Date Published: June 30, 2017
Publisher: Public Library of Science
Author(s): Jessica A. Inskip, Henrike (Rianne) J. C. Ravensbergen, Inderjeet S. Sahota, Christine Zawadzki, Lowell T. McPhail, Jaimie F. Borisoff, Victoria E. Claydon, Yih-Kuen Jan.
Innovative wheelchairs allow individuals to change position easily for comfort and social situations. While these wheelchairs are beneficial in multiple ways, the effects of position changes on blood pressure might exacerbate hypotension and cerebral hypoperfusion, particularly in those with spinal cord injury (SCI) who can have injury to autonomic nerves that regulate cardiovascular control. Conversely, cardiovascular benefits may be obtained with lowered seating. Here we investigate the effect of moderate changes in wheelchair position on orthostatic cardiovascular and cerebrovascular reflex control.
Nineteen individuals with SCI and ten neurologically-intact controls were tested in supine and seated positions (neutral, lowered, and elevated) in the Elevation™ wheelchair. Participants with SCI were stratified into two groups by the severity of injury to cardiovascular autonomic pathways. Beat-to-beat blood pressure, heart rate and middle cerebral artery blood flow velocity (MCAv) were recorded non-invasively.
Supine blood pressure and MCAv were reduced in individuals with lesions to autonomic pathways, and declined further with standard seating compared to those with preserved autonomic control. Movement to the elevated position triggered pronounced blood pressure and MCAv falls in those with autonomic lesions, with minimum values significantly reduced compared to the seated and lowered positions. The cumulative duration spent below supine blood pressure was greatest in this group. Lowered seating bolstered blood pressure in those with lesions to autonomic pathways.
Integrity of the autonomic nervous system is an important variable that affects cardiovascular responses to orthostatic stress and should be considered when individuals with SCI or autonomic dysfunction are selecting wheelchairs.
This work was supported in part by the Heart and Stroke Foundation of British Columbia and the Yukon (V.E.C).
Innovative variable positioning wheelchairs facilitate mobility and improve quality of life for wheelchair users. Some of these new devices permit dynamic modification of seating position, height, and tilt, to better navigate physical and social barriers. Seating positions can easily be adjusted in real time to suit particular activities, maximizing function, efficiency and independence [1, 2]. There may also be physiological benefits to dynamic seating, including reduction of pain, improved comfort, relieving pressure points, increasing bone density and improving baroreflex function [3–11]. However, altered seating positions likely also influence the physiological stressors placed on the cardiovascular system.
We certify that all applicable institutional and governmental regulations concerning the ethical use of human volunteers were followed during the course of this research. This study conformed to the principles outlined in the Declaration of Helsinki , and received ethical approval from the Simon Fraser University Office of Research Ethics, and the Vancouver Coastal Health Research Institute. All participants provided written informed consent.
Participant characteristics are shown in Table 1. We did not detect any differences in sex distribution, age, height, or weight between groups. For comparisons between the two SCI groups, we did not detect any differences in time since injury, but there were more participants with cervical injuries in the autonomically-incomplete SCI group (p = 0.002), and there tended to also be more participants with motor and sensory complete lesions (AIS A) in this group (p = 0.057).
Wheelchair technologies continue to improve to meet the needs of individuals living with disability. Our results show that caution is warranted before encouraging all individuals to adopt and use new wheelchairs without prior education and planning. Individuals with high-level SCI and damage to autonomic pathways tend to have low resting blood pressure, particularly when seated. In this population, moderate changes in body position can result in periods of low blood pressure and cerebral blood flow that can potentially trigger symptoms of presyncope or even syncope [18, 34]; lowered seating positions may somewhat mitigate these effects.