Dynamic elastance and tissue resistance of isolated liquid-filled
rat lungs.
Navajas, D., A. Moretto, M. Rotger, T. Nagase, M. J. Dallaire, and M.
S. Ludwig.
Meakins-Christie Laboratories, Royal Victoria Hospital, McGill
University, Montreal, Quebec H2X 2P2, Canada; and Laboratori
Biof[acute]isica i Bioenginyeria, Facultat Medicina, Universitat
Barcelona, 08028-Barcelona, Spain
APStracts 2:0296A, 1995.
The effect of the surface forces of the alveolar air-liquid interface
in the dynamic behaviour of lung tissue was investigated in five
isolated liquid-filled rat lungs. The lungs were subjected to 0.04 Hz
sinusoidal oscillation (1.5 ml tidal volume) at lung volumes (VL)
ranging from Vo + 4 ml to Vo + 10 ml (Vo = volume at zero pressure).
Oscillations were performed at each VL after inflating the lungs from
Vo. Alveolar pressure (PA) was measured with an alveolar capsule
attached to the visceral pleura. Dynamic elastance (Edyn), tissue
resistance (Rti) and hysteresivity ([theta] = Rti /Edyn; = 2[pi] x
frequency) were computed from PA and lung volume changes. Edyn was
59.6 +/- 4.3 Pa/ml at Vo + 4 ml and varied little up to Vo + 7 ml.
Thereafter, Edyn increased markedly with VL, reaching 102 +/- 16
Pa/ml at Vo + 10 ml. No significant difference was found between
elastance computed from PA and from pressure recorded at the airway
opening. Rti was 35.2 +/- 3.6 Pa.s/ml and exhibited a VL dependence
similar to that of Edyn. As a result, was 0.16 and did not vary
significantly in the explored VL range. We conclude that alveolar
pressure can be reliably measured in the liquid-filled lung by means
of alveolar capsules. In the liquid-filled lung, Edyn was smaller
than and similar to values reported for air-filled lungs. Hence,
surface tension account for a considerable part of elastance and
tissue resistance of the air-filled lung within the volume range of
normal breathing.
Received 5 December 1994; accepted in final form 26 June 1995.
APS Manuscript Number A1239-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 11 July 1995.