Inter-subject analysis of transfer function coherence in studies of dynamic cerebral autoregulation

Abstract

Objective: The gain and phase of the arterial blood pressure (BP)-cerebral blood flow velocity (CBFV) relationship, assessed by transfer function analysis (TFA), are widely used dynamic cerebral autoregulation (CA) metrics, but their reliability depend on the statistical significance of the magnitude squared coherence (MSC) function. We tested a new approach, based on inter-subject data, to estimate the confidence limits of MSC. Approach: Five minute beat-to-beat time series of mean arterial BP (MAP, Finometer) and CBFV (transcranial Doppler) were used for intra-subject (MAP and CBFV from same subject) and intersubject (BP and CBFV swapped between subjects) estimates of MSC. The 95% confidence limit of MSC was obtained by non-parametric methods for the cases of single frequency harmonics in the range [0.02-0.50 Hz], and also from the mean value of all possible frequency intervals in this range. Main results: Intra-subject estimates of MSC were obtained from 100 healthy subjects (48 female, age range: 21-82 years old) allowing calculation of 9,900 inter-subject estimates, with 95% confidence limits in excellent agreement with classical values derived from surrogate random data. Confidence limits of MSC, derived from mean values, decreased asymptotically to around 0.16 with the increasing number of harmonics averaged. Significance: Replacing estimates of MSC at a single frequency harmonic by the mean calculated over the range [0.02-0.30 Hz] could lead to more robust studies of dynamic CA with greater acceptance of recordings, an important consideration in clinical studies where measurements tend to be more susceptible to noise and artefacts.

The critical closing pressure contribution to dynamic cerebral autoregulation in humans: influence of arterial partial pressure of CO2

“…A problem exists, though, when the criterion is applied to multiple transfer functions, as was our case. The 95% confidence limit for the mean coherence function in the range 0.15-0.25 Hz that we found in previous studies was approximately 0.190 when using 5 min recordings, with five segments of 102.4 s duration and 50% superposition (Claassen et al 2016;Panerai et al 2016Panerai et al , 2018. However, when applying this approach to multiple transfer functions, also subjected to the condition that it must be satisfied for both normocapnia and hypercapnia, the 95% limit is likely to be much lower and further studies of this joint distribution would be needed.…”

“…2016; Panerai et al . 2016, 2018). However, when applying this approach to multiple transfer functions, also subjected to the condition that it must be satisfied for both normocapnia and hypercapnia, the 95% limit is likely to be much lower and further studies of this joint distribution would be needed.…”

Cardiovascular and cerebrovascular responses to urodynamics testing after spinal cord injury: The influence of autonomic injury

“…Increases in TFG indicated impaired autoregulation, whereby changes in CMAP elicit larger changes in MCAv m . Decreased phase suggests reduced autoregulatory function, as changes in CMAP rapidly induce changes in MCAv (Panerai et al, 2018).…”

The upper frequency limit of dynamic cerebral autoregulation

“…Similar conclusions were reached by a different study based on the properties of the coherence function, also showing that the 0.07 Hz break point was not justified as a meaningful separation of two distinct frequency bands (Panerai et al . ). Above all, the demonstration that F upLim is closely associated with (Fig.…”