Patients with severe COPD often exhibit a ventilatory limit to exercis
e. This is associated with a shallow breathing pattern when compared w
ith normal control subjects. It is unclear, however, what factors affe
ct differences in breathing patterns within this patient population. T
o further investigate the tidal volume (VT) response to exercise in se
vere COPD, nine patients were recruited to undergo a maximal increment
al exercise test. Pulmonary function tests, collection of expired gase
s, and continuous pulse oximetry were performed. As a group, the resul
ts were as follows (mean +/- SD): The FEV1 was 31 +/- 7 percent of pre
dicted, the FRC was 143 +/- 18 percent of predicted, and the Dco was 4
7 +/- 15 percent of predicted. Exercise testing showed an oxygen consu
mption at peak exercise of only 44 +/- 9 percent predicted, a dyspnea
index of 101 +/- 19 percent predicted, a heart rate at peak exercise o
f 75 +/- 12 percent predicted, a tidal volume at peak exercise (PKVT)
of 1.23 +/- .35, a respiratory rate at peak exercise (PKfb) of 26 +/-
6, and an oxygen saturation at peak exercise (PKo2sat) of 96 +/- 4 per
cent. An anaerobic threshold (AT) occurred in seven of the nine patien
ts at a mean of 31 +/- 8 percent predicted maximal oxygen consumption.
Regression analysis showed the PKVT to be inversely correlated with t
he FEV1 (r = -0.76; p = 0.01) and the PKfb (r= -0.85; p = 0.003), whil
e positively correlating with the FRC (r = +0.80; p = 0.01) and the PK
o2sat (r = +0.69; p = 0.04). Additionally, there was a trend for the P
KVT to be inversely related with the AT (r = - 0. 72; p = 0.06). In CO
PD, the more severe the obstruction and hyperinflation, the larger the
VT response to exercise. This may serve to avoid a deleterious increa
se in autoPEEP by promoting a lengthening of the expiratory time. Furt
hermore, given the association of an earlier AT and a higher PKo2sat w
ith a larger PKVT, this would suggest that such a response may minimiz
e the effects of dead space and/or autoPEEP on O2 delivery (early AT).