Two arterial effective reflecting sites may appear as one to the heart.

Abstract

The relation between reflected waves and features of ascending aortic pressure waveforms and impedance patterns was investigated with a modified T-tube model of the systemic arterial circulation. Ascending aortic pressure and flow and descending aortic flow were measured in 10 dogs under basal conditions and under the effect of an agent (methoxamine) that caused vasoconstriction and an increase of mean aortic pressure. A broad range of aortic pressure amplitudes and features was obtained. These waveshapes were classified into four groups. Under basal conditions, cases for which a prominent diastolic fluctuation was present (n = 8) were grouped in A. Cases for which this fluctuation was absent (n = 2) were grouped in B. Groups C (n = 4) and D (n = 3) included cases that, under vasoconstricted conditions, did or did not display, respectively, a diastolic fluctuation in pressure. Arterial T-tube model parameters were estimated by simultaneously fitting the model to both ascending and descending aortic flow with aortic pressure as input. A good fit was obtained in any case considered. After parameter estimation, forward and reflected waves and impedance patterns at the entrance of head circulation (head and upper limbs) and body circulation (trunk and lower limbs) as well as their merger in the ascending aorta were determined. T-tube input impedance compared well with impedance data points obtained from the ratio of corresponding harmonics of ascending aortic pressure and flow. In some cases (group A), modulus and phase spectra displayed two distinct minima, in the range from 0 to 10 Hz. In some other circumstances, these minima were less distinct (groups B and C) and could even appear as one (group D). Whether one or two minima appeared in the ascending aortic impedance spectra at low frequency and whether a prominent diastolic fluctuation did or did not appear in aortic pressure, pressure and flow waveshapes proximal to the heart were explained by the presence of two effective reflecting sites in the systemic circulation. In group B, a diastolic fluctuation in pressure was absent despite the fact that head-end and body-end reflected waves were distinct. This happened because body-end reflected waves peaked corresponding to a minimum of the head-end reflected wave. In group D, a diastolic fluctuation in aortic pressure was absent because the body-end reflected wave moved into systole and superimposed on the head-end reflected wave. This superimposition was due to increased pulse wave velocity in the body transmission path as a result of decreased arterial distensibility.(ABSTRACT TRUNCATED AT 400 WORDS)

Ventricular–vascular coupling in hypertension

“…9 Although there are multiple reflection sites in the upper and lower parts of the body, the reflected waves merge together, appearing as a main reflected wave when they reach the heart. 10 Backward secondary waves, originating from peripheral reflection sites or generated by re-reflection phenomena, are functionally negligible because they occur later and have significantly lower amplitude than the main component. When the reflected wave is optimally timed, as usually occurs in young healthy individuals, the reflected component meets the forward wave in ascending aorta during the early phase of diastole, contributing to coronary perfusion (Fig.…”

The arterial Windkessel

“…The arterial system has been modeled in many ways: lumped models [18,73], tube models [8,41,80] and anatomically based distributed models [42,64,71]. In this paper we will discuss the lumped or Windkessel models.…”

Aortic Aging in ESRD: Structural, Hemodynamic, and Mortality Implications

“…3,4 The partial reflections summate to form an apparently unique backward-traveling reflected wave. 5 In the presence of impedance gradient and low aortic PWV, the backward wave returns to the aorta at end systole and early diastole, thereby enhancing late diastolic pressure and coronary perfusion 4 and attenuating the transmission of pulsatile pressure to the microcirculation. 3,6 The central effect of aortic stiffness on impedance gradient attenuation and resulting excessive transfer of pressure and pulsatile flow into microvasculature is mainly observed in low-resistance circulations: the kidney or brain.…”

“…[14][15][16] Those interrelated measurements of arterial function differ considerably in their relationships to the design of the cardiovascular system and arterial lumen radius, PWV = k(Eh/R) 0.5 and characteristic impedance (Zc) = k(Eh/R 5 ) 0. 5 , where E is the elastic modulus, h is arterial wall thickness, and R is artery radius. [14][15][16] Consequently, the aorta undergoes marked geometric changes with aging, becoming tortuous and dilatated, [17][18][19][20] with alterations of aortic taper affecting the pressure wave transmission and the sites, timing, and intensity of wave reflections.…”