Venous occlusion plethysmography vs. Doppler ultrasound in the assessment of leg blood flow kinetics during different intensities of calf exercise

Multi-modality imaging for assessment of the microcirculation in peripheral artery disease: Bench to clinical practice

Peripheral artery disease (PAD) is a highly prevalent disorder with a high risk of mortality and amputation despite the introduction of novel medical and procedural treatments. Microvascular disease (MVD) is common among patients with PAD, and despite the established role as a predictor of amputations and mortality, MVD is not routinely assessed as part of current standard practice. Recent pre-clinical and clinical perfusion and molecular imaging studies have confirmed the important role of MVD in the pathogenesis and outcomes of PAD. The recent advancements in the imaging of the peripheral microcirculation could lead to a better understanding of the pathophysiology of PAD, and result in improved risk stratification, and our evaluation of response to therapies. In this review, we will discuss the current understanding of the anatomy and physiology of peripheral microcirculation, and the role of imaging for assessment of perfusion in PAD, and the latest advancements in molecular imaging. By highlighting the latest advancements in multi-modality imaging of the peripheral microcirculation, we aim to underscore the most promising imaging approaches and highlight potential research opportunities, with the goal of translating these approaches for improved and personalized management of PAD in the future.

Plethysmography: A game changer for chronic venous insufficiency diagnosis, treatment, and follow-up

OBJECTIVE

Chronic Venous Insufficiency (CVI) presents a various clinical symptoms and treatment options. Although it is generally known which treatment option is more appropriate in which situations in CVI, it is even more difficult to find the right option in some uncertain situations. In this study, we aimed to evaluate the potential contribution of Digital Photoplethysmography (D-PPG) in the diagnosis of CVI and especially in the selection of treatment options.

PATIENTS AND METHOD

This retrospective study was conducted at Bursa Heart and Arrhythmia Hospital, involving 721 consecutive patients diagnosed with CVI and with Endovenous Laser Ablation (EVLA) indication. The patients were divided into 2 groups according to the extent of the failure in Doppler USG. In Group 1, the insufficiency ended above the knee, and in Group 2, the insufficiency progressed to below the knee. Patients were evaluated based on anamnesis, physical examination, Doppler USG, and D-PPG. Clinical classification, Venous Clinic Severity Score (VCSS), Quality of Life (QoL) assessment, venous pump capacity (VPC), and venous refill time (VRT) were measured.

RESULTS

The study included 263 male and 458 female patients with a mean age of 52.37 ± 12.26 years. Significant differences were observed between Group 1 (above knee reflux) and Group 2 (below knee reflux) patients in terms of VCSS, QoL, VPC, and VRT values. The mean values of VCSS, patient complaints, VPC, and VRT were higher in Group 2 patients. Similar findings were observed within the CEAP 2 subgroup.

CONCLUSION

D-PPG shows potential as a valuable tool in the diagnosis and treatment of CVI. By providing information about venous hemodynamics and volume changes, it can assist in optimizing treatment decisions, including saphenous vein preservation. Combining D-PPG with Doppler USG may improve the comprehensive assessment of CVI and change the treatment option, especially for CEAP 2 patients. More research is needed to confirm these findings and explore wider applications of plethysmographic methods in the management of CVI.

Plethysmographic assessment of vasomotor response in patients with congestive heart failure before and after heart transplantation

Sympathetic vasomotor response is the most important part of the autonomic regulation of circulation, which determines the quality of life. It is disrupted in a number of diseases, particularly in patients with congestive heart failure (CHF). However, experimental evaluation of reflex vasoconstriction is still a non-trivial task due to the limited set of available technologies. The aim of this study is to assess the dynamics of vasomotor response of forearm vessels due to both the deactivation of cardiopulmonary baroreceptors and cold stress using a newly designed imaging plethysmograph (IPG) and compare its performance with classical air plethysmograph (APG). In both vasoconstriction tests, vasomotor response was assessed as a change in the blood flow rate due to venous occlusion compared to that at rest. Both tests were carried out in 45 CHF patients both before and after heart transplantation, as well as in 11 age-matched healthy volunteers. Prior to transplantation, both APG and IPG showed a significant decrease in vasomotor response in CHF patients due to both tests as compared to the control group. After heart transplantation, an increase in vasomotor reactivity was revealed in both vasoconstriction tests. We have found that both plethysmographic techniques provide correlated assessment of changes in the vasomotor response. In addition, we have found that IPG is more resistant to artifacts than APG. The new IPG method has the advantage of measuring blood flow in a contactless manner, making it very promising for experimental evaluation of vasomotor response in clinical conditions.

The effect of increasing work rate amplitudes from a common metabolic baseline on the kinetic response of V̇o2p, blood flow, and muscle deoxygenation

A step-transition in external work rate (WR) increases pulmonary O2 uptake (V̇o2p) in a monoexponential fashion. Although the rate of this increase, quantified by the time constant (τ), has frequently been shown to be similar between multiple different WR amplitudes (ΔWR), the adjustment of O2 delivery to the muscle (via blood flow; BF), a potential regulator of V̇o2p kinetics, has not been extensively studied. To investigate the role of BF on V̇o2p kinetics, 10 participants performed step-transitions on a knee-extension ergometer from a common baseline WR (3 W) to: 24, 33, 45, 54, and 66 W. Each transition lasted 8 min and was repeated four to six times. Volume turbinometry and mass spectrometry, Doppler ultrasound, and near-infrared spectroscopy were used to measure V̇o2p, BF, and muscle deoxygenation (deoxy[Hb + Mb]), respectively. Similar transitions were ensemble-averaged, and phase II V̇o2p, BF, and deoxy[Hb + Mb] were fit with a monoexponential nonlinear least squares regression equation. With increasing ΔWR, τV̇o2p became larger at the higher ΔWRs (P < 0.05), while τBF did not change significantly, and the mean response time (MRT) of deoxy[Hb + Mb] became smaller. These findings that V̇o2p kinetics become slower with increasing ΔWR, while BF kinetics are not influenced by ΔWR, suggest that O2 delivery could not limit V̇o2p in this situation. However, the speeding of deoxy[Hb + Mb] kinetics with increasing ΔWR does imply that the O2 delivery-to-O2 utilization of the microvasculature decreases at higher ΔWRs. This suggests that the contribution of O2 delivery and O2 extraction to V̇O2 in the muscle changes with increasing ΔWR.NEW & NOTEWORTHY A step increase in work rate produces a monoexponential increase in V̇o2p and blood flow to a new steady-state. We found that step transitions from a common metabolic baseline to increasing work rate amplitudes produced a slowing of V̇o2p kinetics, no change in blood flow kinetics, and a speeding of muscle deoxygenation kinetics. As work rate amplitude increased, the ratio of blood flow to V̇o2p became smaller, while the amplitude of muscle deoxygenation became greater. The gain in vascular conductance became smaller, while kinetics tended to become slower at higher work rate amplitudes.

Differential effects of sex on adaptive responses of skeletal muscle vasodilation to exercise training in type 2 diabetes

AIMS

We tested the hypotheses that exercise training improves the peak and dynamic responses of leg vascular conductance (LVC) in males and females with type 2 diabetes (T2DM).

METHODS

Forty-one males and females with T2DM were assigned to two training groups and two control groups. Twelve weeks of aerobic/resistance training was performed three times per week, 60-90 min per session. Responses of calf muscle blood flow and systemic arterial pressure during incremental and constant-load (30% maximal voluntary contraction) intermittent plantar-flexion protocols in the supine position were recorded.

RESULTS

Training significantly increased peak LVC in males (4.86 ± 1.88 to 6.06 ± 2.06 ml·min^-1·mm Hg^-1) and females (3.91 ± 1.13 to 5.40 ± 1.38 ml·min^-1·mm Hg^-1) with no changes in control groups. For dynamic responses, training significantly increased the amplitude of the fast growth phase of LVC (1.81 ± 1.12 to 2.68 ± 1.01 ml·min^-1·mm Hg^-1) and decreased the time constant of the slow growth phase (43.6 ± 46.4 s to 16.1 14.0 s) in females, but no improvements were observed in control females or in any of the two male groups.

CONCLUSIONS

These data suggest that training increases the peak vasodilatory response in males and females, whereas the speed of the dynamic response of vasodilation is improved in females but not males.

Skeletal muscle microvascular perfusion responses to cuff occlusion and submaximal exercise assessed by contrast-enhanced ultrasound: The effect of age

Impairments in skeletal muscle microvascular function are frequently reported in patients with various cardiometabolic conditions for which older age is a risk factor. Whether aging per se predisposes the skeletal muscle to microvascular dysfunction is unclear. We used contrast‐enhanced ultrasound (CEU) to compare skeletal muscle microvascular perfusion responses to cuff occlusion and leg exercise between healthy young (n = 12, 26 ± 3 years) and older (n = 12, 68 ± 7 years) adults. Test–retest reliability of CEU perfusion parameters was also assessed. Microvascular perfusion (microvascular volume × flow velocity) of the medial gastrocnemius muscle was measured before and immediately after: (a) 5‐min of thigh‐cuff occlusion, and (b) 5‐min of submaximal intermittent isometric plantar‐flexion exercise (400 N) using CEU. Whole‐leg blood flow was measured using strain‐gauge plethysmography. Repeated measures were obtained with a 15‐min interval, and averaged responses were used for comparisons between age groups. There were no differences in post‐occlusion whole‐leg blood flow and muscle microvascular perfusion between young and older participants (p > .05). Similarly, total whole‐leg blood flow during exercise and post‐exercise peak muscle microvascular perfusion did not differ between groups (p > .05). The overall level of agreement between the test–retest measures of calf muscle perfusion was excellent for measurements taken at rest (intraclass correlation coefficient [ICC] 0.85), and in response to cuff occlusion (ICC 0.89) and exercise (ICC 0.95). Our findings suggest that healthy aging does not affect muscle perfusion responses to cuff‐occlusion and submaximal leg exercise. CEU muscle perfusion parameters measured in response to these provocation tests are highly reproducible in both young and older adults.

Sports compression garments improve resting markers of venous return and muscle blood flow in male basketball players

BACKGROUND

The benefits associated with sports compression garments are thought to be closely related to enhanced blood flow. However, findings are equivocal, possibly due to heterogeneity in the techniques used for measuring blood flow, the garment types used, and the pressures applied. This study combined Doppler ultrasound and near-infrared spectroscopy technologies to provide the first comprehensive assessment of the effects of 3 sports compression garment types on markers of venous return and muscle blood flow at rest.

METHODS

Resting lower-limb blood flow measures (markers of venous return, muscle blood flow, and muscle oxygenation) of 22 elite, junior, male basketball players (age = 17.2 ± 0.9 years, mean ± SD) were assessed in 4 separate conditions: no compression (CON), compression tights (TIGHTS), compression shorts (SHORTS), and compression socks (SOCKS). Markers of venous return (cross-sectional area, time-averaged mean and peak blood flow velocity, and venous blood flow) were measured via Doppler ultrasound at the popliteal and common femoral veins. Muscle blood flow and muscle oxygenation were measured in the gastrocnemius medialis and vastus lateralis using near-infrared spectroscopy.

RESULTS

Popliteal markers of venous return were higher in TIGHTS compared to CON (p < 0.01) and SHORTS (p < 0.01), with SOCKS values higher compared with CON (p < 0.05). Common femoral vein markers of venous return were higher for all conditions compared to CON (p < 0.05), with TIGHTS values also higher compared to SOCKS (p < 0.05). Gastrocnemius medialis blood flow was higher for TIGHTS compared to CON (p = 0.000), SOCKS (p = 0.012), and SHORTS (p = 0.000), with SOCKS higher compared to SHORTS (p = 0.046). Vastus lateralis blood flow was higher for TIGHTS compared to CON (p = 0.028) and SOCKS (p = 0.019), with SHORTS also higher compared to CON (p = 0.012) and SOCKS (p = 0.005). Gastrocnemius medialis oxygenation was higher for TIGHTS compared to CON (p = 0.003), SOCKS (p = 0.033), and SHORTS (p = 0.003), with SOCKS higher compared to CON (p = 0.044) and SHORTS (p = 0.032). Vastus lateralis oxygenation was higher for TIGHTS compared to CON (p = 0.020) and SOCKS (p = 0.006).

CONCLUSION

Markers of venous return, muscle blood flow, and muscle oxygenation are increased with sports compression garments. TIGHTS are most effective, potentially because of the larger body area compressed.

Skin blood flow measurements during heat stress: technical and analytical considerations

During heat stress, the skin vasculature can greatly increase conductance secondary to vasodilation. The subsequent increase in skin blood flow allows for convective heat transfer from the core to the skin and between the skin surface and the surrounding environment. Measurement of skin blood flow, therefore, provides valuable information regarding heat exchange between the body and the environment. In addition, assessment of skin blood flow can be used to study vascular control mechanisms. Most often, skin blood flow is measured by venous occlusion plethysmography, Doppler ultrasound, laser-Doppler flowmetry, and, more recently, optical coherence tomography. However, important delimitations to each of these methods, which may be dependent on the research question, must be considered when responses from these approaches are interpreted. In this brief review, we discuss these methods of skin blood flow measurement and highlight potential sources of error and limitations. We also provide recommendations to guide the interpretation of skin blood flow data.

Effect of obesity on oxygen uptake and cardiovascular dynamics during whole-body and leg exercise in adult males and females

Obesity has been associated with a slowing of V˙O₂ dynamics in children and adolescents, but this problem has not been studied in adults. Cardiovascular mechanisms underlying this effect are not clear. In this study, 48 adults (18 males, 30 females) grouped according to body mass index (BMI) (lean < 25 kg·m⁻², overweight = 25–29.9 kg·m⁻², obese ≥30 kg·m⁻²) provided a fasting blood sample, completed a maximal graded exercise test and six bouts of submaximal exercise on a cycle ergometer, and performed two protocols of calf exercise. Dynamic response characteristics of V˙O₂ and leg vascular conductance (LVC) were assessed during cycling (80% ventilatory threshold) and calf exercise (30% MVC), respectively. Dynamic responses of cardiac output, mean arterial pressure and total systemic vascular conductance were also assessed during cycling based on measurements at 30 and 240 sec. The time constant of the second phase of the V˙O₂ response was significantly greater in obese than lean subjects (39.4 (9.2) vs. 29.1 (7.6) sec); whereas dynamic responses of cardiac output and systemic vascular conductance were not affected by BMI. For calf exercise, the time constant of the second growth phase of LVC was slowed significantly in obese subjects (22.1 (12.7) sec) compared with lean and overweight subjects (11.6 (4.5) sec and 13.4 (6.7) sec). These data show that obesity slows dynamic responses of V˙O₂ during cycling and the slower phase of vasodilation in contracting muscles of male and female adults.

Cuff inflation time significantly affects blood flow recorded with venous occlusion plethysmography

Purpose

We tested whether the values of limb blood flow calculated with strain-gauge venous occlusion plethysmography (VOP) differ when venous occlusion is achieved by automated, or manual inflation, so providing rapid and slower inflation, respectively.

Method

In 9 subjects (20–30 years), we calculated forearm blood flows (FBF) values at rest and following isometric handgrip at 70% maximum voluntary contraction (MVC) when rapid, or slower inflation was used.

Result

Rapid and slower cuff inflation took 0.23 ± 0.01 (mean ± SEM) and 0.92 ± 0.02 s, respectively, reflecting the range reported in published studies. At rest, FBF calculated from the 1st cardiac cycle after rapid and slower inflation gave similar values: 10.5 ± 1.4 vs. 9.6 ± 1.3 ml dl^− 1 min^− 1, respectively (P > 0.05). However, immediately post-contraction, FBF was ~ 40% lower with slower inflation: 54.6 ± 5.1 vs. 33.8 ± 4.2 ml dl^− 1 min^− 1 (P < 0.01). The latter value was similar to that calculated over the 3rd cardiac cycle following rapid inflation: 2nd cardiac cycle: 40.5 ± 4.5; 3rd cycle: 32.6 ± 4.5 ml dl^− 1 min^− 1. Regression analyses of FBFs recorded at intervals post-contraction showed those calculated over the 1st, 2nd, or 3rd cardiac cycles with rapid inflation correlated well with those from the 1st cardiac cycle with manual inflation (r = 0.79, 0.82, 0.79; P < 0.01). However, only the slope for the 3rd cycle with rapid inflation vs. slower inflation was close to unity (2.07, 1.34, and 0.94, respectively).

Conclusion

These findings confirm that the 1st cardiac cycle following venous occlusion should be used when calculating FBF using VOP and, but importantly, indicate that cuff inflation should be almost instantaneous; just ≥ 0.9 s leads to substantial underestimation, especially at high flows.

Leg blood flow and skeletal muscle microvascular perfusion responses to submaximal exercise in peripheral arterial disease

Peripheral arterial disease (PAD) is characterized by stenosis and occlusion of the lower limb arteries. Although leg blood flow is limited in PAD, it remains unclear whether skeletal muscle microvascular perfusion is affected. We compared whole leg blood flow and calf muscle microvascular perfusion after cuff occlusion and submaximal leg exercise between patients with PAD ( n = 12, 69 ± 9 yr) and healthy age-matched control participants ( n = 12, 68 ± 7 yr). Microvascular blood flow (microvascular volume × flow velocity) of the medial gastrocnemius muscle was measured before and immediately after the following: 1) 5 min of thigh-cuff occlusion, and 2) a 5-min bout of intermittent isometric plantar-flexion exercise (400 N) using real-time contrast-enhanced ultrasound. Whole leg blood flow was measured after thigh-cuff occlusion and during submaximal plantar-flexion exercise using strain-gauge plethysmography. Postocclusion whole leg blood flow and calf muscle microvascular perfusion were lower in patients with PAD than control participants, and these parameters were strongly correlated ( r = 0.84, P < 0.01). During submaximal exercise, total whole leg blood flow and vascular conductance were not different between groups. There were also no group differences in postexercise calf muscle microvascular perfusion, although microvascular blood volume was higher in patients with PAD than control participants (12.41 ± 6.98 vs. 6.34 ± 4.98 arbitrary units, P = 0.03). This study demonstrates that the impaired muscle perfusion of patients with PAD during postocclusion hyperemia is strongly correlated with disease severity and is likely mainly determined by the limited conduit artery flow. In response to submaximal leg exercise, microvascular flow volume was elevated in patients with PAD, which may reflect a compensatory mechanism to maintain muscle perfusion and oxygen delivery during recovery from exercise.

NEW & NOTEWORTHY This study suggests that peripheral arterial disease (PAD) has different effects on the microvascular perfusion responses to cuff occlusion and submaximal leg exercise. Patients with PAD have impaired microvascular perfusion after cuff occlusion, similar to that previously reported after maximal exercise. In response to submaximal exercise, however, the microvascular flow volume response was elevated in patients with PAD compared with control. This finding may reflect a compensatory mechanism to maintain perfusion and oxygen delivery during recovery from exercise.