Novel skeletal muscle microvascular oxygenation indices as a function of chronic heart failure severity in rats

Chronic heart failure (CHF) impairs skeletal muscle O 2 delivery‐utilization matching (i.e., microvascular PO 2 ) and produces complex alterations in microvascular PO 2 kinetics (mean response time; MRT) during contractions that appear quantitatively disproportional to cardiovascular dysfunction severity. Indices such as the area under the microvascular PO 2 curve ( PO 2AREA ) may better describe this relationship by incorporating kinetic parameters and minimizing model fitting errors. We tested the hypothesis that reductions in PO 2AREA and increases in the area demarcated by the undershoot (i.e., values falling transiently below the steady‐state; U AREA ) during muscle contractions would correlate to a central hemodynamic index of CHF (left ventricular end‐diastolic pressure; LVEDP). Microvascular PO 2 was measured via phosphorescence quenching ( Microcirculation 11:317; 2004) in the spinotrapezius muscle of 21 healthy (LVEDP: 5 ± 1 mmHg) and 38 CHF (LVEDP: 18 ± 2 mmHg) rats during twitch contractions. As expected, MRT was not associated with LVEDP. However, consistent with our hypothesis, smaller PO 2AREA correlated with elevated LVEDP (r = −0.4; P <0.05) and greater U AREA correlated with elevated LVEDP (r = 0.5; P <0.05). These findings indicate that PO 2AREA and U AREA relate contracting muscle microvascular oxygenation quantitatively to central cardiovascular dysfunction severity. (KSU SMILE, AHA)