The patient was moderately obese, had normal vital signs, and had a normal physical examination except for the inguinal hernia and mild bilateral lymphedema of legs, but Spo2 was 85% at rest. Pulmonary function tests showed a mild restrictive pattern with a borderline normal diffusing capacity, and chest radiographic findings were normal. The serum metabolic panel was normal, including the levels of phosphorus and thyroid-stimulating hormone. The CBC was normal, with a hemoglobin level of 14.4 g/dL. A simple pulmonary stress test was performed on a stationary bike. The patient stopped exercising 6 min into the test (at 75 W) due to general fatigue, without dyspnea. Her Spo2 dropped to 81% within the first minute of exercise and remained at this level throughout the exercise. After 3 min of rest, her Spo2 increased back to 85%. She did not have exercise-induced bronchospasm, or ECG changes. Arterial blood gas measurement (ABL 700 series; Radiometer; Copenhagen, Denmark) showed a pH 7.42; Paco2, 31 mm Hg; Pao2, 85mm Hg; and arterial oxygen saturation of 86% at rest on room air. Co-oximetry showed no methemoglobinemia, and both fetal and carboxy hemoglobin levels of < 1%.