Early atherosclerotic lesions spiraling through the femoral artery.

Atherosclerosis is common in the adductor hiatus region. The aim of this study was to evaluate atherosclerosis in relation to themorphological structure of the femoropopliteal region. Two anatomic features are thought to play an important role in the origin of these lesions: (1) curvature of the vessel, which may lead to unfavorable local hemodynamic factors that change during leg flexion; and (2) abrupt changes in stiffness of surrounding tissues of the vessel. The distal part of 23 postmortem femoral arteries were investigated. Cross sections were obtained every 1 mm over a length of 100 mm. For each cross section, lesion thickness was measured at 12 points along the circumference of the vessel. No apparent relation was found between surrounding structures of the femoral artery and location of atherosclerotic lesions. Three-dimensional reconstructions showed that atherosclerotic lesions were spiraling through the artery in 18 of 23 cases. Spiraling atherosclerotic lesions may be consistent with expected flow patterns in this part of the femoral artery.

Impact of local atherosclerotic remodeling on the calculation of percent luminal narrowing.

The choice of the reference site in order to calculate percent luminal narrowing mainly depends on which diagnostic tool is used for examination. In intravascular ultrasound or histology, the local area encompassed by the internal elastic lamina (IEL) area is used as a reference. However, the local IEL area, and thereby the reference value, may have been altered by atherosclerotic remodeling. In the present study we examined the impact of local arterial remodeling on the calculation of luminal narrowing. Forty-five human femoral arteries were analyzed, 32 postmortem and 20 in vivo, by intravascular ultrasound. Cross sections were examined every 0.5 cm over an arterial segment length of 10 to 15 cm. In each cross section we measured the lumen area and the IEL area. Two reference areas were used to calculate percent luminal narrowing: (1) the lumen area in the cross section that contained the least amount of plaque (distant reference); and (2) the local IEL area (local reference). In each cross section, the IEL area was expressed as percent of the IEL area in the cross section that contained the least amount of plaque (relative IEL area). Using the distant reference, we found that less luminal narrowing was observed for cross sections with a relative IEL area > 100% (indicating compensatory enlargement) than for those with a relative IEL area < 100% (indicating shrinkage), whereas percent luminal narrowing calculated using the local reference hardly differed between cross section with a relative IEL area > 100% and < 100%. Thus, arterial wall remodeling makes the local IEL area an unreliable reference for calculation of percent luminal narrowing. The calculated percent luminal narrowing using a distant, nondiseased reference site reflects the actual change of the luminal area more accurately.

Numerical simulation of blood flow in an artery with two successive bends.

Blood flow in an artery with two successive bends is simulated by a finite-element computation of steady flow of a Newtonian viscous fluid through a rigid tube having the same shape as a specific part of the femoral artery. Notwithstanding the fact that the bends in the model geometry are rather gentle, the axial and secondary flow patterns, computed for a range of values of the Reynolds number Re, show strong and complicated three-dimensional flow effects. In particular, the flow pattern in the second bend for relatively small values of Re (Re < 240) turns out to be drastically different from that for larger Re-values.

Atherosclerotic arterial remodeling in the superficial femoral artery. Individual variation in local compensatory enlargement response.

BACKGROUND: In previous studies on atherosclerotic arterial remodeling, compensatory enlargement of the artery in response to plaque accumulation was inferred from pooled data based on one cross section per artery. We assessed local arterial remodeling individually by analyzing 45 artery segments at 0.5-cm intervals over a length of 10 to 15 cm. METHODS AND RESULTS: Twenty patients were studied by 30-MHz intravascular ultrasound (IVUS) before balloon angioplasty of the superficial femoral artery (370 cross sections), and 25 femoral artery segments were studied postmortem (551 cross sections). In each cross section, the area surrounded by the internal elastic lamina (IEL area) and the plaque area were measured. The IEL area was larger in the cross section with the largest plaque area than in the cross section with the smallest plaque area (32.5+/-13.0 and 32.0+/-11.5 mm2 versus 28.9+/-9.7 [P=NS] and 26.7+/-10.1 [P<.05] mm2 for IVUS and histology, respectively [mean+/-SD]). A significant positive correlation was found between plaque area and IEL area for the pooled data (r=.61 and r=.47 and slope=1.07 and 0.90 for IVUS and histology, respectively; both P<.001). In 12 of 20 and 16 of 25 individual arterial segments, however, no significant correlation was observed between plaque area and IEL area for IVUS and histology, respectively. A large variation was found in the correlation of the regression of plaque to IEL area (IVUS, r=-.40 to .89; histology, r=-.13 to .91) and slope (IVUS, -0.28 to 1.29; histology, -0.18 to 1.32). CONCLUSIONS: In the majority of atherosclerotic femoral arteries, significant compensatory enlargement could not be determined. It is inferred that arterial remodeling in response to plaque formation may vary among individuals.

Arterial tortuosity in the femoropopliteal region during knee flexion: a magnetic resonance angiographic study.

Dynamic changes in curvature are expected in the femoropopliteal region during knee flexion. The location of the artery dorsal to the axis of movement implicates a relative length excess that may influence local morphology. To study arterial morphology in vivo, magnetic resonance angiography was performed in 22 healthy volunteers (aged 23-68 y). The curvature of the femoral vessels was studied and quantified in stretched and flexed positions. During knee flexion the vessel followed the movement of the leg and in the sagittal plane one curve was visible distal to the adductor hiatus. Three or more small curves were seen proximal to the knee joint in all volunteers. In the group aged under 30 y these minor curves were located proximal to the adductor hiatus as if the artery curls up in Hunter's canal. In the group aged over 45 y one or more curves were located distal to the adductor hiatus in the popliteal fossa. In volunteers aged 60 y and older some of these curves did not disappear during knee extension. In older individuals, natural elongation and loss of arterial elasticity will contribute to the formation of these curves. Impairment of the free gliding mechanism of the femoral vessels in the adductor canal could explain the differences in location of these minor curves between younger and older subjects. It is concluded that morphological changes in the femoral artery occur during knee flexion and that this tortuosity is age dependent. This may influence local haemodynamics and therefore possibly contribute to atherogenesis.

Paradoxical arterial wall shrinkage may contribute to luminal narrowing of human atherosclerotic femoral arteries.

BACKGROUND: This study was done to assess how local changes in vessel size, together with plaque load, determine luminal narrowing in atherosclerotic arteries. Fifty-one human femoral arteries were analyzed: 32 postmortem and 19 in vivo by 30-MHz intravascular ultrasound. METHODS AND RESULTS: Histological and intravascular ultrasound cross sections were examined every 0.5 cm over an arterial segment 10 to 15 cm long. In each cross section we measured the lumen area and the area circumscribed by the internal elastic lamina (the IEL area). In each arterial segment, the cross section that contained the least amount of plaque was the reference site. For each cross section, the lumen area stenosis was expressed as percent of the lumen area in the reference site. Similarly, the IEL area was expressed as percent of the IEL area in the reference site (the relative IEL area). There was a significant negative correlation between the relative IEL area and the lumen area stenosis percentage (r = -.62, P < .001 for histology and r = -.66, P < .001 for intravascular ultrasound). When lumen area stenosis was less than about 25%, mainly compensatory enlargement was observed. When lumen area stenosis exceeded about 25%, however, mainly a decrease of the IEL area was observed, which is consistent with arterial wall shrinkage. Furthermore, the increase in plaque area does not account for the total loss of luminal area. There was a moderate correlation between an increase in plaque area and reduction of the corresponding lumen area (r = .49 and r = .56 for histology and intravascular ultrasound, respectively). CONCLUSIONS: The decrease in luminal area cannot be attributed to plaque increase alone. Arterial wall shrinkage is a paradoxical mechanism that may contribute to severe luminal narrowing of the atherosclerotic human femoral artery.