THE MECHANICS OF BREATHING IN NORMAL SUBJECTS AND IN PATIENTS WITH CARDIOPULMONARY DISEASE

Abstract

Twenty-five normal subjects and 75 patients were studied in the basal state and in the supine position. Transpulmonary pressures, instantaneous air flow rates, and tidal volumes were continuously recorded. Pulmonary compliance and mean mechanical resistance during inspiration and expiration were determined during quiet breathing and voluntary hyperventilation using the esophageal balloon technique. Vital capacity and maximal breathing capacity were measured the same day. The prediction formulae of Baldwin were used for the calculation of the air velocity index. In addition, the cardiac patients underwent right heart or combined heart catheterization. Compliance and mechanical resistance were significantly different in the normal and the patient groups. Patients with bronchospastic disease were characterized by a decrease in compliance during increased respiratory rates and markedly elevated values for mechanical resistance during normal respiration. The expiratory resistance was often increased out of proportion in comparison to the increase of inspiratory resistance. In some of the emphysematous patients, the physiological disturbances within the parenchymal structures (loss of elasticity) seemed to predominate over the bronchospastic component of the disease. Patients with either restrictive or fibrotic pulmonary diseases were characterized by low and relatively stable compliance values. The resistance values were less elevated than in the bronchospastic group. Patients with cardiac disease showed changes similar to the pulmonary fibrotic group. Compliance correlated well with vital capacity in all groups with the exception of the emphysema group. High vital capacity and maximal breathing capacity were usually associated with low resistance values. The air velocity index correlated poorly with compliance, mechanical resistance, or the overall time constant of the lung. In the patients with heart disease, no significant correlation between the physical properties of the lung and pulmonary hemodynamics was found.