|Budget Amount *help
¥1,900,000 (Direct Cost : ¥1,900,000)
Fiscal Year 1997 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1996 : ¥1,200,000 (Direct Cost : ¥1,200,000)
In healthy humans, the breathlessness intensity (BS) during exercise increases mainly with an increase in pulmonary ventilation (V_E). Recently, we demonstrated that those with lower hypoxic ventilatory responsiveness of the peripheral chemoreceptors (HVR) exhibited lower BS at given levels of V_E during exercise (J.Physiol.499 : 843-848,1997). On the other hand, it has been reported that those with higher physical fitness tend to have lower HVR and exertional breathlessness. The following two studies were conducted to examine the influences of HVR and physical fitness, which was evaluated by Vo_2max, on BS during exercise.
(1) Longitudinal study : Eleven nonathletes were asked to perform an endurance training (20-min running, 3 times/week) for 4 weeks. Vo_2max, HVR and V_E-BS relations during an incremental cycle exercise were measured every week. With the time course of the training, rightward shifts of the V_E-BS relation (reduction of BS at given V_E), and finally 14%-increase in Vo_<>max and tendency of lowering of HVR were produced. A multiple linear regression analysis using these data showed that 28% of the rightward shift of V_E-BS relation was explained by the increase in Vo_2max and 16% by the lowering of HVR.(2) Cross sectional study : V_E-BS relation as in the longitudinal study was measured in 14 sprint and 9 endurance athletes. It was found that V_E-BS relation was similar in the two types of athletes, in which HVR was similar but Vo_2max was much greater in the endurance than in the sprint athletes. In addition, V_E-BS relation after 4-week training in the nonathletes was similar to those in the athletes. These results suggest that the sensation of breathlessness during exericise can be reduced by exercise training, with such a training effect mediated partly by increased Vo_2max and decreased HVR but largely by familiarization with breathlessness sensation.