Cardiovascular and ventilatory responses to dorsal, facial, and whole-head water immersion in eupnea.

OBJECTIVE: Facial cooling can regulate reflexes of the dive response whereas further body cooling generally induces the cold-shock response. We examined the cardiovascular and ventilatory parameters of these responses during 3-min immersions of the head dorsum, face, and whole head in 17 degrees C water while breathing was maintained. METHODS: From a horizontal position, the head was inserted into a temperature controlled immersion tank in which the water level could be changed rapidly. On four occasions, either the head dorsum, face or whole head (prone and supine) were exposed to water. RESULTS: Mean decrease in heart rate (14%) and increases in systolic (9%) and diastolic (5%) blood pressures were seen during immersion. Relative mean finger skin blood flow had an early transient decrease (31%) for 90 s and then returned to baseline values. A strong transient increase was seen in minute ventilation (92%) at 20 s of immersion via tidal volume (85%). There were no consistent differences between the head dorsum, face, and whole head for all variables in response to immersion. CONCLUSIONS: The cold-shock response (increased minute ventilation and tidal volume) predominated over the dive response in the initial moments of immersion only. The order of emergence of these responses provides further recommendation to avoid head submersion upon cold water entry. It is important to protect the face, with a facemask, and the head dorsum, with an insulative hood, in cold water.

Clothing buoyancy and underwater horizontal swim distance after exiting a submersed vehicle simulator.

BACKGROUND: Winter road workers, who drive heavy vehicles over ice-covered waterways, are at risk for ice failure, vehicle submersion, and subsequent drowning in frigid water. Although some jurisdictions require these workers to wear flotation clothing, there are concerns that, following an underwater exit in fast-moving water, increased clothing buoyancy may reduce ability to swim against the current to safely return to the ice opening. METHODS: Using a simulator in a swimming pool (3.7 m deep, 28 degrees C), 11 volunteers (5 women) were submersed 8 times each to test the effects from both an Upright and an Inverted position of a normal nonflotation winter jacket (Control), a flotation Jacket, a flotation Overall, and a personal inflatable vest which was inflated (Inflated Vest) on underwater horizontal swim distance. Subjects also rated exit difficulty and impedance, psychological stress, and thermal comfort. RESULTS: Compared to Control, Jacket, and Overall, the Inflated Vest generally increased exit difficulty, escape impedance, and psychological stress, while greatly decreasing the ability to swim horizontally underwater before reaching the surface (Control, 6.1 m; Jacket, 5.0 m; Overall, 3.4 m; and Inflated Vest only 1.4 m). Swim distance with the Overall was also significantly shorter than Control, but not Jacket. DISCUSSION: Flotation clothing (either Jackets or Overalls) is recommended for vehicle travel on ice because they do not impede underwater exit from a vehicle and allow significant horizontal underwater swim distance. An inflatable vest is not recommended because inappropriate premature inflation could increase exit impedance and decreased underwater swim distance.

Whole-body hypothermia has central and peripheral influences on elbow flexor performance.

The superimposed twitch technique was used to study the effect of whole-body hypothermia on maximal voluntary activation of elbow flexors. Seven subjects [26.4 ± 4 years old (mean ± SD)] were exposed to 60 min of either immersion in 8°C water (hypothermia) or sitting in 22°C air (control). Voluntary activation was assessed during brief (3 s) maximal voluntary contractions (MVCs) and then during a 2 min fatiguing sustained MVC. Hypothermia (core temperature 34.8 ± 0.9°C) decreased maximal voluntary torque from 98.2 ± 1.0 to 82.8 ± 5.8% MVC (P < 0.001) and increased central conduction time from 7.9 ± 0.4 to 9.1 ± 0.7 ms (P < 0.05). Hypothermia also decreased maximal resting twitch amplitude from 17.6 ± 4.0 to 10.0 ± 1.7% MVC (P < 0.005) and increased the time-to-peak twitch tension from 55.4 ± 4.0 to 79.0 ± 11.7 ms (P < 0.001). During the 2 min contraction, hypothermia decreased initial torque (P < 0.01) but attenuated the subsequent rate of torque decline (control from 95.5 ± 4 to 29.4 ± 8% MVC; and hypothermia from 85.3 ± 8 to 37.3 ± 5% MVC; P < 0.01). Cortical superimposed twitches increased as fatigue developed but were always lower in the hypothermic conditions. Cortical superimposed twitches increased from a value of 0.4 ± 0.3% MVC prefatigue to 3.9 ± 1.4% MVC postfatigue (P < 0.001) in the hypothermic conditions and from 1.7 ± 0.9 to 5.5 ± 2.3% MVC in control conditions. Our results suggest that hypothermia decreases MVCs primarily via peripheral mechanisms and attenuates the rate of fatigue development by reducing central fatigue.

Shivering heat production and body fat protect the core from cooling during body immersion, but not during head submersion: a structural equation model.

Previous studies showed that core cooling rates are similar when only the head or only the body is cooled. Structural equation modeling was used on data from two cold water studies involving body-only, or whole body (including head) cooling. Exposure of both the body and head increased core cooling, while only body cooling elicited shivering. Body fat attenuates shivering and core cooling. It is postulated that this protection occurs mainly during body cooling where fat acts as insulation against cold. This explains why head cooling increases surface heat loss with only 11% while increasing core cooling by 39%.

Core cooling and thermal responses during whole-head, facial, and dorsal immersion in 17 degrees C water.

This study isolated the effects of dorsal, facial, and whole-head immersion in 17 degrees C water on peripheral vasoconstriction and the rate of body core cooling. Seven male subjects were studied in thermoneutral air (approximately 28 degrees C). On 3 separate days, they lay prone or supine on a bed with their heads inserted through the side of an adjustable immersion tank. Following 10 min of baseline measurements, the water level was raised such that the water immersed the dorsum, face, or whole head, with the immersion period lasting 60 min. During the first 30 min, the core (esophageal) cooling rate increased from dorsum (0.29 ± 0.2 degrees C h-1) to face (0.47 ± 0.1 degrees C h-1) to whole head (0.69 ± 0.2 degrees C h(-1)) (p < 0.001); cooling rates were similar during the final 30 min (mean, 0.16 ± 0.1 degrees C h(-1)). During the first 30 min, fingertip blood flow (laser Doppler flux as percent of baseline) decreased faster in whole-head immersion (114 ± 52% h(-1)) than in either facial (51 ± 47% h-1) or dorsal (41 ± 55% h(-1)) immersion (p < 0.03); rates of flow decrease were similar during minutes 30 to 60 (mean, 22.5 ± 19% h(-1)). Total head heat loss over 60 min was significantly different between whole-head (120.5 ± 13 kJ), facial (86.8 ± 17 kJ), and dorsal (46.0 ± 11 kJ) immersion (p < 0.001). The rate of core cooling, relative to head heat loss, was similar in all conditions (mean, 0.0037 ± 0.001 degree C kJ(-1)). Although the whole head elicited a higher rate of vasoconstriction, the face did not elicit more vasoconstriction than the dorsum. Rather, the progressive increase in core cooling from dorsal to facial to whole-head immersion simply correlates with increased heat loss.

Field torso-warming modalities: a comparative study using a human model.

OBJECTIVE: To compare four field-appropriate torso-warming modalities that do not require alternating-current (AC) electrical power, using a human model of nonshivering hypothermia. METHODS: Five subjects, serving as their own controls, were cooled four times in 8 degrees C water for 10-30 minutes. Shivering was inhibited by buspirone (30 mg) taken orally prior to cooling and intravenous (IV) meperidine (1.25 mg/kg) at the end of immersion. Subjects were hoisted out of the water, dried, and insulated and then underwent 120 minutes of one of the following: spontaneous warming only; a charcoal heater on the chest; two flexible hot-water bags (total 4 liters of water at 55 degrees C, replenished every 20 minutes) applied to the chest and upper back; or two chemical heating pads applied to the chest and upper back. Supplemental meperidine (maximum cumulative dose of 3.5 mg/kg) was administered as required to inhibit shivering. RESULTS: The postcooling afterdrop (i.e., the continued decrease in body core temperature during the early period of warming), compared with spontaneous warming (2.2 degrees C), was less for the chemical heating pads (1.5 degrees C) and the hot-water bags (1.6 degrees C, p < 0.05) and was 1.8 degrees C for the charcoal heater. Subsequent core rewarming rates for the hot-water bags (0.7 degree C/h) and the charcoal heater (0.6 degree C/h) tended to be higher than that for the chemical heating pads (0.2 degree C/h) and were significantly higher than that for spontaneous warming rate (0.1 degrees C/h, p < 0.05). CONCLUSION: In subjects with shivering suppressed, greater sources of external heat were effective in attenuating core temperature afterdrop, whereas sustained sources of external heat effectively established core rewarming. Depending on the scenario and available resources, we recommend the use of charcoal heaters, chemical heating pads, or hot-water bags as effective means for treating cold patients in the field or during transport to definitive care.

Survey of public knowledge and responses to educational slogans regarding cold-water immersion.

OBJECTIVES: Cold water temperature is a significant factor in North American drownings. These deaths are usually attributed to hypothermia. Survey questions were administered to 661 attendees of cold-stress seminars-including medical, rescue, law enforcement and lay attendees-to determine general knowledge of the effects of ice water immersion and responses to 2 public service educational slogans. METHODS: Five questions were posed at the beginning of seminars to 8 groups (ranging in size from 46 to 195) during a 2-year period. Pi(2) analyses were used to determine if responses within any occupational category differed from the group responses. RESULTS: A high portion of respondents greatly underestimated the time to become hypothermic in ice water (correct answer >30 minutes; 84% stated 15 minutes or less) and the time until cooling was life threatening (correct answer >60 minutes; 85% stated 30 minutes or less). There were no occupational differences in these responses. Most of the respondents identified a correct cause of death during cold stress (81% stated cardiac arrest, hypothermia, or drowning). Although both educational slogans had some advantages, between 40% (Slogan #1) to 50% (Slogan #2) of respondents did not respond correctly. CONCLUSIONS: The majority of respondents underestimated the time available for survival during ice water immersion. It is important to educate the public accurately to decrease the probability of panic under these circumstances. More work is required to develop effective educational slogans that provide proper information and actions for victims of cold-water immersion.

Longitudinal study of quality of life and psychological functioning for active, fluctuating, and inactive disease patterns in inflammatory bowel disease.

BACKGROUND: The aim was to assess quality of life (QOL) and psychological functioning in inflammatory bowel disease (IBD) as related to patterns of disease activity over time. METHODS: Study participants were 388 recently diagnosed individuals from the population-based Manitoba IBD Cohort Study. They completed mail-out surveys at 6-month intervals and clinical interviews annually. Based on their 2-year pattern of self-reported disease activity, participants were assigned to 1 of 3 groups: consistently active, fluctuating, or consistently inactive disease. Disease type (Crohn's disease [CD] or ulcerative colitis [UC]) was confirmed through chart review. Change over time was modeled for measures of QOL and positive and negative psychological functioning using mixed-effects regression analyses. RESULTS: Half of the participants had fluctuating disease activity, while almost one-third of participants reported consistent active disease. Participants with the fluctuating activity pattern showed significant improvement in disease-specific QOL compared to participants with consistent activity. Perceived stress, health anxiety, and pain anxiety decreased while pain catastrophizing and mastery increased over time, although the amount of change was not significantly different among disease activity patterns. However, when the data were averaged over time there were significant differences among disease activity patterns on most outcomes. Significant effects of CD versus UC were observed only for the pain measures. CONCLUSIONS: Change in IBD QOL is influenced by one's longitudinal profile of disease activity, but change in psychological functioning is not. Effects of disease activity on psychological functioning were modest, suggesting that disease has an impact even when patients are not experiencing active symptoms.

Shivering heat production and core cooling during head-in and head-out immersion in 17 degrees C water.

INTRODUCTION: Many cold-water scenarios cause the head to be partially or fully immersed (e.g., ship wreck survival, scuba diving, cold-water adventure swim racing, cold-water drowning, etc.). However, the specific effects of head cold exposure are minimally understood. This study isolated the effect of whole-head submersion in cold water on surface heat loss and body core cooling when the protective shivering mechanism was intact. METHODS: Eight healthy men were studied in 17 degrees C water under four conditions: the body was either insulated or exposed, with the head either out of the water or completely submersed under the water within each insulated/exposed subcondition. RESULTS: Submersion of the head (7% of the body surface area) in the body-exposed condition increased total heat loss by 11% (P < 0.05). After 45 min, head-submersion increased core cooling by 343% in the body-insulated subcondition (head-out: 0.13 +/- 0.2 degree C, head-in: 0.47 +/- 0.3 degree C; P < 0.05) and by 56% in the body-exposed subcondition (head-out: 0.40 +/- 0.3 degree C and head-in: 0.73 +/- 0.6 degree C; P < 0.05). DISCUSSION: In both body-exposed and body-insulated subconditions, head submersion increased the rate of core cooling disproportionally more than the relative increase in total heat loss. This exaggerated core-cooling effect is consistent with a head cooling induced reduction of the thermal core, which could be stimulated by cooling of thermosensitive and/or trigeminal receptors in the scalp, neck, and face. These cooling effects of head submersion are not prevented by shivering heat production.

Thermal effects of whole head submersion in cold water on nonshivering humans.

This study isolated the effect of whole head submersion in cold water, on surface heat loss and body core cooling, when the confounding effect of shivering heat production was pharmacologically eliminated. Eight healthy male subjects were studied in 17 degrees C water under four conditions: the body was either insulated or uninsulated, with the head either above the water or completely submersed in each body-insulation subcondition. Shivering was abolished with buspirone (30 mg) and meperidine (2.5 mg/kg), and subjects breathed compressed air throughout all trials. Over the first 30 min of immersion, exposure of the head increased core cooling both in the body-insulated conditions (head out: 0.47 +/- 0.2 degrees C, head in: 0.77 +/- 0.2 degrees C; P < 0.05) and the body-exposed conditions (head out: 0.84 +/- 0.2 degrees C and head in: 1.17 +/- 0.5 degrees C; P < 0.02). Submersion of the head (7% of the body surface area) in the body-exposed conditions increased total heat loss by only 10%. In both body-exposed and body-insulated conditions, head submersion increased core cooling rate much more (average of 42%) than it increased total heat loss. This may be explained by a redistribution of blood flow in response to stimulation of thermosensitive and/or trigeminal receptors in the scalp, neck and face, where a given amount of heat loss would have a greater cooling effect on a smaller perfused body mass. In 17 degrees C water, the head does not contribute relatively more than the rest of the body to surface heat loss; however, a cold-induced reduction of perfused body mass may allow this small increase in heat loss to cause a relatively larger cooling of the body core.