Some cardiovascular responses in anesthetized dogs during repeated decompressions to a near-vacuum

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Cooke, Julian P

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Repeated, rapid decompressions of anesthetized dogs from ambient pressures of 250 or 200 mm Hg absolute within 1 second to approximately 1 mm Hg, followed by exposures from 55 to 240 seconds before...

Repeated, rapid decompressions of anesthetized dogs from ambient pressures of 250 or 200 mm Hg absolute within 1 second to approximately 1 mm Hg, followed by exposures from 55 to 240 seconds before recompression, carried out within a 4-hour period, have shown that the hearts of most animals tolerate such exposures well. A progressively severe degree of bradycardia was proportional to the length of each anoxic exposure. Following initial and repeated decompressions, the customary sub-atmospheric pressure in the superior vena cava was elevated to 60 or 70 mm Hg within 2 seconds, and the arterial pressure approached comparable values within 4 to 10 seconds. To a great degree, former pre-decompression values were restored upon recompression as barometric pressure surpassed that of water vapor.

All such exposures are potentially dangerous and the possibility of cardiac damage, even for a short exposure, is ever present. Failure to survive such exposures, however, appears to be more dependent on damage to vital structures other than the heart.

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