Human autonomic and cerebrovascular responses to inspiratory impedance.
BACKGROUND
We evaluated the influence of breathing through an inspiratory Impedance Threshold Device (ITD) on autonomic neural and cerebrovascular function.


METHODS
Eight subjects breathed through a sham ITD (0 cmH2O) and an active ITD (-7 cmH2O) in the supine position. We recorded the ECG, finger photoplethysmographic arterial pressure, cerebral blood flow velocity, and muscle sympathetic nerve activity (MSNA). In a randomized, counterbalanced design, subjects breathed spontaneously and also breathed at a set cadence of 15 breaths/min (0.25 Hz) for 3 minutes each. Data were analyzed in both time and frequency domains.


RESULTS
Breathing through the active ITD increased mean arterial pressure by approximately 5 mm Hg, heart rate by 2 bpm, and mean cerebral blood flow velocity by 10% (p<0.05) with no effect on MSNA or estimates of vagal-cardiac control (p>0.05). The active ITD did not affect oscillations of interbeat R-R intervals, arterial pressures, or cerebral flow velocities within the low frequency (LF) domain of the power spectrum (p>0.05). Cross spectral analysis revealed no effect of the active ITD on transfer function magnitudes among arterial pressures and R-R intervals, or between arterial pressures and cerebral blood flow velocities at the LF (p>0.05).


CONCLUSIONS
Our results demonstrate that the ITD increases arterial pressure, heart rate, and cerebral blood flow velocity independent of changes in autonomic cardiovascular control or dynamic cerebral autoregulation. Use of an active ITD in situations of acute central hypovolemia, such as during hemorrhage, may slow the progression to hemodynamic instability in bleeding patients who retain the ability to ventilate spontaneously and robustly.
Cooke
William H
WH
Department of Health and Kinesiology, University of Texas at San Antonio (W.H.C.), San Antonio, Texas, and Department of Emergency Medicine, Minneapolis Medical Research Foundation and Hennepin County Medical Center, Minneapolis, Minnesota, USA.
Lurie
Keith G
KG
Rohrer
Mary Jo
MJ
Convertino
Victor A
VA
D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology*; D001783:Blood Flow Velocity; D002560:Cerebrovascular Circulation; D005260:Female; D006439:Hemodynamics; D006706:Homeostasis; D006801:Humans; D008297:Male; D012138:Respiratory Therapy / Q000295:instrumentation*; D012151:Resuscitation / Q000295:instrumentation*; D012771:Shock, Hemorrhagic / Q000628:therapy; D014939:Work of Breathing / Q000502:physiology*