Patients with severe COPD often exhibit a ventilatory limit to exercise. This is associated with a shallow breathing pattern when compared with normal control subjects. It is unclear, however, what factors affect differences in breathing patterns within this patient population. To further investigate the tidal volume (VT) response to exercise in severe COPD, nine patients were recruited to undergo a maximal incremental exercise test. Pulmonary function tests, collection of expired gases, and continuous pulse oximetry were performed. As a group, the results were as follows (mean +/- SD): The FEV1 was 31 +/- 7 percent of predicted, the FRC was 143 +/- 18 percent of predicted, and the DCO was 47 +/- 15 percent of predicted. Exercise testing showed an oxygen consumption at peak exercise of only 44 +/- 9 percent predicted, a dyspnea index of 101 +/- 19 percent predicted, a heart rate at peak exercise of 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 percent. An anaerobic threshold (AT) occurred in seven of the nine patients at a mean of 31 +/- 8 percent predicted maximal oxygen consumption. Regression analysis showed the PKVT to be inversely correlated with the FEV1 (r = -0.76; p = 0.01) and the PKfb (r = -0.85; p = 0.003), while positively correlating with the FRC (r = +0.80; p = 0.01) and the PKO2sat (r = +0.69; p = 0.04). Additionally, there was a trend for the PKVT to be inversely related with the AT (r = -0.72; p = 0.06). In COPD, the more severe the obstruction and hyperinflation, the larger the VT response to exercise. This may serve to avoid a deleterious increase in autoPEEP by promoting a lengthening of the expiratory time. Furthermore, given the association of an earlier AT and a higher PKO2sat with a larger PKVT, this would suggest that such a response may minimize the effects of dead space and/or autoPEEP on O2 delivery (early AT).