Table 1.
Baseline epidemiologic and physiologic data.
Fig 1.
Measurement of ventilatory response to hypoxemia.
Illustration of 4 metrics to calculate ventilatory response to hypoxemia (HVR): Hypoxia-all, Hypoxia-90, Regression (Hypoxia-all) and Regression (Hypoxia-90). The first two variables were calculated by taking the increase in minute ventilation (ΔVe) between baseline and maximal hypoxemia (mh) and dividing it by the corresponding change in SpO2 (ΔSpO2). Baseline minute ventilation differed for Hypoxia-all and Hypoxia-90. In Hypoxia-all baseline minute ventilation was the minute ventilation at the beginning of the study (bl). In Hypoxia-90 baseline minute ventilation was the minute ventilation measured at 90% saturation (90%SpO2). Hypoxia-all was calculated using the equation Whereas, Hypoxia-90 was calculated using the equation
Linear regression was applied to the measurements. Regression (Hypoxia-all) used the regression line of all measurements. Regression (Hypoxia-90) used only measurements done when SpO2 was 90% or lower.
Fig 2.
Measurement of ventilatory response to hypercapnia.
Illustration of 2 different methods to calculate the ventilatory response to hypercapnia (HCVR) using the following 2 variables: Hypercapnia-all and Regression (Hypercapnia-all). Hypercapnia-all is the change in Ve (ΔVe) between baseline and the end of the study, divided by the reciprocal change in EtCO2 (ΔEtCO2) in the following form: HCVR = ΔVe/ΔCO2. Regression (Hypercapnia-all) is the slope of regression line of all measurements.
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.
Fig 3.
Correlation between test and re-test of hypoxic (N = 28 participants) and hypercapnic (N = 16 participants) responses.
Table 3.
Hypoxic (HVR) and hypercapnic (HCVR) ventilatory responses in males vs females.
Fig 4.
Association between Hypoxic and Hypercapnic Ventilatory Responses.
R = 0.392, p<0.001.