The measurement of the function of the lungs.

The measurement and evaluation of pulmonary function has been a difficult procedure. The common approach to this problem has been the crude method of judging pulmonary function by noting whether a subject shows evidence of dyspnea after exercise (walking up and down a ward or up a flight of stairs). This method is still the most frequent one employed in the majority of institutions where there is a need of knowing the capability of lung function. The measurement of vital capacity is used in many places for determining pulmonary function. This method denotes only one phase of lung function, namely the ventilatory one: it is the function of bringing sufficient air into the lungs for diffusion of oxygen through the alveolar membranes into the alveolar capillary bed. This measurement of the ventilatory process does not therefore foretell the ability of the alveoli to diffuse oxygen into the pulmonary capillaries and carbon dioxide out of the capillaries into the alveolar spaces. There is therefore another phase of pulmonary function-a diffusion one. Pulmonary function therefore depends upon both a ventilatory and a diffusion phase. Before discussing methods of determining lung ventilation and diffusion of oxygen and carbon dioxide it would be logical to review some new concepts in lung ventilation and diffusion of gases in the pulmonary alveoli. Ornstein, Herman, Friedman and Friedlander’ stated, after investigating 170 subjects with impaired lungs, that the capability of the lungs to ventilate had no relationship to their capability to diffuse oxygen and carbon dioxide; that when ventilation was in the normal range, diffusion was usually good and only occasionally was ventilation good and diffusion poor. On the other hand, when ventilation was impaired the diffusion of oxygen and carbon dioxide had no relationship to the reduced ventilation. The above authors further stated that in subjects with marked Impaired lungs and with great reduction in ventilation, diffusion of oxygen and carbon dioxide could be on a normal level. They further state the impaired lung tissues take little or no part in the ventilation and the movement of air in the lung by-passes