The role of lung function testing in the assessment of and treatment of: AIRWAYS DISEASE RHYS JEFFERIES ARTP education
Learning Objectives Examine the clinical features of airways disease to distinguish between COPD and asthma Explore the pathogenesis of obstructive airways disease and relate these to patterns of lung function impairment
Overview of Airways Disease
Asthma: Pathology
Asthma: Pulmonary Function Bronchoconstriction causes increased airway resistance and work of breathing Demonstrated by reduced measures of expiratory flow: PEF FEV1 FEV1/FVC% MEF values
Asthma: Pulmonary Function Airway narrowing may cause gas trapping leading to increased RV Bronchoconstriction may lead to increased FRC and hyperinflation Airway resistance decreases with lung volume (as airway calibre increases) Tidal volume shifts to higher lung volume in order to minimise work of breathing (dynamic hyperinflation)
Asthma: Pulmonary Function There is no gas exchange defect however uneven ventilation may reduce effective VA, and therefore reduce area for gas exchange KCO likely to be normal or high TLCO normal or slightly reduced (due to reduced VA), or raised due to increased vasculature of respiratory bronchioles TLC likely to be significantly greater than VA (low VA/TLC ratio)
Asthma: Pulmonary Function Between exacerbations airway function may be normal Normal PFT s do not exclude asthma According to BTS guideline: Confirmation hinges on demonstration of airflow obstruction varying over short periods of time This can be assessed by: Bronchodilator reversibility testing Steroid treatment trial Airway provocation testing
Reversibility Testing Bronchodilator Reversibility Criteria ARTP/BTS Guidelines ERS Recommendations ATS Recommendations 160ml increase in FEV1, or 330ml increase in VC >12% in FEV1 %predicted, and 200ml absolute 12% and 200ml increase in baseline FEV1 or FVC BTS COPD Guidelines 200ml and 15% increase in FEV1 from baseline GOLD Guidelines 200ml and 12% increase in FEV1 from baseline
40 yr old female Non-smoker Wheeze, allergy to cats and dogs
47 yr old female Non-smoker BMI 47 Hx exertional breathlessness Frequent RTI
46 yr old female Smoker 25 pack yrs Frequent RTI Reports asthma attacks requiring hospitalization
52 year old male Ex-smoker 30 pack yr Hx wheeze, SOB on exertion
COPD Definition: COPD is characterised by airflow obstruction that is not fully reversible. The airflow obstruction does not change markedly over several months and is usually progressive in the long term. (NICE 2010) COPD is a progressive airway disease which unlike asthma is only partially reversible COPD essentially comprised of two disorders: Chronic bronchitis Emphysema Both are present but clinical presentation varies according to which predominates
Emphysema Panacinar (no regional preference) Centriacinar (mostly apex) Paraseptal (adjacent to pleura or intra-lobular septa)
Emphysema
COPD: Chronic Bronchitis Chronic Bronchitis Defined as persistent cough, for at least 3 months of the year, for 2 consecutive years Hyperplasia and hypertrophy of mucous glands produce excess intra-luminal secretions Small airways are narrowed by: mucous plugs, mucosal oedema, smooth muscle hypertrophy, and bronchoconstriction
Chronic Bronchitis
COPD: Pulmonary Function PEF, FEV1 and FEV1% are reduced Dynamic compression during forced exhalation causes premature closure of airways This limits the volume of gas that can be exhaled and therefore reduces FVC During a slower exhalation (VC) transmural pressure is lower so collapse is less likely VC likely to be greater than FVC
COPD: Pulmonary Function Several features of COPD cause hyperinflation: Loss of elastic tissue caused by emphysema component increases lung compliance - Lungs become more easily stretched Mucous plugging and airway narrowing makes emptying of some compartments difficult - causing hyperinflation Dynamic hyperinflation occurs as increased airway resistance encourages ventilation at higher lung volumes (airway calibre is greater at higher volumes Helium dilution likely to be slow Large difference between TLC He and TLC pleth TLC, FRC and RV will be raised
COPD: Pulmonary Function Gas transfer: Emphysema causes reduction in alveolar surface area and so TLCO and KCO may be impaired Airway narrowing makes gas mixing slow and so effective VA typically reduced The exact pattern of impairment for PFT s will vary according to: The predominance of components of COPD, i.e. Bronchitis vs Emphysema, +/- asthma The severity of disease
Grading Severity NICE (2004) ATS/ERS 2004 GOLD 2008 NICE (2010) FEV 1 % predicted FEV 1 /FVC Postbronchodilator Postbronchodilator Postbronchodilator Postbronchodilator < 0.7 80% Mild < 0.7 < 0.7 50 79% Mild Moderate Stage 1 (mild) Stage 2 (moderate) 30 49% Moderate Severe Stage 3 (severe) < 0.7 < 30% Severe Very severe Stage 4 (very severe) Stage 1 (mild) Stage 2 (moderate) Stage 3 (severe) Stage 4 (very severe)
52 year old female smoker of 35 years Dx of asthma since early 20 s
61 year old male smoker frequent exacerbations Notable barrel chested with productive cough
49 year old male Smoker with 30 yrs pack hx BMI 16 Evidently dyspnoeic even at rest with ++ use of accessory muscles Vt
COPD v Asthma NICE Guidelines: Clinically significant COPD is not present if FEV1 and FEV1% return to normal with drug therapy Asthma may be present if.. There is a 400ml response to bronchodilators....or 30mg prednisolone for 2/52
Summary: COPD vs Asthma Features COPD Asthma Smoker? Nearly all Possible Symptoms under age of 35 Rare Common Chronic productive cough Common Uncommon Breathlessness Persistent Variable Night-time waking with SOB/wheeze Duirnal or day to day variation in symptoms? Uncommon Uncommon Remember Asthma and COPD may both be present Common Common