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.

CTV News reports on COPD

To anyone working in this field, it has been known for a while that COPD is an increasingly important and deadly disease. Today, COPD is the fourth leading cause of death, and the World Health Organization predicts that it will rise to third place by 2020. Nonetheless, the disease is still little known to much of the public, and large epidemiological studies to quantify the lifetime risk factors associated with COPD are still few and far between. So it's a good thing that one such study by Gershon et al., recently published in The Lancet¹, was readily picked up by CTV health reporter Avis Favaro and featured in their national evening news on September 8. The clip describes COPD as a "little-known lung disorder" that is "a bigger problem than people think". Watch it here.

Watch for the cough...

One of the interesting things that this clip shows is what it’s like for many patients to take a spirometry exam. If you watch the very start of the clip, you may notice two things. First, the lady taking the test doesn't look very comfortable after she has performed the manoeuvre and blown into the spirometer. Second, you can clearly see that the spirometry test triggers a cough response in this patient. Any RT will happily tell you that this is a common occurrence that can severely interfere with performing the manoeuvre. Obtaining three valid consecutive spirometry manoeuvres in a patient like this may prove to be quite a challenge, without any fault on behalf of the patient or the technician.

The starting sequence of this clip therefore illustrates quite nicely what many experts have said for years: although spirometry is considered quite useful when it is performed well, it also has many shortcomings and limitations, especially for those patients that would benefit the most from accurate and reliable lung function assessment.

Forced Oscillations

The Forced Oscillation Technique (FOT) is still in its infancy compared to decades-old spirometry. Because a patient simply breathes quietly through an FOT device such as our tremoFlo, though, the FOT has the potential to provide a better alternative to measure lung function - especially in patients like Eileen Anderson who need it the most.

¹Andrea S Gershon, Laura Warner, Paul Cascagnette, J Charles Victor, Teresa To. Lifetime risk of developing chronic obstructive pulmonary disease: a longitudinal population study. The Lancet, Vol. 378 (9795): 991-996, September 2011.

THORASYS Exhibits at ATS 2011

The International Conference of the American Thoracic Society (ATS) recently took place in Denver, Colorado, attracting an estimated 12,000 clinicians and scientists from the fields of respiratory, critical care and sleep medicine. For the first time in our corporate history, Thorasys was represented in the ATS exhibit hall to publicly present a pre-production prototype of our tremoFlo Oscillation Spirometer at a major international conference. We received a lot of visitors to our booth, and we would like to thank all of those who stopped by for this strong and enthusiastic response!

Outside the exhibit hall, we were also happy to see that the Forced Oscillation Technique (FOT) continues to show strong momentum, with a continuously increasing number of studies and presentations using this technique. With many of these studies employing large and/or "home-made" FOT devices, the need for a portable commercial FOT device like the tremoFlo was more evident than ever.  

As we continue to push towards the commercial release of the tremoFlo, we look forward to seeing you again at the European Respiratory Society (ERS) meeting in Amsterdam in September, and at ATS 2012 in San Francisco. In the meantime, don't hesitate to write a comment on this blog or send us your questions at info@thorasys.com.

Welcome to THORASYS

Hello, and welcome to the Thorasys blog!

Thorasys Thoracic Medical Systems is an innovative medical device start-up located in Halifax, Nova Scotia, Canada. Our activities focus on the development of the tremoFlo, a novel medical device for the diagnosis and monitoring of respiratory diseases such as Asthma and COPD. The tremoFlo is scheduled to reach the market in 2012.

The tremoFlo is a small, portable device that uses the Forced Oscillation Technique (FOT) to provide accurate measurements of airway resistance and reactance. The tremoFlo does not require patient effort or cooperation and can hence be used comfortably by a wide range of paediatric, adult and elderly subjects, including mobility impaired patients and those who are unable to perform a voluntary manoeuvre. The tremoFlo can potentially replace so-called "spirometers" that require patient effort and cooperation to assess lung function.

The tremoFlo is currently being field tested at several sites throughout North America, and field testing in Europe is expected to start soon. This blog will provide regular updates about the tremoFlo development as we prepare for commercial release in several jurisdictions in the first half of 2012.