Biomedical subjects

J S Hayward

Publications and source records attributed to J S Hayward.

At least 19 recordsLinked to original sources

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↗

PubMed1996

Wet-cold exposure and hypothermia: thermal and metabolic responses to prolonged exercise in rain.

Simulated conditions of hiking in rain, wind, and cold, without protective rainwear, were used to investigate wet-cold hypothermia in 18 male subjects. Thermal, metabolic, and motor responses were monitored during an attempted 5-h walk (5.1 km/h) at 5 degrees C, with continuous exposure to rain (7.4 cm/h) and wind (8.0 km/h) over the final 4 h. The majority of subjects (11) could not complete the protocol because of intolerance of wet-cold conditions during the last 2 h. Therefore, data from 5 subjects who completed the protocol in rain and control conditions were used to describe the general pattern of response. During the 1st h of walking, core temperature rose 1 degree C to 38.1 degrees C. The subsequent 2 h of rain caused substantial cold stress, indicated by a 40% increase in heat production due to shivering and significant loss of strength and manual dexterity. However, core temperature only decreased to 37.1 degrees C, merely eliminating the initial exercise hyperthermia. Over the last 2 h of rain, core temperature remained relatively stable at 36.8 degrees C, decreasing slightly to 36.4 degrees C by 5 h. Two other subjects developed significant hypothermia (35 degrees C). One demonstrated fatigue of shivering after 2.5 h of rain, confirming the exhaustion hypothesis of wet-cold hypothermia. The older cooled rapidly when he failed to maintain the walking pace. We conclude that if a person can tolerate the intense discomfort of prolonged wet-cold exposure, he or she has the potential to resist significant core hypothermia for at least 4 h of walking under the conditions of this experiment. Exceptions to this generalization occur, making exposure of < 4 h a hypothermia risk for some individuals. Exposures > 4 h would involve increasing probability of rapid decline into hypothermia, associated with exhaustion of shivering and exercise heat production.

Adult↗

PubMed1989

Hyperventilation response to cold water immersion: reduction by staged entry.

Staged immersion of humans into cold water was investigated to determine whether the hyperventilation response could be reduced by this behavioral technique. A simple, two-stage procedure involving immersion to the waist for 30 s before full immersion to neck level was compared to non-staged immersion. For the staged immersion, maximum values of respiratory minute volume and respiratory frequency were significantly reduced by 35% and 38%, respectively, from the maxima observed for non-staged immersion. These results indicate that if staged immersion into cold water is possible, it can attenuate the hyperventilation response and, therefore, the probability of sudden drowning. We recommend that this knowledge be incorporated into teaching programs concerning cold water safety.

Adult↗

PubMed1989

Effect of hyperthermia on breath-alcohol analysis.

Mild hyperthermia to the extent of a 2.5 degrees C increase above normal body temperature was produced by immersion of ethanol-intoxicated subjects in a warm water bath. Hyperthermia did not influence the blood-alcohol decay curve of the subjects. Hyperthermia did cause a significant distortion of the breath-alcohol decay curve, up to as much as a 23% increase above blood-alcohol concentration. The magnitude of this distortion effect was calculated to be a 8.62% increase in breath-alcohol concentration over blood-alcohol concentration for each degree C increase in core body temperature. The forensic relevance of these results is that further support is given to previous recommendations that temperature monitoring be included in procedures for breath-alcohol analysis. This leads to the recommendation that mouth temperature be measured before breath sampling to screen for abnormal body temperature and to allow for potential use of a "temperature correction factor." This modification to existing analytical procedures would optimize the reliability of breath-ethanol analysis for prediction of blood-ethanol concentration.

Adult↗

PubMed1988

A photodetection device for luminol-based immunodot and Western blotting assays.

A photodetection device permitting rapid and direct photographic recording of light emission from luminol-based immunodot and Western blotting assays is described in detail. This device permits contact exposure on Polaroid film of luminescent samples on nitrocellulose strips, and thus obviates the need for darkroom and film processing facilities. Immunodetection of mouse alpha-fetoprotein in brown fat homogenate and immunoglobulin E in nonimmune human sera employing luminol-based Western blotting and immunodot assays were used to demonstrate the versatility and operational simplicity of the detection device. The use of the detection device in combination with luminol-based immunoassays resulted in greater signal intensities and increased sensitivity over that attainable with the commonly used chromogenic substrate, 4-chloro-1-naphthol.

Adipose Tissue, Brown↗

PubMed1987

Dive response of children in relation to cold-water near-drowning.

The strength of the dive response, as judged by the combination of breath-hold duration (BHD) and bradycardia, was compared in 87 children (4-13 yr old) and 68 adults (20-68 yr old) during simulated dives in 29 degrees C water. Mean BHD in children (16.1 s) was only 37.4% (P less than 0.001) of adult BHD (43.0 s). Within children, BHD was significantly (P less than 0.001) dependent on age (A in yr) according to the regression BHD = -1.46 + 2.27A. No age dependency of BHD occurred in adults. Due to the low BHD of children, only 14/87 (16.1%) were able to breath hold for the 25 s necessary to develop full diving bradycardia. For these 14 children, their bradycardia (36.1% reduction) was insignificantly different (P greater than 0.50) from that of adults (36.4%). These experimental findings demonstrate that the dive response of children is extremely weak, due mainly to their very low BHD. Since lower water temperature would probably accentuate the shortness of BHD (according to previous findings for adults), it is concluded that the dive response is unlikely to make a significant contribution to the prolonged resuscitatibility of children who are victims of cold-water near-drowning.

Adult↗

PubMed1987

Effect of hypothermia on breath-alcohol analysis.

Mild hypothermia, induced by experimental immersion of ten subjects in cold water, distorted the decay curve of breath ethanol of intoxicated subjects by as much as 22% while not altering overall ethanol clearance rate. The results provide in vivo verification of the in vitro temperature correction factor of 6.8% X degrees C-1, and support previous recommendations that temperature monitoring be included in procedures for breath-ethanol testing. We recommend that mouth temperature be obtained before breath sampling to screen for abnormal body temperature and to allow for potential use of a temperature correction factor. This modification to existing analytical procedures would help to optimize the reliability of breath-ethanol analysis in predicting blood-ethanol concentration.

Adult↗

PubMed1987

Immersion hypothermia: comparative protection of anti-exposure garments in calm versus rough seas.

To evaluate the thermal performance of anti-exposure garments in rough seas, eight garment-ensembles were studied: 7 foam-insulated garments (2 tight-fitting "wet" suits, 3 loose-fitting "wet" garments, 2 "dry" suits) and 1 uninsulated, loose-fitting control. Mean calm and rough water temperatures were 10.7 and 11.1 degrees C, respectively. Rectal temperature, back skin temperature, heart rate, and subjective evaluations of garment protection were measured. Loose-fitting, "wet" garments allowed significantly greater (approximately 50-100%) mean rectal temperature cooling rates and significantly larger declines in skin temperature in rough water than in calm water. Such differences were not found for either the tight-fitting "wet" suits or the "dry" suits. Heart rates were significantly higher in rough seas than in calm seas for all garments. Rectal and skin temperature changes were positively correlated with each other and with subjective evaluation of cold water flushing; they were negatively correlated with warmth and tightness-of-fit. "Dry" garments provided better protection than did "wet" garments in both sea conditions, and tight-fitting "wet" garments provided better protection than did loose-fitting "wet" garments in rough but not in calm seas. Accidental immersion in rough seas may be associated with significantly lower survival times than previously estimated from calm-water studies.

Adult↗

PubMed1986

Effect of mesomorphy on hyperthermia during exercise in a warm, humid environment.

The hyperthermic response to exercise in a warm (30 degrees C), humid (80% relative humidity) environment was obtained for 27 men who exhibited a wide range of body physique in terms of the mesomorphy component of somatotype. Increase in tympanic temperature (Yty) was significantly dependent on mesomorphy rating (X) according to the regression equation Yty = -0.390 + 0.088X. Increase in rectal temperature (Yre) was also significantly dependent on mesomorphy rating according to the equation Yre = -0.100 + 0.066X. The hyperthermic response was significantly correlated with other measures of physique, including ectomorphy, surface area/weight ratio, and body weight, but was not correlated with fatness or fitness. The results support the generalization that during exercise in a warm, humid environment individual differences in heat strain can be highly dependent on physique, especially if fitness and fatness are similar. In this context, mesomorphy appears to provide the optimum description of physique variation. Individuals with a mesomorphy rating greater than 7 warrant designation as being at high risk for heat intolerance during exercise in environments that significantly impair the rate of body heat loss.

Adolescent↗

PubMed1986

Physique and thermoregulation in prepubertal males during exercise in a warm, humid environment.

The hyperthermic response to exercise in a warm (30 degrees C), humid (80% relative humidity) environment was obtained for 23 prepubertal males. After the initial increase of core temperatures (tympanic and rectal) to elevated set points, further hyperthermia was minimal and was unrelated to any physique variable except for the case of endomorphy, which was weakly correlated with hyperthermia at the rectal site. This result for boys is attributed to the combination of small body size (relative to adults) and absence of pronounced, age-dependent muscular development as evidenced by low rating and small variation of the mesomorphy component of somatotype. Both of these factors were associated with a high surface area to weight ratio compared to adults, which facilitated heat loss. It is concluded that prepubertal males thermoregulate efficiently during moderate exercise in a warm, humid environment. Other than cases of obesity, variation in physique is not an important consideration for assessing the risk of heat strain.

Adolescent↗

PubMed1984

EEG and visual evoked potentials of conscious man during moderate hypothermia.

Five conscious, normal humans were cooled by water immersion until their core temperatures were near 33.5 degrees C. When hypothermic at this level, small shifts of EEG frequencies to more theta and beta and less alpha activity occurred in comparison to normothermia. There was no significant change in the amplitude of the EEG. Although 10-20% increases in the latency of peaks in the visual evoked potential occurred in some subjects when hypothermic, this was not statistically significant, nor was the slight amplitude reduction. The results confirm for conscious, unanesthetized humans that moderate hypothermia to the level of 33.5 degrees C is on the borderline for significant alteration of brain electrical activity by cold, a general conclusion that was known previously only for anesthetized or immobilized humans and other mammals.

Adult↗

PubMed1984

Thermal and cardiovascular changes during three methods of resuscitation from mild hypothermia.

The interrelations among core temperatures (cardiac, esophageal, tympanic, rectal), skin temperature, and cardiovascular function (cardiac output, arterial pressure, heart rate, total peripheral resistance) were studied in a conscious subject during entry into mild hypothermia through cold water (10 degrees C) immersion, and during rewarming by three basic procedures: peripheral heat donation (bath); core heat donation (inhalation); and no exogenous heat (spontaneous). Swan-Ganz catheterization of the heart enabled measurement of cardiac temperature as well as cardiac output by the thermal dilution method. During cooling, all sites of core temperature measurement showed similar rates of entry into hypothermia. However, during the rewarming procedures, divergent patterns of temperature change among the four sites occurred. Rectal and tympanic temperatures were not representative of cardiac temperature, but esophageal temperature was, and is therefore most suitable as a criterion for experimental evaluation of the thermal benefit of various core rewarming techniques. During the first 30 min of rewarming, rates of increase in cardiac temperature for bath, inhalation, and spontaneous procedures varied according to the proportions 4:2:1, respectively. No afterdrop of cardiac temperature occurred with the inhalation or spontaneous procedures, but an afterdrop at this site did occur during the first 15 min of bath rewarming as soon as skin temperature was greater than 30 degrees C. This afterdrop coincided with cardiovascular changes including abrupt decreases in arterial pressure and total peripheral resistance, along with increases in heart rate and cardiac output. Such evidence of increased peripheral circulation was not observed with the inhalation and spontaneous methods. The findings relate to experimental evaluation of rewarming techniques and principles for resuscitation of hypothermia victims, especially in the first-aid situation.

Baths↗

PubMed1984

Temperature effect on the human dive response in relation to cold water near-drowning.

To facilitate analysis of mechanisms involved in cold water near-drowning, maximum breath-hold duration (BHD) and diving bradycardia were measured in 160 humans who were submerged in water temperatures from 0 to 35 degrees C at 5 degrees C intervals. For sudden submersion BHD was dependent on water temperature (Tw) according to the equation BHD = 15.01 + 0.92Tw. In cold water (0-15 degrees C), BHD was greatly reduced, being 25-50% of the presubmersion duration. BHD after brief habituation to water temperature and mild, voluntary hyperventilation was more than double that of sudden submersion and was also dependent on water temperature according to the equation BHD = 38.90 + 1.70Tw. Minimum heart rate during both types of submersions (diving bradycardia) was independent of water temperature. The results are pertinent to accidental submersion in cold water and show that decreased breath-holding capacity caused by peripheral cold stimulation reduces the effectiveness of the dive response and facilitates drowning. These findings do not support the postulate that the dive response has an important role in the enhanced resuscitatibility associated with cold water near-drowning, thereby shifting emphasis to hypothermia as the mechanism for this phenomenon.

Adult↗

PubMed1984

Thermal protection performance of survival suits in ice-water.

Five models of dry and insulative survival suits for cold-water immersion were studies for their thermal protection while worn by subjects floating in ice-water at 1 degree C for 6 h. Rectal temperature, extremity skin temperatures, and heart rate were monitored. No significant differences occurred in the thermal or heart rate responses of the subjects wearing the five models of suits. The immersion induced only mild hypothermia; the overall amount of rectal cooling during the 6-h period was 0.80 degree C, or a rate of 0.13 degree C/h. Extremity temperatures fell within the first 2 h to levels that induced strong sensation of cold and moderate shivering. The results show that dry and insulative survival suits can provide excellent protection against fatal levels of hypothermia resulting from ice-water immersion. Predicted survival time, given the very low cooling rate observed, exceeds 1 d if drowning can be avoided.

Adult↗

PubMed1984

Physiological responses and survival time prediction for humans in ice-water.

Lightly-clothed, nonexercising humans - 10 females and 11 males - were immersed in 0 degree C water for durations of 25-40 min until their core temperatures decreased to 35 degrees C. Ventilation rate increased 434% in the first 1-2 min of immersion, which increased the respiratory exchange ratio from 0.8 to 1.4. After 10 min of immersion, mean skin temperature had fallen to 5 degrees C and mean rectal and tympanic cooling rates were 6.02 and 5.40 degrees C/h, respectively. No sex differences occurred. By 15-20 min of immersion, maximum shivering metabolism was attained with levels nearly 4 times the preimmersion metabolic rate. This metabolic response was accompanied by heart rates in the range of 90-110 beats/min and increases in respiratory minute volume that were 250-300% greater than preimmersion. Predictions of survival time in 0 degree C water (based on hypothermia rather than drowning) were 1-1.5 h for the average person under the conditions of this study.

Adult↗

PubMed1980

Effect of cold water immersion and its combination with alcohol intoxication on urine flow rate of man.

Urine flow rate was determined for man before and after immersion in either thermoneutral (33 degrees C) or cold (10 degrees C) water. The effect of alcohol intoxication of a level of approximately 80 mg dL-1 was also evaluated for the cold water immersion. Immersion and cold were additive in their effect, resulting in a mean urine flow rate of 4.25 mL min-1, approximately 3.5 times the preimmersion level. Alcohol intoxication in conjunction with cold water immersion caused a further large increase in urine flow to 8.03 mL min-1. These results permit better evaluation of the importance of volume diuresis as it relates to the reduction of insulative performance of dry-type immersion suits for cold water survival, and to the possible enhancement of "rewarming shock" during therapy for hypothermia victims. The increased urine production observed when alcohol treatment was added to cold immersion provides information for speculation on mechanisms of volume diuresis.

Adult↗

PubMed1980

Accidental hypothermia: the effect of initial body temperatures and physique on the rate of rewarming.

After cooling in sea water, 14 subjects having varied core temperatures were rewarmed by inhalation of saturated air at 44 degrees C. Multiple linear regression analyses were computed for best possible subsets relating rectal and tympanic rewarming rates, phi i (i = R, T), to physiological and anthropometric measures. It was found that there was a good correlation between phi i and metabolic or ventilatory rates (0.61 less than r less than 0.74). Rewarming rates phi i could be more closely predicted by a combination of initial core temperatures and (height/weight)0.5 or by a combination of initial core temperatures and initial skin temperatures (0.75 less than r less than 0.88). The effectiveness of inhalation rewarming has been challenged and experimental studies appear contradictory. It is shown that the different inhalation rewarming rates measured are predictable and can be explained largely in physiological terms.

Adolescent↗

PubMed1979

Effect of alcohol on thermal balance of man in cold water.

The effects of alcohol on core cooling rates (rectal and tympanic), skin temperatures, and metabolic rate were determined for 10 subjects rendered hypothermic by immersion for 45 min in 10 degrees C water. Experiments were duplicated with and without a 20-min period of exercise at the beginning of cold water immersion. Measurements were continued during rewarming in a hot bath. With blood alcohol concentrations averaging 82 mg 100 mL-1, core cooling rates and changes in skin temperatures were insignificantly different from controls, even if the exercise period was imposed. Alcohol reduced shivering metabolic rate by an overall mean of 13%, insufficient to affect cooling rate. Alcohol had no effect on metabolic rate during exercise. During rewarming by hot bath, the amount of 'afterdrop' and rate of increase in core temperature were unaffected by alcohol. It was concluded that alcohol in a moderate dosage does not influence the rate of progress into hypothermia or subsequent, efficient rewarming. This emphasizes that the high incidence of alcohol involvement in water-related fatalities is due to alcohol potentiation of accidents rather than any direct effects on cold water survival, although very high doses of alcohol leading to unconsciousness would increase rate of progress into hypothermia.

Adult↗