Effect of cardiac cycle on ultrasound assessment of endothelial function

Non-invasive monitoring of cardiac contractility: Trans-radial electrical bioimpedance velocimetry (TREV)

We describe methods and software resources for a bioimpedance measurement technique, 'trans-radial electrical bioimpedance velocimetry' (TREV) that allows for the non-invasive monitoring of relative cardiac contractility and stroke volume. After reviewing the relationship between the measurement and cardiac contractility, we describe the general recording methodology, which requires impedance measurements of the forearm. We provide open-source Jupyter-based software (operable on most computers) for deriving cardiac contractility from the impedance measurements. The software includes tools for removing variance associated with heart rate and respiration. We demonstrate the ability of this bioimpedance measurement for tracking beat-to-beat changes of contractility in a maximal grip force production task. Critically, the results demonstrate both a reactive increase in contractility with force production, and suggest there is a learned increase in contractility prior to grip onset, consistent with anticipatory allostatic autonomic regulation mediated by sympathetic inotropy. The method and software should be of broad utility for investigations of event-related cardiac dynamics in psychophysical studies.

Analysis of the Velocity Profile of the Popliteal Artery and Its Relevance During Blood Flow Studies

The mean blood velocity is required to calculate blood flow and to determine the associated shear rate. The maximal blood flow velocity is assumed to have a parabolic velocity profile; therefore, the mean velocity is half of the maximal value. Previous studies have been carried out on vessels such as the brachial and femoral artery, but none have been reported for the popliteal artery. To assess the velocity profile of the popliteal artery, a spectral Doppler analysis was performed on ten healthy patients during varied flow states (resting, distal occlusion, hyperemia). The results were then averaged over the entire cardiac cycle. The flow described in these patients’ popliteal artery had a blunted parabolic flow profile with a TAVmean:TAVmax ratio of 0.68 ± 0.07 at baseline. The baseline measures were compared to a TAVmean:TAV max ratio of 0.68 ± 0.12 during distal occlusion and 0.67 ± 0.16 during reactive hyperemia. These descriptive results may suggest that adjustments may be needed for a blunted parabolic profile, especially when calculating the mean velocity of the popliteal artery.

Upper arm venous compliance and fitness in stable coronary artery disease patients and healthy controls

OBJECTIVES

Arteries have been examined extensively in coronary artery disease (CAD), while less attention has been paid to veins.

AIMS

(1) To determine whether venous compliance or venous outflow in the upper arm is reduced in CAD patients compared to healthy age- and fitness-matched controls; and (2) to examine the association between upper arm venous compliance and total blood volume.

DESIGN

Fifteen patients with stable CAD (age 62·1 ± 5·7 years, body mass index 26·5 ± 3·2 kg·m² , fat-free mass 59·3 ± 7·6 kg, mean arterial pressure 98·9 ± 8·0 mmHg, VO_2peak : 2·92 ± 0·53 l min^-1 ) were compared to twelve healthy age- and fitness-matched controls (age 62·2 ± 3·7 years, body mass index 26·2 ± 2·3 kg m² , fat-free mass 61·0 ± 9·2 kg, mean arterial pressure 96·5 ± 9·1 mmHg, VO_2peak : 3·24 ± 0·48 l min^-1 ). Venous compliance was examined using high-resolution ultrasound and Doppler in the basilic vein. Blood volumes were measured by the optimized CO rebreathing method.

RESULTS

Equal upper arm venous compliance normalized to blood volume (patients: 0·28 ± 0·26 mm³  mmHg^-1  l^-1 , healthy controls: 0·16 ± 0·11 mm³ mmHg^-1  l^-1 ) and peak venous outflow normalized to blood volume (patients: 10·4 ± 3·9 cm s^-1  l^-1 , healthy controls: 8·3 ± 0·8 cm s^-1  l^-1 ) were found in patients with CAD and healthy age- and fitness-matched controls. Additionally, no difference was found in blood volume (patients: 6·06 ± 0·79 l, healthy controls: 6·68 ± 1·27 l) or VO_2peak .

CONCLUSION

Comparable upper arm venous compliance and venous outflow in CAD patients and healthy age- and fitness-matched controls might indicate that high VO_2peak and blood volume could prevent possible disease-induced reductions in venous compliance in CAD.

Endothelial Dysfunction in Patients With Coronary Artery Disease

Background:

The use of flow-mediated dilation (FMD) as a surrogate indicator for the extent of coronary artery disease (CAD) remains largely unknown. We assessed FMD at the brachial artery in 89 consecutive patients undergoing coronary angiography.

Methods and Results:

Patients were classified in groups 0 to 3 according to the number of diseased vessels and the SYNTAX score was calculated. The FMD decreased significantly from groups 0 to 3 ( P < .001). There was a significant linear relation between SYNTAX score and FMD (corrected r2 = .64, P < .001). In multivariate analysis, a reduced FMD was the only significant independent predictor of the presence of CAD (odds ratio [OR] 1.78, P = .032) and of CAD severity (OR 1.85, P = .005).

Conclusion:

This study confirms that FMD is reduced in patients with CAD and that such reduction in FMD is related to the extent of the disease. Therefore, FMD at the brachial artery is likely to represent a reliable indicator of CAD burden.

Measuring FMD in the brachial artery: how important is QRS gating?

Recommendations for the measurement of brachial flow-mediated dilation (FMD) typically suggest images be obtained at identical times in the cardiac cycle, usually end diastole (QRS complex onset). This recommendation presumes that inter-individual differences in arterial compliance are minimized. However, published evidence is conflicting. Furthermore, ECG gating is not available on many ultrasound systems; it requires an expensive software upgrade or increased image processing time. We tested whether analysis of images acquired with QRS gating or with the more simplified method of image averaging would yield similar results. We analyzed FMD and nitroglycerin-mediated dilation (NMD) in 29 adults with type 2 diabetes mellitus and in 31 older adults and 12 young adults without diabetes, yielding a range of brachial artery distensibility. FMD and NMD were measured using recommended QRS-gated brachial artery diameter measurements and, alternatively, the average brachial diameters over the entire R-R interval. We found strong agreement between both methods for FMD and NMD (intraclass correlation coefficients = 0.88-0.99). Measuring FMD and NMD using average diameter measurements significantly reduced post-image-processing time (658.9 ± 71.6 vs. 1,024.1 ± 167.6 s for QRS-gated analysis, P < 0.001). FMD and NMD measurements based on average diameter measurements can be performed without reducing accuracy. This finding may allow for simplification of FMD measurement and aid in the development of FMD as a potentially useful clinical tool.

Noninvasive assessment of subclinical atherosclerosis in children and adolescents: recommendations for standard assessment for clinical research: a scientific statement from the American Heart Association

Deterioration in endothelial function and arterial stiffness are early events in the development of cardiovascular diseases. In adults, noninvasive measures of atherosclerosis have become established as valid and reliable tools for refining cardiovascular risk to target individuals who need early intervention. With limited pediatric data, the use of these techniques in children and adolescents largely has been reserved for research purposes. Therefore, this scientific statement was written to (1) review the current literature on the noninvasive assessment of atherosclerosis in children and adolescents, (2) make recommendations for the standardization of these tools for research, and (3) stimulate further research with a goal of developing valid and reliable techniques with normative data for noninvasive clinical evaluation of atherosclerosis in pediatric patients. Precise and reliable noninvasive tests for atherosclerosis in youth will improve our ability to estimate future risk for heart attack and stroke. Currently, large longitudinal studies of cardiovascular risk factors in youth, such as the Bogalusa and Muscatine studies, lack sufficient adult subjects experiencing hard outcomes, such as heart attack and stroke, to produce meaningful risk scores like those developed from Framingham data.

Ultrasound measurement of the brachial artery flow-mediated dilation without ECG gating

The methods commonly used for noninvasive ultrasound assessment of endothelium-dependent flow-mediated dilation (FMD) require an electrocardiogram (ECG) signal to synchronize the measurements with the cardiac cycle. In this article, we present a method for assessing FMD that does not require ECG gating. The approach is based on temporal filtering of the diameter-time curve, which is obtained by means of a B-mode image processing system. The method was tested on 22 healthy volunteers without cardiovascular risk factors. The measurements obtained with the proposed approach were compared with those obtained with ECG gating and with both systolic and end-diastolic measurements. Results showed good agreement between the methods and a higher precision of the new method due to the fact that it is based on a larger number of measurements. Further advantages were also found both in terms of reliability of the measure and simplification of the instrumentation. (E-mail: gemi@ifc.cnr.it).