Am. J. Respir. Crit. Care Med., Vol 154, No. 5, Nov 1996, 1318-1322.
Effects of bronchomotor tone and gas density on time dependence of forced expiratory vital capacity maneuver
E D'Angelo, J Milic-Emili and L Marazzini
Istituto di Fisiologia Umana I, Universita di Milano, Italy.
It has been shown that in normal subjects and chronic obstructive pulmonary
disease (COPD) patients the maximal expiratory flows and FEV1 are
significantly higher if the FVC maneuver is preceded by a rapid inspiration
without an end-inspiratory pause (maneuver 1) compared with a slow
inspiration with an end-inspiratory pause of approximately 5 s (maneuver
2). This time dependency of FVC was attributed primarily to loss of lung
recoil (stress relaxation) during breath-holding at TLC, in association
with time constant inequality within the lungs, and changes in bronchomotor
tone. To examine the role of bronchomotor tone on time dependency of FVC,
11 COPD and 10 asthmatic patients performed FVC maneuvers 1 and 2 before
and after administration of a bronchodilator drug (salbutamol). In
addition, using the same approach, the effects of changing airway
resistance per se were assessed in another group of 10 COPD patients and 10
normal subjects, while breathing air and after equilibration with 80%
helium in oxygen. Main findings were: peak expiratory flow (PEF), FEV1, and
maximal midexpiratory flow rate (MMF) were significantly larger with
maneuver 1 than 2; after salbutamol administration and during helium-oxygen
breathing, all indices increased significantly with both maneuvers but the
relative differences between maneuvers 1 and 2 were unchanged. We conclude
that time dependency of maximal expiratory flow-volume (MEFV) curves, as
indexed by PEF, FEV1, and MMF, is largely independent of bronchomotor tone
and gas density, and probably reflects mainly stress relaxation of the
respiratory tissues. The relevance of time dependency of FVC maneuver in
the assessment of bronchodilator response and density dependence is
discussed.
