Superior fitting of arterial resistance and compliance parameters with genetic algorithms in models of dynamic cerebral autoregulation

Abstract Objective: The capacity of discriminating between normal and impaired dynamic cerebral autoregulation (dCA), based on spontaneous fluctuations in arterial blood pressure (ABP) and cerebral blood flow (CBF), has considerable clinical relevance. This study aimed to quantify the separate contributions of vascular resistance and compliance as parameters that could reflect myogenic and metabolic mechanisms to dCA. Methods: Forty-five subjects were studied under normo and hypercapnic conditions induced by breathing a mixture of 5% carbon dioxide in air. Dynamic cerebrovascular resistance and compliance models with ABP as input and CBFV as output were fitted using Genetic Algorithms to identify parameter values for each subject, and respiratory condition. Results: The efficiency of dCA was assessed from the models generated CBFV response to an ABP step change, corresponding to an autoregulation index of 5.561.57 in normocapnia and 2.381.73 in hypercapnia, with an area under the ROC curve (AUC) of 0.9 between both conditions. Vascular compliance increased from 0.750.7 ml/mmHg in normocapnia to 5.8212.0 ml/mmHg during hypercapnia, with an AUC of 0.88. Conclusion: we demonstrated that Genetic Algorithms are a powerful tool to provide accurate identification of model parameters expressing the performance of human CA Significance: Further work is needed to validate this approach in clinical applications where individualised model parameters could provide relevant diagnostic and prognostic information about dCA impairment Index Terms arterial compliance, autoregulation impairment, cerebral blood flow, Genetic Algorithms, hypercapnia

Can we use short recordings for assessment of dynamic cerebral autoregulation? A sensitivity analysis study in acute ischaemic stroke and healthy subjects.

Objective: It is unclear whether the duration of recordings influences estimates of dynamic cerebral autoregulation (dCA). Therefore, we performed a retrospective study of the effects of reducing recording durations on dCA estimates; with the potential to inform recording duration for reliable estimates in challenging clinical populations. Approach: Seventy-eight healthy control subjects and 79 acute ischaemic stroke (AIS) patients were included. Cerebral blood flow velocity was recorded with transcranial Doppler and continuous blood pressure with the Finapres device. The autoregulation index (ARI), derived with transfer function analysis, was calculated for recording durations at one-minute intervals between 1 and 5 minutes using the same starting point of each recording. Main results: Though recording duration did not affect the overall ARI value, when compared to control subjects, AIS patients had significantly lower ARI values for durations between 3 and 5 (p<0.0001), but not 1 and 2 minutes. The intraclass correlation coefficient of all participants, for reproducibility of the five recording durations, was 0.69. AIS patients classified as having impaired cerebral autoregulation (CA; ARI≤4) at 5 min, had a 7.1% rate of false negatives for both 4 and 3 min recordings, reaching 42.9% for 1 min recording. The percentage of false-positives also increased with reduced recording durations (from 0% at 5 to 16.2% at 1 minute). Significance: Reducing recording durations from 5 to 3 min can still provide reliable estimates of ARI, and may facilitate CA studies in potentially medically unstable AIS patients, as well as in other patient groups

Selecting portable ankle/toe brachial pressure index systems for a peripheral arterial disease population screening programme: A systematic review, clinical evaluation exercise, and consensus process.

Objective To provide an overview of systems available for peripheral arterial disease (PAD) screening, together with respective accuracies and a clinical evaluation to identify a system suitable for use in a community screening programme. Methods A systematic review of the diagnostic accuracy of six ankle brachial pressure index (ABPI) and toe brachial pressure index (TBPI) devices deemed to be portable, which were Conformité Européenne (CE) marked, and were automated or semi-automated was carried out compared with gold standard handheld Doppler and duplex ultrasound. The devices were MESI-ABPI-MD, Huntleigh Dopplex Ability, Huntleigh ABPI and TBPI systems, Systoe TBPI system, and BlueDop. Seven databases (MEDLINE, EMBASE, Scopus, Web of Science, Cochrane Database of Systematic Reviews, Cochrane Register of Controlled Trials (CENTRAL), and Cumulative Index to Nursing and Allied Health Literature (CINAHL)) were searched, and 11 studies were identified as eligible for review. This was followed by hands on clinical evaluation by abdominal aortic aneurysm (AAA) screening staff (n = 39). During this, devices were demonstrated to staff which they then tested on volunteers and gave feedback using pre-designed questionnaires on their suitability for use in a screening programme. Finally, accuracy data and staff preferences were combined during a consensus conference that was held between study and screening staff to determine the most appropriate device to use in a community screening programme. Results Generally, the evaluated systems have a moderate level of sensitivity and a high level of specificity: Dopplex ability sensitivity 20% – 70%, specificity 86% – 96%; MESI sensitivity 57% – 74%, specificity 85% – 99%; BlueDop sensitivity 95%, specificity 89%; and Systoe sensitivity 71%, specificity 77%. Clinical evaluation by screening staff identified a preference for the MESI system. The consensus conference concluded that the MESI device was a good candidate for use in a community PAD screening programme. Conclusion The MESI system is a good candidate to consider for community PAD screening.</p