Cardiopulmonary Exercise Testing Demonstrates Maintenance of Exercise Capacity in Patients With Hypoxemia and Pulmonary Arteriovenous Malformations

BACKGROUND: Patients with pulmonary arteriovenous malformations (PAVMs) are unusual because hypoxemia results from right-to-left shunting and not airway or alveolar disease. Their surprisingly well-preserved exercise capacity is not generally appreciated. METHODS: To examine why exercise tolerance is preserved, cardiopulmonary exercise tests were performed while breathing room air in 21 patients with radiologically proven PAVMs, including five restudied 3 to 12 months aft er embolization when their PAVMs had regressed. Where physiologic matching was demonstrable, comparisons were made with 12 healthy control subjects. RESULTS: The majority of patients achieved their predicted work rate despite a resting arterial oxygen saturation (Sao(2)) of 80% to 96%. Peak work rate and oxygen consumption ((V) over dot o(2)) were no lower in patients with more hypoxemia. Despite higher Sao2 following embolization (median, 96% and 90 %; P = .009), patients achieved similar work rates and similar peak (V) over dot o(2). Strikingly, treated patients reset to virtually identical peak oxygen pulses (ie, (V) over dot o(2) per heart beat) and in many cases to the same point on the peak oxygen pulse/work rate plot. The 21 patients had increased minute ventilation ((V) over dot E) for given increases in CO2 production ((V) over dot E/(V) over dot co(2) slope), but perceived dyspnea was no greater than in the 12 control subjects or in the same patients before compared to aft er embolization comparison. Overall, work rate and peak (V) over dot o(2) were associated not with oxygenation parameters but with (V) over dot E/(V) over dot co(2) slope, BMI, and anaerobic threshold. CONCLUSIONS: P atients with hypoxemia and PAVMs can maintain normal oxygen delivery/(V) over dot o(2) during peak exercise. Following improvement of Sao(2) by embolization, patients appeared to reset compensatory mechanisms and, as a result, achieved similar peak (V) over dot o(2) per heart beat and peak work rates.