Effect of lung volume on forced expiratory flows during rapid
thoracoabdominal compression in infants.
Hammer, J[umlaut]urg, Md, and Christopher J. L. Newth, Mb, Frcp(c).
Division of Pediatric Critical Care, Children's Hospital of Los Angeles,
University of Southern California, Los Angeles, California 90027
APStracts 2:0010A, 1995.
The rapid thoracoabdominal compression (RTC) technique is commonly used in
pulmonary function laboratories to assess flow-volume relationships in
infants unable to produce a voluntary forced expiration maneuver. This
technique produces forced expiratory flows only over a small lung volume
segment (i.e. tidal volume). It has been argued that the RTC technique should
be modified to measure flow-volume relationships over a larger portion of the
vital capacity range to imitate the voluntary maximal forced expiratory
maneuver obtained in older children and adults. We examined the effect of
volume history on forced expiratory flows by generating forced expiratory
flow-volume curves by RTC from well-defined inspiratory volumes delineated by
the inspiratory pressures +10, +20, +30 and +40 cm H2O, down to residual
volume (i.e. the reference volume) in seven intubated and anesthetized
infants with normal lungs (age [mean +/- SE] = 8.0 +/- 2.0 months, weight =
6.7 +/- 0.6 kg). We compared maximal expiratory flows (MEF) at isovolume points
(25% and 10% of forced vital capacity) and found no significant differences
in maximal isovolume flow rates measured from the different lung volumes. We
conclude that there is no obvious need to initiate RTC from higher lung
volumes if the technique is used for flow comparisons. However, in comparison
to measurements of maximal flows at functional residual capacity (maxFRC) by
RTC from endtidal inspiration, the initiation of RTC from a defined and
reproducible inspiratory level appears to decrease the intrasubject
variability of MEF at low lung volumes.
Received 20 September 1994; accepted in final form 6 January 1995.
APS Manuscript Number A980-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 February 1995.