Comparison of morphometric, structural, mechanical, and physiologic characteristics of human superficial femoral and popliteal arteries

A Viscoelastic Constitutive Framework for Aging Muscular and Elastic Arteries

The evolution of arterial biomechanics and microstructure with age and disease plays a critical role in understanding the health and function of the cardiovascular system. Accurately capturing these adaptative processes and their effects on the mechanical environment is critical for predicting arterial responses. This challenge is exacerbated by the significant differences between elastic and muscular arteries, which have different structural organizations and functional demands. In this study, we aim to shed light to these adaptive processes by comparing the viscoelastic mechanics of autologous thoracic aortas (TA) and femoropopliteal arteries (FPA) in different age groups. We have extended our fractional viscoelastic framework, originally developed for FPA, to both types of arteries. To evaluate this framework, we analyzed experimental mechanical data from TA and FPA specimens from 21 individuals aged 13 to 73 years. Each specimen was subjected to a multi-ratio biaxial mechanical extension and relaxation test complemented by bidirectional histology to quantify the structural density and microstructural orientations. Our new constitutive model accurately captured the mechanical responses and microstructural differences of the tissues and closely matched the experimentally measured densities. It was found that the viscoelastic properties of collagen and smooth muscle cells (SMCs) in both the FPA and TA remained consistent with age, but the viscoelasticity of the SMCs in the FPA was twice that of the TA. Additionally, changes in collagen nonlinearity with age were similar in both TA and FPA. This model provides valuable insights into arterial mechanophysiology and the effects of pathological conditions on vascular biomechanics. STATEMENT OF SIGNIFICANCE: Developing durable treatments for arterial diseases necessitates a deeper understanding of how mechanical properties evolve with age in response to mechanical environments. In this work, we developed a generalized viscoelastic constitutive model for both elastic and muscular arteries and analyzed both the thoracic aorta (TA) and the femoropopliteal artery (FPA) from 21 donors aged 13 to 73. The derived parameters correlate well with histology, allowing further examination of how viscoelasticity evolves with age. Correlation between the TA and FPA of the same donors suggest that the viscoelasticity of the FPA may be influenced by the TA, necessitating more detailed analysis. In summary, our new model proves to be a valuable tool for studying arterial mechanophysiology and exploring pathological impacts.

Treatment extent of femoropopliteal disease and clinical outcomes following endovascular therapy

BACKGROUND

Endovascular therapy (EVT) has become the preferred treatment modality for femoropopliteal disease. However, there is limited evidence regarding its procedural and clinical outcomes according to the affected area.

AIMS

The aim of this study is to investigate clinical outcomes and device effectiveness according to treatment extent in the superficial femoral artery (SFA), popliteal artery (PA), or both.

METHODS

In this study, we analysed EVT for SFA (2,404 limbs), PA (155 limbs), SFA/PA (383 limbs) using the population in the K-VIS ELLA (Korean Vascular Intervention Society Endovascular Therapy in Lower Limb Artery Diseases) registry. The primary endpoint was target lesion revascularisation (TLR) at 2 years.

RESULTS

The SFA/PA group exhibited a higher prevalence of anatomical complexity, characterised by long lesions, moderate to severe calcification, and total occlusion. The procedures were successful in 97.2% of SFA, 92.9% of PA, and 95.6% of SFA/PA EVTs. The 2-year TLR rates were 21.1%, 18.6%, and 32.7% in the SFA, PA, and SFA/PA groups, respectively. SFA/PA EVT was associated with a significantly increased risk for TLR compared to the SFA group (adjusted hazard ratio [HR] 1.48 [1.09-2.00]; p=0.008) and a trend towards an increased risk compared to the PA group (adjusted HR 1.80 [1.00-3.27]; p=0.052). After overlap weighting, the use of a drug-coated balloon (DCB) was shown to be beneficial, with the lowest TLR rate after SFA and SFA/PA EVT.

CONCLUSIONS

In this large real-world registry, SFA/PA EVT was associated with an increased risk for TLR at 2 years compared to the SFA or PA EVT groups, with favourable outcomes when using a DCB or drug-eluting stent in the SFA/PA EVT group.

Sitting knee-flexion angle does not influence endothelial-dependent vasodilation in laboratory or free-living conditions

INTRODUCTION

Single bouts of prolonged bent-legged sitting attenuate popliteal endothelial-dependent vasodilation (as assessed via flow-mediated dilation [FMD]), which is partially attributed to arterial 'kinking'. However, the impact of knee-flexion angle on sitting-induced popliteal FMD is unknown. The objective of this study was to perform separate laboratory and free-living studies to test the hypotheses that: (1) popliteal FMD impairments would be graded between knee flexions at 90° (bent-legged sitting) > 45° > 0° (straight-legged sitting) following a 3-hour bout of sitting; and (2) more habitual time spent bent-legged sitting (< 45°) would be associated with lower FMD.

METHODS

The laboratory study included eight young, healthy adults (24 ± 2 years; four women) who underwent two sitting bouts over 2 days with one leg positioned at a knee-flexion angle of 0° or 90° and the opposite leg at 45° knee flexion. Popliteal FMD was assessed at pre- and postsitting timepoints.

RESULTS

Sitting-induced reductions in FMD were similar between all knee-flexion angles (all, p > 0.674). The free-living study included 35 young, healthy adults (23 ± 3 years; 16 women) who wore three activPAL monitors (torso, thigh, shin) to determine detailed sedentary postures. Time spent sedentary (624 ± 127 min/day), straight-legged sitting (112 ± 98 min/day), and bent-legged sitting (442 ± 106 min/day) were not related to relative FMD (5.3 ± 1.8%; all, p > 0.240).

CONCLUSION

These findings suggest that knee-flexion angle-mediated arterial 'kinking' during sitting is not a major contributor toward sitting-induced popliteal endothelial-dependent vasodilatory dysfunction.

Mechanical, structural, and morphological differences in the iliac arteries

Iliac arteries play a crucial role in peripheral blood circulation. They are susceptible to various diseases, including aneurysms and atherosclerosis. Structure, material properties, and biomechanical forces acting on different regions of the iliac vasculature may contribute to the localization and progression of these pathologies. We examined 33 arterial specimens from common iliac (CI), external iliac (EI), and internal iliac (II) arteries obtained from 11 human donors (62 ± 12 years). We conducted morphometric, mechanical, and structural analyses using planar biaxial tests, constitutive modeling, and bi-directional histology on transverse and axial sections. The iliac arteries exhibited increased tortuosity and varying disease distribution with age. CI and II arteries displayed non-uniform age-related disease progression around their circumference, while EI remained healthy even in older individuals. Trends in load-free and stress-free thickness varied along the iliac vasculature. Longitudinally, EI exhibited the highest compliance compared to other iliac vessels. In contrast, CI was stiffest longitudinally, and EI was the stiffest circumferentially. Material parameters for all iliac vessels are reported for four common constitutive relations. Elastin near the internal elastic lamina displayed greater waviness in EI and II compared to CI. Also, EI had the least glycosaminoglycans (GAGs) and the highest elastin content. Our findings highlight variations in the morphological, mechanical, and structural properties of iliac arteries along their length. This data can inform vascular disease development and computational studies, and guide the development of biomimetic repair materials and devices tailored to specific iliac locations, improving vascular repair strategies.

Influence of material parameter variability on the predicted coronary artery biomechanical environment via uncertainty quantification

Central to the clinical adoption of patient-specific modeling strategies is demonstrating that simulation results are reliable and safe. Indeed, simulation frameworks must be robust to uncertainty in model input(s), and levels of confidence should accompany results. In this study, we applied a coupled uncertainty quantification-finite element (FE) framework to understand the impact of uncertainty in vascular material properties on variability in predicted stresses. Univariate probability distributions were fit to material parameters derived from layer-specific mechanical behavior testing of human coronary tissue. Parameters were assumed to be probabilistically independent, allowing for efficient parameter ensemble sampling. In an idealized coronary artery geometry, a forward FE model for each parameter ensemble was created to predict tissue stresses under physiologic loading. An emulator was constructed within the UncertainSCI software using polynomial chaos techniques, and statistics and sensitivities were directly computed. Results demonstrated that material parameter uncertainty propagates to variability in predicted stresses across the vessel wall, with the largest dispersions in stress within the adventitial layer. Variability in stress was most sensitive to uncertainties in the anisotropic component of the strain energy function. Moreover, unary and binary interactions within the adventitial layer were the main contributors to stress variance, and the leading factor in stress variability was uncertainty in the stress-like material parameter that describes the contribution of the embedded fibers to the overall artery stiffness. Results from a patient-specific coronary model confirmed many of these findings. Collectively, these data highlight the impact of material property variation on uncertainty in predicted artery stresses and present a pipeline to explore and characterize forward model uncertainty in computational biomechanics.

Structural and Mechanical Properties of Human Superficial Femoral and Popliteal Arteries

The femoropopliteal artery (FPA) is the main artery in the lower limb. It supplies blood to the leg muscles and undergoes complex deformations during limb flexion. Atherosclerotic disease of the FPA (peripheral arterial disease, PAD) is a major public health burden, and despite advances in surgical and interventional therapies, the clinical outcomes of PAD repairs continue to be suboptimal, particularly in challenging calcified lesions and biomechanically active locations. A better understanding of human FPA mechanical and structural characteristics in relation to age, risk factors, and the severity of vascular disease can help develop more effective and longer-lasting treatments through computational modeling and device optimization. This review aims to summarize recent research on the main biomechanical and structural properties of human superficial femoral and popliteal arteries that comprise the FPA and describe their anatomy, composition, and mechanical behavior under different conditions.

Mechanical, structural, and physiologic differences between above and below-knee human arteries

Peripheral Artery Disease (PAD) affects the lower extremities and frequently results in poor clinical outcomes, especially in the vessels below the knee. Understanding the biomechanical and structural characteristics of these arteries is important for improving treatment efficacy, but mechanical and structural data on tibial vessels remain limited. We compared the superficial femoral (SFA) and popliteal (PA) arteries that comprise the above-knee femoropopliteal (FPA) segment to the infrapopliteal (IPA) anterior tibial (AT), posterior tibial (PT), and fibular (FA) arteries from the same 15 human subjects (average age 52, range 42-67 years, 87 % male). Vessels were imaged using μCT, evaluated with biaxial mechanical testing and constitutive modeling, and assessed for elastin, collagen, smooth muscle cells (SMCs), and glycosaminoglycans (GAGs). IPAs were more often diseased or calcified compared to the FPAs. They were also twice smaller, 53 % thinner, and significantly stiffer than the FPA longitudinally, but not circumferentially. IPAs experienced 48 % higher physiologic longitudinal stresses (62 kPa) but 27 % lower circumferential stresses (24 kPa) and similar cardiac cycle stretch of <1.02 compared to the FPA. IPAs had lower longitudinal pre-stretch (1.12) than the FPAs (1.29), but there were no differences in the stored elastic energy during pulsation. The physiologic circumferential stiffness was similar in the above and below-knee arteries (718 kPa vs 754 kPa). Structurally, IPAs had less elastin, collagen, and GAGs than the FPA, but maintained similar SMC content. Our findings contribute to a better understanding of segment-specific human lower extremity artery biomechanics and may inform the development of better medical devices for PAD treatment. STATEMENT OF SIGNIFICANCE: Peripheral Artery Disease (PAD) in the lower extremity arteries exhibits distinct characteristics and results in different clinical outcomes when treating arteries above and below the knee. However, their mechanical, structural, and physiologic differences are poorly understood. Our study compared above- and below-knee arteries from the same middle-aged human subjects and demonstrated distinct differences in size, structure, and mechanical properties, leading to variations in their physiological behavior. These insights could pave the way for creating location-specific medical devices and treatments for PAD, offering a more effective approach to its management. Our findings provide new, important perspectives for clinicians, researchers, and medical device developers interested in treating PAD in both above- and below-knee locations.

Influence of Material Parameter Variability on the Predicted Coronary Artery Biomechanical Environment via Uncertainty Quantification

Central to the clinical adoption of patient-specific modeling strategies is demonstrating that simulation results are reliable and safe. Indeed, simulation frameworks must be robust to uncertainty in model input(s), and levels of confidence should accompany results. In this study, we applied a coupled uncertainty quantification-finite element (FE) framework to understand the impact of uncertainty in vascular material properties on variability in predicted stresses. Univariate probability distributions were fit to material parameters derived from layer-specific mechanical behavior testing of human coronary tissue. Parameters were assumed to be probabilistically independent, allowing for efficient parameter ensemble sampling. In an idealized coronary artery geometry, a forward FE model for each parameter ensemble was created to predict tissue stresses under physiologic loading. An emulator was constructed within the UncertainSCI software using polynomial chaos techniques, and statistics and sensitivities were directly computed. Results demonstrated that material parameter uncertainty propagates to variability in predicted stresses across the vessel wall, with the largest dispersions in stress within the adventitial layer. Variability in stress was most sensitive to uncertainties in the anisotropic component of the strain energy function. Moreover, unary and binary interactions within the adventitial layer were the main contributors to stress variance, and the leading factor in stress variability was uncertainty in the stress-like material parameter that describes the contribution of the embedded fibers to the overall artery stiffness. Results from a patient-specific coronary model confirmed many of these findings. Collectively, these data highlight the impact of material property variation on uncertainty in predicted artery stresses and present a pipeline to explore and characterize forward model uncertainty in computational biomechanics.

Quantitative and large-format histochemistry to characterize peripheral artery compositional gradients

The femoropopliteal artery (FPA) is a long, flexible vessel that travels down the anteromedial compartment of the thigh as the femoral artery and then behind the kneecap as the popliteal artery. This artery undergoes various degrees of flexion, extension, and torsion during normal walking movements. The FPA is also the most susceptible peripheral artery to atherosclerosis and is where peripheral artery disease manifests in 80% of cases. The connection between peripheral artery location, its mechanical flexion, and its physiological or pathological biochemistry has been investigated for decades; however, histochemical methods remain poorly leveraged in their ability to spatially correlate normal or abnormal extracellular matrix and cells with regions of mechanical flexion. This study generates new histological image processing pipelines to quantitate tissue composition across high-resolution FPA regions-of-interest or low-resolution whole-section cross-sections in relation to their anatomical locations and flexions during normal movement. Comparing healthy ovine femoral, popliteal, and cranial-tibial artery sections as a pilot, substantial arterial contortion was observed in the distal popliteal and cranial tibial regions of the FPA which correlated with increased vascular smooth muscle cells and decreased elastin content. These methods aim to aid in the quantitative characterization of the spatial distribution of extracellular matrix and cells in large heterogeneous tissue sections such as the FPA. RESEARCH HIGHLIGHTS: Large-format histology preserves artery architecture. Elastin and smooth muscle content is correlated with distance from heart and contortion during flexion. Cell and protein analyses are sensitive to sectioning plane and image magnification.

Investigating Balloon-Vessel Contact Pressure Patterns in Angioplasty: In Silico Insights for Drug-Coated Balloons

Drug-Coated Balloons have shown promising results as a minimally invasive approach to treat stenotic arteries, but recent animal studies have revealed limited, non-uniform coating transfer onto the arterial lumen. In vitro data suggested that local coating transfer tracks the local Contact Pressure (CP) between the balloon and the endothelium. Therefore, this work aimed to investigate in silico how different interventional and device parameters may affect the spatial distribution of CP during the inflation of an angioplasty balloon within idealized vessels that resemble healthy femoral arteries in size and compliance. An angioplasty balloon computational model was developed, considering longitudinal non-uniform wall thickness, due to its forming process, and the folding procedure of the balloon. To identify the conditions leading to non-uniform CP, sensitivity finite element analyses were performed comparing different values for balloon working length, longitudinally varying wall thickness, friction coefficient on the balloon-vessel interface, vessel wall stiffness and thickness, and balloon-to-vessel diameter ratio. Findings indicate a significant irregularity of contact between the balloon and the vessel, mainly affected by the balloon's unfolding and longitudinal thickness variation. Mirroring published data on coating transfer distribution in animal studies, the interfacial CP distribution was maximal at the middle of the balloon treatment site, while exhibiting a circumferential pattern of linear peaks as a consequence of the particular balloon-vessel interaction during unfolding. A high ratio of balloon-to-vessel diameter, higher vessel stiffness, and thickness was found to increase significantly the amplitude and spatial distribution of the CP, while a higher friction coefficient at the balloon-to-vessel interface further exacerbated the non-uniformity of CP. Evaluation of balloon design effects revealed that the thicker tapered part caused CP reduction in the areas that interacted with the extremities of the balloon, whereas total length only weakly impacted the CP. Taken together, this study offers a deeper understanding of the factors influencing the irregularity of balloon-tissue contact, a key step toward uniformity in drug-coating transfer and potential clinical effectiveness.

A viscoelastic constitutive model for human femoropopliteal arteries

High failure rates present challenges for surgical and interventional therapies for peripheral artery disease of the femoropopliteal artery (FPA). The FPA's demanding biomechanical environment necessitates complex interactions with repair devices and materials. While a comprehensive understanding of the FPA's mechanical characteristics could improve medical treatments, the viscoelastic properties of these muscular arteries remain poorly understood, and the constitutive model describing their time-dependent behavior is absent. We introduce a new viscoelastic constitutive model for the human FPA grounded in its microstructural composition. The model is capable of detailing the contributions of each intramural component to the overall viscoelastic response. Our model was developed utilizing fractional viscoelasticity and tested using biaxial experimental data with hysteresis and relaxation collected from 10 healthy human subjects aged 57 to 65 and further optimized for high throughput and automation. The model accurately described the experimental data, capturing significant nonlinearity and hysteresis that were particularly pronounced circumferentially, and tracked the contribution of passive smooth muscle cells to viscoelasticity that was twice that of the collagen fibers. The high-throughput parameter estimation procedure we developed included a specialized objective function and modifications to enhance convergence for the common exponential-type fiber laws, facilitating computational implementation. Our new model delineates the time-dependent behavior of human FPAs, which will improve the fidelity of computational simulations investigating device-artery interactions and contribute to their greater physical accuracy. Moreover, it serves as a useful tool to investigate the contribution of arterial constituents to overall tissue viscoelasticity, thereby expanding our knowledge of arterial mechanophysiology. STATEMENT OF SIGNIFICANCE: The demanding biomechanical environment of the femoropopliteal artery (FPA) necessitates complex interactions with repair devices and materials, but the viscoelastic properties of these muscular arteries remain poorly understood with the constitutive model describing their time-dependent behavior being absent. We hereby introduce the first viscoelastic constitutive model for the human FPA grounded in its microstructures. This model was tested using biaxial mechanical data collected from 10 healthy human subjects between the ages of 57 to 65. It can detail the contributions of each intramural component to the overall viscoelastic response, showing that the contribution of passive smooth muscle cells to viscoelasticity is twice that of collagen fibers. The usefulness of this model as tool to better understand arterial mechanophysiology was demonstrated.

Histology Image Viewer and Converter (HIVC): A High-Speed Freeware Software to View and Convert Whole Slide Histology Images

Histology images are widely used to assess the microstructure of biological tissues, but scanners often save images in bulky SVS and multi-layered TIFF formats. These formats were designed to archive image blocks and high-resolution textual information and are not compatible with conventional image analysis software. Our goal was to create a freeware Histology Image Viewer and Converter (HIVC) with a graphical user interface that allows viewing and converting whole-slide images in batch. HIVC was developed using C# Language for Windows x64 operating system. HIVC's performance was assessed by converting 20 whole-slide images to a JPG format at 20x and 40x resolution and comparing the results to ImageJ, Cell Profiler, QuPath, Nanoborb, and Aperio ImageScope. HIVC was more than 8-times faster in converting images than other software packages. This software allows high-speed batch conversion of histology images to traditional formats, permitting platform-independent secondary analyses.

A method of assessing peripheral stent abrasiveness under cyclic deformations experienced during limb movement

Poor outcomes of peripheral arterial disease stenting are often attributed to the inability of stents to accommodate the complex biomechanics of the flexed lower limb. Abrasion damage caused by rubbing of the stent against the artery wall during limb movement plays a significant role in reconstruction failure but has not been characterized. Our goals were to develop a method of assessing the abrasiveness of peripheral nitinol stents and apply it to several commercial devices. Misago, AbsolutePro, Innova, Zilver, SmartControl, SmartFlex, and Supera stents were deployed inside electrospun nanofibrillar tubes with femoropopliteal artery-mimicking mechanical properties and subjected to cyclic axial compression (25%), bending (90°), and torsion (26°/cm) equivalent to five life-years of severe limb flexions. Abrasion was assessed using an abrasion damage score (ADS, range 1-7) for each deformation mode. Misago produced the least abrasion and no stent fractures (ADS 3). Innova caused small abrasion under compression and torsion but large damage under bending (ADS 7). Supera performed well under bending and compression but caused damage under torsion (ADS 8). AbsolutePro produced significant abrasion under bending and compression but less damage under torsion (ADS 12). Zilver fractured under all three deformations and severely abraded the tube under bending and compression (ADS 15). SmartControl and SmartFlex fractured under all three deformations and produced significant abrasion due to strut penetration (ADS 20 and 21). ADS strongly correlated with clinical 12-month primary patency and target lesion revascularization rates, and the described method of assessing peripheral stent abrasiveness can guide device selection and development. STATEMENT OF SIGNIFICANCE: Poor outcomes of peripheral arterial disease stenting are related to the inability of stents to accommodate the complex biomechanics of the flexed lower limb. Abrasion damage caused by rubbing of the stent against the artery wall during limb movement plays a significant role in reconstruction failure but has not been characterized. Our study presents the first attempt at assessing peripheral stent abrasiveness, and the proposed method is applied to compare the abrasion damage caused by Misago, AbsolutePro, Innova, Zilver, SmartControl, SmartFlex, and Supera peripheral stents using artery-mimicking synthetic tubes and cyclic deformations equivalent to five life-years of severe limb flexions. The abrasion damage caused by stents strongly correlates with their clinical 12-month primary patency and target lesion revascularization rates, and the described methodology can be used as a cost-effective and controlled way of assessing stent performance, which can guide device selection and development.

One-year results of long femoropopliteal lesions stenting with fasciotomy lamina vastoadductoria

OBJECTIVE

Fasciotomy can increase the mobility of the superficial femoral artery and decrease the incidence of stent fractures. This study aimed to compare the long-term patency of drug-eluting nitinol stents with and without fasciotomy in patients with prolonged SFA occlusions.

METHODS

A randomized clinical trial was conducted in 60 (1:1) patients with long femoropopliteal steno-occlusive lesions more than 200 mm. Patients in group 1 (Zilver) underwent recanalization of femoropopliteal artery occlusion with stenting. In group 2 (ZilverFas), the femoropopliteal occlusion was recanalized with stenting and fasciotomy of Gunter's canal. The follow-up assessment of the patency took place after 6, 12 months.

RESULTS

12-month primary patency in Zilver and ZilverFas groups was 51% and 80%, respectively (p = 0.02). The freedom from target revascularization (TLR) in Zilver and ZilverFas groups was 50% and 76%, respectively (p = 0.04). At one-year, primary-assisted and secondary patency for the ZilverFas and Zilver groups were 83% versus 62% (p = 0.07), 86% versus 65% (p = 0.05), respectively. In Zilver and ZilverFas groups, the number of stents fractures was 14 and 7, respectively (p = 0.05). The multivariables Cox regression indicated that the stent fracture and diabetes mellitus were the independent predictors of restenosis and reocclusion. Fasciotomy reduced the risk of reocclusion and restenosis by 2.94 times.

CONCLUSIONS

Our study has shown that a decompressing the stented segment with fasciotomy significantly improves the patency of the femoropopliteal segment and significantly reduces the number and severity of stent fractures.

Impact of habitual sedentary patterns on popliteal artery endothelial-dependent vasodilation in healthy adults

Introduction:

Acute, laboratory-based bouts of prolonged sitting attenuate lower-limb arterial endothelial-dependent vasodilation. However, the impact of habitual sedentary patterns on popliteal artery endothelial health is unclear. We tested the hypothesis that greater habitual total sedentary time, more time spent in prolonged sedentary bouts, and fewer sedentary breaks would be associated with worse popliteal flow-mediated dilation (FMD) responses.

Methods:

This cross-sectional study used 98 healthy participants (19–77 years, 53 females) that wore an activPAL monitor on the thigh for 6.4 ± 0.8 days to objectively measure sedentary activity and completed a popliteal ultrasound assessment to determine FMD. Both relative (%baseline diameter) and absolute (mm) FMD were calculated. Using bivariate correlation and multiple regression analyses, we examined if there were relationships between sedentary outcomes and FMD while statistically controlling for any potential confounders.

Results:

In the multiple regression model, age (p = 0.006, β = −0.030, 95% CI = −0.051, −0.009) and total time in sedentary bouts > 1 hour (p = 0.031, β = −0.005, 95% CI = −0.009, −0.001) were independent predictors of relative FMD. Age (β = −0.002, 95% CI = −0.003, −0.001), mean blood flow (β = 0.013, 95% CI = 0.002, 0.024), moderate-intensity physical activity (β = 155.9E⁻⁵, 95% CI = 22.4E⁻⁵, 289.4E⁻⁵), sedentary breaks (β = 0.036, 95% CI = 0.007, 0.066), and total time spent in sedentary bouts > 1 hour (β = −25.02E⁻⁵, 95% CI = −47.67E⁻⁵, −2.378E⁻⁵) were predictors of absolute FMD (all, p < 0.047). All independent outcomes remained significant after partially controlling for all other predictor variables (all, p < 0.031).

Conclusions:

Habitual prolonged sedentary bouts and sedentary breaks, but not total sedentary time, were predictors of popliteal endothelial-dependent vasodilatory function. The patterns by which sedentary time is accumulated may be more important than the total sedentary time on lower-limb arterial health.

A larger low-flow-mediated constrictor response is associated with augmented flow-mediated dilation in the popliteal artery

In the brachial artery, conflicting evidence exists regarding the relationship between the low-flow-mediated constriction (L-FMC) and subsequent flow-mediated dilation (FMD) responses, which may confound interpretation of the latter. The popliteal artery is a common site for atherosclerotic development, which is preceded by endothelial dysfunction. We aimed to determine whether the magnitude of popliteal L-FMC impacted FMD responses, which is currently unknown. L-FMC and FMD were assessed in the popliteal artery via high-resolution duplex ultrasonography and quantified as the percent change in diameter (from baseline) during ischaemia and in response to hyperaemia, respectively. Using partial correlations and multiple regression analyses, we evaluated the association between popliteal L-FMC on FMD in 110 healthy participants (60 females; 42 ± 22 [19-77] years). All variables univariately associated (p < 0.05) with popliteal relative FMD (relative L-FMC, log-SR_AUC , age, systolic blood pressure, diastolic blood pressure, resting shear rate) were inputted into a model that explained 35% of the variance. The reactive hyperaemia stimulus (log-SR_AUC : β = 1.10) and relative L-FMC (β = -0.39) were the only independent predictors of FMD (both, p < 0.01). Relative L-FMC was negatively correlated to relative FMD, after controlling for the significant univariate predictor variables listed above (R = -0.30; p = 0.002). An augmented (ie healthier) L-FMC response was linked with a larger FMD response as determined by the independent inverse association observed between these shear-stress-mediated measures of vasoreactivity.