Effects of age and exercise on physiological dead space during simulated dives at 2.8 ATA

Physiological dead space (Vds), end-tidal CO2(Pet CO2 ), and arterial CO2(PaCO2 ) were measured at 1 and 2.8 ATA in a dry hyperbaric chamber in 10 older (58–74 yr) and 10 younger (19–39 yr) air-breathing subjects during rest and two levels of upright exercise on a cycle ergometer. At pressure, Vd(liters btps) increased from 0.34 ± 0.09 (mean ± SD of all subjects for normally distributed data, median ± interquartile range otherwise) to 0.40 ± 0.09 ( P= 0.0060) at rest, 0.35 ± 0.13 to 0.45 ± 0.11 ( P = 0.0003) during light exercise, and 0.38 ± 0.17 to 0.45 ± 0.13 ( P = 0.0497) during heavier exercise. During these conditions, PaCO2 (Torr) increased from 33.8 ± 4.2 to 35.7 ± 4.4 ( P = 0.0059), 35.3 ± 3.2 to 39.4 ± 3.1 ( P < 0.0001), and 29.6 ± 5.6 to 37.4 ± 6.5 ( P < 0.0001), respectively. During exercise, Pet CO2 overestimated PaCO2 , although the absolute difference was less at pressure. Capnography poorly estimated PaCO2 during exercise at 1 and 2.8 ATA because of wide variability. Older subjects had higher Vd at 1 ATA but similar changes in Vd, PaCO2 , and Pet CO2 at pressure. These results are consistent with an effect of increased gas density.

Effects of age and exercise on physiological dead space during simulated dives at 2.8 ATA Journal Articles