Cardiac Output in Postural Hypotension 1

Abstract

The arterial pressure is kept at a nearly constant level in normal man by simultaneous adjustments of the cardiac output and calibre of the arterioles. The normal response on motionless standing is arteriolar constriction and a moderate fall in cardiac output. The arteriolar constriction is usually sufficient to prevent a fall in mean pressure. In certain persons a marked fall in arterial pressure occurs on motionless standing. The purpose of this study is to evaluate the relative importance of an abnormal decline in cardiac output and of a failure of normal vasoconstriction in producing the fall in arterial pressure. METHODSAmong the 12 patients studied, postural hypotension was idiopathic in three, associated with diabetes mellitus in five, with tabes dorsalis in two, with probable syringomyelia in one, and followed bilateral sympathectomy (T. through LJ) for hypertension in one case.3 All subjects were studied in the morning, usually after a light breakfast. Observations were made on a tilting table in the supine position, and at a foot-down angle which was usually 60°from the horizontal. In the latter position the patient was supported by a foot-plate. The tilted position was maintained for three to four minutes before beginning air collection for determination of oxygen c6n-sumption. The air collection usually occupied two minutes, and toward the end of this time blood samples were drawn and pressure measurements were begun. The total duration of tilt was seven to eight minutes. The time allowed for adjustment to the tilted position is therefore quite short. However, if more time is allowed to reach a steady state during the tilt, there is danger of collapse. None of these subjects showed evidence of impending collapse. In one subject (J. D.) A-V blood oxygen differences were determined three minutes apart during the tilt, and in two subjects (C. G. and J. P.) duplicate venous samples were taken approximately one minute apart (before and after drawing the arterial sample). The results, presented in Table I, do not indicate rapid shifts in A-V oxygen difference during the period of measurement.Albumin infusion consisted of 75 gm. of human serum albumin4 made up with normal saline to a volume of 1,300 cc. and given intravenously within a period of 15 minutes.Cardiac outputs were determined by the Fick principle following intracardiac catheterization (1). Mixed venous blood was obtained from the atrium or the pulmonary artery; arterial blood, from the brachial artery through an inlying needle. Blood oxygen contents were determined by a spectrophotometric method (2) or by the method of Van Slyke and Plazin (3). In the latter case, duplicate analyses were required to check within 0.1 vol. %. With the spectrophotometric method, duplicate determinations are not in general done because of the simplicity of the technique. Repeated determinations of arterio-venous oxygen difference on the same blood samples yield results within 0.2 vol. %, unless the hemolyzed samples are grossly turbid. All samples are checked for t...

Haemodynamic responses during head-up tilt and tilt reversal in two groups with chronic autonomic failure: pure autonomic failure and multiple system atrophy

“…There was a fall in SV (-24 %) and CO (-22 %) with a rise in MAP (16 %), HR (5 %) and TPR (38 %) in the controls. These results are in agreement with other studies in normal humans, reporting activation of compensatory mechanisms that maintain blood pressure when upright [28,29]. In both PAF and MSA however, head-up tilt caused substantial postural hypotension, with a greater fall in PAF (-41 ± 4 mm Hg) than in MSA (-19 ± 4 mm Hg).…”

Idiopathic Orthostatic Hypotension

“…After tilting to 40°, cardiac output, blood pressure, stroke volume as well as circulating blood volume decreased without any significant change in heart rate or total peripheral resistance. These findings were in ac cordance with previous data obtained in idiopathic orthostatic hypotension [3,10,13,23,25,29,38], Recently, in patients with autonomic insufficiency, significantly low cardiac index was found [26].…”

Hemodynamics in Shy-Drager Syndrome and Treatment with Indomethacin

“…M-mode echocardiography revealed that the stroke volume, at 80 0 tilting, decreased by not less than 50% immediately after the tilting while the pulse rate remained mostly constant. This is a large decrease, compared with the less than 25% decrease in the car diac output of normal subjects in an upright position as reported by Hicham et al [6], This finding proved that the decreased car diac output was one of the factors greatly responsible for hemodynamic abnormalities in orthostatic hypotension in SDS for the first time.…”