THE EFFECT OF HYPERVENTILATION ON THE SIZE AND SHAPE OF ALVEOLI

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Abstract
Four groups of living anaesthetized guineapigs were artificially hyperventilated for 2 breaths, 5 min, 10 min or 15 min, with a constant negative and positive pressure cycle, and rapidly frozen at the instant of cessation of ventilation at a preselected point on the respiratory cycle. The dimensions of alveoli and alveolar ducts were measured by histological morphometric methods and related to the degree of lung inflation at the instant of freezing. Hyperventilation reduced the alveolar volume fraction, the total alveolar volume and the total alveolar surface area, but did not alter the alveolar duct volume fraction or the total alveolar duct volume. The reduction in the size of alveoli was related to the duration of hyperventilation, being maximal during the first 5 minutes. The alveolar surface-to-volume ratio tended to be reduced following hyperventilation. The possible functional significance of these findings is discussed with particular reference to the actions of pulmonary surfactant.

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