Journal of Applied Physiology, Vol 52, Issue 6 1667-1671, Copyright © 1982 by American Physiological Society
An intercostal retractometer for estimation of intrapleural pressure changes in infants
G. P. Heldt, J. A. Clements, M. B. McIlroy and W. H. Tooley
An intercostal retractometer was developed for estimation of intrapleural
pressure changes in infants. It consists of a flat reference plate which
floats over the interspace and is attached to the skin by a flexible
plastic film. The pressure inside the device is measured with a strain
gauge. The volume inside the device is adjusted, so that the intercostal
space is brought to a condition of flatness and pressure changes in the
device correlate linearly with intrapleural pressure changes. The
retractometer is calibrated against overall intrapleural pressure changes
by matching its output to changes in airway pressure during occlusion of
the airway. The calibration factor is qualitatively proportional to the
thickness of the subcutaneous tissue. Retractometer and intrapleural
pressures were simultaneously measured in two infant rhesus monkeys with
small pneumothoraces. Esophageal and retractometer pressures were compared
in seven preterm infants with an average weight of 1345 g. The device
estimated the monkeys' intrapleural pressure changes to within 1.2 cmH2O
and the human preterm infants' esophageal pressure changes to within 1.3
cmH2O (95% confidence limits of a linear regression).
