A method to estimate wall shear rate with a clinical ultrasound scanner.

A simple technique to estimate the wall shear rate in healthy arteries using a clinical ultrasound scanner has been developed. This method uses the theory of fully developed oscillatory flow together with a spectral Doppler trace and an estimate of mean arterial diameter. A method using color flow imaging was compared with the spectral Doppler method in vascular phantoms and found to have errors that were on average 35% greater. Differences from the theoretic value for the time averaged wall shear rate using the spectral Doppler method varied by artery: brachial -9 (1) %; carotid -7 (1) %; femoral -22 (4) %; and fetal aorta -17 (10) %. Test measurements obtained from one healthy volunteer demonstrated the feasibility of the technique in vivo.

Characterization of an abdominal aortic velocity waveform in patients with abdominal aortic aneurysm.

Haemodynamics studies of abdominal aortic aneurysm require data on the velocity in the normal section of the aorta. Centreline velocity waveforms were measured in abdominal aortic aneurysm patients proximal to the aneurysm using spectral Doppler ultrasound. Characteristic points were automatically found on 21 of the waveforms and their parameters were used to create an archetypal centreline velocity waveform. The maximum velocity was 45 +/- 13 cm s(-1), the minimum velocity was -15 +/- 11 cm s(-1) and the maximum diastolic velocity was 2.7 +/- 4.7 cm s(-1). The velocity wave is suitable for use as an input to in vitro or in silico investigations of abdominal aortic aneurysm haemodynamics.

Accuracy of pulse interval timing in ambulatory blood pressure measurement.

Blood pressure (BP) monitors rely on pulse detection. Some blood pressure monitors use pulse timings to analyse pulse interval variability for arrhythmia screening, but this assumes that the pulse interval timings detected from BP cuffs are accurate compared with RR intervals derived from ECG. In this study we compared the accuracy of pulse intervals detected using an ambulatory blood pressure monitor (ABPM) with single lead ECG. Twenty participants wore an ABPM for three hours and a data logger which synchronously measured cuff pressure and ECG. RR intervals were compared with corresponding intervals derived from the cuff pressure tracings using three different pulse landmarks. Linear mixed effects models were used to assess differences between ECG and cuff pressure timings and to investigate the effect of potential covariates. In addition, the maximum number of successive oscillometric beats detectable in a measurement was assessed. From 243 BP measurements, the landmark at the foot of the oscillometric pulse was found to be associated with fewest covariates and had a random error of 9.5 ms. 99% of the cuff pressure recordings had more than 10 successive detectable oscillometric beats. RR intervals can be accurately estimated using an ABPM.

Opportunistic detection of atrial fibrillation using blood pressure monitors: a systematic review.

BACKGROUND: Atrial fibrillation (AF) affects around 2% of the population and early detection is beneficial, allowing patients to begin potentially life-saving anticoagulant therapies. Blood pressure (BP) monitors may offer an opportunity to screen for AF. AIM: To identify and appraise studies which report the diagnostic accuracy of automated BP monitors used for opportunistic AF detection. METHODS: A systematic search was performed of the MEDLINE, MEDLINE In-Process and EMBASE literature databases. Papers were eligible if they described primary studies of the evaluation of a BP device for AF detection, were published in a peer-reviewed journal and reported values for the sensitivity and specificity. Included studies were appraised using the QUADAS-2 tool to assess their risk of bias and applicability to opportunistic AF detection. Values for the sensitivity and specificity of AF detection were extracted from each paper and compared. RESULTS AND CONCLUSIONS: We identified seven papers evaluating six devices from two manufacturers. Only one study scored low risk in all of the QUADAS-2 domains. All studies reported specificity >85% and 6 reported sensitivity >90%. The studies showed that BP devices with embedded algorithms for detecting arrhythmias show promise as screening tools for AF, comparing favourably with manual pulse palpation. But the studies used different methodologies and many were subject to potential bias. More studies are needed to more precisely define the sensitivity and specificity of opportunistic screening for AF during BP measurement before its clinical utility in the population of interest can be assessed fully.

Decreased peripheral arterial volume distensibility in patients with branch retinal vein occlusion in comparison with normal subjects.

This study aimed to quantify arterial volume distensibility in patients with branch retinal vein occlusion (BRVO) in comparison with normal subjects and to investigate factors associated with their differences. 40 normal subjects and 30 BRVO patients were studied. Brachial-ankle pulse wave velocity (baPWV) was measured to determine arterial volume distensibility. In comparison with the normal subjects, after adjusting for pulse pressure, baPWV in the BRVO patients was significantly higher by 2.3 m/s (P < 0.01) and arterial distensibility was significantly lower by 0.015% per mmHg (P < 0.01). No subject in the normal group had an arterial distensibility lower than 0.04% per mmHg, in comparison with 67% (20/30) in the BRVO group. Arterial distensibility was significantly related to systolic and diastolic blood pressures (SBP and DBP) and ageing for both groups (all P < 0.05), but in the BRVO group, blood pressures and ageing had more prominent effect on arterial volume distensibility. Peripheral arterial distensibility has been shown to be significantly lower in BRVO patients in comparison with normal subjects. The more prominent effect of SBP, DBP and ageing on arterial distensibility indicates the potential underlying mechanisms of the interaction between higher blood pressures, ageing and BRVO disease.

Non-Invasive Estimation Of Left Atrial Dominant Frequency In Atrial Fibrillation From Different Electrode Sites: Insight From Body Surface Potential Mapping.

The dominant driving sources of atrial fibrillation are often found in the left atrium, but the expression of left atrial activation on the body surface is poorly understood. Using body surface potential mapping and simultaneous invasive measurements of left atrial activation our aim was to describe the expression of the left atrial dominant fibrillation frequency across the body surface. 20 patients in atrial fibrillation were studied. The spatial distributions of the dominant atrial fibrillation frequency across anterior and posterior sites on the body surface were quantified. Their relationship with invasive left atrial dominant fibrillation frequency was assessed by linear regression analysis, and the coefficient of determination was calculated for each body surface site. The correlation between intracardiac and body surface dominant frequency was significantly higher with posterior compared with anterior sites (coefficient of determination 67±8% vs 48±2%, p<0.001). The site with largest coefficient of determination was 79.6% (p<0.001) and was a posterior site. In comparison with the site closest to lead V1 it had a coefficient of determination of 23.0% (p=0.033), and with the posterior body surface site closest to lead V9 had a coefficient of determination of 70.3% (p<0.001). Left atrial dominant fibrillation frequency was more closely represented at posterior body surface sites.

A dual-phantom system for validation of velocity measurements in stenosis models under steady flow.

A dual-phantom system is developed for validation of velocity measurements in stenosis models. Pairs of phantoms with identical geometry and flow conditions are manufactured, one for ultrasound and one for particle image velocimetry (PIV). The PIV model is made from silicone rubber, and a new PIV fluid is made that matches the refractive index of 1.41 of silicone. Dynamic scaling was performed to correct for the increased viscosity of the PIV fluid compared with that of the ultrasound blood mimic. The degree of stenosis in the models pairs agreed to less than 1%. The velocities in the laminar flow region up to the peak velocity location agreed to within 15%, and the difference could be explained by errors in ultrasound velocity estimation. At low flow rates and in mild stenoses, good agreement was observed in the distal flow fields, excepting the maximum velocities. At high flow rates, there was considerable difference in velocities in the poststenosis flow field (maximum centreline differences of 30%), which would seem to represent real differences in hydrodynamic behavior between the two models. Sources of error included: variation of viscosity because of temperature (random error, which could account for differences of up to 7%); ultrasound velocity estimation errors (systematic errors); and geometry effects in each model, particularly because of imperfect connectors and corners (systematic errors, potentially affecting the inlet length and flow stability). The current system is best placed to investigate measurement errors in the laminar flow region rather than the poststenosis turbulent flow region.