Journal of Applied Physiology, Vol 51, Issue 6 1657-1661, Copyright © 1981 by American Physiological Society
Noninvasive ventilatory monitoring by respiratory inductive plethysmography in conscious sheep
W. M. Abraham, H. Watson, A. Schneider, M. King, L. Yerger and M. A. Sackner
The respiratory inductive plethysmograph is a noninvasive device that has
been used to measure tidal volume (VT) in humans from changes in
self-inductance of wire coils excited by an oscillator circuit placed about
the rib cage and abdomen. We investigated its accuracy in conscious sheep
utilizing a new calibration procedure during quiet breathing and breathing
associated with bronchospasm provoked by aerosolized carbachol. Seven sheep
were intubated with a nasotracheal tube and an esophageal balloon placed
for determination of transpulmonary pressure. Base-line mean pulmonary flow
resistance (RL) in the sheep was 1.5 +/- 0.7 (SD) cmH2O X l-1 X s. After
carbachol inhalation, mean RL increased to a maximum of 8.8 +/- 2.8 cmH2O X
l-1 X s (P less than 0.002). AT base line, mean VT estimated by respiratory
inductive plethysmography over a 20-s period fell within +/- 6% of
spirometry. After carbachol VT in five of the sheep remained close to the
initial validation, but in two, it deviated +/- 11% from spirometry.
Analysis of the continuous recording of timing and volume components of the
breaths revealed that bronchoprovocation did not significantly alter mean
VT or frequency. However, there was a slight increase in both parameters
resulting in an increase in minute ventilation from 7.6 +/- 2.4 to 9.6 +/-
2.8 l/min (P less than 0.02). Similarly, a slight decline in inspiratory
time coupled with the slight rise in VT produced an increase in mean
respiratory flow from a base-line value of 0.35 +/- 0.12 to 0.44 +/- 0.17
l/s (P less than 0.05). These results indicate that the respiratory
inductive plethysmography accurately monitors breathing pattern in
conscious sheep even during severe bronchospasm.
