Abstract
The ability to discriminate between normal and impaired dynamic cerebral autoregulation (CA), based on measurements of spontaneous fluctuations in arterial blood pressure (BP) and cerebral blood flow (CBF), has considerable clinical relevance. We studied 45 normal subjects at rest and under hypercapnia induced by breathing a mixture of carbon dioxide and air. Non-linear models with BP as input and CBF velocity (CBFV) as output, were implemented with support vector machines (SVM) using separate recordings for learning and validation. Dynamic SVM implementations used either moving average or autoregressive structures. The efficiency of dynamic CA was estimated from the model’s derived CBFV response to a step change in BP as an autoregulation index for both linear and non-linear models. Non-linear models with recurrences (autoregressive) showed the best results, with CA indexes of 5.9 ± 1.5 in normocapnia, and 2.5 ± 1.2 for hypercapnia with an area under the receiver-operator curve of 0.955. The high performance achieved by non-linear SVM models to detect deterioration of dynamic CA should encourage further assessment of its applicability to clinical conditions where CA might be impaired.
Highlights
New advances in the continuous, non-invasive measurement of arterial blood pressure (BP) and cerebral blood flow (CBF), have facilitated the evaluation of dynamic cerebral autoregulation (CA) at the bed side or during physiological maneuvers [1]
We have previously reported that support vector machines (SVM) [17] have particular advantages to model dynamic CA, including its potential to capture non-linear behavior, one aspect of dynamic CA that has not received enough attention
In the transfer function analysis (TFA) analysis, one baseline case and two cases of hypercapnia did not meet the bounds imposed by the coherence function
Summary
New advances in the continuous, non-invasive measurement of arterial blood pressure (BP) and cerebral blood flow (CBF), have facilitated the evaluation of dynamic cerebral autoregulation (CA) at the bed side or during physiological maneuvers [1]. CA is the mechanism responsible for maintaining CBF relatively constant, despite changes in mean BP in the range 60–150 mmHg [2,3]. Dynamic CA has been defined as the transient response of CBF, usually estimated as CBF velocity (CBFV) with transcranial Doppler, to a sudden change in BP. Initially proposed as the CBFV response to a BP drop induced by the rapid release of compressed thigh cuffs [4], a number of other maneuvers have been proposed to induce changes in BP to provoke corresponding changes in CBFV [5,6,7,8].
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