The ventilatory responses to hypoxia and hypercapnia of 5 Amas (Kachido) were compared with those of 5 controls of similar ages, physical characteristics and lung volumes. The responses to hypoxia and hypercapnia were analyzed by the equations originally proposed [a] by Lloyd et al. and [b] by Kronenberg et al. as follows:
[a] VN=(PCO2-B')·D·(1+A/PO2-C) +VB'.
[b] VN=(PCO2-B')·D·(1+R0·exp (-k·PO2)) +VB'.
The CO2-response slope in hyperoxia, D, of the Ama (1.820±0.441 liters·min-1·Torr-1) was slightly higher than that of the control (1.148±0.586 liters·min-1·Torr-1), but the difference was not significant. However, the slope of CO2-response in hypoxia at PETO2=44 Torr, S44, was almost the same in the two groups (Ama, 1.822±0.689 liters·min-1·Torr-1; control, 1.742±0.902 liters·min-1·Torr-1). The ratio of S44 to D was significantly lower (p<0.05) in the Ama (1.039±0.377) than in the control (1.529±0.249). Comparing the hypoxic response in terms of the ventilation ratio (VR), the elevation of ventilation with augmentation of hypoxia in the Ama was exceeded by that in the control.Thus, it was suggested that the difference in the ventilatory response to hypoxia between the Ama (Kachido) and the control may have been derived from the respiratory adaptation of the Ama (Kachido) acquired by their daily diving activities.
