The repeatability of cerebral autoregulation assessment using sinusoidal lower body negative pressure

Abstract

A forced periodic variation in blood pressure produces a similar variation in cerebral blood velocity. The amplitudes and phases of the pressure and velocity waveforms are indicative of the dynamic response of the cerebral autoregulation. The phase of the velocity leads the pressure; the greater the phase difference the faster the autoregulation response. Various techniques have been employed to oscillate arterial blood pressure but measurement reproducibility has been poor. The purpose of this study was to assess the reproducibility of phase measurements when sinusoidal lower body negative pressure is used to vary blood pressure. Five healthy volunteers were assessed at two vacuum levels on each of eight visits. For each measurement a 12 s sinusoidal cycle was maintained for 5 min. The Fourier components of blood pressure and the middle cerebral artery velocity were determined at the oscillation frequency. The phase of velocity consistently led the pressure. The mean phase difference was 42+/-13 degrees for the stronger vacuum and 36+/-42 degrees for the weaker vacuum. The variation given is the within-subjects standard deviation estimated from a one-way analysis of variance. Sinusoidal lower body negative pressure is a useful stimulus for investigating autoregulation; it has advantages over other methods. High vacuums show good reproducibility but are too uncomfortable for patient use.

The Leicester cerebral haemodynamics database: normative values and the influence of age and sex

“…Frequency domain parameters and ARI, derived from TFA, have shown to be sensitive to physiological changes in patients with a variety of diseases. It is important to note that in addition to TFA, alternative methods have been used to assess the relationship between CBFV and BP such as multimodal pressure flow analysis which may be more resilient to unstable variation in BP and/or CBFV (Czosnyka et al 1996, Dawson et al 2000, Panerai 2008, Zhang et al 1998, Birch, Neil-Dwyer & Murrills 2002, Mitsis et al 2006. A relationship has been established between impaired CA and clinical outcome, such as traumatic brain injury, cerebral ischaemia, occlusive carotid disease and Alzheimer's disease.…”

“…The autoregulation index (ARI) proposed by Tiecks et al (Tiecks et al 1995), usually obtained from thigh cuff manoeuvres (Tiecks et al 1995, Aaslid et al 1989, can also be derived by TFA (Panerai et al 1998b) and together with phase has been shown to be the most sensitive parameter to detect abnormalities in CBF regulation (Panerai 2008). Both the ARI and phase have been shown to have satisfactory, but not outstanding, reproducibility (Birch, Neil-Dwyer & Murrills 2002, Brodie et al 2009, Gommer et al 2010. Despite these encouraging studies, normative values of ARI and phase have not been reported for two main reasons.…”

Transcranial Doppler for evaluation of cerebral autoregulation

“…In the original study of Aaslid et al [3], BP changes were induced by the sudden release of bilateral thigh-cuffs that were inflated above systolic BP for 3 min. Several other manoeuvres have been adopted to induce changes in BP such as the Valsalva manoeuvre [143], low frequency breathing [35], periodic squatting [8] and other changes in posture [79], handgrip [67], cold stress test [102], and lower-body negative pressure (LBNP) [9]. Preliminary studies have not detected differences in the CBFV response to different manoeuvres [102], but this possibility should be kept in mind when comparing reports in the literature based on different approaches to provoke changes in BP.…”

“…It is important to clarify that the positive phase is only observed at steady-state and it is caused by the physical delay in the smooth muscle response to modify arteriolar diameter and hence cerebrovascular resistance (CVR) [58,107]. Sinusoidal-like oscillations in BP can be induced by synchronized breathing [35], repetitive squatting [8] or LBNP [9]. These manoeuvres, however, cannot be easily applied to all groups of patients or used frequently for bedside monitoring.…”

Nonlinear, multiple-input modeling of cerebral autoregulation using Volterra Kernel estimation

“…In order to assess dCA a few methods to induce large, rapid changes in ABP have been proposed in the literature: thigh cuff release produces a sudden step decrease in BP [2], lower body negative pressure can give sinusoidal variation in CBFV [3], the valsalva maneuver provokes characteristic change in BP and CBFV [4], and periodic breathing, squatting and head-up tilt [5], [6], [7] have all been used. Spontaneous variations in blood pressure and pCO2 (an example is shown in fig 1) may also provide sufficient excitation to assess autoregulation, while minimizing interference with the patient which is clearly desirable for clinical studies.…”