Inspiratory resistance improves postural tachycardia: a randomized study

Abstract

Background: The objective of this study was to determine the effect of inspiratory resistance through an impedance threshold device (ITD) on orthostatic tolerance in patients with postural tachycardia syndrome. We hypothesized that the ITD would result in a greater negative intrathoracic pressure to enhance cardiac venous return, improve stroke volume, and reduce heart rate in these patients.

Methods and results: We compared the effect of a sham device (sham, no resistance) versus an ITD (increased inspiratory resistance) in 26 patients with postural tachycardia syndrome in a randomized, single-blind, crossover study. Hemodynamic assessments were performed at baseline while supine and during head-up tilt to 70° for 10 minutes. We did not find differences in baseline hemodynamic parameters between the ITD and the sham devices. After 10 minutes of head-up tilt, the heart rate was lower with the ITD versus sham device (102±4 versus 109±4 beat/min, respectively; P=0.003). The ITD also improved stroke volume compared with the sham device (35±2 versus 26±1 mL; P=0.006).

Conclusions: These findings suggest that increasing negative intrathoracic pressure with ITD breathing improves heart rate control in patients with postural tachycardia syndrome during upright posture.

Clinical trial registration: clinicaltrials.gov; Unique Identifier: NCT00962728.

Keywords: autonomic nervous system; postural tachycardia syndrome; stroke volume; tachycardia.

Figure 1

Study Design. A. Top Panel - Schematic diagram of the study protocol. On the study day, subjects were tilted head-up to 70 degrees, twice in a randomized manner, either with the active impedance threshold device (ITD) or the sham device. Lower panel - A typical continuous tracing of blood pressure and heart rate during head up tilt is shown. B. Picture showing the apparatus setup for both sham (left side) and ITD devices (right side), connected in sequence with the Innocor device used to measure cardiac output.

Figure 1

Study Design. A. Top Panel - Schematic diagram of the study protocol. On the study day, subjects were tilted head-up to 70 degrees, twice in a randomized manner, either with the active impedance threshold device (ITD) or the sham device. Lower panel - A typical continuous tracing of blood pressure and heart rate during head up tilt is shown. B. Picture showing the apparatus setup for both sham (left side) and ITD devices (right side), connected in sequence with the Innocor device used to measure cardiac output.

Figure 2

Enrollment and Randomization of Study Participants

Figure 3

Effect of ITD breathing on supine hemodynamic parameters. All panels show supine hemodynamic parameters at baseline breathing without any device (WO, blank bars) or using a breathing device (With, black bars). The left side of each panel shows the change with the impedance threshold device (ITD) and the right side with the Sham device. Breathing with the ITD did not change heart rate (HR; Panel A) or mean arterial pressure (MAP; Panel B), but decreased stoke volume (SV; Panel C) and increased total peripheral resistance (TPR; Panel D). Breathing with the sham device did not alter any of the hemodynamic parameters studied. The heart rate at the end of the supine period, however, was significantly higher while breathing with the ITD compared with the sham device (Panel A).

Figure 4

Hemodynamic changes during head up tilt with the ITD or sham device. Changes in hemodynamic parameters from baseline (white bars for ITD, gray bars for Sham) to 70 degrees of head up tilt (black bars for ITD and checkered bars for Sham). Breathing through both the ITD and sham devices resulted in an increase in heart rate (HR; Panel A), mean arterial pressure (MAP; Panel B) and total peripheral resistance (TPR; Panel D) and a decrease in stroke volume (SV; Panel C). At 10 minutes following head-up tilt, however, heart rate was lower (Panel A) and stroke volume was higher (Panel C) with the ITD versus sham device.