Regional Blood Flow Characteristics in Response to Maximal Voluntary Contractions are Attenuated in Stroke Patients.

Abstract

Individuals with stroke have difficulty sustaining or generating forces in their leg muscles. Currently, the mechanisms underlying these force deficits are not fully understood. The contribution of blood flow patterns to isolated muscle function in stroke patients is not completely understood but it can be speculated that abnormalities exist in the presence of vascular disease and muscle atrophy due to stroke. Near infrared spectroscopy devices measure regional oxygen saturations (rSO2) and provide a global assessment of regional blood flow. PURPOSE: We sought to evaluate the regulation of blood flow to the exercising muscle during maximal voluntary contractions (MVC) in patients having suffered a stroke compared to healthy controls. METHODS: A pilot investigation of 5 patients having suffered a stroke and 5 controls was performed to assess regional flow patterns via NIRS during MVC with the leg at 90 degrees (Biodex: Shirley, New York). The dominant leg of controls as well as both paretic and non-paretic legs in patients were tested. NIRS values were used to evaluate regional flow in the rectus femoris and reported as a high, low, and percent change during the MVC effort. RESULTS: Control subjects had a greater peak torque (241.8 ± 32.2 Nm) when compared to the non-paretic leg (87.4 ± 24.8Nm) or paretic leg (59.4 ± 31.4 Nm) of the patients with stroke (ANOVA, p<0.001). The rSO2 prior to MVC did not differ significantly between groups, however there was a robust desaturation noted in the controls (-30.8 ± 17.9 % decline) that was significantly beyond that appreciated in either the non-paretic (-5.9 ± 8.11 % decline) or paretic leg (-5.2 ± 7.7 % decline) of the stroke patients (ANOVA, p=0.01). A linear relationship exist between MVC and percent change in rSO2 for the control group (r= .929, P=0.023) that did not exist in either the non-paretic or paretic leg of the stroke patients. CONCLUSIONS: Individuals having suffered from a stroke have an attenuated blood flow response as assessed by NIRS monitoring during a MVC maneuver. These findings are not isolated to the paretic leg but exist equally in the non-paretic limb suggesting the potential of global perfusion issues in the patients having suffered a stroke. Further investigation into the mechanisms behind these improvements and the impact on leg function is warranted.