Effect of upright tilt on ventricular/vascular coupling in chronically instrumented primates

Abstract

Studies of the hydraulic loading conditions on the heart in humans, especially pulsatile load, have primarily been limited to the supine state. Therefore, we have chosen a nonhuman primate model, the baboon, to assess left ventricular/vascular coupling in both supine and upright positions. Primate subjects were studied by catheterization under sedation and then after surgical implantation of transducers. This allowed the evaluation of postural stress in the chronically instrumented conscious baboon and then after light dissociative doses of ketamine. Basic hemodynamic variables were evaluated for baboons in supine and upright positions. Fourier analysis was applied to aortic pressure and flow to obtain input and characteristic impedance and the ratio of pulsatile (Wp) to total (Wt) left ventricular power (Wp/Wt). The aortic reflected, or backward, pressure was also calculated. Peripheral resistance increased (P = 0.01) and reflected pressure decreased (17.74 +/- 1.50 vs. 15.21 +/- 2 mmHg; P < 0.01) in upright subjects. Characteristic impedance and Wp/Wt were unchanged. Postoperatively, peripheral resistance increased (2,651 +/- 311 vs. 3,667 +/- 276; P < 0.05) and mean power and Wt decreased (P < 0.01) without changes in reflected pressure. All variables were unchanged after light dissociative doses of ketamine. Thus there is no significant change in efficiency of left ventricular/vascular coupling formulated in terms of Wp/Wt or input impedance with postural stress.

Responses to mechanical stimuli of isolated basilar and femoral arteries of the rhesus monkey are different

“…Cardiac output in primates is significantly different (up to 20%) in the supine and standing positions [23,24]. Cardiac output in primates is significantly different (up to 20%) in the supine and standing positions [23,24].…”

Chronology of the push pull effect on nonhuman primates—shift of the arterial pressure threshold

“…Rhesus monkeys were chosen, because the blood supplied to their brains like that of humans comes from internal carotid arteries and the vertebrobasilar system, through the circle of Willis. Furthermore, they are capable of maintaining their cardiac output during Gstress (Burton 1986;Tran et al 1993;Werchan et al 1996). Procedures employed conform to the Guiding Principles in the Care and Use of Animals and were approved by an Institutional Animal Care and Use Committee.…”

Contribuição dos grandes vasos arteriais na adaptação cardiovascular a ortostase

“…The first studies performed with the objective of assessing the effects of gravitational stress on hemodynamic parameters and its infl uence on the contour of the aortic pulse wave were carried out in primates [82][83][84] . It was observed that the central hemodynamics presented a pattern of response to gravitational stress that had well-defi ned phases.…”

“…An increase in the systolic volume and peripheral vascular resistance could also contribute to an increase in wave refl ection. According to the authors, the aim of this response would be to maintain the effi ciency of the ventricular/vascular coupling, in opposition to the gravitational effect 83 .…”