Hyperbaric whole-body plethysmograph for rodents.

Described is a rodent size whole-body plethysmograph constructed of two concentric Plexiglas cylinders. Chamber temperature is controlled by circulating water of constant temperature between the cylinders, the entry gas also being preconditioned to a desired temperature. An aluminum plate partitions the chamber into an animal compartment (1.4 liters without the rat) and a transducer compartment (1.1 liters). Dynamic calibration indicates the system response is uniform between 60 and 270 cycles/min. Static calibration shows a linear correlation between the transducer output (in microV) and the calibration volume. Under hyperbaric conditions such linear correlation also exists, but the transducer outputs are greater for a given calibration volume. For a given volume of injection the transducer output is a linear function of log-ambient pressure. Respiratory variables measured with this plethysmograph are comparable to those reported in the literature both for 1 ATA and under hyperbaric conditions. The plethysmograph is also adaptable for measurement of oxygen consumption and CO2 production, under elevated ambient pressure. Caution for this application is given in regard to 1) the protracted time requirement for reaching a steady state, 2) accumulation of CO2 in the chamber, and 3) diminishing gas concentration of interest between the entering and existing gases, suggesting a trade-off in selecting chamber size, ventilation rate, and level of acceptable CO2 in the chamber.

Hana kai ii: a 17-day dry saturation dive at 18.6 ATA. V. Maximal oxygen uptake.

Cardiorespiratory responses of four men to submaximal and maximal cycling exercise were observed during 17 days at 18.6 ATA. Inspired gas at pressure consisted of hyperoxic (PO2 = 232 mmHg) and normoxic (PO2 = 159 mmHg) helium mixtures with relative gas densities of 3.8 and 2.8, respectively. The average of pre- and postdive VO2max (1 ATA air), which were not significantly different, was 3.10 liters - min-1. During 5 min of submaximal exercise at 50% of VO2max, no significant difference in work rate, VO2, VCO2, VE, respiratory rate, heart rate (HR), stroke volume, blood pressures, or rectal temperature was noted at 18.6 ATA compared to 1 ATA with either gas mixture. Submaximal HR tended to decrease by 5 to 10 beats - min-1 at pressure, and in hyperoxia the VO2/HR ratio was significantly higher. Maximal exercise was performed to exhaustion at work rates requiring about 120% of VO2max. Significant increased in VO2max of 0.10 liter - min-1 (3%) and in endurance time of 2 min (48%) were found during hyperoxic gas breathing, whereas normoxic values at 18.6 ATA were similar to those at 1 ATA. Significant reductions in maximal HR of 8 beats - min-1 (4%) were observed with both gas mixtures at pressure, and VE was significantly decreased by 36 liters - min-1 (26%) in hyperoxia and 29 liters - min-1 (21%) in normoxia. No change was found in the calculated cardiac output. Maximal voluntary ventilation, which was measured only for the hyperoxic gas, fell significantly by 80 liters - min-1 (40%). Results indicate that aerobic power and endurance performance were affected by oxygen pressure. Normoxic work capacity, however, was not decreased at 18.6 ATA, despite marked reductions in HR and VE.

Hana Kai II: a 17-day dry saturation dive at 18.6 ATA. VII: Auditory, visual, and gustatory sensations.

Five divers were tested for alterations in auditory, visual, and gustatory functioning during a 17-day saturation exposure to He-O2 at 18.6 ATA. No evidence of permanent hearing loss was disclosed. Critical flicker fusion was not affected, but peripheral visual thresholds were significantly increased during the first two weeks at 18.6 ATA; this was interpreted to be evidence of severe psychological and physiological stress. Foveal vision was unaffected across testings. Magnitude estimation techniques disclosed changes in taste sensitivity, with sweet sensitivity increasing over time and sour sensitivity declining over the course of the dive. Subjects were more sensitive to bitter stimuli at maximum pressure than at sea level, and less sensitive to salt at maximum pressure. The results indicate that appreciable alterations in sensory functioning can occur during saturation exposures, although the sense modalities were differentially affected by such environmental stressors as pressure, psycho-social stress, fatigue, and perceptual deprivation.