Cerebral hemodynamic response to upright position in acute ischemic stroke

 Didn't your competent? doctor start working on cerebral perfusion/head of bed positioning a long time ago? NO? So you DON'T HAVE A FUNCTIONING STROKE DOCTOR, do you?

• cerebral perfusion (3 posts to October 2019)

  • head of bed (6 posts to May 2012)

   

Cerebral hemodynamic response to upright position in acute ischemic stroke

Lilian B. Carvalho^1*Tina Kaffenberger¹Brian Chambers²Karen Borschmann^1,3Christopher Levi⁴Leonid Churilov⁵Vincent Thijs^1,2Julie Bernhardt¹

• ¹Stroke Theme, Florey Institute of Neuroscience and Mental Health, University of Melbourne, Heidelberg, VIC, Australia
• ²Neurology Department, Austin Health, Melbourne, VIC, Australia
• ³Allied Health, St Vincent's Hospital, Melbourne, VIC, Australia
• ⁴John Hunter Hospital, University of Newcastle, Newcastle, NSW, Australia
• ⁵Department of Medicine (Austin Health) and Melbourne Brain Centre at Royal Melbourne Hospital, Melbourne Medical School, University of Melbourne, Melbourne, VIC, Australia

Introduction: Concerns exist that a potential mechanism for harm from upright activity (sitting, standing, and walking) early after an acute ischaemic stroke could be the reduction of cerebral perfusion during this critical phase. We aimed to estimate the effects of upright positions (sitting and standing) on cerebral hemodynamics within 48 h and later, 3–7 days post-stroke, in patients with strokes with and without occlusive disease and in controls.

Methods: We investigated MCAv using transcranial Doppler in 0° head position, then at 30°, 70°, 90° sitting, and 90° standing, at <48 h post-stroke, and later at 3–7 days post-stroke. Mixed-effect linear regression modeling was used to estimate differences in MCAv between the 0° and other positions and to compare MCAv changes across groups.

Results: A total of 42 stroke participants (anterior and posterior circulation) (13 with occlusive disease, 29 without) and 22 controls were recruited. Affected hemisphere MCAv decreased in strokes with occlusive disease (<48 h post-stroke): from 0° to 90° sitting (−9.9 cm/s, 95% CI[−16.4, −3.4]) and from 0° to 90° standing (−7.1 cm/s, 95%CI[−14.3, −0.01]). Affected hemisphere MCAv also decreased in strokes without occlusive disease: from 0° to 90° sitting (−3.3 cm/s, 95%CI[−5.6, −1.1]) and from 0° to 90° standing (−3.6 cm/s, 95%CI [−5.9, −1.3]) (p-value interaction stroke with vs. without occlusive disease = 0.07). A decrease in MCAv when upright was also observed in controls: from 0° to 90° sitting (−3.8 cm/s, 95%CI[−6.0, −1.63]) and from 0° to 90° standing (−3 cm/s, 95%CI[−5.2, −0.81]) (p-value interaction stroke vs. controls = 0.85). Subgroup analysis of anterior circulation stroke showed similar patterns of change in MCAv in the affected hemisphere, with a significant interaction between those with occlusive disease (n = 11) and those without (n = 26) (p = 0.02). Changes in MCAv from 0° to upright at <48 h post-stroke were similar to 3–7 days. No association between changes in MCAv at <48 h and the 30-day modified Rankin Scale was found.

Discussion: Moving to more upright positions <2 days post-stroke does reduce MCAv in the affected hemisphere; however, these changes were not significantly different for stroke participants (anterior and posterior circulation) with and without occlusive disease, nor for controls. The decrease in MCAv in anterior circulation stroke with occlusive disease significantly differed from without occlusive disease. However, the sample size was small, and more research is warranted to confirm these findings.

1 Introduction

The effects of upright positions (sitting and standing) on cerebral hemodynamics in acute ischemic stroke are not well understood. In theory, lying flat could increase cerebral perfusion, and upright activities could worsen perfusion, further damaging viable tissue. However, there is not enough evidence to support these statements and, therefore, to inform the development of head positioning protocols early post-stroke (1). In our recent systematic review of head positioning in ischemic stroke, which incorporated varied imaging techniques, cerebral blood flow (CBF) parameters were greater when lying flat compared to elevated head positions in most studies (2). However, most studies were underpowered, the reported changes were insignificant, and they did not assess longer-term outcomes. Our review also highlighted the lack of studies that examined changes in CBF parameters in upright positions in acute stroke. Sitting was assessed in only three studies: two within a week of stroke (3, 4) and one many years post-stroke (5). Standing was only assessed years post-stroke (5). To date, no studies have included all the postural changes from lying flat, head-up tilt, sitting, and standing to examine changes in CBF parameters in people with stroke compared to controls.

The international AVERT trial, which showed that stroke patients (ischemic and hemorrhagic) treated with very early, intensive, upright mobilization started < 24 h (VEM) after stroke had worse 3-month outcomes, raised concerns about the possible harms of early upright activity (6). A potential mechanism for harm in those with ischemic stroke is that VEM-associated upright activity (sitting, standing, and walking) worsens cerebral perfusion within penumbral tissue. A number of potential mechanisms may contribute to reduced cerebral perfusion during early upright activity. First, gravitational forces may act and lead to orthostatic reductions in cerebral perfusion as the head rises above the heart. While these changes are immediately controlled by cerebral autoregulation in healthy individuals, (7, 8) cerebral autoregulation is commonly impaired in acute stroke (9–11) and in people with occlusive disease (12, 13). Therefore, in upright postures, a defective cerebral autoregulation system may be unable to maintain sufficient blood flow to the ischaemic tissue, potentially promoting further damage. Second, occlusive disease, e.g., large vessel occlusion or severe arterial stenosis, often present in people with acute ischemic stroke, could hinder CBF downstream and further reduce CBF to the ischaemic penumbra. This could happen due to a reduction in the arterial lumen caused by the presence of a thrombus or atherosclerotic plaque in a large vessel supplying the affected ischaemic area. Moreover, cerebral autoregulation is known to be more affected in people with these conditions (12–14). Unfortunately, occlusive disease status was not recorded in AVERT, nor were there studies in our review examining CBF in upright positions in this population (2). Therefore, the specific effects of early upright activity on those with and without occlusive disease are unknown.

We aimed to investigate the effects of changes in head position from lying flat (0°) to 30°, 70°, 90° sitting, and 90° standing on middle cerebral artery mean velocity (MCAv) using transcranial Doppler (TCD) in people with ischemic stroke < 48 h of onset, with or without occlusive disease, and in controls. Our primary hypothesis was that a reduction in MCAv from lying flat (0°) to upright positions (sitting or standing) on the affected hemisphere would be greater in stroke participants with occlusive disease than those without. The secondary aim was to investigate whether changes in MCAv from lying flat (0°) to upright positions in the affected hemisphere in patients with ischaemic stroke would differ from those in the unaffected hemisphere and controls. We hypothesized that there would be a greater reduction in MCAv at upright positions in the affected hemisphere compared to the unaffected hemisphere in patients with stroke, and these changes would also be greater compared to controls. We also aimed to investigate whether changes in MCAv from 0° to upright observed < 48 h of stroke modified over time (comparing to 3–7 days post-stroke). Given the limited data on the relationship between early response to upright positions and later functional outcome, we also explored the association between changes in MCAv from lying flat (0°) to upright in stroke participants < 48 h and 30-day functional outcome (modified Rankin Scale, mRS). Finally, we described how physiological measures [systolic blood pressure (BP), diastolic BP, heart rate (HR), and oxygen saturation] changed with head positions.

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