Slow sinusoidal tilt movements demonstrate the contribution to orthostatic tolerance of cerebrospinal fluid movement to and from the spinal dural space. Issue 4 (27th February 2019)

• Record Type: Journal Article
• Authors: Stok, Wim J.; Karemaker, John M.; Berecki‐Gisolf, Janneke; Immink, Rogier V.; van Lieshout, Johannes J.
• Is Part Of: Physiological reports. Volume 7:Issue 4(2019)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2019-02-27
• Subjects: Body position -- cerebrospinal fluid -- cerebrovascular autoregulation -- computer model -- orthostasis; Physiology -- Periodicals; 571
• DOI: 10.14814/phy2.14001
• Languages: English
• ISSNs: 2051-817X

Abstract

Abstract: Standing up elicits a host of cardiovascular changes which all affect the cerebral circulation. Lowered mean arterial blood pressure (ABP) at brain level, change in the cerebral venous outflow path, lowered end‐tidal PCO 2 (PET CO2 ), and intracranial pressure (ICP) modify cerebral blood flow (CBF). The question we undertook to answer is whether gravity‐induced blood pressure (BP) changes are compensated in CBF with the same dynamics as are spontaneous or induced ABP changes in a stable position. Twenty‐two healthy subjects (18/4 m/f, 40 ± 8 years) were subjected to 30° and 70° head‐up tilt (HUT) and sinusoidal tilts (SinTilt, 0°↨60° around 30° at 2.5–10 tilts/min). Additionally, at those three tilt levels, they performed paced breathing at 6–15 breaths/min to induce larger than spontaneous cardiovascular oscillations. We measured continuous finger BP and cerebral blood flow velocity (CBFv) in the middle cerebral artery by transcranial Doppler to compute transfer functions (TFs) from ABP‐ to CBFv oscillations. SinTilt induces the largest ABP oscillations at brain level with CBFv gains strikingly lower than for paced breathing or spontaneous variations. This would imply better autoregulation for dynamic gravitational changes. We demonstrate in a mathematical model that this difference is explained by ICP changes due to movement of cerebrospinal fluid (CSF) into and out of the spinal dural sack. Dynamic cerebrovascular autoregulation seems insensitive to how BP oscillations originate if the effect of ICP is factored in. CSF‐movement in‐and‐out of the spinal dural space contributes importantly to orthostatic tolerance by its effect on cerebral perfusion pressure. Abstract : Cerebrovascular autoregulation in the face of orthostatic challenged seems more effective than when guessed from resting, supine measurements. This effect is mainly due to changes in intracranial pressure when cerebrospinal fluid flows from the cerebral to the spinal compartment, thus improving the inflow of arterial blood. This appears to be an important mechanism to uphold cerebral blood flow in orthostasis.