Reduced Systolic Volume: Main Pathophysiological Mechanism in Patients with Orthostatic Intolerance?

Abstract

Background: Orthostatic intolerance patients' pathophysiological mechanism is still obscure, contributing to the difficulty in their clinical management.

Objective: To investigate hemodynamic changes during tilt test in individuals with orthostatic intolerance symptoms, including syncope or near syncope.

Methods: Sixty-one patients who underwent tilt test at - 70° in the phase without vasodilators were divided into two groups. For data analysis, only the first 20 minutes of tilting were considered. Group I was made up of 33 patients who had an increase of total peripheral vascular resistance (TPVR) during orthostatic position; and Group II was made up of 28 patients with a decrease in TPVR (characterizing insufficient peripheral vascular resistance). The control group consisted of 24 healthy asymptomatic individuals. Hemodynamic parameters were obtained by a non-invasive hemodynamic monitor in three different moments (supine position, tilt 10' and tilt 20') adjusted for age.

Results: In the supine position, systolic volume (SV) was significantly reduced in both Group II and I in comparison to the control group, respectively (66.4 ±14.9 ml vs. 81.8±14.8 ml vs. 101.5±24.2 ml; p<0.05). TPVR, however, was higher in Group II in comparison to Group I and controls, respectively (1750.5± 442 dyne.s/cm5 vs.1424±404 dyne.s/cm5 vs. 974.4±230 dyne.s/cm5; p<0.05). In the orthostatic position, at 10', there was repetition of findings, with lower absolute values of SV compared to controls (64.1±14.0 ml vs 65.5±11.3 ml vs 82.8±15.6 ml; p<0.05). TPVR, on the other hand, showed a relative drop in Group II, in comparison to Group I.

Conclusion: Reduced SV was consistently observed in the groups of patients with orthostatic intolerance in comparison to the control group. Two different responses to tilt test were observed: one group with elevated TPVR and another with a relative drop in TPVR, possibly suggesting a more severe failure of compensation mechanisms.

Figure 1

Non-invasive hemodynamic index monitor records. A) Patient in Group I – observe the compensatory elevation of TPVR index during inclination. B) Patient in Group II – observe the unexpected drop in TPVR during inclination.

Figure 2

A and B) Means and confidence intervals of 95% for SV and CD means adjusted for age: comparison between the groups at each moment of analysis (supine, tilt 10' and tilt 20'). SV: systolic volume; CD: cardiac debit.

Figure 3

Means and confidence intervals of 95% for TPVR means adjusted for age: comparison between the groups at each moment of analysis (supine, tilt 10' and tilt 20').

Figure 4

A and B) Means and confidence intervals of MBP and HR means adjusted for age: comparison between the groups at each moment of analysis (supine, tilt 10' and tilt 20'). MBP: mean blood pressure; HR: heart rate.

Figure 5

a (Group I), b (Group II) and c (Control group). Scatter diagrams for SV and TPVR at 10' during tilt test; r: Pearson correlation coefficient. SV: systolic volume;TPVR: total peripheral vascular resistance.