Why the study?
Does tilting at 70° from the horizontal affect middle cerebral artery volume flow compared to supine position?
Does tilting at 70° from the horizontal affect middle cerebral artery volume flow compared to supine position?
Middle cerebral artery volume flow is maintained during orthostasis in healthy subjects due to autoregulatory vasodilation, but drops significantly in patients with orthostatic dysregulation.
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Suggests preserved autoregulation during orthostasis in health; hypothesis-generating for flow impairment in dysregulation and requires prospective validation.
Fifteen healthy subjects were tilted at 70° from the horizontal during a period of 4 min while recording the Doppler signal from the middle cerebral artery. Digital signal analysis carried out off-line provided the following data: mean spatial velocity (v), signal power (p) as an index of cross-sectional area, (v•p) as an index of volume flow. Flow as averaged over the entire period of tilted position was found to be 101 ± 25% of the supine steady state. There was evidence for autoregulatory vasodilation including the trunk of the middle cerebral artery. In a patient suffering from orthostatic dysregulation flow fell to 49% of its value as measured in supine position. From the evidence of this observation the clinical application of the method seems to warrant further study.
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Müller et al. (1991) studied this question.
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