No abstract

No abstract

Arterial end-tidal carbon dioxide gradients were measured and alveolar-arterial oxygen gradients were estimated in dogs during intermittent positive pressure ventilation at constant inflating pressure using four curves having differing pressure profiles. The smallest gradients for both oxygen and carbon dioxide occurred when mean pressure during respiratory cycles was high and decreases in mean pressure were consistently associated with increases in both oxygen and carbon dioxide gradients. Profile of the applied pressure curve per se did not influence magnitude of the gradients. It is concluded that during intermittent positive pressure breathing, relative distribution of pulmonary capillary blood flow and inspired gas may vary with mean pressure during the respiratory cycle and is more uniform when mean pressure during the respiratory cycle is high. artificial ventilation; intermittent positive pressure breathing; alveolar-arterial; carbon dioxide gradient; distribution of inspired gas; pulmonary capillary blood flow Submitted on December 13, 1962

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Distribution of inspired gas was compared during spontaneous ventilation in the conscious state, during spontaneous ventilation in the anesthetized state, and during artificial ventilation in the anesthetized, paralyzed state in nine human subjects. Uniformity of distribution of inspired gas was measured using an open-circuit nitrogen-washout method. Rate and pattern of nitrogen elimination during oxygen breathing as well as calculated indices of uniformity of distribution of inspired gas and efficiency of over-all pulmonary ventilation did not vary significantly among the three conditions studied. Induction of anesthesia or substitution of artificial ventilation for spontaneous ventilation, therefore, caused no detectable change in uniformity of distribution of inspired gas. intrapulmonary mixing; respiratory changes during anesthesia Submitted on January 24, 1963