Rhesus brain gas tension and learned task performance responses to normoxic and hyperoxic breathing.

The impact of extended exposure to 21 and 100% O2 breathing mixtures on brain tissue oxygenation and performance of a learned task was studied in seven rhesus monkeys. Trained in the Sidman Avoidance Task, the animals were exposed to either breathing mixture for a period of 3.5 h in which brain tissue PO2, PCO2, and PN2 were observed. With 100% O2, PO2 and PCO2 rose significantly (less than 0.01 and less than 0.05, respectively) above control levels while PN2 fell significantly (less than 0.01) below its baseline value. With 100% O2 no statistically significant difference in gas tension values was shown for performance vs. nonperformance conditions. There was no difference in the number of shocks received with either breathing mixture. Lever press response frequency decreased throughout the experiment for both groups. During the last performance session, response frequency for the 100% O2 group leveled off, whereas for the 21% O2 group it continued to decrease.

Determination of cerebral and neck subcutaneous tissue PO2 with 3 and 4 +Gz in M. mulatta.

Four male and four female, fully conscious, M. mulatta were exposed twice each to diphasic accelerations of 3 or 4 +Gz (3 min) with a 10-min, 1-G intersession. One polarographic electrode was inserted intracortically and another one into neck subcutaneous tissue. With the first of two 3 or 4 +Gz exposures, cerebral PO2 fell from 15.11 to 5.73 and 2.92 torr, respectively; subcutaneous PO2 fell from 27.6 to 7.72 and 4.8 torr, respectively. Cerebral tissue exhibits post-G hyperoxia, related to initial stress intensity; even after the 10-min intersession, it is capable of mitigating the O2 desaturation effect of the second stress. Cerebral and subcutaneous tissue oxygen desaturation with G onset are comparable, but re-oxygenation in the latter tissue is apparently inertia-ridden and a simple relationship between the overall responses of cerebral and subcutaneous PO2 to +Gz acceleration could not be demonstrated.

Effects of increased ambient CO2 on brain tissue oxygenation and performance in the hypoxic rhesus.

Alterations of cerebral gas tensions and performance in response to hypoxia, with or without 5% CO2 in the ambient inspirate, were studied in eight conscious rhesus monkeys. The animals were trained to perform a lever press (Sidman) avoidance task. Physiological and performance data were obtained during exposures to normal (21% O2) and hypoxic (12, 10, and 8% O2--all with N2 balance) breathing atmospheres, with or without the addition of 5% CO2. With hypoxia, cerebral PO2 and PCO2 declined steadily, but a significant performance decrement was noted only at the 8% O2 level. With the addition of 5% CO2 to the inspired atmospheres, cerebral PO2 was elevated relatively but still declined as hypoxia intensified. Cerebral PCO2 and the avoidance task performance were sustained at near baseline values with the 5% CO2 inspirate.

A head enclosure for exposing monkeys to selected gas mixtures.

An acrylic head enclosure, permitting rapid exchanges of atmospheric gases, was developed for investigations of physiologic and performance responses of small nonhuman primates to graded hypoxic hypoxia and hypercapnia. The total system included a neck yoke plate which served both as a physical barrier to arm and hand movements in the head area and as a base on which to rest the head enclosure. The transparent, airtight, head enclosure permitted rapid exchanges of controlled gas mixtures and the execution of performance tasks in an apparently comfortable experimental environment.

Head and neck cooling by air, water, or air plus water in hyperthermia.

The effects of air, water, and air plus water head cooling on thermoregulatory responses and human operator performance were studied in nonacclimatized, heat-exposed men. Forty chamber exposures (46 degrees C, 30 mm Hg water vapor pressure) were conducted under noncooled and the aforementioned subconditions of head cooling. Five subjects, exposed for 80 min, were monitored for mean skin and rectal temperatures, heart rate, sweat loss, and compensatory tracking performance. A modified Air Force helmet shell provided facial air ventilation (24 degrees C) at 8 cfm. Eight interconnected neoprene modules fastened beneath a helmet linear provided water cooling (20 degrees C at 0.9 l/min). Tracking performances was unchanged across conditions. Elevation of rectal temperature and heart rate, sweat loss, and Physiological Index of Strain were significantly reduced by each condition of head cooling. Air is as effective as water as a cooling agent. Air ventilation acts synergistically with water cooling in reducing physiological strain. Relative merits of each approach to head cooling, in an operational context, are discussed.