Human Autonomic and Cerebrovascular Responses to Inspiratory Impedance
Abstract
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 5 mm Hg, heart rate by 2 bpm, and mean cerebral blood flow velocity by 10% (p less than 0.05) with no effect on MSNA or estimates of vagal-cardiac control (p greater than 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 greater than 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 greater than 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.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 2006
- Accession Number
- ADA627974
Entities
People
- Keith G. Lurie
- Mary J. Rohrer
- Victor A Convertino
- William H. Cooke
Organizations
- United States Army Institute of Surgical Research