Journal of Applied Physiology, Vol 64, Issue 2 681-688, Copyright © 1988 by American Physiological Society
Bolus technique for assessing distribution of inspired gas during tidal breathing
K. I. Arita, S. M. Lewis and C. Mittman
Respiratory Disease Department, City of Hope Medical Center, California, Duarte 91010.
The washout of an insoluble tracer from the lung may be represented by a
model with two ventilatory compartments representing poorly and
better-ventilated regions. Using boli of a second insoluble gas delivered
at a given point during inspirations of a multibreath washout test, the
proportions of labeled inspired ventilation reaching the poorly and
well-ventilated regions may be determined by analyzing the kinetics of the
exhaled tracer. We studied eight normal subjects breathing through
large-bore solenoid valves controlled to maintain tidal volume at 600 or
900 ml. Boli consisting of 15 ml of 80% He-20% O2 were delivered over 75
ms; this labeled approximately 125 ml of inspired gas. Boli were delivered
after 50 ml had been inspired to mark early inspiration and after 300 ml
had been inspired to mark midinspiration. Using 900-ml tidal breaths, late
inspiration was marked by boli delivered at 600 ml. Subjects were studied
in the seated and the supine positions. In both positions, significantly
more of the early breath went to the poorly ventilated compartment. Several
possible physiological mechanisms, singly or in combination, could account
for these observations, but differences in dead space path length are most
likely involved.
