The effects of posture and isoproterenol on the velocity of left ventricular contraction in man

Abstract

A B S T R A C T A study was performed in five normal men in whom left ventricular volume was measured by thermodilution in the supine and 600 head-up postures. in the control state, and then during steady-state response to isoproterenol. The mean rate of circumferential shortening of the left ventricle was calculated for each of the postures in both inotropic states and was found to remain constant in the control state at 12.5 ±0.6 cm/sec in the supine posture and 13.3 +0.5 cm/sec in the tilted posture. Similarly, mean rate of circumferential shortening remained constant in response to the positive inotropic effect of isoproterenol at 20.9 ±0.5 cm/sec in the supine position and 20.7 ±0.5 cm/sec in the tilted pos-

Adrenoceptor blockade of the circulatory responses to intravenous isoproterenol

“…* Indeed, with the use of a thermodilation teehnique, it has been shown that in normal subjects stroke output inereases after low doses of isoproterenol to a similar extent as in oUf subjeets. 7 By means of a dye-dilution teehnique, it has been shown that cardiac output and heart rate after cumulative doses of isoproterenol also follow patterns similar to those in our stud y. 3 It seems probable therefore that the changes in stroke output measured in our study provided a reliable estimate of the real changes.…”

Heart rate--left ventricular ejection time relations. Variations during postural change and cardiovascular challenges.

“…Increased ejection rate via improved contractility or Starling effect would also explain decreased LVET (Braunwald et al, 1958). However, tilt does not appear to change contractility (Paley et al, 1971) and reduces preload (Abelmann and Fareeduddin, 1969). Improved ejection rate, therefore, does not seem to be a factor effecting the progressively greater shortening of LVET with increasing HR during tilt as compared with rest and IHG.…”

Left ventricular function: time-varying elastance and left ventricular aortic coupling

“…Stroke work incorporates afterload since it is pressure afterload × stroke volume. In some versions “input” was changed to end-diastolic volume [ 6 ]. This addressed the issue of non-linear diastolic compliance [ 5 ].…”

“…An interesting extension relates these isovolumic pressure measurements to sarcomere shortening. Vmax [ 6 ], the maximum rate of sarcomere shortening, was calculated by considering units of cardiac muscle (sarcomeres) to be made up of a contractile element and a linear series elastic element—the series elastic element converting contractile element shortening into pressure. In analogy to cardiac muscle velocity–length relationships [ 10 ], the maximum velocity of shortening can be extrapolated from a plot of dP/dt (representing velocity of contractile element shortening) versus ventricular pressure (representing contractile element length).…”

“…The ESPVR incorporates afterload so that indices of ventricular contractility derived from the ESPVR are independent of afterload [ 23 ]. Emax is an excellent measure of intrinsic ventricular contractility, which is less load sensitive than other indices of ventricular contractility [ 6 ] and is insensitive to heart rate within the normal physiologic range [ 23 ]. If Emax increases, it can be seen (Fig.…”