Kinetics of skeletal muscle O2 delivery and utilization at the onset of heavy-intensity exercise in pulmonary arterial hypertension

Impaired O-2 delivery relative to O-2 demands at the onset of exercise might influence the response profile of muscle fractional O-2 extraction (congruent to Delta[deoxy-Hb/Mb] by near-infrared spectroscopy) either by accelerating its rate of increase or creating an overshoot'' (OS) in patients with pulmonary arterial hypertension (PAH). We therefore assessed the kinetics of O-2 uptake (V) over dot O-2), Delta[deoxy-Hb/Mb] in the vastus lateralis, and heart rate (HR) at the onset of heavy-intensity exercise in 14 females with PAH (connective tissue disease, IPAH, portal hypertension, and acquired immunodeficiency syndrome) and 11 age-and gender-matched controls. Patients had slower (V) over dot O-2 and HR dynamics than controls (tau(V) over dot O-2 = 62.7 +/- 15.2 s vs. 41.0 +/- 13.8 s and t(1/2) -HR = 61.3 +/- 16.6 s vs. 43.4 +/- 8.8 s, respectively; p < 0.01). No study participant had a significant reduction in oxyhemoglobin saturation. In OS(-) subjects (6 patients and 7 controls), the kinetics of Delta[deoxy-Hb/Mb] relative to (V) over dot O-2 were faster in patients (p = 0.05). Larger area under the OS and slower kinetics (MRT) of the downward component indicated greater O-2 delivery-to-utilization mismatch in OS(+) patients versus OS(+) controls (477.4 +/- 330.0 vs. 78.1 +/- 65.6 a.u. and 74.6 +/- 18.8 vs. 46.0 +/- 17.0 s, respectively; p < 0.05). Resting pulmonary vascular resistance was higher in OS(+) than OS(-) patients (23.1 +/- 12.0 vs. 10.7 +/- 4.0 Woods, respectively; p < 0.05). We conclude that microvascular O-2 delivery-to-utilization inequalities slowed the rate of adaptation of aerobic metabolism at the start of heavy-intensity exercise in women with PAH.