Pulmonary emphysema, cardio-respiratory disturbance.

Pulmonary emphysema, as the term is generally used clinically, refers to an overinfiation or distention of the lungs (localized or diffuse), characterized by a relative increase in the amount of air which cannot be blown out with a forced expiration. The residual air capacity plus the vital capacity equals total observed lung capacity (TLC) for the individual, and in pulmonary emphysema the TLC value may be the normal predicted , increased or decreased.' Wide individual variations of the total lung capacity have been noted in patients with pulmonary emphysema, in some cases the TLC was increased as much as 40 per cent above the normal predicted, and in other cases decreased more than 65 per cent below the normal predicted. In order to determine the total lung capacity, the residual air, that which remains at the end of a forced expiration, must be measured and added to the vital capacity. The severity of emphysema cannot be evaluated unless the residual air be considered in relation to TLC, for although the residual volume may be less than the predicted , the ratio to TLC may be markedly increased in some cases because vital capacity is greatly reduced. Even when the absolute value of the residual air is markedly increased above the predicted normal, in order to assess accurately the degree of pulmonary emphysema present, this volume must be expressed as a ratio or percentage of total lung capacity. If the residual air occupies 35 to 45 per cent of total lung capacity a moderate , but significant degree of pulmonary emphysema exists, from 45 to 55 per cent an advanced or severe degree of pulmonary emphysema is present and above 55 per cent there is a far advanced or very severe degree of pulmonary emphysema.2 The normal ratio of residual air is less than 35 per cent of TLC in the 15 to 70 year age group.3 The residual per cent of total lung capacity presents a reliable consistent reference measurement , and in general the average ratio does not change significantly from the supine to standing or even walking.4' The functional residual capacity (FRC) does vary significantly from the supine to the standing position because of the shift in the level of the diaphragm which changes the expiratory reserve air, and the activity of exercise further alters the FRC to various degrees. In emphysema hyperventilation is the compensatory mechanism which …