Abstract
Purpose: Passive in-bed cycling (PC) can provide the benefits of early mobilization to critically ill patients who are unable to exercise actively. However, the effect of PC on global hemodynamics and perfusion of ischemia-prone organs, such as the brain and the heart, is unknown. Therefore, prior to studying the effects of PC in hemodynamically fragile critically ill patients, we characterized hemodynamic, brain blood flow, and cardiac function responses to a graded increase in PC cadence in a cohort of healthy subjects.Methods: We measured global hemodynamic indices, middle cerebral artery velocity (MCAv), and cardiac function in response to a graded increase in PC cadence. Using 5 min stages, we increased cadence from 5 to 55 RPM in increments of 10 RPM, preceded and followed by 5 min baseline and recovery periods at 0 RPM. The mean values obtained during the last 2 min of each stage were compared within and between subjects for all metrics using repeated measures ANOVA.Results: 11 healthy subjects (6 females) completed the protocol. Between subjects, there was no change in MCAv, cardiac function or hemodynamics with the graded increase in cadence with one exception. There was a 7% increase in mean arterial pressure (MAP) from baseline to 55RPM, that persisted through the recovery period. Across subjects, responses were heterogeneous, with some experiencing reduction in cardiac index, cerebral blood flow (CBF) and cardiac function, especially at higher cadence.Conclusions: In healthy adults, increasing PC cadence increased MAP in all subjects, while cardiac index, CBF, and cardiac function responses varied between subjects. Application of PC to critically ill patients must therefore consider individual variation in responses and tailor the PC to the patient. It is essential to further characterize these responses to PC in the critically ill prior to wide-scale clinical implementation.
Highlights
Ill patients spend 96% of their time inactive in bed [1]
We only studied eleven subjects, we noted that their hemodynamic, cerebral blood flow (CBF) and cardiac function responses to graded passive cycling can be grouped into three patterns (Figure 3)
We demonstrated that increasing passive cycling cadence had no effect on mean CBF, cardiac function or hemodynamics, apart from a small dose-dependent increase in the mean arterial pressure (MAP)
Summary
Ill patients spend 96% of their time inactive in bed [1]. This inactivity is associated with cognitive, musculoskeletal, pulmonary, and cardiovascular complications [2] which translate into functional disability [3] and decreased quality of life [4]. Mobilization counteracts these deleterious effects and has been shown to shorten the duration of acute cognitive impairment (delirium), mechanical ventilation, hospital length of stay, and improve functional outcomes at hospital discharge [5]. Given tenuous hemodynamics, and impaired autoregulation [7,8,9] in the critically ill, passive inbed cycling may impair global hemodynamics or organ perfusion of ischemia-prone organs, such as the brain and the heart, with potential dose dependent effects
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