Figure 77-10 Effects of semistarvation on metabolic rate and hypoxic and hypercapnic ventilatory responses. The hypoxic response is quantitated by A, defined in the equation VE = V_o + A/(PaO₂ − 32), in which VE is minute ventilation, PaO₂ is alveolar oxygen tension, and V_o is the asymptote for ventilation obtained by extrapolation. The hypercapnic response is quantitated by S, defined in the equation VE = S(PaCO₂ − B), in which PaCO₂ is end-tidal CO₂ tension, and B is the extrapolated intercept on the abscissa (PaCO₂ axis). ψO₂ and ψCO₂ declined, reaching the lowest level by the 10th day, as did the hypoxic response. The hypercapnic response declined slightly but not significantly. The asterisk denotes a significant difference from the control (P < .05), and brackets indicate ± SEM. (Adapted from Doekel RC Jr, Zwillich CW, Scoggin CH, et al: Clinical semi-starvation: Depression of hypoxic ventilatory response. N Engl J Med 295:358, 1976.)