Assessment of exercise capacity in pulmonary hypertension.

PAH. In such patients, the testing is typically interrupted due to intolerable dyspnea. Dyspnea on exertion is characteristic of patients with PAH up to New York Health Association functional class IV, and limitations in the performance of activities of daily living characterizes the most prevalent clinical presentations (functional class II and III), as well as, obviously, functional class IV, resulting in impaired quality of life for all such patients. The consequent operational difficulties in performing cardiopulmonary exercise testing in patients with PAH call for the use of tests of submaximal effort, which would more closely approximate activities of daily living, in the evaluation of these patients. Based on the twelve-minute run test devised by Cooper,(4) which was designed to evaluate the physical aptitude of healthy young men, McGavin et al.(5) introduced the “twelve-minute walking test” in 1976. The authors applied their twelve-minute walking test as an exercise test in a group of 35 patients, between 40 and 70 years of age, with chronic bronchitis or obstructive lung disease. The results were compared with those of other indices of respiratory function, in order to evaluate their potential value in guiding the evaluation of impaired pulmonary function. The authors concluded that the twelve-minute walking test provided useful, objective data regarding exercise tolerance in patients with chronic bronchitis. Butland et al.,(6) who hypothesized that shorter times might be more appropriate for patients with severe dysfunction, compared the distance covered in 12 min with that covered in 2 min and 6 min. The authors studied a group of 53 patients with obstructive lung disease. They determined that, on the twelve-minute walking test, after a peak of velocity, patients began to walk at a constant velocity, suggesting that shorter tests would be equally useful. The strong correlation found among the distances covered at the three times studied led to the conclusion The pulmonary circulation, organized in series with the systemic circulation and receiving all of the cardiac output, is a vascular circuit of high compliance, characterized by high flow, low resistance and low relative pressures. (1) Physical exercise, at low to moderate levels and under conditions of normality, has little effect on pulmonary artery pressure, which typically does not exceed the upper limits of normality during exercise. The elevation of cardiac output that occurs during exercise produces vasodilation (distention), as well as recruitment and redistribution of the pulmonary blood flow, making the pulmonary pressure gradients increase proportionally less, and, as a consequence, the estimated pulmonary vascular resistance is reduced. (1) The structural and functional exchanges that constitute remodeling of the vascular walls, principally of the pulmonary artery segment in pulmonary hypertension, significantly reduce compliance in the pulmonary circulation. This remodeling, which characterizes pulmonary arterial hypertension (PAH) and reduces the capacity for vasodilation, leads to a reduction in the cross-sectional area of the pulmonary vascular bed. This creates the conditions for the elevation of pressure values and pulmonary vascular resistance in response to increased cardiac output, such as that occurring on exertion, during controlled exercise or even at rest, being proportional to the degree of remodeling and to the reduction in the functional reserve of the pulmonary circulation. (1,2) Cardiopulmonary exercise testing,(3) which is an excellent resource for measuring physical capacity, has been employed in the evaluation of the functional reserve and as a prognostic marker in patients with heart disease or lung disease. It is known that such testing requires instrumentation that is more specialized, as well as requiring trained operators. In addition, the maximal effort level might not be attained by patients incapable of producing a significant increase in cardiac output, such as patients with Assessment of exercise capacity in pulmonary hypertension