Am. J. Respir. Crit. Care Med., Volume 161, Number 3, March 2000, 910-917

Peripheral Airway Smooth Muscle Mechanics in Obstructive Airways Disease

ANABELLE M. OPAZO SAEZ, CHUN Y. SEOW, and PETER D. PARÉ

UBC Pulmonary Research Laboratory, St. Paul's Hospital; and Department of Pharmacology and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada

The purpose of this study was to determine whether altered airway smooth muscle (ASM) contractility contributes to the pathogenesis of obstructive airways diseases such as chronic obstructive pulmonary disease (COPD) and asthma. The passive and active mechanical properties of isolated human peripheral airways were measured in vitro by myography. The amount of ASM was measured by morphometry. Pulmonary function was assessed before surgery by the FEV₁ (%pred) and the FEV₁/ FVC (%). Fifteen airways were studied from nonobstructed (NOB) patients, and 15 from obstructed (OB, FEV₁/FVC < 70%) patients (62 ± 10 yr, mean ± SD). The maximal isometric force (Fmax), stress (Fmax/ASM), airway diameter at Lmax (Dmax), maximal isotonic shortening (%Lmax), and normalized airway smooth muscle (ASM/Dmax) were determined in all patients. There was a significant correlation between Fmax and FEV₁ (%pred) (r = 0.579, p < 0.004), between Fmax and FEV₁/FVC (%) (r = 0.720, p < 0.003), and between stress and FEV₁/FVC (%) (0.611, p < 0.002). There was no correlation between isotonic shortening and either measure of pulmonary function. A positive correlation was found between force and shortening (r = 0.442, p < 0.05), and stress and shortening (r = 0.538, p < 0.01). Both force and stress were significantly increased (p < 0.05) in OB (Fmax = 0.87 ± 0.8 g, stress = 76 ± 47 mN/mm²) versus NOB (Fmax = 0.42 ± 0.18 g, stress = 51 ± 21 mN/mm²) patients, while isotonic shortening was not different between the two groups. ASM and ASM/Dmax were both significantly increased in the OB patient group (p < 0.05). These results suggest that obstructive airways disease is associated with an increase in the ability of the ASM to generate force. (Values represent means ± SD.) Opazo Saez AM, Seow CY, Paré PD. Peripheral airway smooth muscle mechanics in obstructive airways disease.

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