Exercise physiology in health and disease

Abstract

In this review, a great deal of information is given from quantitative exercise testing, particularly in the area of differential diagnosis. By these procedures, dyspnea secondary to cardiovascular causes can be differentiated without much difficulty from that attributable to primary respiratory causes. The low anaerobic threshold is characteristic of all of the cardiovascular diseases, and the reduced W170 and O2 pulse is characteristic of most. Changes in the ECG suggesting myocardial ischemia commonly occur in the cardiac patient, especially when appropriately stressed. Dead space/tidal volume VD/VT), arterial blood gas analyses, and expiratory flow patterns during exercise compared with those at rest assist in identifying the cause as respiratory. In contrast to the cardiac patients, the anaerobic threshold can often not be defined by gas exchange methods in patients with diseases of the respiratory system. This is because the subject is too respiratory limited to deplete appreciably the O2 in the mitochondria to a level that could significantly stimulate anaerobic ATP production. Alternatively, the respiratory limited patient may be unable to increase ventilation sufficiently to compensate for the metabolic acidosis induced by anaerobic metabolism, thus limiting exercise tolerance. In the latter case, training may improve the work tolerance of these patients by reducing the H+ stimulus to breathing. Dyspnea stemming from pulmonary vascular occlusive disorders is usually distinguishable from diseases due to primary cardiovascular and respiratory disorders. Characteristically, the VD/VT is high and arterial PO2 and (A-a)PO2 change in opposite directions as work rate is incremented. In addition, arterial end tidal PCO2 is increased. These changes along with the absence of those that characterize the exercise test of the patient with primary cardiovascular or respiratory diseases, help support a diagnosis of a pulmonary vascular occlusive disorder. The physical signs of the patient during exercise testing should not be ignored and can be of great value. These observations should be a standard part of testing. The discovery of wheezes or rales, or a murmur originating from the heart or pulmonary circulation that becomes more prominent during exercise are very important diagnostic information. Finally, observing the patient's facial expression and degree of cooperation permit a more judicious analysis of the data and makes an invaluable contribution to the final interpretation of the measures. The authors recognize many inadequacies in the discussion of certain disease states in this review, owing in part to the very limited amount of quantitative work that has been done in certain conditions. However, it is clear that the normal respiratory and cardiovascular responses are well orchestrated by the metabolic demands and not independently dictated by isolated respiratory and cardiovascular control mechanisms. Finally, to evaluate shortness of breath during exercise, it is imperative to measure 'the breath'.