Effect of head‐upright tilt on the dynamic of cerebral autoregulation

Abstract

The effect of head-upright tilting on the rate of cerebral autoregulation was studied in 12 healthy volunteers (nine men and three women; age range 20-36 years). The dynamics of cerebral autoregulation was determined from the rate of change in cerebral resistance (RoR) during a drop in arterial blood pressure induced by rapid deflation of a 3-min ischaemic thigh cuff and from the ratio of changes in cerebral blood flow and arterial blood pressure (CAI) during the recovery period after the drop in arterial blood pressure. The test was performed supine and with 40 degrees head-up tilt (40 degrees HUT). Middle cerebral artery mean blood flow velocity was measured by transcranial Doppler simultaneously with peripheral arterial blood pressure using Finapres. The thigh cuff deflation induced a larger drop in arterial pressure during 40 degrees HUT [median -28% (25 percentile -36, 75 percentile -19)] than in the supine position [-16% (-23, -15)] (P < 0.01) and in cerebral resistance [supine: -12% (-15, -6); 40 degrees HUT: -15% (-20, -12); P < 0.05]. There was no significant change in RoR [15% s-1 (12, 15)] and CAI [1.9 (1.5, 3.1)] measured supine and during 40 degrees HUT [RoR: 13% s-1 (12, 15); CAI: 1.3 (0.99, 1.9)]. During the drop in arterial pressure, the relationship between arterial blood pressure and systolic peak-to-peak interval exhibited an hysteresis loop, indicating a cardiopulmonary and/or baroreflex activation that was not observed with cerebral resistance. The rate of autoregulation is an intrinsic property of the cerebral vascular bed and is not affected by the vasodilator state in the range of arterial blood pressure changes induced by the tight cuff method.

Cerebral Autoregulatory Responses to Head-Up Tilt in Normal Subjects and Patients With Recurrent Vasovagal Syncope

“…In addition, we have demonstrated that similar changes occur in patients with recurrent VVS. The conclusion of Leftheriotis et al 17 that dynamic CA is preserved in normal subjects at low levels of orthostatic stress is similarly supported by our initial data after head-up tilt, which also demonstrate similar preservation of dynamic CA in patients with recurrent VVS.…”

“…27 More recently, Leftheriotis et al 17 used rapid thigh-cuff deflation to demonstrate preserved dynamic CA in normal subjects 5 minutes after 40°head-up tilt. In many ways, this study forms a link between the studies of Zhang et al 19 and Leftheriotis et al 17 and shows that the findings of all 3 studies are compatible with each other. The finding of Zhang et al 19 that dynamic CA deteriorates in normal subjects during presyncope is supported by our demonstration of decreased ARI values during presyncope in the syncopal control group.…”

“…6 -12 Arterial, end-tidal, and transcutaneous CO 2 levels have also been shown to fall significantly in normal subjects immediately after head-up tilt, [12][13][14][15][16] and Cencetti et al 12 showed a significant link between the declines in CBFV and CO 2 after head-up tilt. Despite the fall in CBFV during orthostatic stress, its effect on dynamic CA is unclear, with both intact 17,18 and impaired 19 CA being reported in normal subjects.…”

Cerebral blood flow during orthostasis: role of arterial CO2

“…In addition, a paradoxical cerebral vasoconstriction in healthy (5,6,22,38) and orthostatically intolerant (13,14) individuals has been reported during postural stress and LBNP. However, our previous work (38), as well as that of others (8,21), showed that cerebral autoregulation remains intact during HUT in healthy subjects, suggesting that decreases in perfusion pressure were unlikely to be the cause of the decrease in cerebral flow. Similarly, analysis of transfer function gain between CFV and blood pressure found no change in gains during tilt in these subjects (data not shown).…”

Dynamic Cerebral Autoregulation in Acute Lacunar and Middle Cerebral Artery Territory Ischemic Stroke

“…The latency in dCA as derived from spontaneous MAP decreases provides confirmatory information regarding impaired CA, as well as produced data akin to rapid thigh-cuff deflation as a stimulus for dCA. 13 CA in stroke is controversial. In large MCAS, a transient rise in BP by phenylephrine raises MCA V mean on the affected side only, indicating unilaterally impaired static CA.…”