Pulmonary Function Tests: Applications, Observations, Interpretations

A Brief Summary of the Physiology of the Lung Together with a Discussion of the More Commonly Used Pulmonary Function Tests

The several functions of the lungs can be divided into certain definite categories for which there are tests whose number is legion, but which, with all their number and complexity, do not replace clinical evaluation of the patient.

Ventilatory impairments are either obstructive, restrictive, or mechanical. The tests, in general, which provide the most information in regard to the performance of the respiratory bellows are the conventional vital capacity, the timed vital capacity, and the maximal breathing capacity. However, in ventilatory impairments, the important consideration is in regard to the adequacy of the alveolar ventilation.

Distribution of inspired air and of mixed venous blood to the alveoli must be uniform if the blood is to be maximally arterialized. Variations in the ventilation/blood flow ratio is a frequent cause of hypoxemia in clinical medicine.

The facility with which the respiratory gases diffuse across the alveolar-capillary membrane can be judged by a study of the arterial blood gases, or by determination of the diffusing capacity of the lung. A determination of the diffusing capacity is helpful in that it supplies information not obtained from simple blood gas studies.