title: Hemodynamics associated with breathing through an inspiratory impedance threshold device in human volunteers.
abstract: 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.
  
  
  METHODS
  Randomized, blinded, controlled trial.
  
  
  METHODS
  Laboratory.
  
  
  METHODS
  Ten women and ten men.
  
  
  METHODS
  We measured hemodynamic and respiratory responses during two separate ITD conditions: 1) breathing through a face mask with an ITD (impedance of 6 cm H2O [0.59 kPa]) and 2) breathing through the same face mask with a sham ITD (control). Stroke volume was measured by thoracic bioimpedance.
  
  
  RESULTS
  Compared with the control condition, ITD produced higher stroke volume (124 +/- 3 vs. 137 +/- 3 mL; p = .013), heart rate (63 +/- 3 vs. 68 +/- 3 beats/min; p = .049), cardiac output (7.69 vs. 9.34 L/min; p = .001), and systolic blood pressure (115 +/- 2 to 122 +/- 2 mm Hg [15.33 +/- 0.3 to 16.26 +/- 0.3 kPa]; p = .005) without affecting expired minute ventilation (6.2 +/- 0.4 to 6.5 +/- 0.4 L/min; p = .609).
  
  
  CONCLUSIONS
  Breathing with an ITD at relatively low impedance increases systolic blood pressure by increasing stroke volume and cardiac output. The ITD may provide short-term protection against cardiovascular collapse induced by orthostatic stress or hemorrhage.
authors.affiliation: US Army Institute of Surgical Research, Fort Sam Houston, TX, USA.
authors.forename: Victor A
authors.initials: VA
authors.lastname: Convertino
authors.forename: Duane A
authors.initials: DA
authors.lastname: Ratliff
authors.forename: Kathy L
authors.initials: KL
authors.lastname: Ryan
authors.forename: Donald F
authors.initials: DF
authors.lastname: Doerr
authors.forename: David A
authors.initials: DA
authors.lastname: Ludwig
authors.forename: Gary W
authors.initials: GW
authors.lastname: Muniz
authors.forename: Deanna L
authors.initials: DL
authors.lastname: Britton
authors.forename: Savran D
authors.initials: SD
authors.lastname: Clah
authors.forename: Kathleen B
authors.initials: KB
authors.lastname: Fernald
authors.forename: Alicia F
authors.initials: AF
authors.lastname: Ruiz
authors.forename: Keith G
authors.initials: KG
authors.lastname: Lurie
authors.forename: Ahamed H
authors.initials: AH
authors.lastname: Idris
mesh_terms: D000328:Adult; D001794:Blood Pressure; D002307:Cardiography, Impedance / Q000295:instrumentation*; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008397:Masks; D012119:Respiration; D013318:Stroke Volume