Continuous estimates of dynamic cerebral autoregulation: influence of non-invasive arterial blood pressure measurements

R B Panerai,J F Potter,W E Rathbone,S M Smith,S Bentley,E L Sammons,N J Samani

doi:10.1088/0967-3334/29/4/006

R B Panerai, J F Potter + Show 5 more

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https://doi.org/10.1088/0967-3334/29/4/006

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Abstract

Temporal variability of parameters which describe dynamic cerebral autoregulation (CA), usually quantified by the short-term relationship between arterial blood pressure (BP) and cerebral blood flow velocity (CBFV), could result from continuous adjustments in physiological regulatory mechanisms or could be the result of artefacts in methods of measurement, such as the use of non-invasive measurements of BP in the finger. In 27 subjects (61 ± 11 years old) undergoing coronary artery angioplasty, BP was continuously recorded at rest with the Finapres device and in the ascending aorta (Millar catheter, BPAO), together with bilateral transcranial Doppler ultrasound in the middle cerebral artery, surface ECG and transcutaneous CO2. Dynamic CA was expressed by the autoregulation index (ARI), ranging from 0 (absence of CA) to 9 (best CA). Time-varying, continuous estimates of ARI (ARI(t)) were obtained with an autoregressive moving-average (ARMA) model applied to a 60 s sliding data window. No significant differences were observed in the accuracy and precision of ARI(t) between estimates derived from the Finapres and BPAO. Highly significant correlations were obtained between ARI(t) estimates from the right and left middle cerebral artery (MCA) (Finapres r = 0.60 ± 0.20; BPAO r = 0.56 ± 0.22) and also between the ARI(t) estimates from the Finapres and BPAO (right MCA r = 0.70 ± 0.22; left MCA r = 0.74 ± 0.22). Surrogate data showed that ARI(t) was highly sensitive to the presence of noise in the CBFV signal, with both the bias and dispersion of estimates increasing for lower values of ARI(t). This effect could explain the sudden drops of ARI(t) to zero as reported previously. Simulated sudden changes in ARI(t) can be detected by the Finapres, but the bias and variability of estimates also increase for lower values of ARI. In summary, the Finapres does not distort time-varying estimates of dynamic CA obtained with a sliding window combined with an ARMA model, but further research is needed to confirm these findings in healthy subjects and to assess the influence of different physiological manoeuvres.

Highlights

Under normal physiological conditions, blood flow to the brain is controlled by multiple mechanisms, including cerebral pressure-autoregulation (CA), which maintains cerebral blood flow (CBF) relatively constant for changes in arterial blood pressure (BP) in the range 60-150 mmHg (Paulson et al 1990)
Dynamic CA cannot be observed without changes in mean BP, relatively fast changes can be induced by several different manoeuvres such as the thigh cuff test (Aaslid et al 1989), Valsalva manoeuvre (Tiecks et al 1996), cold pressor test (Panerai et al 2001), synchronized breathing (Diehl et al 1995) or repeated squatting (Birch et al 1995)
4.1 Influence of the Finapres In a previous study, estimates of dynamic CA obtained with the Finapres were shown to produce single values of autoregulation index (ARI) that were greater than corresponding measures derived from intra-aortic BP recordings, the differences were relatively small (Sammons et al 2007)

Summary

Introduction

Blood flow to the brain is controlled by multiple mechanisms, including cerebral pressure-autoregulation (CA), which maintains cerebral blood flow (CBF) relatively constant for changes in arterial blood pressure (BP) in the range 60-150 mmHg (Paulson et al 1990). Dynamic CA has several advantages when compared to the static approach, mainly that it does not require the induction of long lasting changes in mean BP, usually achieved with the use of pharmacological agents (Panerai 1998). Dynamic CA cannot be observed without changes in mean BP, relatively fast changes can be induced by several different manoeuvres such as the thigh cuff test (Aaslid et al 1989), Valsalva manoeuvre (Tiecks et al 1996), cold pressor test (Panerai et al 2001), synchronized breathing (Diehl et al 1995) or repeated squatting (Birch et al 1995). Of considerable interest is the possibility of using spontaneous fluctuations in BP and CBFV to model dynamic CA since this avoids any physiological perturbation and does not require any collaboration from the subject (Panerai 1998)

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