Noninvasive determination of arterial elasticity and blood pressure. Part II: elastogram and blood pressure determination.

OBJECTIVE: The oscillometric method is used in the medical practice for measurement of arterial blood pressure and, rarely, for estimation of arterial elasticity. In the previous paper of this series, the relations between arterial volume pulsations and volume-to-pressure curve (elastogram) were examined resolving the problem for evaluation of arterial volume pulsations from known elastogram and systolic (ps)/diastolic (pd) blood pressure. Some features were found that are considered to be elastogram attributes. The aim of the present work is to resolve the inverse problem - graphical reconstruction of the elastogram from oscillometric data and determination of blood pressure. PARTICIPANTS AND METHODS: The elastograms of an idealized arterial model as well as of experimental oscillometric records (five men, five women) are processed graphically. RESULTS: The method for reconstruction is developed with the idealized volume pulsations of the arterial model, establishing full correspondence of the elastogram fixed in the model with those determined here. The accuracy of this reconstruction is assessed: a pulse pressure variability of 12% leads to an ~2-9% error of the reconstructed elastogram. Thereafter, experimental elastograms are reconstructed graphically, and the correct pulse pressure and blood pressure are determined. The experimentally determined blood pressure is statistically compared with that simultaneously auscultatory measured. Satisfactory correspondence between values of ps/pd is found. A method of objective comparison between elastograms after normalization is suggested. CONCLUSION: A novel graphical, nonempirical method for a noninvasive reconstruction of the elastogram and determination of blood pressure is presented. The method can be applied easily in automated blood pressure measurement devices.

Noninvasive determination of arterial elasticity and blood pressure. Part I: arterial volume pulsations and elastogram.

OBJECTIVE: The oscillometric method is widely used for noninvasive blood pressure measurement and rarely for assessment of arterial elasticity (volume-to-pressure curve/elastogram) in the systolic (ps)/diastolic (pd) pressure interval. In a wide range of physiologically normal pressures, the elastogram is obtained mostly invasively. In the present study (in two papers), the potential of the oscillometric method for a noninvasive estimation of complete elastogram and blood pressure is examined. The aim of the present first paper is to study the relations between oscillometric arterial volume pulsations and elastogram. METHODS: The interactions between transmural pressure, arterial volume pulsations, and elastogram are examined graphically on an idealized model of artery, thereafter proved on experimental oscillometric records (10 patients). RESULTS: A precise determination of the transmural pressure pulsations at descendent external pressure (as in oscillometry) is presented. The basic relationships between these pulsations and arterial volume pulsations in three specific pressure zones are clarified, which allow a strict dependence to be obtained between the arterial volume pulsations envelope and elastogram. The specific cut-off of transmural pressure and arterial volume pulsations, coincidence of the arterial volume pulsations envelope with the elastogram in the ps/pd interval, and two discontinuities (jumps) of the arterial volume pulsations envelope, at ps and pd, were found. The same was observed by noninvasive arterial oscillometry in humans, with good correspondence to the model excluding narrow intervals around ps and pd, in which the jumps are not clearly distinguishable. CONCLUSION: These specific features are assumed as elastogram attributes in the second paper, in which a noninvasive determination of both elastogram and blood pressure is carried out.

Viscoelastic characteristics of in vitro vital and devitalized rat aorta and human arterial prostheses.

The arterial wall viscoelasticity plays an essential role in the vascular responsiveness to vasoactive drugs or pathologies. The aim of this investigation was to derive and compare resonance curve (RC), natural frequency (f(0)), dynamic modulus of elasticity (E'), and coefficient of viscosity (beta) of (i) vital and devitalized preparations of rat thoracic and abdominal aorta, (ii) human arterial prostheses, and to study the histomorphology of vital and devitalized rat aorta. The method of low frequency forced oscillations was employed. RC of vital preparations showed a hardening type of elasticity whereas in devitalized preparations it was of softening type. E' increased nonlinearly, f(0) decreased and beta increased linearly with equivalent intraluminal pressure (p(eqi)). Distensibility of abdominal aorta was lower than thoracic aorta. Distensibility decreased with increasing p(eqi). E', f(0), and beta increased significantly after devitalization. It was suggested that postmortem viscoelastic characteristics should not be used directly to specify the vital arteries viscoelasticity. RC of human prostheses showed a softening type of elasticity. Arterial prostheses have low circumferential distensibility with E'-values higher than reported in the literature for human arteries. The method of forced oscillations could be employed for studying the arterial wall biomechanics and viscoelasticity of arterial prostheses.