Collapse and viscoelasticity of diseased human arteries

Pseudo-hypertension and arterial stiffness: a review

Hypertension is a condition of persistently elevated blood pressure, associated with increased cardiovascular risk. Non-invasive BP measurement using Korotkoff sounds is the most common method of screening for the condition. The possibility of inaccurate readings leading to a false diagnosis of hypertension (pseudo-hypertension) is of concern. Stiffened arteries in the elderly have been proposed as being the primary cause of pseudo-hypertension. Non-invasive detection of pseudo-hypertension remains problematic. This paper reviews clinical literature on pseudo hypertension and approaches to measuring the compressive stiffness of arteries, as well as biomechanical literature regarding models of arterial stiffness and the origin of Korotkoff sounds. Models of the latter show the importance of the relationship between transmural pressure and cross-sectional area (P1/Csa curve) of the brachial artery as it closes under the influence of the pressure cuff. The review concludes that future research on pseudo-hypertension should include development of new instrumentation to measure the P1/Csa curve of the brachial artery in vivo using non-invasive techniques suitable for application to an elderly population.

Collapse of diseased arteries with eccentric cross section

The mechanism of atherosclerotic plaque rupture is not fully understood. Mechanical stress may be one of the factors contributing to the instability of the fibrous plaque cap. The existence of a severe stenosis may lower the transmural pressure enough to cause the collapse of arteries leading to high concentrated compressive and tensile stresses. This study presents quantitative estimates of the stresses and deformations in the collapsed thick-walled artery. The results of large deformation finite element calculations identify the locations of the high stress concentrations and their magnitudes which cannot be precisely predicted under a thin-wall assumption. The maximum compressive stress calculated reached 80% of the Young's modulus for fairly small negative transmural pressures. Results are useful to predict likely locations of the plaque cap rupture due to compressive stresses. The tube law of area as a function of transmural pressure showed a large discrepancy from a thin-wall calculation. The buckling pressure calculated for the outer-to-inner wall surface radius ratio of 1.60 was nearly 30% lower than that of the elastic thin-wall buckling theory. An increase in eccentricity further reduced this buckling pressure. The results indicate that a thick plaque which is eccentric increases the likelihood of collapse of stenotic arteries.

The effect of cooling on toe systolic pressures in subjects with and without Raynaud's syndrome in the lower extremities

The effect of changes in local and body temperature on the toe systolic pressures was studied in 20 subjects with and 30 without Raynaud's syndrome in the toes. The pressures were significantly lower in the group with Raynaud's syndrome under all experimental conditions (P less than 0.01). The pressures were significantly lower during body cooling than during body warming in both groups (P less than 0.01). The mean decrease with body cooling was 58 mmHg in the group with Raynaud's syndrome and 24 mmHg in the control subjects (P less than 0.01). During body cooling pressures fell to less than 30 mmHg in 70% of subjects with Raynaud's syndrome and in 3% of the controls. Local cooling from 30 to 10 degrees C during body cooling resulted in a significant mean decrease in pressure of over 40 mmHg in both groups (P less than 0.01) and the pressure fell below 30 mmHg in over 90% of the group with and in 26% of those without Raynaud's attacks. The results indicate the importance of body cooling and local temperature in the mechanism of vasospasm in the toes. They are also relevant to the diagnosis of Raynaud's syndrome in the lower limbs and have implications for the testing of patients with arteriosclerotic occlusion since erroneously low pressure values could be obtained in tests when the feet are cold.

Apparent finger systolic pressures during cooling in patients with Raynaud's syndrome

Despite considerable research, the mechanisms responsible for the vasospasm associated with Raynaud's syndrome are not well understood and there is no reliable diagnostic test. In the present studies, measurements of systolic pressure in locally cooled fingers were used to address these issues. We found that local cooling produced a marked decrease or loss of the apparent finger systolic pressure in patients with Raynaud's syndrome in whom a standardized vasoconstriction had been induced by body cooling. Abnormal responses were encountered in 109 of 125 patients with secondary Raynaud's syndrome, in 21 of 37 patients with primary Raynaud's disease or the syndrome of uncertain cause, and in two of 63 subjects without symptoms of Raynaud's. These data suggest a high accuracy of the test in patients with secondary Raynaud's syndrome and lower accuracy in those with disease of primary or uncertain cause. We studied responses of systolic pressures to alterations in body and local temperatures in fingers with and without low pressures secondary to proximal arterial obstruction. Our data show that although local cooling has a small independent effect that increases vascular tone: (1) sympathetic vasoconstriction induced by body cooling is necessary to produce vasospasm and often produces it without local cooling, (2) high local temperature (30 degrees C) protects from vasospasm, and (3) low finger blood pressure predisposes to it. Delayed opening of the vessels observed after sudden deflation of blood pressure cuffs suggests that abnormal responses of finger systolic pressure to cold represent combined effects of high vascular tone, delayed opening, and local blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)