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.


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.
Convertino
Victor A
VA
US Army Institute of Surgical Research, Fort Sam Houston, TX, USA.
Ratliff
Duane A
DA
Ryan
Kathy L
KL
Doerr
Donald F
DF
Ludwig
David A
DA
Muniz
Gary W
GW
Britton
Deanna L
DL
Clah
Savran D
SD
Fernald
Kathleen B
KB
Ruiz
Alicia F
AF
Lurie
Keith G
KG
Idris
Ahamed H
AH
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