Age and microvascular responses to knee extensor exercise in women

This study examined the relation between femoral artery hyperemic responses to leg exercise and microvascular oxygen extraction in nine young [(mean ± S.E.M) Y: 25 ± 1 years] and 13 older (O: 67 ± 1 years) healthy women. Femoral artery blood flow (FBF; Doppler ultrasound), mean arterial pressure (MAP), and femoral vascular conductance (FVC; FBF/MAP) were assessed at rest and during 9 min of ∼ 17-18 W single knee extensor exercise. Near-infrared spectroscopy (NIRS) in the vastus lateralis was used to measure changes in deoxyhemoglobin (HHb) and oxyhemoglobin (O₂Hb) to assess oxygen extraction (δ HHb), microvascular blood volume (δ HHb + O₂Hb), and spatial heterogeneity of blood volume (relative dispersion, defined as the coefficient of variation of measurements from all NIR sensors). During exercise, FBF and FVC were lower (p < 0.05) in O compared to Y (Y: 1,430 ± 101 mL min^-1 and 16.6 ± 1.2 mL min^-1 per mmHg versus O: 1,127 ± 64 mL min^-1 and 10.9 ± 0.6 mL min^-1per mmHg). While oxygen extraction increased more rapidly in Y, there were no age differences (p > 0.10) beyond the fourth min of exercise. In addition, the relative increase in microvascular blood volume was not significantly different during exercise in Y versus O (age effect: p = 0.87), although Y demonstrated an increase in blood volume heterogeneity in both the active and inactive leg (p = 0.02 and <0.05, respectively) not observed in O(p = 0.71 and 0.28, respectively). NIRS-derived measurements of changes in deoxygenated hemoglobin do not support the hypothesis that older women compensate for the blunted leg hyperemic response to knee extensor exercise through an augmentation of quadriceps oxygen extraction; knee extensor work may be accomplished by other metabolic or microvascular adjustments to exercise in older women.