The influence of the hand circulation on the assessment of venous distensibility of the human forearm with venous occlusion plethysmography

A review of methodologies evaluating superficial vein properties in viv: focus on compliance and reactivity

The saphenous vein (SV) is a hindlimb superficial vein which has aroused a considerable interest because of its implication in chronic venous disease and its use in coronary artery or lower limb bypass grafts. The morphology and patency of the SV are commonly assessed for diagnosis and management, but the dynamic properties of the vein - compliance, elasticity and reactivity, less widely studied, are also fundamental issues. The subject of this review is neither to review the pathologies, nor the treatments or surgical procedures. The goal is to gather together all existing types of investigation on the superficial vein and to focus on the dynamic venous properties in vivo. The data collected indicate that plethysmography (PG) and ultrasound (US) are extensively used to evaluate SV patency, reflux and morphology. Their use to evaluate superficial vein compliance is less widespread but highly necessary. The protocols used via venous occlusion are described and the various parameters used to accurately measure compliance and distensibility versus elasticity are presented and discussed. The advantage of US diameter measurement is shown, including additional pulsatile compliance evaluation. The overview of venous reactivity greatly differs, being poorly studied in vivo, mainly by optical methods in humans or US echotracking in animals. Existing methodologies are potent but could be certainly developed and improved further for better characterization of the SV in human and for investigations of new devices, surgical techniques and pharmacological treatment in preclinical animal studies.

Cardiovascular and Autonomic Responses after a Single Bout of Resistance Exercise in Men with Untreated Stage 2 Hypertension

The aim of this paper is to assess the integrated responses of ambulatory blood pressure (BP), cardiac autonomic modulation, spontaneous baroreflex sensitivity (BRS), and vascular reactivity after a single bout of resistance exercise (RE) in men with stage 2 hypertension who have never been treated before. Ten hypertensive men were subjected to a RE session of three sets of 20 repetitions and an intensity of 40% of the 1-repetition maximum (RM) test in seven different exercises. For the control (CTR) session, the volunteers were positioned on the exercise machines but did not perform any exercise. Forearm blood flow was measured by venous occlusion plethysmography. We also analyzed the heart rate variability (HRV), ambulatory BP, blood pressure variability (BPV), and BRS. All measurements were performed at different timepoints: baseline, 20 min, 80 min, and 24 h after both RE and CTR sessions. There were no differences in ambulatory BP over the 24 h between the RE and CTR sessions. However, the area under the curve of diastolic BP decreased after the RE session. Heart rate (HR) and cardiac output increased for up to 80 and 20 min after RE, respectively. Similarly, forearm blood flow, conductance, and vascular reactivity increased 20 min after RE (p < 0.05). In contrast, HRV and BRS decreased immediately after exercise and remained lower for 20 min after RE. We conclude that a single bout of RE induced an increase in vascular reactivity and reduced the pressure load by attenuating AUC of DBP in hypertensive individuals who had never been treated with antihypertensive medications.

Acute hydrocortisone administration reduces cardiovagal baroreflex sensitivity and heart rate variability in young men

KEY POINTS

A surge in cortisol during acute physiological and pathophysiological stress may precipitate ventricular arrhythmia and myocardial infarction. Reduced cardiovagal baroreflex sensitivity and heart rate variability are observed during acute stress and are associated with an increased risk of acute cardiac events. In the present study, healthy young men received either a single iv bolus of saline (placebo) or hydrocortisone, 1 week apart, in accordance with a randomized, placebo-controlled, cross-over study design. Hydrocortisone acutely increased heart rate and blood pressure and reduced cardiovagal baroreflex sensitivity and heart rate variability in young men. These findings suggest that, by reducing cardiovagal baroreflex sensitivity and heart rate variability, acute surges in cortisol facilitate a pro-arrhythmic milieu and provide an important mechanistic link between stress and acute cardiac events ABSTRACT: Surges in cortisol concentration during acute stress may increase cardiovascular risk. To better understand the interactions between cortisol and the autonomic nervous system, we determined the acute effects of hydrocortisone administration on cardiovagal baroreflex sensitivity (BRS), heart rate variability (HRV) and cardiovascular reactivity. In a randomized, placebo-controlled, single-blinded cross-over study, 10 healthy males received either a single iv bolus of saline (placebo) or 200 mg of hydrocortisone, 1 week apart. Heart rate (HR), blood pressure (BP) and limb blood flow were monitored 3 h later, at rest and during the sequential infusion of sodium nitroprusside and phenylephrine (modified Oxford Technique), a cold pressor test and a mental arithmetic stress task. HRV was assessed using the square root of the mean of the sum of the squares of differences between successive R-R intervals (rMSSD). Hydrocortisone markedly increased serum cortisol 3 h following infusion and also compared to placebo. In addition, hydrocortisone elevated resting HR (+7 ± 4 beats min^-1 ; P < 0.001) and systolic BP (+5 ± 5 mmHg; P = 0.008); lowered cardiovagal BRS [geometric mean (95% confidence interval) 15.6 (11.1-22.1) ms/mmHg vs. 26.2 (17.4--39.5) ms/mmHg, P = 0.011] and HRV (rMSSD 59 ± 29 ms vs. 84 ± 38 ms, P = 0.004) and increased leg vasoconstrictor responses to cold pressor test (Δ leg vascular conductance -45 ± 20% vs. -23 ± 26%; P = 0.023). In young men, an acute cortisol surge is accompanied by increases in HR and BP, as well as reductions in cardiovagal BRS and HRV, potentially providing a pro-arrhythmic milieu that may precipitate ventricular arrhythmia or myocardial infarction and increase cardiovascular risk.

Measurement of peripheral blood flow in patients with peripheral artery disease: Methods and considerations

Peripheral artery disease (PAD) is a manifestation of generalized atherosclerosis which results in hemodynamic compromise of oxygen and substrate delivery to the lower extremity skeletal muscles. Hemodynamic assessments are vital in PAD diagnosis and in the evaluation of strategies aimed at treating claudication (i.e. exercise training, revascularization, and pharmacological agents). Venous occlusion plethysmography (VOP) is a century-old, non-invasive technique used to quantify limb blood flow and has been used to evaluate hemodynamic compromise in patients with PAD. However, the literature suggests a wide array of methodological variability in the measurement and analysis of limb blood flow using VOP. In this manuscript, we overview the clinical application of VOP measurement, and secondly we review the methodological variation that occurs during the measurement and analysis of VOP in healthy individuals and in patients with claudication.

Reproducibility and variability of digital thermal monitoring of vascular reactivity

BACKGROUND

Previous studies demonstrated that digital thermal monitoring (DTM) of vascular reactivity, a new test for vascular function assessment, is well correlated with Framingham Risk Score, coronary calcium score and CT angiography. This study evaluates the variability and reproducibility of DTM measurements. We hypothesized that DTM is reproducible, and its variability falls within the accepted range of clinical diagnostic tests.

METHOD

A fully automated DTM device (VENDYS, Endothelix Inc., Houston, TX, USA) was used for repeated measurement of vascular function in 18 healthy volunteers (age 35 ± 4 years, 74% men) after 24 h. All subjects underwent overnight fasting, and the test was preceded by 30-min rest in a supine position inside a dimmed room with temperature 22-24°C. The measurements were obtained during and after a 2-min supra systolic arm-cuff occlusion-induced reactive hyperaemia procedure. As a part of this study, the Doppler ultrasound hyperaemic, low-frequency, blood velocity of radial artery and a fingertip DTM of vascular function were compared simultaneously. Postcuff deflation temperature rebound and area under the curve, DTM indices of vascular function, were studied.

RESULTS

Temperature rebound area under the curve correlated closely with Doppler hyperaemic, low-frequency, blood velocity (r = 0·97, P = 0·0001). Day-to-day intra-subject variability was 6·2% for baseline temperature, 8·7% for mean blood pressure and 11·4% for heart rate. The coefficient of repeatability of temperature rebound and area under the curve were 2·4% and 2·8%.

CONCLUSION

In a controlled environment, the repeatability of DTM is excellent. DTM can be used as a reproducible and operator-independent test for non-invasive measurement of vascular function.

Impaired hemodynamic response to mental stress in subjects with prehypertension is improved after a single bout of maximal dynamic exercise

INTRODUCTION

High blood pressure during mental stress in subjects with prehypertension is associated with blunted vasodilation in skeletal muscles, which might be improved by an acute bout of exercise.

OBJECTIVE

To investigate the hemodynamic responses to mental stress before and after a bout of exercise in subjects with prehypertension.

METHOD

Eighteen subjects with prehypertension and 16 with normotension underwent a mental stress test before and after a maximal cardiopulmonary exercise test on a treadmill. Blood pressure was measured by auscultation, and forearm blood flow was measured by venous occlusion plethysmography; from these measurements, the vascular conductance was calculated.

RESULTS

Subjects with prehypertension had a higher mean blood pressure during mental stress (prehypertension 112 ± 2 vs. normotension 101 ± 3 mm Hg, p<0.05), and their vascular conductance did not increase (baseline 0.025 ± 0.004 vs. mental stress 0.022 ± 0.003 a.u., p.0.05). After the exercise bout, the mean blood pressure during mental stress was lower in subjects with prehypertension (before exercise 112 ± 2 vs. after exercise 107 ± 2 mm Hg, p<0.05), and vascular conductance increased (baseline 0.011 ± 0.001 vs. mental stress 0.024 ± 0.004 a.u., p<0.05).

CONCLUSION

Subjects with prehypertension had elevated blood pressure and a blunted vasodilator response during mental stress, but their blood pressure was attenuated and their vasodilator response was normalized after a single bout of maximal dynamic exercise.

Effect of the 894G>T polymorphism of the endothelial nitric oxide synthase on vascular reactivity following maximal dynamic exercise

BACKGROUND

Considering that the role of nitric oxide as a vasodilator is increased after an acute bout of exercise and that the 894G>T polymorphism of the endothelial nitric oxide synthase seems to reduce the nitric oxide release in response to shear stress, the present study investigated the 894G>T polymorphism in relation to vascular reactivity following maximal dynamic exercise.

METHOD

We studied 110 healthy volunteers (wild-type group 45.5% and polymorphic group 54.5%). The protocol included vascular reactivity assessment at baseline and during reactive hyperemia, before, 10, 60 and 120 min after a maximal cardiopulmonary exercise test. Genomic DNA was extracted from blood samples to determine the 894G>T polymorphism.

RESULTS

There were no differences between the wild-type and polymorphic groups concerning anthropometric, metabolic and hemodynamic characteristics. Blood flow, before maximal exercise, was similar between the wild-type and the polymorphic groups. The polymorphic group presented lower vascular reactivity regardless of time (P = 0.019 for group main effect), and posthoc analysis revealed that polymorphic patients had lower values than wild-type only at the 120 min measurement (P = 0.002). Concerning within-group analysis, vascular reactivity increased at 10 min after exercise (P = 0.029) returning to baseline at 120 min (P = 0.005) in the polymorphic group.

CONCLUSION

Patients with the 894G>T polymorphism had lower vascular reactivity after a single bout of exercise.

Intra- and inter-tester reproducibility of venous occlusion plethysmography: comparison between a manual and a semi-automatic method of blood flow analysis

Venous occlusion plethysmography (VOP) is a valid non-invasive method to assess peripheral blood flow (BF) in humans. Our aim was to determine intra- and inter-tester reproducibility of BF analysis using a traditional manual method and a novel system, based on a semi-automatic approach. Ten healthy subjects and ten subjects with chronic heart failure (CHF) were evaluated. Blood flow was measured on the forearm at baseline and after 5 min of circulatory occlusion (reactive hyperemia (RH)). Two testers independently and blindly analyzed each VOP recording. Both methods were highly reproducible intra- and inter-testers. In addition, there was a high association between the methods, since the intraclass correlation coefficients (ICCs) for healthy subjects were 0.99, 0.99 and 0.99, and the coefficients of variation (CVs) were 1.8, 2.4 and 1.6% for baseline, RH peak and RH area under the curve, respectively. For CHF subjects, the ICCs were 0.99, 0.98 and 0.99, and the CVs were 2.9, 3.6 and 2.0%. In addition, the time spent on the semi-automatic analyses was shorter (p < 0.05). In conclusion, both methods demonstrated high intra- and inter-tester reproducibility for baseline and RH BF analysis. However, since the semi-automatic method was faster to generate the results, the present study supports its usage for the analysis of BF measured by VOP.