Ventilatory response to incremental and constant-workload exercise in the presence of a thoracic restriction

In the presence of an externally applied thoracic restriction, conflicting ventilatory responses to exercise have been reported, which could be accoun ted for by differences in exercise protocol. Seven male subjects performed two incremental and two constant-workload ergometer tests either unrestrict ed or in the presence of an inelastic corset. Ventilatory variables and art erial estimates of P-CO2 were obtained breath by breath. Subjects hypervent ilated in the presence of restriction during the constant-workload test (38 .4 +/- 3.0 vs. 32.8 +/- 3.0 l/min for the average of the last 3 min of exer cise, P < 0.05), whereas, at an equivalent workload during the incremental test, ventilation was similar to unrestricted values (unrestricted = 26.3 /- 1.6 vs. restricted = 27.9 +/- 2.3 l/min, P = 0.36). We used a first-orde r linear model to describe the effects of change in workload on minute vent ilation (24). When the time constants and minute ventilation values measure d during unrestricted and restricted constant-workload exercise were used t o predict the ventilatory response to the respective incremental exercise t ests, no significant difference was observed. This suggests that hyperventi lation is not seen in the restricted incremental test because the temporal dynamics of the ventilatory response are altered.