Abstract

Introduction: Tilt tables enable early mobilization of patients by providing verticalization. But there is a high risk of orthostatic hypotension provoked by verticalization, especially after neurological diseases such as spinal cord injury. Robot-assisted tilt tables might be an alternative as they add passive robotic leg exercise (PE) that can be enhanced with functional electrical stimulation (FES) to the verticalization, thus reducing the risk of orthostatic hypotension. We hypothesized that the influence of PE on the cardiovascular system during verticalization (i.e., head-up tilt) depends on the verticalization angle, and FES strengthens the PE influence. To test our hypotheses, we investigated the PE effects on the cardiovascular parameters heart rate (HR), and systolic and diastolic blood pressures (sBP, dBP) at different angles of verticalization in a healthy population.Methods: Ten healthy subjects on a robot-assisted tilt table underwent four different study protocols while HR, sBP, and dBP were measured: (1) head-up tilt to 60° and 71° without PE; (2) PE at 20°, 40°, and 60° of head-up tilt; (3) PE while constant FES intensity was applied to the leg muscles, at 20°, 40°, and 60° of head-up tilt; (4) PE with variation of the applied FES intensity at 0°, 20°, 40°, and 60° of head-up tilt. Linear mixed models were used to model changes in HR, sBP, and dBP responses.Results: The models show that: (1) head-up tilt alone resulted in statistically significant increases in HR and dBP, but no change in sBP. (2) PE during head-up tilt resulted in statistically significant changes in HR, sBP, and dBP, but not at each angle and not always in the same direction (i.e., increase or decrease of cardiovascular parameters). Neither adding (3) FES at constant intensity to PE nor (4) variation of FES intensity during PE had any statistically significant effects on the cardiovascular parameters.Conclusion: The effect of PE on the cardiovascular system during head-up tilt is strongly dependent on the verticalization angle. Therefore, we conclude that orthostatic hypotension cannot be prevented by PE alone, but that the preventive effect depends on the verticalization angle of the robot-assisted tilt table. FES (independent of intensity) is not an important contributing factor to the PE effect.

Highlights

  • Tilt tables enable early mobilization of patients by providing verticalization

  • Since our goal was to evaluate the potential effect of passive robotic leg exercise (PE) on orthostatic hypotension at different tilt angles, we considered the changes in cardiovascular variables heart rate (HR), systolic blood pressure (sBP), and diastolic blood pressure (dBP) for the analysis

  • We proved that the effect of the PE of robot-assisted tilt table is strongly dependent on the tilt angle, and cannot be generalized to different tilt angles

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Summary

Introduction

Tilt tables enable early mobilization of patients by providing verticalization. But there is a high risk of orthostatic hypotension provoked by verticalization, especially after neurological diseases such as spinal cord injury. We investigated the PE effects on the cardiovascular parameters heart rate (HR), and systolic and diastolic blood pressures (sBP, dBP) at different angles of verticalization in a healthy population Diseases such as stroke or spinal cord injury often constrain patients to prolonged bed rest. It is believed that integration of the PE can enhance blood circulation and prevent orthostatic hypotension during head-up tilt (Czell et al, 2004; Colombo et al, 2005) This is because PE is consisted of passive robotic leg movements and cyclic leg loadings (provided by the springs beneath the subject’s legs, see Figure 1), which result in improved muscle pump function and venous return, and improved cardiovascular stability (Luther et al, 2008). The PE mechanism has been used to develop biofeedback systems for early rehabilitation (Giggins et al, 2013), ranging from systems assuming complete passive inclusion of the subject in the biofeedback loop (Wieser et al, 2014; Sarabadani Tafreshi et al, 2015) to systems supposing active participation of the patient in the loop (Laubacher et al, 2015; Saengsuwan et al, 2015a,b)

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