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

Abstract

Oscillations of arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV) can be used for non-invasive assessment of cerebral autoregulation using transfer function analysis. Either spontaneous oscillations (SPO) around 0.1 Hz or respiratory induced oscillations during deep breathing (DB) at a rate of 6/min have been used so far. We investigated 168 patients with severe carotid stenosis or occlusion to evaluate transfer function analysis and compare the SPO and DB approaches. ABP was assessed non-invasively (Finapres), CBFV was measured in the middle cerebral artery using transcranial Doppler sonography. Transfer function phase (P) and gain (G) were extracted from the respective spectra in a low (0.06-0.12 Hz) and high (0.20-0.30 Hz) frequency range (LF, HF) of SPO and from the 0.1 (LF) and 0.2 (HF) Hz peaks induced by DB. For SPO, significant side-to-side differences and differences between groups of severe and critical stenosis were found for P(LF), while P(HF) did not prove to be a significant parameter. G(LF) showed significant side-to-side differences, while G(HF) additionally differed significantly between severe and critical stenosis and occlusion, respectively. For DB, significant side-to-side differences were found for P(LF, HF). Mainly G(HF) differed significantly between the affected and contralateral sides, while both HF and LF gains showed lower values in groups with a higher degree of stenosis. Correlation between G and P values was generally poor. Using Bland-Altman plots a poor inter-method agreement was found mainly for P. Correlations between SPO and DB were higher for G than for P (LF r = 0.64 versus 0.44, HF 0.69 versus 0.28). Analysing reproducibility in 16 patients, only for P(LF, HF) of DB was a highly significant correlation found (Spearman's r up to 0.78). For G(LF, HF) correlations were significant for both SPO and DB with slightly higher r coefficients for SPO. In conclusion, the present study showed that (1) transfer functions P and G represent different information for characterization of dynamic cerebral autoregulation in the frequency domain. (2) Inter-method agreement between DB and SPO is poor for P and moderate for G values. (3) P extracted from DB has a higher reproducibility. (4) The extraction of P and G from the SPO phase spectra is critical and future work on standardizing this process is needed. (5) At present, the DB protocol might be slightly advantageous as a routine diagnostic tool.

Coherent hemodynamics spectroscopy in a single step

“…2, middle and bottom panels), with a temporal offset (or relative phase) between ΔO(t) and ΔD(t), as well as between MAP and ΔT(t) that is frequency dependent. For the four investigated subjects, the time delay of ΔT(t) with respect to MAP during the step response and the cyclic occlusion protocols was measured to be between 0.5 and 2.5 s. This time delay is in agreement with a previously reported phase lag of ~20° for ΔT vs. MAP oscillations at 0.1 Hz (a phase lag of 20° at 0.1 Hz corresponds to a time delay of 0.56 s) [1]. …”

“…We observe that the autoregulation relationship in Eq. (4) considers blood volume as a surrogate for blood pressure because it is known that the dynamics of total hemoglobin concentration (which is a direct measure of blood volume) closely match those of arterial blood pressure, with a relatively small time delay [1] that will be reported and discussed in this work.…”

“…The underlying sources of such time-dependent hemodynamics are changes in cerebral blood volume (CBV), cerebral blood flow (CBF), and metabolic rate of oxygen (CMRO 2 ). Spontaneous oscillations in hemoglobin concentrations have also been observed and correlated to spontaneous oscillations in mean arterial blood pressure (MAP) [1]. In addition to spontaneous occurrence, oscillations can be induced by paced breathing [1,2], repeated head-up tilting [3], squat-stand maneuvers [4], and cyclic thigh cuff inflation-deflation [5].…”

“…Spontaneous oscillations in hemoglobin concentrations have also been observed and correlated to spontaneous oscillations in mean arterial blood pressure (MAP) [1]. In addition to spontaneous occurrence, oscillations can be induced by paced breathing [1,2], repeated head-up tilting [3], squat-stand maneuvers [4], and cyclic thigh cuff inflation-deflation [5]. Those maneuvers have typically been used to induce oscillations at ~0.1 Hz in MAP and cerebral blood flow that have been measured using finger plethysmography and transcranial Doppler ultrasound (TCD), respectively [6].…”

Identification of Pressure Passive Cerebral Perfusion and Its Mediators after Infant Cardiac Surgery

“…We then subjected each 5-min epoch to a uniform and consistent computation. CPA is believed to be frequency specific (11,12). Therefore, we analyzed the relationship between MAP and HbD in a frequency-specific manner, using transfer function analysis in the frequency domain.…”