Experimental Alteration of Pulmonary Functions

¹ The Cardiorespiratory Laboratory, Grasslands Hospital, and Department of Physiology, Albert Einstein College of Medicine.

Methods for producing limitation of one or more of the three pulmonary functions have been discussed and are summarized in Table I. Inadequate [See TABLE I in Source Pdf.] ventilatory function may be produced by anesthetic agents and by muscular paralysis. Reduction of alveolar ventilation in the presence of increased total ventilation may be produced by the addition of an artificial dead space. Reduction of lung compliance may be produced by experimental pulmonary edema. Impaired diffusion results from resection of pulmonary tissue and from extensive pulmonary embolization, but pulmonary fibrosis and diffusion limitation from increased thickness of the alveolar-capillary membrane has not been produced in experimental animals. Impaired distribution, in the form of different ventilation/perfusion ratios in different parts of the lung, may be produced by partial collapse of the lung, and effective right-to-left shunt of mixed venous blood may be produced by pulmonary edema or by the surgical construction of a pulmonary arteriovenous fistula. The anoxemia that might be expected to result from complete lung collapse is prevented by effective shunting of blood away from the atelectatic lung, and functional limitation would only be expected to occur when large amounts of pulmonary tissue are collapsed. The functional reserve of the lung, in terms of the circulatory bed and diffusion surface, is obviously large, and mechanisms exist to prevent the development of anoxemia due to impaired distribution under abnormal conditions. Measurements of vital capacity are impossible in the experimental animal, but, by inference from human data, ventilatory reserve is also great, and after resection of pulmonary tissue, inadequate diffusion surface and pulmonary vascular bed prove to be limiting factors before alveolar ventilation becomes inadequate.