Contribution of arterial blood pressure and Pa_CO2 to the cerebrovascular responses to motor stimulation

Abstract

Motor stimulation induces a neurovascular response that can be detected by continuous measurement of cerebral blood flow (CBF). Simultaneous changes in arterial blood pressure (ABP) and Pa(CO(2)) have been reported, but their influence on the CBF response has not been quantified. Continuous bilateral recordings of CBF velocity (CBFV), ABP, and end-tidal CO(2) (ET(CO(2))) were obtained in 10 healthy middle-aged subjects at rest and during 60 s of repetitive, metronome-controlled (1 Hz) elbow flexion. A multivariate autoregressive-moving average model was adopted to quantify the relationship between beat-to-beat changes in ABP, breath-by-breath ET(CO(2)), and the motor stimulus, represented by the metronome on-off signal (inputs), and the CBFV response to stimulation (output). All three inputs contributed to explain CBFV variance following stimulation. For the ipsi- and contralateral hemispheres, ABP explained 20.3 ± 17.3% (P = 0.0007) and 19.5 ± 17.2% (P = 0.01) of CBFV variance, respectively. Corresponding values for ET(CO(2)) and metronome signals were 22.0 ± 24.2% (P = 0.008), 24.0 ± 24.1% (P = 0.037), 32.7 ± 22.5% (P = 0.0015), and 43.2 ± 25.1% (P = 0.013), respectively. Synchronized population averages suggest that the initial sudden change in CBFV was largely due to ABP, while the influence of ET(CO(2)) was more erratic. The component due to elbow flexion showed a well-defined pattern, with rise time slower than the main CBFV change but reaching a stable plateau after 15 s of stimulation. Identifying and removing the influences of ABP and Pa(CO(2)) to motor-induced changes in CBF should lead to more robust estimates of neurovascular coupling and better understanding of its physiological covariates.

Active, passive, and motor imagery paradigms: component analysis to assess neurovascular coupling

“…Although the temporal course of beat-to-beat CBFv response across the three paradigms is consistent with previous studies (24,30,31), CBFv response and the individual CBFv inputs were significantly different during motor imagery compared with active and passive motor responses. Stimulus was shown to be the major contributor of CBFv increases during the paradigm performance ranging from 103.0 (2.4)% to 110.6 (5.2)%, as detailed in Tables 1 and 2.…”

“…Ninety-seven of the 102 recordings analyzed showed satisfactory model fitting as given by the comparison between model-predicted CBFv responses and the real data (24). Five recordings from two subjects resulted in poor fitting using the original model orders (orders [2,4,1,1]).…”

“…As described in APPENDIX and in previous work (24), the ARMA model allows quantification of the simultaneous influences of BP, EtCO2, and SS to the CBFv response to stimulation. Briefly, the separate contributions of BP, EtCO2, and stimulus to CBFv response were obtained as model predictions, with the use of ARMA coefficients.…”

“…It is possible that the interplay of other cerebral mechanisms (cerebral autoregulation and cerebrovascular reactivity) and the contribution of covariates (BP and Pa CO 2 ) may affect the accuracy of the raw CBF response in representing underlying cerebral activity (4). To derive more robust NVC measures, Panerai et al (24) have recently proposed an innovative methodological approach to assess the individual contribution of BP, EtCO 2 , and the metabolic stimulus to the CBF responses. This new approach has considerable potential to improve the sensitivity and overall diagnostic accuracy of NVC studies in stroke.…”

Multiple-input nonlinear modelling of cerebral haemodynamics using spontaneous arterial blood pressure, end-tidal CO 2 and heart rate measurements

“…figs 6 and 3 in [18]). ETCO 2 was found to have a slightly larger contribution to CBFV variability than ABP-albeit more variable across subjects and subsequently less statistically significant (table 1 in [18]). However, this could be due to the fact that there appears to be a strong correlation between the third input of their model (elbow flexion) and ABP, and also to that the mean value of ABP and CBFV increased during elbow flexion.…”