Does Passive Cycling Induce Changes in Peripheral Blood Flow in Persons With Spinal Cord Injury?

Abstract

persons with spinal cord injury (SCI). Ballaz concluded that passive leg cycling increases blood flow velocity in the common femoral artery (CFA) of people with SCI. We read this article with great interest, because we recently published a study on the effect of passive movements on blood flow and found opposite results, that is, no effect of passive leg cycling on blood flow. 2 Unfortunately, very few studies have addressed the interesting and clinically relevant question whether passive cycling can improve leg blood flow. However, when reading the current study, we had some methodologic concerns, which relate to the timing of and posture in which the measurements of red blood cell velocity after ceasing the passive leg cycling were performed. Within 7 seconds of ceasing passive leg cycling, the measurements of blood flow velocity in the CFA were performed. Within this already short time frame, the back of a standardized wheelchair was bent backward (150°). People with SCI, when performing passive leg cycling in a sitting position, are brought to an intermediate position, between sitting and supine, within the same 7 seconds. A change in body position, from upright to supine, causes a change in blood distribution, which leads to an instantaneous rise, within 10 seconds, in venous return, stroke volume, cardiac output, and blood pressure. 3 Consequently, leg blood flow will increase, assuming no change in peripheral vascular resistance. The latter cannot be calculated because no blood pressure measurements were taken. The observed increase in red blood cell velocity found in the Ballaz study could be explained by the change in body position rather than by passive leg cycling itself. Moreover, from a physiologic standpoint, it is hard to explain why and how leg blood flow would increase when there is no increase in oxygen demand, as is the case with paralyzed leg muscles during passive cycling. The conclusion that passive leg cycling exercise leads to an increase in blood flow velocity in the CFA of people with SCI cannot, in our opinion, be drawn. We believe that this is a particularly relevant point, considering the clinical implications: patients with SCI who have a poor leg blood flow, and consequently clinical problems such as edema and poor wound healing, can gain no leg blood flow benefit from passive cycling but need to exercise their paralyzed legs using electric