Single Limb Exercise Influences Cardiovascular Function Following Stroke: "A One-Sided View"

Abstract

Despite the recommendations of health care professionals, the research community and even pharmaceutical companies, exercise remains a neglected daily regimen for most individuals. Very simply, exercise is any activity that engages our muscles and increases oxygen delivery and uptake with the goal of improving cardiorespiratory health. As physical therapists, we prescribe and encourage exercise training for our patients. For those individuals with neurological deficits such as stroke, the complexity of exercise prescription and training becomes significantly more difficult. Many questions come to mind such as what modality will work with various neuromuscular deficits, will the exercise response be normal or abnormal, and what types of exercise training will improve cardiovascular control and cardiorespiratory fitness. This dissertation explores the central and peripheral cardiovascular responses of an exercise training program using the hemiparetic limb after stroke. Two primary questions guided this dissertation project. First, does single limb exercise (SLE) training improve femoral artery blood flow in the hemiparetic limb? Second, what is the effect of SLE on the central and peripheral cardiovascular system? Before we could address these questions, we needed an exercise modality that would accommodate stroke-related deficits. Obtaining cardiorespiratory fitness values from a maximal effort graded exercise test has been challenging in the post-stroke population. Previous studies have reported that traditional modalities such as the cycle or treadmill prove difficult secondary to neuromuscular and balance deficits. To address these problems, we developed an exercise test for a total body recumbent stepper (TBRS) and assessed its validity and reliability in healthy individuals. Next, participants with stroke were recruited to examine the feasibility and validity of a modified version of this exercise test (mTBRS-XT). These individuals performed two exercise tests on separate days: one using the mTBRS-XT and one on the cycle ergometer. We reported that individuals post-stroke with varying levels of lower extremity motor performance could perform the mTBRS-XT. In addition, cardiorespiratory fitness values were higher using the all-extremity exercise test, implying a more accurate description of peak oxygen uptake. The cardiovascular system continually adjusts to changes in position and to meet the body's needs during dynamic movements and exercise. These vascular changes occur to maintain pressure and regulate blood flow based on the metabolic demands of the body (rest vs exercise). Previous literature suggests that decreased oxygen consumption combined with physical inactivity can alter the vascular composition and blood flow in the lower extremities. However, femoral artery adaptations such as reduced diameter, slower blood flow velocity and increased wall thickness in the hemiparetic limb in people post-stroke have not been previously investigated. Therefore, we sought to examine whether the hemiparetic lower extremity demonstrates vascular changes in the femoral artery when compared to the less affected side. To address this question, seventeen people with chronic stroke had Doppler ultrasound imaging to bilateral femoral arteries. Comparisons between the less affected and hemiparetic limb were interesting in that the femoral artery in the hemiparetic limb demonstrated vascular changes. This may be indicative of reduced oxygen consumption associated with decreased use. Next, we focused on an exercise intervention as a method for improving femoral artery blood flow. Human research in both healthy and clinical populations has reported increased arterial blood flow and diameter in response to exercise. Twelve people with stroke participated in a 4-week single limb exercise (SLE) training intervention using the hemiparetic limb. After SLE, the hemiparetic limb increased both femoral artery diameter and blood flow. No significant changes were observed in the non-trained limb. These data support previous literature that suggests an exercise intervention improves arterial blood flow. Cardiorespiratory fitness can be evaluated during a maximal effort graded exercise test to obtain peak oxygen uptake (VO2 peak) or during submaximal exercise to assess oxygen uptake at a specific workload/workrate. Submaximal performance was evaluated during Days 1 and 12 during SLE. VO2 peak was obtained during an all-extremity maximal effort graded exercise test using the mTBRS-XT. For the 12 participants, SLE had a greater effect on oxygen uptake during submaximal work than VO2 peak. This finding illustrates the hemiparetic limb may have become more efficient (decreased energy expenditure) during exercise. In conclusion, individuals with stroke with varying levels of lower extremity motor function and vast ranges in time post-stroke demonstrated femoral artery adaptations in the hemiparetic limb. A focused training intervention such as single limb exercise, which encourages use of the hemiparetic limb only, was beneficial for improving peripheral cardiovascular function.