 0.10 degrees C) than shivering (0.41 +/- 0.06 degrees C) (P < 0.005). Within the first 5 min after subjects entered the warm bath the initial rate of rewarming (previously established during shivering or exercise, approximately 0.07 degrees C/min) decreased. The attenuation was 0.088 +/- 0.03 degrees C/min (P < 0.025) after shivering and 0.062 +/- 0.022 degrees C/min (P < 0.025) after exercise. In 4 of 10 trials (2 after shivering and 2 after exercise) a second afterdrop occurred during this period. We suggest that increased perfusion of cold tissue is one probable mechanism responsible for attenuation or reversal of the initial rewarming rate. These results have important implications for treatment of hypothermia victims, even when treatment commences long after removal from cold water.

Adult↗
PubMed1992

Decrement in manual arm performance during whole body cooling.

Six subjects performed three manual arm tasks: 1) prior to immersion in 8 degrees C water; 2) soon after immersion to the neck, but prior to any decrease in core temperature; and 3) every 15 min until core temperatures decreased 2-4.5 degrees C. The tasks were speed of flexion and extension of the fingers, handgrip strength and manual dexterity. There was no immediate effect of cold immersion; however, all scores decreased significantly after core temperature decreased 0.5 degrees C. Further decrease in core temperature was associated with a progressive impairment of performance, although at a slower rate than during the first 0.5 degrees C decrease. Flexion and extension of the fingers was affected relatively more than handgrip strength or manual dexterity. Decrement in performance is a result of peripheral cooling on sensorimotor function with a probable additional effect of central cooling on cerebral function.

Adult↗