Human mammary artery endothelial sparing with fibrous jaw clamping

BACKGROUND

Temporary clamping of the internal mammary artery pedicle is required for visualization during coronary artery bypass grafting. A nylon fibril jaw surface has been developed for these clamps that exerts pressure only at discrete sites on the pedicle surface. The effect of this new jaw surface on endothelial cell function and integrity after compression is investigated in this study.

METHODS

Internal mammary artery specimens from 10 patients each were divided into three separate rings, and two of these rings were clamped for 30 minutes with either a smooth or fibrous jaw clamp. Isometric tensions were measured in organ chambers after contraction by relaxing the rings with the endothelium-dependent agent acetylcholine followed by the endothelium-independent agent sodium nitroprusside. The intimal surfaces of similar rings were silver stained to assess the percentage of intact endothelium.

RESULTS

Endothelium-dependent relaxation was spared after fibrous jaw clamping (75% versus 89%) but significantly impaired after smooth jaw clamping (25% versus 89%; p < 0.001). Endothelium-independent relaxation was unaffected by either intervention. The percentage of remaining intact endothelium upon silver staining was significantly less after smooth than after fibrous jaw clamping (24% versus 48%; p < 0.01).

CONCLUSIONS

Foam silicone with nylon fibrils on the jaw surface of internal mammary artery clamps preserves endothelial cell function and integrity. The remaining undamaged cells also may facilitate the subsequent regeneration of a confluent endothelial cell layer.

Effects of low and high doses of fosinopril on the structure and function of resistance arteries

It has been suggested that angiotensin-converting enzyme inhibitors may induce a significant regression of cardiovascular hypertrophy not only through blood pressure reduction but also as a possible consequence of growth factor inhibition. The aim of this study was to evaluate the effects of the angiotensin-converting enzyme inhibitor fosinopril, given either at a hypotensive high dose or a nonhypotensive low dose, on structural and functional alterations of mesenteric resistance arteries and on cardiac mass in spontaneously hypertensive rats (SHR) and control Wistar-Kyoto rats. Fosinopril was administered in the drinking water from 6 to 12 weeks of age. Rats were killed at 12 weeks, and the ratio of heart weight to body weight was measured. Mesenteric arterioles were dissected and mounted on a micromyograph (Mulvany's technique). Vascular morphology (media-lumen ratio, media thickness) and endothelial function (response to acetylcholine) were then assessed. During the 6 weeks of treatment, systolic pressure in SHR treated with high-dose fosinopril was significantly lower compared with that in untreated SHR, whereas no difference was observed with low-dose fosinopril. In SHR treated with both high-dose and low-dose fosinopril, a statistically significant reduction of vascular structural alterations, in terms of both media-lumen ratio and media thickness, was observed. The ratio of heart weight to body weight was reduced only in SHR treated with high-dose fosinopril. An improvement in the endothelium-dependent relaxation to acetylcholine was observed in SHR treated with high-dose fosinopril compared with untreated SHR, whereas in SHR treated with low-dose fosinopril no improvement in endothelial function was detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Bending of blood vessel wall: stress-strain laws of the intima-media and adventitial layers

In order to determine the stress-strain relationship of the inner (intima and media) and outer (adventitia) layers of blood vessels in the neighborhood of the zero-stress state, bending experiments were performed on aortic strips of rats. In the experiments, one end of a strip was clamped, and a force was applied on the other end. The deflection curves of the strips were measured. By regarding the aortic strip as a curved beam, the classical beam theory was employed to analyze the strain distribution from the experimental data. A computer program dealing with nonlinear equations and nonlinear least squares optimization was developed. Strains were referred to the zero-stress state. The load-deflection relationship was then used to determine the stress-strain relationship. Certain forms of the stress-strain laws were assumed. The linear laws fit the experimental data accurately, probably because the strains during bending are quite small, although the rotations are large. The Young's modulus of the inner layer, which consists of endothelial and smooth muscle cells and elastic lamina, was found to be three to four times larger than that of the outer layer which consists of collagen with a small amount of fibroblasts and elastin. The residual stresses and strains at the no-load state were calculated from the deduced stress-strain relationship. It is shown that large errors (up to 50 percent) in the values of the residual strains will occur if the wall material was treated as homogeneous, i.e., if the layered constitution was ignored.

Noninvasive measurement of medium-sized artery intima-media thickness in humans: in vitro validation

Recent research in ultrasound technology has led to the development of a high-resolution echo-tracking device. The present study was performed to evaluate the accuracy in the measurement of human radial artery intima-media thickness with this new device. We determined the correlation between histological and ultrasonic measurements of intima-media thickness in 15 radial artery segments obtained from the distal end of the wrist-elbow harvest for coronary bypass grafting in patients with coronary heart disease. For arterial intima-media thickness, a positive correlation was observed between ultrasonic and histological measurements (r = 0.618; p < 0.014), and the difference between ultrasound and histology measurements was 41 +/- 66 microns, with the higher measurements found by the ultrasonic device. In a subgroup of 11 patients, we determined the correlation between in vivo ultrasonic measurements of radial artery intima-media thickness at the preoperative stage and in vitro ultrasonic measurements of intima-media thickness obtained postoperatively in the same arterial segments. Internal diameter was larger in vivo than in vitro, and intima-media thickness was smaller in vivo than in vitro. The cross-sectional area of the arterial wall was calculated from internal diameter and intima-media thickness. In vitro wall cross-sectional area was correlated with in vivo wall cross-sectional area (r = 0.929; p < 0.0001). Repeatability of in vivo intima-media thickness measurements was investigated in 10 subjects through the calculation of the repeatability coefficient as defined by the British Standards Institution.(ABSTRACT TRUNCATED AT 250 WORDS)

Mathematical morphologic analysis of the aortic medial structure. Biomechanical implications

The architecture of the aortic tunica media was studied in 55 autopsy specimens (26 normotensive and 29 hypertensive patients). The purpose of the study was to elucidate whether, as commonly stated, homogeneous disposition of concentric lamellar units could be substantiated or whether an architectural gradient reflecting the decreasing biomechanical gradient in the circumferential stress, concentrated towards the inner wall, was present. The elastin lamellae thickness, interlamellar distance, fibrosis index and fragmentation index were quantitated by mathematical morphology methods. The results did not support classic histologic descriptions but showed that lamellar units were significantly thicker in the inner than in the outer zones of the media--i.e., a morphologic gradient was present. The differences between inner and outer zones were more marked in hypertensive patients than in controls. The fibrosis index increased with age, especially in hypertensive patients. The fragmentation index in hypertensive patients was significantly higher than in controls and more marked in abdominal than in thoracic aorta. This weakening in the biomechanical resistance of elastin fibers could be one of the factors explaining the predominance of aneurysms in the abdominal aorta.

[Three-dimensional analysis of the tunica media of umbilical arteries. Scanning electron microscopy study]

The three-dimensional media structure of the umbilical arteries in their various functional states has up to now been object of numerous investigations, which are predominantly based on light-microscopic findings and have come to extremely differing results. For that reason the electron microscope method with an optically higher resolution was chosen for this thesis. In total, 20 umbilical cords were recovered, and in each case one of the two umbilical cord arteries was kept in a condition of non-contraction by means of perfusion fixation immediately after the omphalotomy. After the necessary preparation longitudinal, diagonal and cross-sections of both non-contracted and fully contracted umbilical arteries as well as of the folds of Hoboken, which occur in the arteries postnatally, were investigated by the scanning electron microscope. During this examination the following findings were made: The media in the wide umbilical cord artery consists of two layers. The outer layer accounts for some three quarters of the wall and is composed of lamellae of parallel muscle fibres which surround the vessel alternatively in gently rising and falling thread-like turns. The inner layer accounts for the remaining quarter and also consists of lamellae the thread-like turns of which, however, run at a much higher pitch. Exactly subendothelial, a very thin layer of irregularly arranged fibres with longitudinal main direction can be clearly identified. The folds of Hoboken are caused by local media contraction in the course of which the outer media restructures itself, thus being the main carrier of the fold.(ABSTRACT TRUNCATED AT 250 WORDS)