Cellular Hypertrophy and Hyperplasia of Airway Smooth Muscles Underlying Bronchial Asthma: A 3-D Morphometric Study

TLDR

The study aimed to determine whether airway muscle thickening in asthma is due to cell hyperplasia or hypertrophy by performing 3‑D morphometry on autopsy lung sections from 10 asthmatics and five controls. Using unbiased 3‑D morphometry with a modified disector stack of serial sections, the authors quantified muscle cell density, mean cell number per airway length, and mean cell volume. They found that Type I asthmatic lungs had increased cell numbers in larger bronchi without hypertrophy, whereas Type II lungs exhibited widespread hypertrophy—especially in bronchioles—with only mild, localized hyperplasia, suggesting distinct pathogenetic mechanisms.

Abstract

In order to study whether hyperplasia or hypertrophy of cells is responsible for the thickening of airway muscles, 3-D morphometry of airway muscle cells was performed on resin-embedded semithin serial sections of autopsied lungs from 10 asthmatics and five control subjects. There were five Type I and five Type II asthmatic lungs, as defined in an earlier study, thickened muscles being found only in the central bronchi in Type I and distributed over the whole airway tree in Type II. The analysis was based on “unbiased” 3-D morphometry to obtain the numerical density Nv of muscle cells using a “disector, ” a spatial probe introduced by Sterio in 1984, which we modified into a stack of serial sections. The mean number Nl of cells per unit airway length and the mean volume Vc of a single muscle cell were also determined. In Type I asthmatics, the number of cells increased in the larger bronchi unaccompanied by cellular hypertrophy at any level of the airway tree. In contrast, in Type II asthmatics, hypertrophy was shown to prevail over the whole airway, but it was most remarkable in the bronchioles, whereas hyperplasia was mild and localized only in the bronchi. The two types of asthmatic lungs may therefore result from different pathogeneses.