Variation in Airway Resistance: A Measure of Airway Heterogeneity?

The objective of the Forced Oscillation measurements that can be performed with the tremoFlo is first and foremost to produce a direct, instantaneous measure of airway resistance. However, there exists a body of recent literature that suggests that looking at the variations in airway resistance (VAR) over time, rather than at resistance itself, may be indicative of certain disease patterns and could possible reflect how well a patient is managed.

VAR & Hetergoneity

For several years now, the VAR technique has been a subject of interest for THROASYS’ Chief Scientific Advisor, Dr. Geoff Maksym, who heads the Biomedical Engineering Department at Dalhousie University in Halifax. In their most recent publication on this topic recently published in the Journal of Applied Physiology(1), Leary et al. further investigated this technique by mathematically modeling the stochastic and spatial heterogeneity in a human airway tree in order to develop a better understanding of the mechanisms that cause temporal variations in respiratory system resistance.

The authors used a multi-branch airway tree model to explore how variation in airway diameter is related to changes in airflow in the lung that are known to occur in asthma. They found that variation in airway resistance was explained not only by fluctuations in airway diameters that might occur with fluctuations in airway smooth muscle activity, but was also sensitive to changes in average airway constriction and the presence of ventilation defects, both of which are also increased in asthma. These findings provide new mechanisms and improve our understanding of why variation in airway resistance is increased in asthma.

Congratulations to Ph.D. students Del Leary and Swati Bhatawadekar for this excellent contribution.

Next Steps

At the recent Annual Biomedical Engineering Society meeting that took place in Hartford, Connecticut from October 13-15, 2011, the authors presented further research on this topic(2-5) carried out in collaboration with colleagues from Harvard University in Boston, Massachusetts and Western University in London, Ontario. Some of these studies feature measurement of airway reactance in asthmatics while others included the use of hyper-polarized gases to image the distribution of ventilation in patients with COPD.

We wish the authors best of luck and look forward to this work appearing in full-length manuscripts.

 

1. Del Leary, Swati A. Bhatawadekar, Grace Parraga, and Geoffrey N. Maksym, “Modeling Stochastic and Spatial Heterogeneity in a Human Airway Tree to Determine Variation in Respiratory System Resistance J Appl Physiol; http://jap.physiology.org/content/early/2011/10/11/japplphysiol.00633.2011.abstract.

2. D. Leary, A. Braune, T. Winkler, and G. Maksym. Modeling and Quantifying Heterogeneity of Airway Narrowing and the Contribution to Lung Mechanics. Platform presentation.

3. D. Leary, G. Parraga, and G. Maksym. Image-guided Stochastic Modeling of the Lung – Influence of Patchy Ventilation on Impedance Variability in Asthma. Platform presentation.

4. S. A. Bhatawadekar, P. Hernandez, C. McParland, S. Fulton, and G. N. Maksym, Bronchodilatory Induced Changes in Airway Reactance and Its Variation in Asthma.

5. A. Braune, D. Leary, G. N. Maksym, and T. Winkler, Effect of Symmetric vs. Asymmetric Tree Geometry and Airway Size on the Emergence of Ventilation Defects.