Influence of lung parenchymal destruction on the different indexes of the methacholine dose-response curve in COPD patients.
OBJECTIVE
The interpretation of nonspecific bronchial provocation dose-response curves in COPD is still a matter of debate. Bronchial hyperresponsiveness (BHR) in patients with COPD could be influenced by the destruction of the parenchyma and the augmented mechanical behavior of the lung. Therefore, we studied the interrelationships between indexes of BHR, on the one hand, and markers of lung parenchymal destruction, on the other.


METHODS
COPD patients were selected by clinical symptoms, evidence of chronic, nonreversible airways obstruction, and BHR, which was defined as a provocative dose of a substance (histamine) causing a 20% fall in FEV(1) (PC(20)) of </= 8 mg/mL. BHR was subsequently studied by methacholine dose-response curves to which a sigmoid model was fitted for the estimation of plateau values and reactivity. Model fits of quasi-static lung pressure-volume (PV) curves yielded static lung compliance (Cstat), the exponential factor (KE) and elastic recoil at 90% of total lung capacity (P90TLC). Carbon monoxide (CO) transfer was measured with the standard single-breath method.


RESULTS
Twenty-four patients were included in the study, and reliable PV data could be obtained from 19. The following mean values ( +/- SD) were taken: FEV(1), 65 +/- 12% of predicted; reversibility, 5.6 +/- 3.1% of predicted; the PC(20) for methacholine, 4.3 +/- 5.2 mg/mL; reactivity, 11.0 +/- 5.6% FEV(1)/doubling dose; plateau, 48.8 +/- 17.4% FEV(1); transfer factor, 76.7 +/- 17.9% of predicted; transfer coefficient for carbon monoxide (KCO), 85.9 +/- 22.6% of predicted; Cstat, 4.28 +/- 2.8 kPa; shape factor (KE), 1.9 +/- 1.5 kPa; and P90TLC, 1.1 +/- 0.8 kPa. We confirmed earlier reported relationships between Cstat, on the one hand, and KE (p < 0.0001), P90TLC (p = 0.0012), and KCO percent predicted (p = 0.006), on the other hand. The indexes of the methacholine provocation test were not related to any parameter of lung elasticity and CO transfer.


CONCLUSIONS
BHR in COPD patients who smoke most probably is determined by airways pathology rather than by the augmented mechanical behavior caused by lung parenchymal destruction.
Verhoeven
G T
GT
Department of Pulmonary and Intensive Care Medicine, University Hospital Dijkzigt, Erasmus Medical Center, Rotterdam, The Netherlands. Verhoeven@lond.azr.nl
Verbraak
A F
AF
Boere-van der Straat
S
S
Hoogsteden
H C
HC
Bogaard
J M
JM
D000280:Administration, Inhalation; D000328:Adult; D000368:Aged; D001944:Breath Tests; D016535:Bronchial Hyperreactivity / Q000150:complications / Q000000981:diagnostic imaging / Q000503:physiopathology; D001985:Bronchial Provocation Tests; D016084:Bronchoconstriction / Q000187:drug effects*; D016085:Bronchoconstrictor Agents / Q000008:administration & dosage*; D002248:Carbon Monoxide / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D005541:Forced Expiratory Volume; D006801:Humans; D008170:Lung Compliance / Q000187:drug effects; D008173:Lung Diseases, Obstructive / Q000150:complications / Q000000981:diagnostic imaging / Q000503:physiopathology*; D016210:Methacholine Chloride / Q000008:administration & dosage*; D008875:Middle Aged; D011379:Prognosis; D011656:Pulmonary Emphysema / Q000000981:diagnostic imaging / Q000209:etiology / Q000503:physiopathology*; D011859:Radiography
D016085:Bronchoconstrictor Agents; D016210:Methacholine Chloride; D002248:Carbon Monoxide