Differences in airway wall compliance as a possible mechanism for wheezing disorders in infants

Abstract

The possibility that developmental differences in airway function might be risk factors for subsequent wheezing disorders in infancy has been systematically studied using, among other methods, the rapid chest compression technique (RTC) [1][2][3][4][5]. However, during flow limitation, maximum flows achieved during expiration are related directly to airway cross-sectional area and inversely to airway wall compliance [6]. The RTC cannot therefore distinguish between changes in airway calibre and airway wall properties, and developmental differences in airway wall properties rather than airway calibre [2-5] could be at least partly responsible for the occurrence of flow limitation in neonates and subsequent wheezing disorders in infants.The hypothesis that airway wall properties might be particularly important in infants has also been raised by investigators who looked into bronchodilator responses in infants. PRENDIVILLE et al. [7] found that in infants pretreat-ed with salbutamol, the maximal flow at functional residual capacity (FRC) (V 'maxFRC) increased at low doses of methacholine but declined at higher doses. They specula-ted that at low doses, methacholine isometrically increased airway smooth muscle tone and facilitated wave propagation in the airways. This hypothesis has implications for understanding the potential adverse effects of bronchodilators on airway smooth muscle tone and therefore airway stability in the developing lung.In order to facilitate the investigation of these issues, we need a noninvasive lung function technique that provides a measure of airway wall properties independently of airway calibre. We have introduced one such new method, the high-speed interrupter technique (HIT) [8], which enables the noninvasive and rapid measurement of high frequency input impedance Z(f) in infants [9]. At highfrequencies Z(f) contains antiresonances, that have been shown to be related to the propagation velocity of pressure waves within the airways (acoustic antiresonances) [9]. This implies that the frequency at which these antiresonances occur is dependent only on gas density, airway pathlength and airway wall properties [10]. High frequency Z(f) potentially enables us therefore to measure airway wall properties noninvasively in infants for the first time.The aim of the current study was to demonstrate that high-frequency Z(f) values from 32-900 Hz were sensitive to changes in airway mechanics during methacholine induced airway obstruction in infants. Furthermore we aimed to demonstrate the importance of airway wall properties for flow limitation in infants by showing that the first antiresonance, as an indirect measure of airway wall compliance, changed at low doses of methacholine before there was any discernible reduction in V 'max- FRC.Differences in airway wall compliance as a possible mechanism for wheezing disorders in infants. U. Frey, A.C. Jackson, M. Silverman. ©ERS Journals Ltd 1998. ABSTRACT: High-frequency input impedance measurements (Z(f)) provide useful noninvasive information on ai...

New aspects of airway mechanics in pre-term infants

“…Thus, far,1, velocity and V'max are related. These considerations can, however, only be qualitative and not quantitative, since the relationship between far,1, airway path length, airway wall compliance and the frequency of the travelling pressure waves is highly nonlinear [26,30,[36][37][38][39][40]. Nevertheless, based on these findings, the present authors hypothesise that the ability of airways to carry large flows is very different in pre-term than in full-term infants.…”

“…The present authors tried to overcome or at least partially compensate for this potential error by using the same face mask and filling it with silicon putty to reduce the dead space, but this could have contributed to the lower values of far,1 among the pre-term infants since the ''effective'' dead space would have been relatively large in relation to body size in this group. Similarly, input impedance measurements include the upper airways, and their influence cannot be distinguished from the lower airways [25,29,40]. On the other hand, study design was strengthened by the fact that measurements were undertaken during spontaneous unsedated sleep, thereby reflecting the complexities of the real dynamic situation.…”

Chest physical therapy is effective in reducing the clinical score in bronchiolitis: randomized controlled trial

“…Wheezing is explained by the oscillation of the bronchial wall and has also been called a "flutter effect" that occurs in the bronchi after the diameter has been reduced by inflammation, swelling and spasm in different structures of the bronchial wall. In children under 12 months of age, wheezing of the small airways is largely generated by mucus that partially obstructs the airflow producing the sound 41,42 . The treatment is directly related to their degree of reversibility and can be total, partial or none 24 .…”

“…Coughing and wheezing are common symptoms of bronchial obstruction in infants, and the genesis of wheezing is in mucosal edema and to a lesser degree in bronchospasm 41,42 . Wheezing is explained by the oscillation of the bronchial wall and has also been called a "flutter effect" that occurs in the bronchi after the diameter has been reduced by inflammation, swelling and spasm in different structures of the bronchial wall.…”

The forced oscillation technique in clinical practice: methodology, recommendations and future developments

“…Similarly to the inclusion of low-frequency components, the elevation of oscillation frequencies above y100 Hz reveals new patterns of frequency dependence of Zrs, with the potential of estimating additional mechanical parameters [159][160][161][162][163]. In particular, at frequencies well above fres, Xrs crosses zero in the negative direction: this is called the first antiresonant frequency (far,1).…”