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.
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 after embolization when their PAVMs had regressed. Where physiologic matching was demonstrable, comparisons were made with 12 healthy control subjects.
The majority of patients achieved their predicted work rate despite a resting arterial oxygen saturation (Sao2) of 80% to 96%. Peak work rate and oxygen consumption ( o2) 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 o2. Strikingly, treated patients reset to virtually identical peak oxygen pulses (ie, o2 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 ( e) for given increases in CO2 production ( e/ co2 slope), but perceived dyspnea was no greater than in the 12 control subjects or in the same patients before compared to after embolization comparison. Overall, work rate and peak o2 were associated not with oxygenation parameters but with e/ co2 slope, BMI, and anaerobic threshold.
Patients with hypoxemia and PAVMs can maintain normal oxygen delivery/ o2 during peak exercise. Following improvement of Sao2 by embolization, patients appeared to reset compensatory mechanisms and, as a result, achieved similar peak o2 per heart beat and peak work rates.