Exercise capacity

Although PAH may not initially be associated with noticeable symptoms, it tends to result in shortness of breath and limitation of everyday activities that involve moderate exertion.2 For assessing and monitoring the severity of the condition, the 6 min walk test is widely used.3 4 Limitation of the distance that a patient is able to walk on the flat in 6 min reflects a combination of pathophysiological factors: increased pulmonary vascular resistance and its effect on pulmonary perfusion, elevation of pulmonary arterial and right ventricular pressures and any resultant deterioration in right ventricular contractile function. The diastolic filling and the subsequent contractile function of the left ventricle may then be compromised by both the presence of a dilated, high pressure right ventricle adjacent to it in the pericardial space and by limitation of pulmonary venous return. There is a consequent reduction in cardiac output and its responsiveness to exercise. The 6 min walk test has the advantages of simplicity, inexpensiveness and sensitivity to change, particularly when supervised serially by the same experienced staff. Treadmill cardiopulmonary exercise testing, if necessary modified to be sensitive to changes in relatively modest levels of exercise, is also a safe, objective measure of exercise capacity,5 6 with oxygen uptake and ventilatory efficiency …