A novel method for assessing cerebral autoregulation in preterm infants using transfer function analysis

Dynamic cerebral autoregulation (CA) describes the transient response of cerebral blood flow (CBF) to rapid changes in arterial blood pressure (ABP). We tested the hypothesis that the efficiency of dynamic CA is increased by brain activation paradigms designed to induce hemispheric lateralization. CBF velocity [CBFV; bilateral, middle cerebral artery (MCA)], ABP, ECG, and end-tidal Pco2 were continuously recorded in 14 right-handed healthy subjects (21–43 yr of age), in the seated position, at rest and during 10 repeated presentations (30 s on-off) of a word generation test and a constructional puzzle. Nonstationarities were not found during rest or activation. Transfer function analysis of the ABP-CBFV (i.e., input-output) relation was performed for the 10 separate 51.2-s segments of data during activation and compared with baseline data. During activation, the coherence function below 0.05 Hz was significantly increased for the right MCA recordings for the puzzle tasks compared with baseline values (0.36 ± 0.16 vs. 0.26 ± 0.13, P < 0.05) and for the left MCA recordings for the word paradigm (0.48 ± 0.23 vs. 0.29 ± 0.16, P < 0.05). In the same frequency range, significant increases in gain were observed during the puzzle paradigm for the right (0.69 ± 0.37 vs. 0.46 ± 0.32 cm·s−1·mmHg−1, P < 0.05) and left (0.61 ± 0.29 vs. 0.45 ± 0.24 cm·s−1·mmHg−1, P < 0.05) hemispheres and during the word tasks for the left hemisphere (0.66 ± 0.31 vs. 0.39 ± 0.15 cm·s−1·mmHg−1, P < 0.01). Significant reductions in phase were observed during activation with the puzzle task for the right (−0.04 ± 1.01 vs. 0.80 ± 0.86 rad, P < 0.01) and left (0.11 ± 0.81 vs. 0.57 ± 0.51 rad, P < 0.05) hemispheres and with the word paradigm for the right hemisphere (0.05 ± 0.87 vs. 0.64 ± 0.59 rad, P < 0.05). Brain activation also led to changes in the temporal pattern of the CBFV step response. We conclude that transfer function analysis suggests important changes in dynamic CA during mental activation tasks.

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Transfer function analysis for clinical evaluation of dynamic cerebral autoregulation a comparison between spontaneous and respiratory-induced oscillations

Physiological Measurement ◽

10.1088/0967-3334/24/1/303 ◽

2002 ◽

Vol 24 (1) ◽

pp. 27-43 ◽

Cited By ~ 70

Author(s):

M Reinhard ◽

T M ller ◽

B Guschlbauer ◽

J Timmer ◽

A Hetzel

Keyword(s):

Transfer Function ◽

Clinical Evaluation ◽

Cerebral Autoregulation ◽

Function Analysis ◽

Transfer Function Analysis ◽

Dynamic Cerebral Autoregulation

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Dexmedetomidine Weakens Dynamic Cerebral Autoregulation as Assessed by Transfer Function Analysis and the Thigh Cuff Method

Anesthesiology ◽

10.1097/aln.0b013e3181862a33 ◽

2008 ◽

Vol 109 (4) ◽

pp. 642-650 ◽

Cited By ~ 29

Author(s):

Yojiro Ogawa ◽

Ken-ichi Iwasaki ◽

Ken Aoki ◽

Wakako Kojima ◽

Jitsu Kato ◽

...

Keyword(s):

Steady State ◽

Transfer Function ◽

Arterial Pressure ◽

Cerebral Autoregulation ◽

Function Analysis ◽

Low Frequency ◽

High Dose ◽

Frequency Range ◽

Transfer Function Analysis ◽

Dynamic Cerebral Autoregulation

Background Dexmedetomidine, which is often used in intensive care units in patients with compromised circulation, might induce further severe decreases in cerebral blood flow (CBF) with temporal decreases in arterial pressure induced by various stimuli if dynamic cerebral autoregulation is not improved. Therefore, the authors hypothesized that dexmedetomidine strengthens dynamic cerebral autoregulation. Methods Fourteen healthy male subjects received placebo, low-dose dexmedetomidine (loading, 3 microg x kg(-1) x h(-1) for 10 min; maintenance, 0.2 microg x kg(-1) x h(-1) for 60 min), and high-dose dexmedetomidine (loading, 6 microg x kg(-1) x h(-1) for 10 min; maintenance, 0.4 microg x kg(-1) x h(-1) for 60 min) infusions in a randomized, double-blind, crossover study. After 70 min of drug administration, dynamic cerebral autoregulation was estimated by transfer function analysis between arterial pressure variability and CBF velocity variability, and the thigh cuff method. Results Compared with placebo, steady state CBF velocity and mean blood pressure significantly decreased during administration of dexmedetomidine. Transfer function gain in the very-low-frequency range increased and phase in the low-frequency range decreased significantly, suggesting alterations in dynamic cerebral autoregulation in lower frequency ranges. Moreover, the dynamic rate of regulation and percentage restoration in CBF velocity significantly decreased when a temporal decrease in arterial pressure was induced by thigh cuff release. Conclusion Contrary to the authors' hypothesis, the current results of two experimental analyses suggest together that dexmedetomidine weakens dynamic cerebral autoregulation and delays restoration in CBF velocity during conditions of decreased steady state CBF velocity. Therefore, dexmedetomidine may lead to further sustained reductions in CBF during temporal decreases in arterial pressure.

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Lack of correlation between cerebral vasomotor reactivity and dynamic cerebral autoregulation during stepwise increases in inspired CO2 concentration

Journal of Applied Physiology ◽

10.1152/japplphysiol.00390.2015 ◽

2016 ◽

Vol 120 (12) ◽

pp. 1434-1441 ◽

Cited By ~ 4

Author(s):

Sung-Moon Jeong ◽

Seon-Ok Kim ◽

Darren S. DeLorey ◽

Tony G. Babb ◽

Benjamin D. Levine ◽

...

Keyword(s):

Transfer Function ◽

Cerebral Autoregulation ◽

Function Analysis ◽

Low Frequency ◽

Frequency Range ◽

Vasomotor Reactivity ◽

Arterial Blood ◽

Transfer Function Analysis ◽

Cerebral Vasomotor Reactivity ◽

Dynamic Cerebral Autoregulation

Cerebral vasomotor reactivity (CVMR) and dynamic cerebral autoregulation (CA) are measured extensively in clinical and research studies. However, the relationship between these measurements of cerebrovascular function is not well understood. In this study, we measured changes in cerebral blood flow velocity (CBFV) and arterial blood pressure (BP) in response to stepwise increases in inspired CO2 concentrations of 3 and 6% to assess CVMR and dynamic CA in 13 healthy young adults [2 women, 32 ± 9 (SD) yr]. CVMR was assessed as percentage changes in CBFV (CVMRCBFV) or cerebrovascular conductance index (CVCi, CVMRCVCi) in response to hypercapnia. Dynamic CA was estimated by performing transfer function analysis between spontaneous oscillations in BP and CBFV. Steady-state CBFV and CVCi both increased exponentially during hypercapnia; CVMRCBFV and CVMRCVCi were greater at 6% (3.85 ± 0.90 and 2.45 ± 0.79%/mmHg) than at 3% CO2 (2.09 ± 1.47 and 0.21 ± 1.56%/mmHg, P = 0.009 and 0.005, respectively). Furthermore, CVMRCBFV was greater than CVMRCVCi during either 3 or 6% CO2 ( P = 0.017 and P < 0.001, respectively). Transfer function gain and coherence increased in the very low frequency range (0.02-0.07 Hz), and phase decreased in the low-frequency range (0.07–0.20 Hz) when breathing 6%, but not 3% CO2. There were no correlations between the measurements of CVMR and dynamic CA. These findings demonstrated influences of inspired CO2 concentrations on assessment of CVMR and dynamic CA. The lack of correlation between CVMR and dynamic CA suggests that cerebrovascular responses to changes in arterial CO2 and BP are mediated by distinct regulatory mechanisms.

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Transfer Function Analysis of Cerebral Hemodynamics in Patients with Carotid Stenosis

Journal of Cerebral Blood Flow & Metabolism ◽

10.1097/00004647-199904000-00012 ◽

1999 ◽

Vol 19 (4) ◽

pp. 460-465 ◽

Cited By ~ 83

Author(s):

Han-Hwa Hu ◽

Terry Bo-Jau Kuo ◽

Wen-Jang Wong ◽

Yun-On Luk ◽

Chang-Ming Chern ◽

...

Keyword(s):

Transfer Function ◽

Carotid Stenosis ◽

Phase Angle ◽

Cerebral Autoregulation ◽

Function Analysis ◽

Low Frequency ◽

High Grade ◽

Vasomotor Reactivity ◽

Transfer Function Analysis ◽

Spontaneous Fluctuations

This study evaluates the validity of the transfer function analysis of spontaneous fluctuations of arterial blood pressure (ABP) and blood flow velocity of the middle cerebral artery (MCAFV) as a simple, convenient method to assess human cerebral autoregulation in patients with carotid stenosis. Eighty-three consecutive patients with various degrees of carotid stenosis and 37 healthy controls were enrolled. The carotid stenosis was graded based on the diagnostic criteria of duplex ultrasound. Instantaneous bilateral MCAFV and ABP of all participants were assessed noninvasively using transcranial Doppler sonography and the servocontrolled infrared finger plethysmography, respectively. Spectral analyses of ABP and MCAFV were performed by fast Fourier transform. The fluctuations in ABP as well as in MCAFV were diffracted into three components at specific frequency ranges designated as high-frequency (HF; 0.15 to 0.4 Hz), low-frequency (LF; 0.04 to 0.15 Hz), and very low-frequency (VLF; 0.016 to 0.04 Hz). Cross-spectral analysis was applied to quantify the coherence, transfer phase, and magnitude in individual HF, LF, and VLF components. Transcranial Doppler CO2 vasomotor reactivity was measured with 5% CO2 inhalation. The LF phase angle (r = −0.53, P < 0.001); magnitude of VLF (r = −0.29, P = 0.002), LF (r = −0.35, P < 0.001), and HF (r = −0.47, P < 0.001); and CO2 vasomotor reactivity (r = −0.66, P < 0.001) were negatively correlated with the severity of stenosis. Patients with unilateral high-grade (greater than 90% stenosis) carotid stenosis demonstrated significant reduction in LF phase angle ( P < 0.001) and HF magnitude ( P = 0.018) on the ipsilateral side of the affected vessel compared with their contralateral side. The study also revealed a high sensitivity, specificity, and accuracy using LF phase angle and HF magnitude to detect a high-grade carotid stenosis. A strong correlation existed between the LF phase angle and the CO2 vasomotor reactivity test (r = 0.62, P < 0.001), and the correlation between the HF magnitude and the CO2 vasomotor reactivity (r = 0.44, P < 0.001) was statistically significant as well. We conclude that transfer function analysis of spontaneous fluctuations of MCAFV and ABP could be used to identify hemodynamically significant high-grade carotid stenosis with impaired cerebral autoregulation or vasomotor reserve.

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Transfer function analysis of dynamic cerebral autoregulation in preeclampsia

Pregnancy Hypertension ◽

10.1016/j.preghy.2015.09.001 ◽

2015 ◽

Vol 5 (4) ◽

pp. 322-324 ◽

Cited By ~ 4

Author(s):

Keith P. Williams ◽

France Galerneau ◽

Maria Small

Keyword(s):

Transfer Function ◽

Cerebral Autoregulation ◽

Function Analysis ◽

Transfer Function Analysis ◽

Dynamic Cerebral Autoregulation

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Cerebral autoregulation index at high altitude assessed by thigh-cuff and transfer function analysis techniques

Experimental Physiology ◽

10.1113/expphysiol.2014.082479 ◽

2015 ◽

Vol 100 (2) ◽

pp. 173-181 ◽

Cited By ~ 16

Author(s):

Andrew W. Subudhi ◽

Katalin Grajzel ◽

Robert J. Langolf ◽

Robert C. Roach ◽

Ronney B. Panerai ◽

...

Keyword(s):

Transfer Function ◽

High Altitude ◽

Cerebral Autoregulation ◽

Function Analysis ◽

Analysis Techniques ◽

Transfer Function Analysis ◽

Autoregulation Index

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A Data-Driven Approach to Transfer Function Analysis for Superior Discriminative Power: Optimized Assessment of Dynamic Cerebral Autoregulation

IEEE Journal of Biomedical and Health Informatics ◽

10.1109/jbhi.2020.3015907 ◽

2020 ◽

pp. 1-1

Author(s):

Jia Liu ◽

Zhen-Ni Guo ◽

David Martin Simpson ◽

Pandeng Zhang ◽

Chang Liu ◽

...

Keyword(s):

Transfer Function ◽

Cerebral Autoregulation ◽

Function Analysis ◽

Data Driven ◽

Discriminative Power ◽

Transfer Function Analysis ◽

Data Driven Approach ◽

Dynamic Cerebral Autoregulation

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Assessment of cerebral autoregulation from ectopic heartbeats

Clinical Science ◽

10.1042/cs20050009 ◽

2005 ◽

Vol 109 (1) ◽

pp. 109-115 ◽

Cited By ~ 6

Author(s):

Penelope J. EAMES ◽

John F. POTTER ◽

Ronney B. PANERAI

Keyword(s):

Transfer Function ◽

Cerebral Autoregulation ◽

Cerebral Blood Flow Velocity ◽

Function Analysis ◽

Linear Interpolation ◽

Data Set ◽

Surface Ecg ◽

Transfer Function Analysis ◽

Time Domains ◽

Step Responses

Transfer function analysis of spontaneous fluctuations in BP (blood pressure) and CBFV (cerebral blood flow velocity) has been widely used to study dynamic CA (cerebral autoregulation). The inverse Fourier transform and its integral, giving the impulse and step responses, have been used to gain perspective of the state of dynamic CA from the frequency and time domains respectively. The occurrence of ectopic heartbeats in the data has usually been treated as an artefact. Data containing multiple ectopic heartbeats were selected from a data set compiled for an acute stroke study which also included bilateral middle CBFV, concurrent surface ECG and non-invasive beat-to-beat BP recordings. Transfer function analysis and impulse and step responses were calculated from these data by (i) retaining ectopic heartbeats, (ii) after removal of ectopic heartbeats and replacement by linear interpolation, and (iii) using a narrow window of data surrounding selected ectopic heartbeats. Coherent averaging of the raw data of the selected ectopic heartbeats also allowed direct visualization of the relationship between BP changes and CBFV. The impulse and step responses were similar in shape whether or not ectopic heartbeats had been removed and showed characteristics of active dynamic CA. Removal of ectopic heartbeats from the CBFV and BP tracings, by linear interpolation or other methods, is not necessary to provide reliable estimates of dynamic autoregulation in subjects with ectopic heartbeat rates of up to eight per min. Additionally, impulse-like disturbances of BP induced by single-beat ectopic heartbeats provide enough information to characterize the autoregulatory response of the subject in agreement with more traditional methods of dynamic autoregulation assessment.

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