Normal humans meet the increased ventilatory need during exercise initially by the increase of tidal volume (TV) and later by the increase of respiratory frequency (Rf). And the inspiratory duty cycle (Ti/Ttot) is also increased more than 50% for the compensation of the decrease of respiratory cycle provoked by the increase of respiratory frequency. The patients with chronic airflow obstruction show rapid and shallow breathing pattern during exorcise because of the degreased ventilatory capacity and the increased dead space ventilation. However, the studies about the change of inspiratory duty cycle are only a few and there is no literature about the relationship between the change of inspiratory duty cycle and the degree of airflow obstruction.

The subjects were the twelve patients with chronic airflow obstruction (CAO) and ten normal people. The incremental exercise test was done. The increase of work load was 10 Win CAO group and 25 Win normal control group. The analysis of the results was done by the comparison of the parameters such as minute ventilation (VE), TV, Rf, physiologic dead space (Vd/vt), and inspiratory duty cycle between the two groups. Each parameters were compared after transformation into % control duration base that means dividing the total exercise time into five fractons and % control duration data were obtained at rest, 20%, 40%, 60%, 80%, and max. Statistical analysis was done by repeated measure ANOVA using SAS program.

The changes of VE and TV were significantly different between two groups while the change of Rf was not significant. The decrease of Vd/vt was significantly low in CAO group. Ti/Ttot was markedly increased from 38.4+3.0% at rest to 48.6+4.5% at max in normal control group while Ti/Ttot showed little change from 40.5+2.2% at rest to 42.6+3.5% at max. And the change of inspiratory duty cycle showed highly good correlation with the degree of airflow obstruction (FEVl%). (r=0.8151, p<0.05)

The increase of Ti/Ttot during exercise observed in normal humans is absent in the patients with CAO and the change of Ti/TtDt is well correlated with the degree of airflow obstruction.