The ventilatory pattern at rest was examined in 28 healthy human volunteers by recording pneumograph tracings for a 1-hr period. The mean respiratory frequency was 19/min in females, 16/min in males, but with considerable variation both within and among subjects. The mean inspiratory phase accounted for one-third of the respiratory cycle, but this fraction increased with increasing respiratory frequency and decreased when the frequency slowed. Tidal volumes varied greatly, and sighing (breaths larger than three times the average tidal volume) occurred at an average rate of 10/hr for females, 9/hr for males. The possible physiologic role of periodic deep breaths, or sighs, in providing reinflation of atelectatic areas is discussed. respiratory cycle at rest; respiratory frequency and tidal volumes; periodic deep breaths (sighing); inspiratory phase as related to expiratory phase; normal breathing; hyperinflation; respiration; rate of respiration; pneumographic tracings Submitted on November 8, 1962
The rate and magnitude of the effects of the pressure-volume history of the lungs on the degree of physiologic shunting (pulmonary venous admixture) were investigated in 20 dogs, anesthetized and curarized. Atelectasis was promoted by decreasing end-expiratory transpulmonary pressure. Ventilation was with 100% oxygen using a constant-volume pump at a frequency of 20 breaths/min. The rates of increase or decrease in the physiologic shunt and of the gradients between derived alveolar oxygen tension and directly measured arterial oxygen tension (A-aD) showed a variation controlled by the pressure-volume history of the lungs. The physiologic shunts produced varied between 0.5% and 80% of the cardiac output. The interrelationships of the components of the shunt equation were studied and their relative value in predicting atelectasis was discussed. The data obtained were related to other observations made in anesthetized man.
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