Wavelet transform coherence based investigation of existence of relationship between the cardiovascular and postural control systems during orthostatic challenge

Previous studies have established the effects of orthostatic challenge on the cardiovascular and postural control systems, but the interdependent behavior of the systems under such condition is unclear. In the present study we examined the simultaneous changes in posture muscle electromyography (EMG) and systolic blood pressure (SBP) during quiet standing in healthy young individuals. Photoplethysmography based SBP, surface EMG, electrocardiogram (Lead II ECG) and posturography data were acquired during the experiment. Wavelet transform coherence (WTC) analysis was applied to identify the zones of interdependent behavior of the systems. The WTC thresholds were identified for the specific data under investigation. The coherence was analyzed in three frequency bands namely, LF (0.05 - 0.1 Hz), VLF (0.01-0.05 Hz) and ULF (0.005 - 0.01 Hz). WTC estimates for the EMG - SBP comparison showed greater than threshold values in all three frequency bands (LF: 0.31 ± 0.02; VLF: 0.41 ± 0.01; ULF: 0.45 ± 0.01). In conclusion this study showed the existence of relationship between the posture muscle EMG and blood pressure during natural orthostatic stress, by validation based on wavelet transform coherence. Further validation is required to objectively characterize this relationship between the two systems during orthostatic stress.