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Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas 75231, and University of Texas Southwestern Medical Center, Dallas, Texas 77231
Received 7 June 1996; accepted in final form 17 March 1997.
Williams, J. S., and T. G. Babb. Differences between
estimates and measured PaCO2 during rest
and exercise in older subjects. J. Appl.
Physiol. 83(1): 312-316, 1997.
Arterial
PCO2 (PaCO2) has been estimated during
exercise with good accuracy in younger individuals by using the Jones
equation
(PJCO2)
(J. Appl. Physiol. 47: 954-960,
1979). The purpose of this project was to determine the utility of
estimating PaCO2 from end-tidal PCO2
(PETCO2) or
PJCO2
at rest, ventilatory threshold (
Th), and maximal
exercise (Max) in older subjects. PETCO2 was determined from
respired gases simultaneously (MGA 1100) with arterial blood gases
(radial arterial catheter) in 12 older and 11 younger subjects at rest
and during exercise. Mean differences were analyzed with paired
t-tests, and relationships between the
estimated PaCO2 values and the actual
values of PaCO2 were determined with
correlation coefficients. In the older subjects, PETCO2 was not significantly
different from PaCO2 at rest (
1.2 ± 4.3 Torr), Th (0.4 ± 2.5), or Max
(0.8 ± 2.7), and the two were significantly
(P < 0.05) correlated at
th (r = 0.84) and
Max (r = 0.87) but not at
rest (r = 0.47).
PJCO2
was similar to PaCO2 at rest (1.0 ± 3.9) and th (1.3 ± 2.3) but significantly lower at Max (3.0 ± 2.6), and the two were
significantly correlated at th
(r = 0.86) and Max
(r = 0.80) but not at rest (r = 0.54).
PETCO2 was significantly
higher than PaCO2 during exercise in the
younger subjects but similar to PaCO2 at rest.
PJCO2
was similar to PaCO2 at rest and
th but significantly lower at Max in younger
subjects. In conclusion, our data demonstrate that
PaCO2 during exercise is better
estimated by PETCO2 than by
PJCO2
in older subjects, contrary to what is observed in younger subjects.
This appears to be related to the finding that
PETCO2 does not exceed
PaCO2 during exercise in older subjects,
as occurs in the younger subjects. However,
PaCO2 at rest is best estimated by
PJCO2
in both younger and older subjects.
aging; blood gases; arterial end-tidal carbon dioxide difference; arterial partial carbon dioxide pressure
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