Abstract
We studied cerebral blood velocity (CBV), and associated hemodynamic parameters during gradual changes in head positioning in a nonstroke group. CBV (transcranial Doppler ultrasound), beat‐to‐beat blood pressure (BP, Finometer), and end‐tidal carbon dioxide (ETCO 2, capnography) were recorded between lying flat (0°) and sitting up (30°) head positions, in 18 volunteers (10 female, mean age, 57 ± 16 years), at two visits (12 ± 8 days). A significant reduction was found between 5‐min FLAT (0°) and 5‐min SIT (30°) positions in CBV (visit 1: 4.5 ± 3.3%, P = 0.006; visit 2: 4.1 ± 3.5%, P = 0.003), critical closing pressure (CrCP; visit 1: 15.5 ± 14.0%, P = 0.0002; visit 2: 14.1 ± 7.8%, P = 0.009) and BP (visit 1: 8.3 ± 7.4%, P = 0.001; visit 2: 11.0 ± 11.3%, P < 0.001). For 5 min segments of data, the autoregulation index and other hemodynamic parameters did not show differences either due to head position or visit. For 30 sec time intervals, significant differences were observed in the following: (BP, P < 0.001; dominant hemisphere (DH) CBV, P < 0.005; nondominant hemisphere (NDH) CBV, P < 0.005; DH CrCP, P < 0.001; NDH CrCP, P < 0.001; DH resistance area product (RAP), P = 0.002; NDH RAP, P = 0.033). Significant static changes in BP, CBV and CrCP, and large transient changes in key hemodynamic parameters occur during 0° to 30°, and vice versa, with reproducible results. Further studies are needed following acute ischemic stroke to determine if a similar responses is present.
Highlights
Cerebral autoregulation (CA) is an important mechanism whereby cerebral perfusion is normally maintained at a constant level, over a relatively wide blood pressure (BP) range (Aaslid et al 1989; Paulson et al 1990)
We studied cerebral blood velocity (CBV), and associated hemodynamic parameters during gradual changes in head positioning in a nonstroke group
We studied the effects of gradual change in head positioning, on both peripheral and cerebral hemodynamic parameters in a nonstroke control group, over two visits
Summary
Cerebral autoregulation (CA) is an important mechanism whereby cerebral perfusion is normally maintained at a constant level, over a relatively wide BP range (Aaslid et al 1989; Paulson et al 1990). Dynamic cerebral autoregulation (dCA) is usually assessed by looking at the response of cerebral blood flow (CBF) following a rapid, and transient alteration in perfusion pressure, usually over a period of seconds (Aaslid et al 1989). Using a standard hospital bed, changing head position from lying flat (0°) to sitting up (30°) could be a straightforward technique in assessing dCA, and would be useful for participants who are medically unstable, difficult to mobilize and/or with cognitive impairment or communication difficulty to ensure compliance with more complex protocols, for example: acute ischemic stroke (AIS) patients. A possible mechanism is that early mobilization, in severe stroke (i.e., NIHSS>16), may result in reduced CBF secondary to acute stroke-associated impairment in CA,
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