Estimation of hypoxic ventilatory dynamics using pseudorandom inputs

Using experimental and simulation studies, we assessed the applicability of pseudorandom binary hypoxic stimulation (PRBS) for estimating the dynamic respiratory response to a single breath of hypoxia. In experimental studies on rats we tested whether the transient ventilatory response to hypoxia based on the PRBS technique converges to the measured response to a true single breath of hypoxia. Plethysmographic volume recordings were obtained from 7 urethane anesthetized, bilaterally vagotomized rats while the inspired O2 level was switched pseudorandomly between 21% and 12%. The psuedorandom estimates were comparable to the ensemble averaged responses to 15-40 trials of a single-breath inspiration of 12% O2. Ventilation peaked in 2-3 breaths and the response lasted for 15-20 breaths and was primarily due to a decrease in breath duration. Changes in CO2 concentration in the blood cause an underestimate of the purely hypoxic transient response. In simulation studies we also demonstrated the applicability of this technique to human subjects using a mathematical model of human respiratory control. We conclude that the pseudorandom technique will provide a very good estimate of the ventilatory dynamics to inhalation of a single breath of hypoxic gas in rats and humans.