scholarly journals Directional sensitivity of dynamic cerebral autoregulation in squat-stand maneuvers

2018 ◽  
Vol 315 (4) ◽  
pp. R730-R740 ◽  
Author(s):  
Ronney B. Panerai ◽  
Sam C. Barnes ◽  
Mintu Nath ◽  
Naomi Ball ◽  
Thompson G. Robinson ◽  
...  
Keyword(s):  
Cerebral Autoregulation ◽  
Moving Average ◽  
Nonlinear Behavior ◽  
Directional Sensitivity ◽  
Autoregressive Moving Average Model ◽  
Arterial Blood ◽  
Cerebral Blood Velocity ◽  
Young Subjects ◽  
End Tidal ◽  
Dynamic Cerebral Autoregulation

Dynamic cerebral autoregulation (CA), the transient response of cerebral blood flow (CBF) to rapid changes in arterial blood pressure (BP), is usually modeled as a linear mechanism. We tested the hypothesis that dynamic CA can display nonlinear behavior resulting from differential efficiency dependent on the direction of BP changes. Cerebral blood velocity (CBV) (transcranial Doppler), heart rate (HR) (three-lead ECG), continuous BP (Finometer), and end-tidal CO2 (capnograph) were measured in 10 healthy young subjects during 15 squat-stand maneuvers (SSM) with a frequency of 0.05 Hz. The protocol was repeated with a median (interquartile range) of 44 (35–64) days apart. Dynamic CA was assessed with the autoregulation index (ARI) obtained from CBV step responses estimated with an autoregressive moving-average model. Mean BP, HR, and CBV were different (all P < 0.001) between squat and stand, regardless of visits. ARI showed a strong interaction ( P < 0.001) of SSM with the progression of transients; in general, the mean ARI was higher for the squat phase compared with standing. The changes in ARI were partially explained by concomitant changes in CBV ( P = 0.023) and pulse pressure ( P < 0.001), but there was no evidence that ARI differed between visits ( P = 0.277). These results demonstrate that dynamic CA is dependent on the direction of BP change, but further work is needed to confirm if this finding can be generalized to other physiological conditions and also to assess its dependency on age, sex and pathology.

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

2013 ◽  
Vol 114 (10) ◽  
pp. 1406-1412 ◽  
Author(s):  
Angela S. M. Salinet ◽  
Thompson G. Robinson ◽  
Ronney B. Panerai
Keyword(s):  
Motor Imagery ◽  
Moving Average ◽  
Neurovascular Coupling ◽  
Neural Activation ◽  
Autoregressive Moving Average Model ◽  
Arterial Blood ◽  
Moving Average Model ◽  
End Tidal ◽  
The Right ◽  
Cognitive Paradigms

The association between neural activity and cerebral blood flow (CBF) has been used to assess neurovascular coupling (NVC) in health and diseases states, but little attention has been given to the contribution of simultaneous changes in peripheral covariates. We used an innovative approach to assess the contributions of arterial blood pressure (BP), PaCO2, and the stimulus itself to changes in CBF velocities (CBFv) during active (MA), passive (MP), and motor imagery (MI) paradigms. Continuous recordings of CBFv, beat-to-beat BP, heart rate, and breath-by-breath end-tidal CO2 (EtCO2) were performed in 17 right-handed subjects before, during, and after motor-cognitive paradigms performed with the right arm. A multivariate autoregressive-moving average model was used to calculate the separate contributions of BP, EtCO2, and the neural activation stimulus (represented by a metronome on-off signal) to the CBFv response during paradigms. Differences were found in the bilateral CBFv responses to MI compared with MA and MP, due to the contributions of stimulation ( P < 0.05). BP was the dominant contributor to the initial peaked CBFv response in all paradigms with no significant differences between paradigms, while the contribution of the stimulus explained the plateau phase and extended duration of the CBFv responses. Separating the neural activation contribution from the influences of other covariates, it was possible to detect differences between three paradigms often used to assess disease-related NVC. Apparently similar CBFv responses to different motor-cognitive paradigms can be misleading due to the contributions from peripheral covariates and could lead to inaccurate assessment of NVC, particularly during MI.

Linear and nonlinear analysis of human dynamic cerebral autoregulation

1999 ◽  
Vol 277 (3) ◽  
pp. H1089-H1099 ◽  
Author(s):  
Ronney B. Panerai ◽  
Suzanne L. Dawson ◽  
John F. Potter
Keyword(s):  
Correlation Coefficient ◽  
Supine Position ◽  
Cerebral Autoregulation ◽  
Moving Average ◽  
Second Order ◽  
Model Parameters ◽  
Nonlinear Component ◽  
Arterial Blood ◽  
Transfer Function Analysis ◽  
Dynamic Cerebral Autoregulation

The linear dynamic relationship between systemic arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV) was studied by time- and frequency-domain analysis methods. A nonlinear moving-average approach was also implemented using Volterra-Wiener kernels. In 47 normal subjects, ABP was measured with Finapres and CBFV was recorded with Doppler ultrasound in both middle cerebral arteries at rest in the supine position and also during ABP drops induced by the sudden deflation of thigh cuffs. Impulse response functions estimated by Fourier transfer function analysis, a second-order mathematical model proposed by Tiecks, and the linear kernel of the Volterra-Wiener moving-average representation provided reconstructed velocity model responses, for the same segment of data, with significant correlations to CBFV recordings corresponding to r = 0.52 ± 0.19, 0.53 ± 0.16, and 0.67 ± 0.12 (mean ± SD), respectively. The correlation coefficient for the linear plus quadratic kernels was 0.82 ± 0.08, significantly superior to that for the linear models ( P < 10−6). The supine linear impulse responses were also used to predict the velocity transient of a different baseline segment of data and of the thigh cuff velocity response with significant correlations. In both cases, the three linear methods provided equivalent model performances, but the correlation coefficient for the nonlinear model dropped to 0.26 ± 0.25 for the baseline test set of data and to 0.21 ± 0.42 for the thigh cuff data. Whereas it is possible to model dynamic cerebral autoregulation in humans with different linear methods, in the supine position a second-order nonlinear component contributes significantly to improve model accuracy for the same segment of data used to estimate model parameters, but it cannot be automatically extended to represent the nonlinear component of velocity responses of different segments of data or transient changes induced by the thigh cuff test.

scholarly journals Cerebrovascular effects of the thigh cuff maneuver

2015 ◽  
Vol 308 (7) ◽  
pp. H688-H696 ◽  
Author(s):  
R. B. Panerai ◽  
N. P. Saeed ◽  
T. G. Robinson
Keyword(s):  
Cerebral Blood Flow Velocity ◽  
Moving Average ◽  
Autoregressive Moving Average ◽  
Strongly Correlated ◽  
Mean Values ◽  
Autoregressive Moving Average Model ◽  
Arterial Blood ◽  
Moving Average Model ◽  
Area Product ◽  
End Tidal

Arterial hypotension can be induced by sudden release of inflated thigh cuffs (THC), but its effects on the cerebral circulation have not been fully described. In nine healthy subjects [aged 59 (9) yr], bilateral cerebral blood flow velocity (CBFV) was recorded in the middle cerebral artery (MCA), noninvasive arterial blood pressure (BP) in the finger, and end-tidal CO2 (ETCO2) with nasal capnography. Three THC maneuvers were performed in each subject with cuff inflation 20 mmHg above systolic BP for 3 min before release. Beat-to-beat values were extracted for mean CBFV, BP, ETCO2, critical closing pressure (CrCP), resistance-area product (RAP), and heart rate (HR). Time-varying estimates of the autoregulation index [ARI( t)] were also obtained using an autoregressive-moving average model. Coherent averages synchronized by the instant of cuff release showed significant drops in mean BP, CBFV, and RAP with rapid return of CBFV to baseline. HR, ETCO2, and ARI( t) were transiently increased, but CrCP remained relatively constant. Mean values of ARI( t) for the 30 s following cuff release were not significantly different from the classical ARI [right MCA 5.9 (1.1) vs. 5.1 (1.6); left MCA 5.5 (1.4) vs. 4.9 (1.7)]. HR was strongly correlated with the ARI( t) peak after THC release (in 17/22 and 21/24 recordings), and ETCO2 was correlated with the subsequent drop in ARI( t) (19/22 and 20/24 recordings). These results suggest a complex cerebral autoregulatory response to the THC maneuver, dominated by myogenic mechanisms and influenced by concurrent changes in ETCO2 and possible involvement of the autonomic nervous system and baroreflex.

scholarly journals Continuous estimates of dynamic cerebral autoregulation during transient hypocapnia and hypercapnia

2010 ◽  
Vol 108 (3) ◽  
pp. 604-613 ◽  
Author(s):  
N. E. Dineen ◽  
F G. Brodie ◽  
T. G. Robinson ◽  
R. B. Panerai
Keyword(s):  
Blood Pressure ◽  
Cerebral Autoregulation ◽  
Moving Average ◽  
Cerebral Arteries ◽  
Transcranial Doppler Ultrasound ◽  
Breath Hold ◽  
New Approach ◽  
Arterial Blood ◽  
The Right ◽  
Dynamic Cerebral Autoregulation

Dynamic cerebral autoregulation (CA) is the transient response of cerebral blood flow (CBF) to rapid blood pressure changes: it improves in hypocapnia and becomes impaired during hypercapnia. Batch-processing techniques have mostly been used to measure CA, providing a single estimate for an entire recording. A new approach to increase the temporal resolution of dynamic CA parameters was applied to transient hypercapnia and hypocapnia to describe the time-varying properties of dynamic CA during these conditions. Thirty healthy subjects (mean ± SD: 25 ± 6 yr, 9 men) were recruited. CBF velocity was recorded in both middle cerebral arteries (MCAs) with transcranial Doppler ultrasound. Arterial blood pressure (Finapres), end-tidal CO2 (ETCO2; infrared capnograph), and a three-lead ECG were also measured at rest and during repeated breath hold and hyperventilation. A moving window autoregressive moving average model provided continuous values of the dynamic CA index [autoregulation index (ARI)] and unconstrained gain. Breath hold led to significant increase in ETCO2 (+5.4 ± 6.1 mmHg), with concomitant increase in CBF velocity in both MCAs. Continuous dynamic CA parameters showed highly significant changes ( P < 0.001), with a temporal pattern reflecting a delayed dynamic response of CA to changes in arterial Pco2 and a maximal reduction in ARI of −5.1 ± 2.4 and −5.1 ± 2.3 for the right and left MCA, respectively. Hyperventilation led to a marked decrease in ETCO2 (−7.2 ± 4.1 mmHg, P < 0.001). Unexpectedly, CA efficiency dropped significantly with the inception of the metronome-controlled hyperventilation, but, after ∼30 s, the ARI increased gradually to show a maximum change of 5.7 ± 2.9 and 5.3 ± 3.0 for the right and left MCA, respectively ( P < 0.001). These results confirm the potential of continuous estimates of dynamic CA to improve our understanding of human cerebrovascular physiology and represent a promising new approach to improve the sensitivity of clinical applications of dynamic CA modeling.

Dynamic cerebral autoregulation during and following acute hypoxia: role of carbon dioxide

2013 ◽  
Vol 114 (9) ◽  
pp. 1183-1190 ◽  
Author(s):  
Jordan S. Querido ◽  
Philip N. Ainslie ◽  
Glen E. Foster ◽  
William R. Henderson ◽  
John R. Halliwill ◽  
...  
Keyword(s):  
Cerebral Autoregulation ◽  
Healthy Subjects ◽  
Acute Hypoxia ◽  
Intravenous Bolus ◽  
Hypoxia Exposure ◽  
Flow Response ◽  
Arterial Blood ◽  
End Tidal ◽  
Dynamic Cerebral Autoregulation

Previous research has shown an inconsistent effect of hypoxia on dynamic cerebral autoregulation (dCA), which may be explained by concurrent CO2 control. To test the hypothesis that hypoxic dCA is mediated by CO2, we assessed dCA (transcranial Doppler) during and following acute normobaric isocapnic and poikilocapnic hypoxic exposures. On 2 separate days, the squat-stand maneuver was used to determine dCA in healthy subjects ( n = 8; 3 women) in isocapnic and poikilocapnic hypoxia exposures (end-tidal oxygen pressure 50 Torr for 20 min). In isocapnic hypoxia, the amplitude of the cerebral blood flow response to increases and decreases in mean arterial blood pressure were elevated (i.e., increases in gain of +35 and +28%, respectively; P < 0.05). However, dCA gain to increases in pressure was reduced compared with baseline (−32%, P < 0.05) following the isocapnic hypoxia exposure. Similarly, intravenous bolus injections of sodium nitroprusside and phenylephrine in a separate group of subjects ( n = 8; 4 women) also demonstrated a reduction in dCA gain to hypertension following isocapnic hypoxia. In contrast, dCA gain with the squat-stand maneuver did not significantly change from baseline during or following poikilocapnic hypoxia ( P > 0.05). Our results demonstrate that dCA impairment in isocapnic hypoxia can be prevented with hypocapnia, and highlight the integrated nature of hypoxic cerebrovascular control, which is under strong CO2 influence.

Contribution of arterial blood pressure and PaCO2 to the cerebrovascular responses to motor stimulation

2012 ◽  
Vol 302 (2) ◽  
pp. H459-H466 ◽  
Author(s):  
Ronney B. Panerai ◽  
Angela S. M. Salinet ◽  
Thompson G. Robinson
Keyword(s):  
Blood Pressure ◽  
Arterial Blood Pressure ◽  
Moving Average ◽  
Sudden Change ◽  
Elbow Flexion ◽  
Autoregressive Moving Average Model ◽  
Arterial Blood ◽  
Moving Average Model ◽  
Aged Subjects ◽  
End Tidal

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 PaCO2 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 CO2 (ETCO2) 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 ETCO2, 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 ETCO2 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 ETCO2 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 PaCO2 to motor-induced changes in CBF should lead to more robust estimates of neurovascular coupling and better understanding of its physiological covariates.

Abstract 2470: Augmented Tonic Activation Of Chemoreceptors May Contribute To Sympathetic Overactivity In Patients With Essential Hypertension

Circulation ◽  
2008 ◽  
Vol 118 (suppl_18) ◽  
Author(s):  
Maciej Sinski ◽  
Jacek Lewandowski ◽  
Joanna Bidiuk ◽  
Piotr Abramczyk ◽  
Anna Dobosiewicz ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Essential Hypertension ◽  
Sympathetic Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Arterial Blood ◽  
Hemoglobin Saturation ◽  
Ambient Oxygen ◽  
Young Subjects ◽  
End Tidal ◽  
Carotid Body Chemoreceptors

Rationale : Peripheral chemoreflex contributes to regulation of arterial blood pressure and chemoreceptors respond not only to hypoxia but they are also continuously activated by normal ambient oxygen concentration. Stimulation of chemoreceptors activates sympathetic traffic and this response may be altered in subjects with essential hypertension.. Objective: The aim of our study was to investigate the effect of deactivation of carotid body chemoreceptors on sympathetic activity directly measured as MSNA (muscle sympathetic nerve activity) in young subjects with mild to moderate untreated hypertension. Methods: Twelve patients with essential hypertension (36±9 years, all men, BMI 29±4 kg/m 2 ,) and 8 controls (37±7, men BMI 27±5kg/m 2 ) participated in the study. None of the patients or controls received any medications. MSNA (burst/minute and mean burst amplitude - au), systolic blood pressure (SBP) and diastolic blood pressure (DBP), heart rate (HR), ECG, hemoglobin saturation with oxygen (Sat%), end tidal CO 2 and respiratory movements were monitored and measured after 10 minute of respiration by non-rebreathing mask with 100% 0 2 or 21% O 2 applied in blinded fashion. Results: Hypertensives had higher resting MSNA (38.6 ±8.6 burst/min vs. 30.3±.7 burst/min, p<0.05), SBP (149.1± 9.9 vs. 124.1 ±11.6, p < 0.05) and DBP (92.1 ±8.6 vs. 78.1 ± 8.9, p< 0.05) than controls. Breathing with 100% oxygen caused significant decrease in MSNA in hypertensives (from 38.6 ± 8.6 burst/min to 26.3 burst/min ± 6.8 and from 100 ± 0 au to 86 ± 18 au, p< 0.05) and no change in MSNA in controls (30.3 ± 5.7 burst/min initially and 27.3 burst/min ± 6.2 after 100% 0 2 , 100 ± 0 au vs. 98 ± 11 au). Blood pressure, end tidal CO 2 , respiration frequency did not change significantly after hyperoxia while HR decreased (from 69.6 ± 9 to 64.1 ± 7 in hypertensives p<0.05 and from 67± 8 to 62.5 ± 7 in controls, p< 0.05). Sat% increased significantly in both groups to 99%. Conclusions: Increased sympathetic activity in young, untreated hypertensives may be caused by the elevated tonic chemoreflex activation.

Prenatal exercise and cardiovascular health (PEACH) study: impact of acute and chronic exercise on cerebrovascular hemodynamics and dynamic cerebral autoregulation

2021 ◽  
Author(s):  
Rachel J. Skow ◽  
Lawrence Labrecque ◽  
Jade A. Rosenberger ◽  
Patrice Brassard ◽  
Craig D. Steinback ◽  
...  
Keyword(s):  
Exercise Training ◽  
Gestational Age ◽  
Cerebral Autoregulation ◽  
Acute Exercise ◽  
Controlled Trial ◽  
Moderate Intensity ◽  
Chronic Exercise ◽  
Arterial Blood ◽  
The Impact ◽  
Dynamic Cerebral Autoregulation

We performed a randomised controlled trial measuring dynamic cerebral autoregulation (dCA) using a sit-to-stand maneuver before (SS1) and following (SS2) an acute exercise test at 16-20 weeks gestation (trimester 2; TM2) and then again at 34-37 weeks gestation (third trimester; TM3). Following the first assessment, women were randomised into exercise training or control (standard care) groups; women in the exercise training group were prescribed moderate intensity aerobic exercise for 25-40 minutes on 3-4 days per week for 14±1weeks. Resting seated mean blood velocity in the middle cerebral artery (MCAvmean) was lower in TM3 compared to TM2 but not impacted by exercise training intervention. dCA was not impacted by gestational age, or exercise training during SS1. During SS2, dCA was altered such that there were greater absolute and relative decreases in mean arterial blood pressure (MAP) and MCAvmean, but this was not impacted by the intervention. There was also no difference in the relationship between the decrease in MCAvmean compared to the decrease in MAP (%/%), or the onset of the regulatory response with respect to acute exercise, gestational age, or intervention; however, rate of regulation was faster in women in the exercise group following acute exercise (interaction effect, p=0.048). These data highlight the resilience of the cerebral circulation in that dCA was well maintained or improved in healthy pregnant women between TM2 and TM3. However, future work addressing the impact of acute and chronic exercise on dCA in women who are at risk for cardiovascular complications during pregnancy is needed.

scholarly journals Quantification of dynamic cerebral autoregulation and CO2 dynamic vasomotor reactivity impairment in essential hypertension

2020 ◽  
Vol 128 (2) ◽  
pp. 397-409
Author(s):  
Vasilis Z. Marmarelis ◽  
Dae C. Shin ◽  
Mareike Oesterreich ◽  
Martin Mueller
Keyword(s):  
Essential Hypertension ◽  
Cerebral Autoregulation ◽  
Input Output ◽  
Physiological Mechanisms ◽  
Control Subjects ◽  
Vasomotor Reactivity ◽  
Model Based ◽  
Arterial Blood ◽  
Transfer Function Analysis ◽  
Dynamic Cerebral Autoregulation

The study of dynamic cerebral autoregulation (DCA) in essential hypertension has received considerable attention because of its clinical importance. Several studies have examined the dynamic relationship between spontaneous beat-to-beat arterial blood pressure data and contemporaneous cerebral blood flow velocity measurements (obtained via transcranial Doppler at the middle cerebral arteries) in the form of a linear input-output model using transfer function analysis. This analysis is more reliable when the contemporaneous effects of changes in blood CO2 tension are also taken into account, because of the significant effects of CO2 dynamic vasomotor reactivity (DVR) upon cerebral flow. In this article, we extract such input-output predictive models from spontaneous time series hemodynamic data of 24 patients with essential hypertension and 20 normotensive control subjects under resting conditions, using the novel methodology of principal dynamic modes (PDMs) that achieves improved estimation accuracy over previous methods for relatively short and noisy data. The obtained data-based models are subsequently used to compute indexes and markers that quantify DCA and DVR in each subject or patient and therefore can be used to assess the effects of essential hypertension. These model-based DCA and DVR indexes were properly defined to capture the observed effects of DCA and VR and found to be significantly different ( P < 0.05) in the hypertensive patients. We also found significant differences between patients and control subjects in the relative contribution of three PDMs to the model output prediction, a finding that offers the prospect of identifying the physiological mechanisms affected by essential hypertension when the PDMs are interpreted in terms of specific physiological mechanisms. NEW & NOTEWORTHY This article presents novel model-based methodology for obtaining diagnostic indexes of dynamic cerebral autoregulation and dynamic vasomotor reactivity in hypertension.

Sign in / Sign up

Export Citation Format

Share Document