Technique for electrocardiographic monitoring of working divers.

An improved technique to record high-equality electrocardiographic (ECG) signals on the surface, from immersed humans during rest and exercise, in both normothermic and hypothermic exposures, has been devised. Recorded tracings were adequate for research purposes. Waveform signals obtained allow accurate continuous monitoring as well. The best recordings resulted from proper selection of electrode placement sites, careful preparation of the skin, and diligent protection of the skin-electrode interface. The resulting signals recorded from male divers working in 3.05 m (10 ft) of water contained very little artifact or shift in baseline of the ECG tracing. Post-dive examination of the placement sites showed neither separation of ECG electrodes from the skin nor intrusion of water between the electrode and skin surface. The relationship of the new ECG recording technique to a previously described system for acquiring physiologic data is described.

Metabolic responses of resting man immersed in 25.5 degrees C and 33 degrees C water.

This study was undertaken to determine the hormonal responses to disabling hypothermia as a result of cold water immersion. Thermally unprotected male divers trained by the U.S. Navy were subjected to total body immersion in water at 25.5 degrees C and 33 degrees C. Plasma epinephrine, norepinephrine, growth hormone, and cortisol were measured. Other variables monitored included oxygen consumption, carbon dioxide production, minute ventilation, and rectal temperature. Immersion without cold stress caused suppression of plasma epinephrine without affecting plasma norepinephrine. Cold stress combined with immersion caused a significant increase in plasma norepinephrine in the absence of other indicators of a generalized stress reaction. The degree of chilling seen in this study will produce disabling hypothermia within 1-2 h and may be shown initially only by an increase in plasma norepinephrine.

Catecholamine levels in divers subjected to stresses of immersion and hyperbaric exposure.

The study was undertaken to determine the changes in plasma catecholamine levels in response to the combined stresses of cool water immersion and hyperbaric exposure. Plasma catecholamines were measured in seven thermally unprotected trained male U.S. Navy divers immersed in water at 25 degrees C and 35 degrees C at 1 ATA and 4 ATA. All measurements were made prior to any decompression procedures. Plasma norepinephrine (NE) levels were higher during cool immersions at both 1 ATA and 4 ATA. Hyperbaric exposure during warm immersion was associated with a small but significant increase in plasma NE levels. Hyperbaric exposure during cool immersion was associated with an increase in plasma NE levels, but this increase was not statistically significant. Hyperbaric exposure in both the cool and warm immersions was associated with a moderate degree of hypoventilation and carbon dioxide retention. Plasma NE levels reflect the overall stress imposed on an individual. This study indicates that plasma NE levels may be too variable to be useful as indicators of specific stress.

Physiological responses of men working in 25.5 degrees C water, breathing air or helium tri-mix.

Fourteen scuba divers in swim trunks did ergometer work while breathing air at 3 m in 25.5 degrees C water. They were stressed by work and cold. Exercise produced increases in heart rate, minute ventilation (VE), oxygen consumption (VO2), and catecholamine excretion. Cold lowered rectal temperature (Tre) despite exercise, and contributed to the increase in VO2 and catecholamine excretion. Immersion, cutaneous vasoconstriction, work, and scuba breathing contributed to a brisk diuresis, probably by centralizing blood volume and thus stimulating central vascular volume receptors. Similar exercise in 25.5 degrees C water, breathing helium tri-mix (gas density less than air), produced higher VE but lower VO2 when compared to air breathing. Tri-mix scuba breathing resulted in a smaller diuresis, perhaps because its lower density leads to lesser atrial distension during work. The fall in Tre during work in 25.5 degrees C water was identical whether air or helium tri-mix was respired, since helium does not accentuate respiratory convective heat transfer.