Increased systolic blood pressure driven skeletal muscle activation following stroke: A causality study

Older individuals following stroke have a higher incidence of orthostatic hypotension, syncope and fall risk. Thus, in a pilot study, we investigated the relationship between the arterial and skeletal muscle pump baroreflexes in 8 older (63 ± 4 years) stroke patients (208 ± 14 days post-insult) and 8 age-matched healthy controls (62 ± 7 years) during quiet standing. Simultaneous continuous non-invasive lower leg muscle activity, electromyography (EMG), 3-lead electrocardiogram (ECG) and blood pressure were recorded continuously during the 5-minute stand portion of a sit-to-stand test. Causality was analyzed between EMG and systolic blood pressure (SBP) in the last 4 minutes of standing. Data were segmented into a time window of 45 seconds, translated with an overlap of 5 seconds on the entire 4-minute data. Convergent cross mapping (CCM) was used for studying the causality between the blood pressure and EMG signals. Spontaneous baroreflex sensitivity (BRS) was calculated using the sequence method. Between the two groups, there was no difference in spontaneous BRS (stroke: 4.85±1.52 ms/mmHg; control: 4.27±1.68 ms/mmHg; p=0.48) or causality from EMG towards SBP (stroke: 0.62±0.15; control: 0.67±0.05, p=0.38). The causal relationship from SBP to EMG was greater in stroke patients (0.48±0.05) compared to controls (0.41±0.05, p<;0.05). Although arterial baroreflex was not different between groups, elevated drive from SBP to EMG activity suggests a potential compensatory action by the baroreflex-mediated muscle pump activation towards blood pressure regulation following stroke.