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Pulmonary Function Tests – a Refresher PULMONARY FUNCTION TESTS – A REFRESHER Khizer Hayat Khan M Rahim Khan York Teaching Hospital INTRODUCTION • Pulmonary function tests (PFTs) are non-invasive tests that show how well the lungs are working. • The tests measure lung volume, capacity, rates of flow, and gas exchange PURPOSE OF PFTs • Diagnosis of symptomatic disease • Screening of early asymptomatic disease • Monitoring response to treatment • Prognostication of known disease TYPES OF PFTs Spirometry STANDARD PFTs Lung volumes Gas transfer Exercise oximetry SPECIALIZED PFTs 6 minute walk test Peak flow CATEGORIES OF LUNG DISEASES • PFTs help classify disease in following categories: • OBSTRUCITVE | This is when air has trouble flowing out of the lungs due to airway resistance. This causes a decreased flow of air • RESTRICTIVE | This is when the lung tissue and/or chest muscles can’t expand enough • PULMONARY VASCULAR DISEASES | SPIROMETRY VALIDITY OF PFTs • Evaluate acceptability & reproducibility • Acceptability • Good effort – a rapid increase in airflow at the start of exhalation • Complete maneuver – at least 6s of exhalation ending up in plateau in flow • Reproducibility • All 3 FEV1 within 200ml of each other • All 3 FVC within 200ml of each other LUNG VOLUMES LUNG VOLUMES VOLUME AGAINST TIME FLOW VOLUME LOOP SPIROMETRY PATTERNS • Normal • Obstructive • Restrictive • Mixed • Fixed upper airway obstruction • Variable intra thoracic upper airway obstruction • Variable extra thoracic upper airway obstruction OBSTRUCTIVE SPIROMETRY • FEV1:FVC ratio <70% • FEV1 falls disproportionately greater than FVC • Conditions such as Asthma, COPD, Bronchiectasis and CF. RESTRICTIVE SPIROMETRY • FEV1:FVC ratio >80% • Reduction of FEV1 and FVC • Conditions such as ILD, pleural disease, NMD, Diaphragm dysfunction, kyphoscoliosis, obesity and pregnancy MIXED OBSTRUCTIVE/RESTRICTIVE • FEV1:FVC ratio<70% • Reduction in FVC FIXED UPPER AIRWAY OBSTRUCTION • Flow volume loop: flattening in both inspiration and expiration • Maximal flow rates limited • Causes: tracheal/bronchial stenosis, goitre, upper airway tumours VARIABLE EXTRA THORACIC OBSTRUCTION • Acceleration of air into the lung reduces intraluminal pressures causing collapse at the site of extra thoracic obstruction. • Flattened inspiratory flow curve • Normal expiratory flow curve • Causes: vocal cord paralysis, airway burns, glottic strictures VARIABLE INTRATHORACIC OBSTRUCTION • Decreased intrathoracic pressure splints open the airway lumen at the site of intrathoracic obstruction • Normal inspiratory flow curve • Flattened expiratory flow curve • Causes: tracheomalacia, polychondritis, low tracheal/bronchial tumours. DIFFUSION CAPACITY OF CO • (DLCO) is also known as the transfer factor for carbon monoxide or TLCO • It is a measure of the conductance of gas transfer from inspired gas to the red blood cells. DLCO Conditions and physiologic states that alter DLCO INCREASED DLCO • Exercise • Asthma • Polycythaemia • Pulmonary haemorrhage DECREASED DLCO • Emphysema • ILD • Anaemia Low Normal/High Assess FVC Assess FEV1/FVC Assess FVC Normal/High Normal lung Assess TLC Assess TLC mechanics Variety of Mixed Obstruction Restriction Assess DLC explanations Pulmonary Assess DLCO Assess DLCO Normal PFTs vascular disease Chronic CWD/NMD/ Emphysema Probable ILD Bronchitis/Asthma Obesity PRACTICAL SCENARIOS Pattern recognition The major limitation of PFTs is how they are interpreted KEYPOINTS PFTs not standalone test Requires organized approach Identify and quantitate the abnormality NORMAL “Triangle over a semicircle” FVC 4.68 FEV1 3.38 FEV/FVC = 3.38/4.68 = 0.72 or 72% TLCO = KCO x VA Don’t mix up TLC & TLCO! TLC – Total Lung Capacity TLCO – Transfer capacity of the Lung for Carbon monoOxide (may also be referred to as DLCO – Diffusion Capacity of the Lung for Carbon monOxide) CASE 1 …53 year old gentleman with history of asthma, complaining of dyspnea, wheeze and cough. He had some relief with inhaled therapy but remains symptomatic. He is an ex-smoker of 22 pack year. I am concerned whether he has developed COPD over the years that he was smoking… 횫 350ml 횫 530ml FEV1/FVC <70% OR <LLN? BRONCHODILATOR REVERSIBILITY GOLD - <70% ≥200ml & ≥12% 횫 in either FEV1 or FVC ATS - <LLN Mild | FEV1 >=80% SEVERITY OF AIRFLOW Moderate | 80%< FEV1 >=50% OBSTRUCTION Severe | 50%< FEV1 >=30% Very severe | FEV1 <30% …..only if FEV1/FVC is obstructive 80-120% | Normal <80% | Restriction 80-120% | Normal >120% | Hyperinflation >120% | Air trapping Airwary inflammation Airway obstruction Moderate severity Positive bronchodilator response Hyperinflation Gas trapping Slightly increased gas transfer ASTHMA CASE 2 …48 year old lady with COPD. Current smoker of 30 cigarettes a day. Remains short of breath despite optimum treatment for her COPD… 횫 0.05ml 횫 0.07ml Severe airways obstruction No reversibility Hyperinflation Gas trapping Reduced transfer factor EMPHYSEMA CASE 3 ...65 year old lady with exertional shortness of breath for 6 months. No other respiratory symptoms. Hx of SLE and recurrent UTIs. She is on Prednisolone, Methotrexate and Nitrofurantoin. She smoked 20 cigarettes a day for 31 years and quit 18 years ago... Restriction is graded by the decrement in FVC or TLC SEVERITY OF % OF PREDICTED RESTRICTION Mild 80-65% Moderate 65-50% Severe <50% FVC FVC TLC RV RV Restriction - Pulmonary or Extrapulmonary? • Extrapulmonary causes of restriction • Large pleural effusion/pleural thickening • Neuromuscular disease • Chest wall deformity • Obesity Restrictive lung disease Moderate severity Reduced gas transfer ILD CASE 4 … 60 year old lady symptomatic with progressive shortness of breath on exertion for several months. No other respiratory symptoms of note. She never smoked and has no past medical history of note. Her only medications is hormone replacement therapy… SPIROMETRY GAS TRANSFER DIAGNOSIS Reduced Emphysema Obstructive Normal Chronic bronchitis Normal / Increased Asthma Reduced Intrinsic lung disease Restrictive Normal Extrapulmonary restriction Anaemia Normal Reduced Pulmonary vascular disease Restrictive/Normal Increased Pulmonary haemorrhage Normal spirometry Normal lung volumes Reduced gas transfer Pulmonary vascular disease CASE 5 ... 25 year old gentleman with mild asthma well controlled with PRN Salbutamol. Has been symptomatic with dyspnea and wheeze for a year. 2 years ago he was involved in a road traffic accident and was intubated and ventilated. He had a tracheostomy that was removed 2 months after his discharge from the hospital... Don’t just look at the numerical values EMPEY’S INDEX FEV1 (ml) / PEF (L/min) >10 suggests upper airway obstruction The higher the ratio, the greater the obstruction REFERENCES / USEFUL RESOURCES • ERS Handbook of Respiratory Medicine 2nd edition • Oxford Handbook of Respiratory Medicine, 3rd edition • www.depts.washington.edu/uwmedres/Library/eLearning/Pulmonary • Interpretting PFTs, Clevelenad Journal of Medicine • Ruppel’s Mannual Of Pulmonary Function Testing, 11th edition • UpToDate.com – Interpretting pulmonary function testing .
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