Physiological interdependence of the cardiovascular and postural control systems under orthostatic stress

Abstract

The cardiovascular system has been observed to respond to changes in human posture and the environment. On the same lines, frequent fallers have been observed to suffer from cardiovascular deficits. The present article aims to demonstrate the existence of interactions between the cardiovascular and postural control systems. The behavior of the two systems under orthostatic challenge was studied through novel adaptations of signal processing techniques. To this effect, the interactions between the two systems were assessed with two metrics, coherence and phase lock value, based on the wavelet transform. Measurements from the cardiovascular system (blood pressure), lower limb muscles (surface electromyography), and postural sway (center of pressure) were acquired from young healthy adults (n = 28, men = 12, age = 20-28 yr) during quiet stance. The continuous wavelet transform was applied to decompose the representative signals on a time-scale basis in a frequency region of 0.01 to 0.1 Hz. Their linear coupling was quantified through a coherence metric, and the synchrony was characterized via the phase information. The outcomes of this study present evidence that the cardiovascular and postural control systems work together to maintain homeostasis under orthostatic challenge. The inferences open a new direction of study for effects under abnormalities and extreme environmental conditions.

Skeletal Muscle Pump Drives Control of Cardiovascular and Postural Systems

“…To represent overall muscle activity in the form of aggregate EMG, the rectified EMG acquired from four different muscles of both legs were added. COPr signal was obtained from medio-lateral (COPx) and anterior-posterior (COPy) center of pressure as a resultant sum of the two vectors15. Data were then resampled to 10 Hz before further processing.…”

“…In the absence of such input, an alteration in postural stability along with blood pressure and muscle activity is observed15. This is indicative of inter-relationship between cardio-postural-musculoskeletal systems16.…”

“…This is indicative of inter-relationship between cardio-postural-musculoskeletal systems16. This inter-relationship has been recently validated during quiet standing by exhibiting the presence of significant coherence (linear coupling) between variables belonging to respective systems151617. However, these studies did not investigate cause and effect relationship between the variables pertaining to such systems.…”

“…Additionally, we thoroughly study the free parameters of choice, i.e., time delay and embedding dimension of reconstruction to ascertain the optimal combination to establish the cardio-postural-musculoskeletal interactions. Further, we study a larger sample size (n = 18) of young and healthy participants to generalize the existence of causal interaction in cardio-postural-musculoskeletal systems via a controlled sit-to-stand experimental protocol, which has been used in the literature to induce orthostatic challenge1544. Lastly, we explored the sensitivity of the CCM method towards discriminating the behavior of skeletal muscle pump mediated blood pressure regulation (EMG → SBP) and baroreflex mediated skeletal muscle activation (SBP → EMG) due to aging.…”

Increased Systolic Blood Pressure driven Skeletal Muscle activation Following Stroke: A causality analysis

“…The role of lower leg muscles is, thus, essential for blood pressure regulation, as under low venous return baroreflex mechanism would have limited effect on blood pressure regulation. Previously, calf skeletal muscles and systolic blood pressure (SBP) have been shown to have linear interaction during quiet standing in order to maintain stable posture [3]. However, the directional information exchange (causality) between EMG and SBP, and any alterations under the pathological conditions, are not clearly understood.…”