Coherent averaging of pseudorandom binary stimuli: is the dynamic cerebral autoregulatory response symmetrical?

Objective: Previous studies on cerebral autoregulation have shown the existence of hemispheric symmetry, which may be altered in stroke and traumatic brain injury. There is a paucity of data however on whether the response is symmetrical between those disturbances that cause cerebral hyperperfusion, to those that cause hypoperfusion. Our aim was to investigate whether the responses of cerebral autoregulation to haemodynamic stimuli of different directions are symmetrical. 
 Approach: Using a previously described assessment method, we employed coherent averaging of the cerebral blood flow velocity (CBFV) responses to thigh cuff inflation and deflation, as driven by pseudorandom binary sequences, whilst simultaneously altering the inspired CO2. The symmetry of the autoregulatory response was assessed with regards to two parameters, its speed and gain. Using the first harmonic method, critical closing pressure (CrCP) and resistance area product (RAP) were estimated, and the gain of the autoregulatory response was calculated by performing linear regression between the coherent averages of arterial blood pressure (ABP) and CBFV, ABP and CrCP and finally ABP and RAP. A two-way repeated measures ANOVA was used to assess for the effect of the direction of change in ABP and the method of CO2 administration. 
 Main results: Our results suggest that whilst the direction of ABP change does not have a significant effect, the effect of CO2 administration method is highly significant (p<10-4). 
 Significance: This is the first report to report to demonstrate the symmetry of the autoregulatory response to stimuli of different directions as well as the short term dynamics of RAP and CrCP under intermittent and constant hypercapnia. As haemodynamic stimulus direction does not appear to have an influence, our findings validate previous work done using different assessment methods

Revisiting the frequency domain: the multiple and partial coherence of cerebral blood flow velocity in the assessment of dynamic cerebral autoregulation

Despite advances in modelling dynamic autoregulation, only part of the variability of cerebral blood flow velocity (CBFV) in the low frequency range has been explained. We investigate whether a multivariate representation can be used for this purpose. Pseudorandom sequences were used to inflate thigh cuffs and to administer 5% CO2. Multiple and partial coherence were estimated, using arterial blood pressure (ABP), end-tidal CO2 (EtCO2) and resistance area product as input and CBFV as output variables. The inclusion of second and third input variables increased the amount of CBFV variability that can be accounted for (p  <  10−4 in both cases). Partial coherence estimates in the low frequency range (<0.07 Hz) were not influenced by the use of thigh cuffs, but CO2 administration had a statistically significant effect (p  <  10−4 in all cases). We conclude that the inclusion of additional inputs of a priori known physiological significance can help account for a greater amount of CBFV variability and may represent a viable alternative to more conventional non-linear modelling. The results of partial coherence analysis suggest that dynamic autoregulation and CO2 reactivity are likely to be the result of different physiological mechanisms

A case of splenic abscess after radiofrequency ablation

Radiofrequency ablation (RFA) is an innovative technique used primarily for the palliative treatment of unresectable liver tumors. Its therapeutic indications however, have been expanded and now include various other organs and diseases. There is a paucity of data regarding technical details and complications of the use of RFA in the spleen. We report a case of partial splenectomy using radiofrequency ablation for splenic hydatid disease, complicated by an abscess formation. (c) 2006 The WJG Press. All rights reserved

Radiofrequency-assisted partial splenectomy: Histopathological and immunological assessment of the splenic remnant in a porcine model

Background Radiofrequency (RF) ablation has recently been expanded from palliative treatment into tissue-preserving surgery with controversial results. RF has been accused of septic complications and dysfunction of the target organ due to uncontrolled energy distribution. The aim of this study was to evaluate the short-and long-term implications of RF energy to the remaining splenic tissue after laparoscopic and open RF-assisted partial splenectomy. Methods Thirty pigs randomly underwent laparoscopic RF partial splenectomy (n = 10), open RF partial splenectomy (n = 10) using the Radionics Cooltip radiofrequency system (Tyco Hellas), while a third group (n = 10) underwent the conventional procedure. Intraoperative parameters were recorded. Complete blood counts, along with splenic function tests, were estimated preoperatively, immediately postoperatively, and at 1 and 6 months after the procedure. Histology was also evaluated. A separate group of five animals randomly undergo conventional resection (n = 2) and open RF resection (n = 3). These animals were sacrificed 1 month postoperatively and were used for histology only. Results The blood loss was minimal in both RF groups. No septic complications were observed throughout the follow-up period. Laboratory values at 1 month postoperatively showed decreased splenic function in both RF groups. Histology at 1 month was indicative of a chronic inflammatory reaction to the RF groups whereas, in the control group, prominent hypervascular granulated tissue was observed. Six months postoperatively, the platelet count remained elevated in the RF groups. Histology revealed intense fibrosis at the ablation site, as opposed to friable granulated tissue in the conventional group. Conclusions Radiofrequency energy acts as an excellent haemostatic tool. The healing process shifts from the thermal injury to chronic inflammatory reaction and, 6 months later, to intense fibrosis as opposed to the hypervascular granulated tissue presented in the nonablated spleen. However, the longer the RF energy is applied, the more the splenic function is transiently affected

Modified radiofrequency-assisted liver resection: A new device

Background: Radiofrequency ablation (RF) is emerging as new therapeutic method for the management of hepatic tumors. So far the RF-assisted hepatectomy has been described using an electrode initially designed for ablation of unresectable tumors. Herein, we describe a new technique for liver resection using a bipolar radiofrequency device. Method: Ten patients undergo liver resection using a bipolar radiofrequency device. A minimal zone of desiccation around the tumor is created between pairs of opposing electrodes as a result of a minimum amount of energy released. This coagulated plane can be divided with a scalpel. Results: The liver parenchyma was divided with minimal blood loss. No intensive care unit admission was needed. There was no postoperative biliary leak or any other septic complication. Conclusion: The technique is safe and feasible, simplifies liver resection and appears to be associated with minimal morbidity and maximum liver parenchyma preservation

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

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

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