Vol. 94, Issue 2, 507-517, February 2003
Effects of age and exercise on physiological dead space
during simulated dives at 2.8 ATA
H. J.
Mummery,
B. W.
Stolp,
G.
deL.
Dear,
P. O.
Doar,
M. J.
Natoli,
A. E.
Boso,
J. D.
Archibald,
G. W.
Hobbs,
H. E.
El-Moalem, and
R. E.
Moon
Department of Anesthesiology, Center for Hyperbaric
Medicine and Environmental Physiology, Duke University Medical
Center, Durham, North Carolina 27710
Physiological dead space
(VDS), end-tidal CO2
(PETCO2), 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,
PETCO2 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
PETCO2 at pressure. These results are
consistent with an effect of increased gas density.
pulmonary gas exchange; hypercapnia; hyperbaric; end-tidal
CO2; arterial CO2; aging
