Steady-state cerebral blood flow and dynamic cerebral autoregulation during neck flexion and extension in seated healthy young adults.

Neck flexion and extension show differences in various physiological factors, such as sympathetic nerve activity and intracranial pressure (ICP). We hypothesized that differences would exist in steady-state cerebral blood flow and dynamic cerebral autoregulation between neck flexion and extension in seated, healthy young adults. Fifteen healthy adults were studied in the sitting position. Data were collected during neck flexion and extension in random order for 6 min each on the same day. Arterial pressure at the heart level was measured using a cuff sphygmomanometer. Mean arterial pressure at the middle cerebral artery (MCA) level (MAP ) was calculated by subtracting the hydrostatic pressure difference between heart and MCA levels from mean arterial pressure at the heart level. Non-invasive cerebral perfusion pressure (nCPP) was estimated as the MAP minus the non-invasive ICP as determined from transcranial Doppler ultrasonography. Waveforms of arterial pressure in the finger and blood velocity in the MCA (MCAv) were obtained. Dynamic cerebral autoregulation was evaluated by transfer function analysis between these waveforms. The results showed that nCPP was significantly higher during neck flexion than during neck extension (p = 0.004). However, no significant differences were observed in mean MCAv (p = 0.752). Likewise, no significant differences were observed in any of the three indices of dynamic cerebral autoregulation in any frequency range. Although non-invasively estimated cerebral perfusion pressure was significantly higher during neck flexion than during neck extension, no differences in steady-state cerebral blood flow or dynamic cerebral autoregulation were evident between neck flexion and extension in seated healthy adults.