The transient respiratory responses of 10 normal male volunteers to step changes in work load from 0 to 300, 600, and 800 kpm/min were determined by breath-by-breath analysis for tidal volume, minute ventilation, respiratory frequency, end-tidal oxygen and carbon dioxide tensins, oxygen uptake, carbon dioxide elimination, respiratory exchange ratio, and heart rate. Ten experiments were averaged on a 5-s interval basis. Quantitative measures of the dynamics (delay times, half-times, times to peaks, times to plateaus, and plateau amplitudes) are presented. These parameters generally vary with work load and reflect the speed of response of various components of the system. Rapid ventilatory responses were seen at the initiation and termination of exercise; however, they required up to 32.5 s for full development. Repeated runs on three subjects at 600 kpm/min indicate that the experiments are grossly repeatable. The data, at the initiation of exercise, are consistent with the concept of cardiodynamic hyperpnea while the results are not as clear-cut at the termination of exercise.
A mathematical model of the human respiratory control system has been developed and utilized, with the aid of an analog computer, to study the influence of the various factors of the system in producing or enhancing Cheyne-Stokes breathing. The model is an extension of Grodins' (1954) two-compartment model (lung and tissue compartments) to which circulation times and ventilatory dead space have been added. The study has shown that only two factors, increased arterial circulation time and increased controller gain (Δ minute ventilation/Δ in respiratory center CO2 concentration), can alone produce sustained oscillation. However, several other factors, such as decreased CO2 production rate and a shift of the controller equation [minute ventilation = a function of respiratory center CO2 concentration] to the right so that more CO2 is exchanged per amount of alveolar ventilation, can enhance the oscillation. periodic breathing; mathematical model Submitted on May 7, 1964
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