Near-infrared spectroscopy detects age-related differences in skeletal muscle oxidative function: promising implications for geroscience

Age is the greatest risk factor for chronic disease and is associated with a marked decline in functional capacity and quality of life. A key factor contributing to loss of function in older adults is the decline in skeletal muscle function. While the exact mechanism(s) remains incompletely understood, age-related mitochondrial dysfunction is thought to play a major role. To explore this question further, we studied 15 independently living seniors (age: 72 ± 5 years; m/f: 4/11; BMI: 27.6 ± 5.9) and 17 young volunteers (age: 25 ± 4 years; m/f: 8/9; BMI: 24.0 ± 3.3). Skeletal muscle oxidative function was measured in forearm muscle from the recovery kinetics of muscle oxygen consumption using near-infrared spectroscopy (NIRS). Muscle oxygen consumption was calculated as the slope of change in hemoglobin saturation during a series of rapid, supra-systolic arterial cuff occlusions following a brief bout of exercise. Aging was associated with a significant prolongation of the time constant of oxidative recovery following exercise (51.8 ± 5.4 sec vs. 37.1 ± 2.1 sec, P = 0.04, old vs. young, respectively). This finding suggests an overall reduction in mitochondrial function with age in nonlocomotor skeletal muscle. That these data were obtained using NIRS holds great promise in gerontology for quantitative assessment of skeletal muscle oxidative function at the bed side or clinic

Evidence of Racial Differences in Microvascular Function Among College-Aged Women

Microvascular dysfunction contributes to the development of hypertension and insulin resistance. The black population is at an elevated risk of both conditions relative to other racial groups. Previous studies indicate that college-aged black men, compared to their white counterparts, have impaired microvascular function as assessed by post-occlusion reactive hyperemia (RH). It is unknown whether this racial disparity is present in healthy, young adult black (BW) and white women (WW). Furthermore, whether nitric oxide-mediated cutaneous microvascular hyperemia during local heating (LH) is different in these populations has not been determined. Purpose: The purpose of this study was to test the hypothesis that college-aged BW exhibit blunted RH and attenuated LH induced cutaneous hyperemia compared to age-matched WW. Methods: College-aged BW (n=7) and WW (n=7) were studied during the early follicular phase of the menstrual cycle. For RH, brachial artery diameter and blood velocity were measured via Doppler ultrasound before and after 5 min of forearm occlusion. For LH, a microdialysis membrane was inserted in the dermis of the forearm and perfused with Ringer’s solution. Red blood cell flux was assessed with laser Doppler after ~40 min of continuous 39ºC LH. Maximal flux was established with 28 mM sodium nitroprusside infusion and 43ºC LH. Brachial BP was measured throughout and cutaneous vascular conductance (CVC) was calculated as flux / MAP and reported as % of max CVC. Results: WW and BW were matched for age (21 ± 3 vs 20 ± 1 y, P = 0.58) and BMI (23 ± 2 vs 23 ± 3 kg/m2, P = 0.94). There were no differences between WW and BW in baseline blood velocity (23.1 ± 5.7 vs 24.4 ± 11.6 cm/s, P = 0.79) or blood flow (98.9 ± 38.3 vs 114.5 ± 80.7 ml/min, P = 0.65). WW and BW also had similar peak blood velocity (109.2 ± 13.8 vs 109.7 ± 28 cm/s, P = 0.97), peak blood flow (453.7 ± 164.7 vs 482.5 ± 187.7 ml/min, P = 0.77), and total blood flow AUC during the 120 s after cuff release (487.4 ± 178.5 vs 486.8 ± 190.1 ml, P = 0.99). However, compared to WW, BW had a significantly blunted CVC during 39ºC LH (66 ± 17 vs 45 ± 10 %max, P = 0.02). Conclusions: BW had blunted blood flow responses to LH compared to WW despite similar blood velocity and flow responses during RH. This suggests that LH is more sensitive than RH to early impairments in microvascular function

Evidence of Racial Differences in Microvascular Function Among College-Aged Women

Microvascular dysfunction contributes to the development of hypertension and insulin resistance. The black population is at an elevated risk of both conditions relative to other racial groups. Previous studies indicate that college-aged black men, compared to their white counterparts, have impaired microvascular function as assessed by post-occlusion reactive hyperemia (RH). It is unknown whether this racial disparity is present in healthy, young adult black (BW) and white women (WW). Furthermore, whether nitric oxide-mediated cutaneous microvascular hyperemia during local heating (LH) is different in these populations has not been determined. Purpose: The purpose of this study was to test the hypothesis that college-aged BW exhibit blunted RH and attenuated LH induced cutaneous hyperemia compared to age-matched WW. Methods: College-aged BW (n=7) and WW (n=7) were studied during the early follicular phase of the menstrual cycle. For RH, brachial artery diameter and blood velocity were measured via Doppler ultrasound before and after 5 min of forearm occlusion. For LH, a microdialysis membrane was inserted in the dermis of the forearm and perfused with Ringer’s solution. Red blood cell flux was assessed with laser Doppler after ~40 min of continuous 39ºC LH. Maximal flux was established with 28 mM sodium nitroprusside infusion and 43ºC LH. Brachial BP was measured throughout and cutaneous vascular conductance (CVC) was calculated as flux / MAP and reported as % of max CVC. Results: WW and BW were matched for age (21 ± 3 vs 20 ± 1 y, P = 0.58) and BMI (23 ± 2 vs 23 ± 3 kg/m2, P = 0.94). There were no differences between WW and BW in baseline blood velocity (23.1 ± 5.7 vs 24.4 ± 11.6 cm/s, P = 0.79) or blood flow (98.9 ± 38.3 vs 114.5 ± 80.7 ml/min, P = 0.65). WW and BW also had similar peak blood velocity (109.2 ± 13.8 vs 109.7 ± 28 cm/s, P = 0.97), peak blood flow (453.7 ± 164.7 vs 482.5 ± 187.7 ml/min, P = 0.77), and total blood flow AUC during the 120 s after cuff release (487.4 ± 178.5 vs 486.8 ± 190.1 ml, P = 0.99). However, compared to WW, BW had a significantly blunted CVC during 39ºC LH (66 ± 17 vs 45 ± 10 %max, P = 0.02). Conclusions: BW had blunted blood flow responses to LH compared to WW despite similar blood velocity and flow responses during RH. This suggests that LH is more sensitive than RH to early impairments in microvascular function