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Journal of the Association of Pulmonologist of Tamil Nadu. Vol. 2, Issue 3, September – December 2019
EDITORIAL
New Challenges in Asthma
How to cite this article: Narasimhan.R, Editorial, JAPT 2019; 2(3):92
Bronchial asthma has always been considered a disease of the large airways and COPD a disease of small airways to start with and gradually progresses towards large airways. We are always aware of the silent zones that lie in the last three generations of the conducting airways. This is considered the reason for the small airways dysfunction that is not easily detected on the routine spirometry. Also one of the reasons why many smokers do not believe that they have a problem in their lung as spirometry do not demonstrate any abnormality.
Since more than a decade there has been a thought that small airways are involved in bronchial asthma. The presence of inflammation in transbronchial biopsies of small airways has been a proof for this. Some of the autopsy specimens in severe asthma specimens also testify to this fact. This fact also underlines the fact that aerosol treatment targeting small airways makes the patient more comfortable than the ones that work only in large airways. Establishing the role of small airways in pathogenesis of asthma has always been a challenge because of the lack of pulmonary functions targeting this zone. Some of the tests that can be done like the gas wash out tests, transbronchial lung biopsies, frequent dependence compliance determination, closing volume
and closing capacity measurements, intrabronchial pressure measurements, forced oscillation technique measurements of resistance and reactance etc., can be done to measure them. But they are not done as a routine.
Anatomically the airways are divided into three zones. A zone consists of major airways, Zone B consists of lobar, segmental and subsegmental airways and Zone C consists of small airways. The particle size determines the place where aerosols are deposited. If the particles are more than 5 microns in diameter they were believed to stay in major and lobar and subsegmental airways to cause bronchodilation. If the particle size is less than 5 microns they would cross over from lungs to systemic circulation and cause systemic effects. This was considered to be a disadvantage and lot of studies were done to determine the optimal size of the particles and inhalers medications merits and demerits were determine by this.
Recently small particle aerosols such HFA (Hydrofluroalkane) beclomethasone and Ciclosenoid which have particle size less than 1 mm size are available with demonstrable good effect. There have also been attempts to make other steroid inhalers and beta agonists in such small particles. The identification of this zone playing a significant role in pathogenesis of asthma and also as therapeutic targets is a significant advancement in our goal for a better control of asthma. There is a large body of clinical evidence to support the role and use small particle aerosols for better control of symptoms and respiratory physiology.
Perhaps the way forward is to focus research on small airways, their anatomy, physiology and pathological significance in asthma and COPD so that better drugs with better targeted and therapeutic response can be made available which will make personalised treatment a reality.
Prof. Dr. Narasimhan R, MD FRCP (E & G)
Editor in Chief
Journal of the Association of Pulmonologist of Tamil Nadu