Immediate ventilatory response to elastic loads and positive pressure in man

Abstract

The immediate effects of elastic loading and of continuous positive-pressure breathing on ventilation were studied in three subjects while conscious and anesthetized. The tidal volume stability during the first elastically loaded breath was found to be greater in the anesthetized than in the conscious state, reflecting a greater “effective” elastance of the respiratory system in the former condition. In conscious state, however, progressive tidal volume compensation from the first to the fifth loaded breath was greater than during anesthesia, probably reflecting a decreased sensitivity of the respiratory system to changes in blood gas composition during anesthesia. Both in conscious and anesthetized state this progressive response was reduced markedly by increasing the O 2, concentration in the inspired gas. Elastic loading during consciousness resulted invariably in increased respiratory frequency, while during anesthesia the latter remained virtually unchanged. During anesthesia acute exposure to positive-pressure breathing caused a decrease in respiratory frequency and a more marked decrease in tidal volume. The decrease in tidal volume was probably caused' chiefly by mechanical impairment of inspiratory muscles by lung inflation. In the conscious state the responses to positive-pressure breathing were not reproducible.