Do Changes In Vastus Lateralis Muscle Oxygenation Reflect The Leg Vascular Response To Sympathetic Stimulation?

Abstract

Changes in local muscle oxygenation, measured by near-infrared spectroscopy (NIRS), have been used to assess the vascular response to sympathetic stimulation. Changes in muscle oxygenation have been shown to reflect changes in forearm vascular resistance. If such a relationship existed in the leg, NIRS derived muscle oxygenation could potentially be used as an index of the vascular response to sympathetic stimulation during large muscle mass dynamic exercise in humans. PURPOSE: To determine whether changes in vastus lateralis muscle oxygenation reflect changes in femoral vascular resistance during sympathetic stimulation. METHODS: Healthy, male volunteers (mean ± SD; Age: 25 ± 3 yrs; Height: 175 ± 4 cm; Body Mass: 76 ± 13 kg; n=6) performed a cold-pressor test (CPT) on 3 separate occasions with at least 24 hours between tests. After a 5 min supine baseline period, subjects placed their hand in ice water (-1°C) for 5 min, followed by a 5 min recovery period. Mean arterial pressure (MAP) was calculated on a beat-by-beat basis from the blood pressure waveform using finger photoplethysmography (Finometer; Finapres Medical Systems). Femoral artery blood flow was measured continuously via Doppler ultrasound (Vivid-I; GE Medical). Femoral vascular resistance (FVR; mmHg·mL·min-1) was calculated. Vastus lateralis muscle oxygenation (Tissue oxygenation index (TOI); %) was determined by NIRS (Hamamatsu Photonics, NIRO 200). CPT trials were time-aligned and averaged and the peak response of each variable was calculated as a percent change from the supine baseline value. Differences between the peak changes in TOI and FVR were determined by T-test, whereas the relationship between variables was determined by Pearson Product correlation. RESULTS: The peak decrease in TOI (13 ± 5 %) was significantly lower (p<0.001) than the peak increase in FVR (133 ± 73%). Additionally, the change in TOI was not correlated with the change in FVR (r=0.275, p=0.60). CONCLUSION: These data indicate that the changes in vastus lateralis muscle oxygenation do not reflect the leg vascular response to sympathetic stimulation. Supported by NSERC, Canada.