Table 2. Correlation (R- value) between test-retest using 4 different variables to express hypoxic ventilatory response and 2 different variables to express hypercapnic ventilatory response.

Variable	Number of Tests	R value	P value
Hypoxia-all = (Ve at maximal hypoxia–Ve at baseline)/(SpO2 at baseline—SpO2 at maximal hypoxia)	28	0.499	0.007
Hypoxia-90 = (Ve at maximal hypoxia–Ve at 90%SpO2)/ (90—SpO2 at maximal hypoxemia)	28	0.389	0.041
Regression (Hypoxia-all) = Slope of the regression line of Ve on SpO2 (all measurements)	28	0.400	0.035
Regression (Hypoxia-90) = Slope of the regression line of Ve on SpO2 (only measurements done when SpO2 </ = 90%)	28	0.468	0.012
Hypercapnia-all = (Ve at maximal hypercapnia–Ve at baseline)/(EtCO2 at maximal hypercapnia—EtCO2 at baseline)	16	0.668	0.005
Regression (Hypercapnia -all) = Slope of the regression line of Ve on SpO2	16	0.509	0.044