Imposed power of breathing associated with use of an impedance threshold device.

Objective: To measure the imposed power of breathing (imposed work of breathing per minute) associated with spontaneous breathing through an active impedance threshold device and a sham impedance threshold device.

Design: Prospective randomized blinded protocol.

Setting: University medical center.

Inspiratory impedance effects on hemodynamic responses to orthostasis in normal subjects.

Background: Breathing through an impedance threshold device (ITD) might prove effective as a countermeasure against post-spaceflight orthostatic hypotension since it increased blood pressure (BP) and cardiac output in supine human subjects.

Objective: We tested the hypothesis that spontaneous breathing through an ITD would attenuate the reduction in stroke volume and BP during orthostasis in human subjects.

Methods: There were 19 volunteers (10 men, 9 women) who completed two 80 degrees head-up tilt (HUT) protocols with (active) and without (sham control) an ITD set to open at -7 cm H2O pressure.

Stroke volume during orthostatic challenge: comparison of two non-invasive methods.

Background: Real time non-invasive determination of stroke volume (SV) is important to astronaut orthostatic testing. We compared simultaneous estimates of SV calculated from peripheral pulse waveforms with a more conventional non-invasive technique.

Methods: Ten men and nine women completed 12-min protocols.

Effects of inspiratory impedance on hemodynamic responses to a squat-stand test in human volunteers: implications for treatment of orthostatic hypotension.

Recent studies in our laboratory demonstrated that spontaneous breathing through an inspiratory impedance threshold device (ITD) increased heart rate (HR), stroke volume (SV), cardiac output (Q), and mean arterial blood pressure (MAP) in supine human subjects. In this study, we tested the effectiveness of an ITD as a countermeasure against development of orthostatic hypotension, provoked using a squat-to-stand test (SST). Using a prospective, randomized blinded protocol, 18 healthy, normotensive volunteers (9 males, 9 females) completed two-counterbalanced 6-min SST protocols with and without (sham) an ITD set to open at 0.

Hemodynamics associated with breathing through an inspiratory impedance threshold device in human volunteers.

Objective: Increased negative intrathoracic pressure during spontaneous inspiration through an impedance threshold device (ITD) causes elevated arterial blood pressure in humans. This study was performed to determine whether the acute increase in blood pressure induced by breathing through an ITD is associated with increased stroke volume and cardiac output.

Design: Randomized, blinded, controlled trial.

Effects of inspiratory impedance on the carotid-cardiac baroreflex response in humans.

We were interested in a therapeutic device designed to increase carotid-cardiac baroreflex sensitivity (BRS) since high BRS is associated with a lower risk for development of hypotension in humans with experimentally-induced central hypovolemia. We hypothesized that spontaneous breathing through an impedance threshold device (ITD) designed to increase negative intrathoracic pressure during inspiration and elevate arterial blood pressure would acutely increase BRS in humans. We tested this hypothesis by measuring heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressures, and carotid-cardiac BRS in 10 female and 10 male subjects breathing through a face mask at three separate ITD conditions: (a) 6 cm H(2)O; (b) 12 cm H(2)O; and (c) a control (0 cm H(2)O).

Effects of repeated Valsalva maneuver straining on cardiac and vasoconstrictive baroreflex responses.

Introduction: We hypothesized that repeated respiratory straining maneuvers (repeated SM) designed to elevate arterial BPs (arterial baroreceptor loading) would acutely increase baroreflex responses.

Methods: We tested this hypothesis by measuring cardiac baroreflex responses to carotid baroreceptor stimulation (neck pressures), and changes in heart rate and diastolic BP after reductions in BP induced by a 15-s Valsalva maneuver in 10 female and 10 male subjects at 1, 3, 6, and 24 h after performing repeated SM. Baroreflex responses were also measured in each subject at 1, 3, 6, and 24 h at the same time on a separate day without repeated SM (control) in a randomized, counter-balanced cross-over experimental design.