Abstract
A culture of exercise testing is firmly embedded in the management of pulmonary arterial hypertension (PAH) but its clinical relevance and utility have recently been under some debate. The six minute walk test (6MWT) has been used as a primary outcome measure to enable the licensing of many of the medications used for this condition. Recent reviews have questioned the validity of this test as a surrogate of clinical outcomes. At the same time, other questions are emerging where exercise testing may be the solution. With the rise in understanding of genetic markers of idiopathic PAH (IPAH), the screening of an otherwise healthy population for incipient pulmonary hypertension (PH) will be required. The proliferation in treatment choices and identification of populations with PH where PAH treatment is not indicated, such as left heart and lung disease, requires more definitive differentiation from patients with PAH. There is a continuing question about the existence and clinical relevance of exercise induced PAH as a cause of unexplained dyspnoea and fatigue and as a latent phase of resting PH. This review presents a summary and critical analysis of the current role of exercise testing in PAH and speculates on future trends.
Highlights
Exercise can be viewed as the process of transferring oxygen from atmosphere to capillaries and its utilisation there by exercising muscles
Severe exercise intolerance due to impairment of oxygen transport is a hallmark of pulmonary arterial hypertension (PAH) and the reasons for that are evident from inspection of the Fick equation
The aim of this review is to summarise the current status of exercise testing in PAH and to highlight recent advances
Summary
Exercise can be viewed as the process of transferring oxygen from atmosphere to capillaries and its utilisation there by exercising muscles. In PAH, inefficient ventilation, i.e., the requirement for a high ventilation to remove the carbon dioxide produced by respiration, is due to a combination of both increased dead space and a lowered set point for arterial carbon dioxide concentration [9] Despite this reduced ventilatory capacity and increased demand, ventilatory limitation is said not to occur in PAH unless there is concomitant lung disease. Peripheral muscle dysfunction has been shown in PAH in the form of reduced capillary density and oxidative enzymes in muscle biopsies of these patients [10] This abnormality can lead to impairment of extraction of oxygen from muscle capillaries and should be reflected in abnormally high values of SvO2 at end-exercise [11]. The aim of this review is to summarise the current status of exercise testing in PAH and to highlight recent advances
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