Brief Summation of Pulmonary Function Tests Useful Websites / References

Pulmonary Function Testing Spirometry – Obstructive conditions Static lung volumes Diffusing capacities Restrictive conditions – Intrapulmonary – Extrapulmonary Other tests Z scores Tips

Spirometry Forced expiratory volume in 1 second (FEV1) – Volume exhaled in the first second of an FVC manoeuvre (forced exhalation from maximal inspiration) Vital capacity (VC) – Total volume exhaled by a exhalation from maximal inspiration – Can be a forced exhalation (FVC) or a relaxed exhalation (RVC) – best one taken as VC FEV1/VC – Ratio between FEV1 and VC

Spirometry

Obstructive Airways Disease FEV 1 ↓↓, VC ↔/↓, FEV1/VC < 0.7 Common causes – COPD Emphysema Chronic bronchitis – Asthma(can be normal if well) Less common causes – Large airway obstruction(ratio may not be < 0.7) – Bronchiectasis(ratio may not be < 0.7) – Obliterative broncholitis(post lung transplant)

Restrictive Lung Disease FEV 1 ↓, VC ↓/ ↓ ↓, ratio ↔ /↑ Can be split into intrapulmonary restrictive and extrapulmonary restrictive causes

Static Lung Volumes Total lung capacity (TLC) – Total volume of air in the lungs at the end of an maximal inspiration Residual volume (RV) – Volume of air remaining in the lungs at the end of a maximal expiration Functional residual volume (FRC) – Volume of air remaining in the lungs at the end of tidal expiration

Technique Whole body plethysmography / body box Calculates FRC – other static lung volumes calculated from this

Causes of Abnormal Lung Volumes Reduced TLC – Restrictive defect (intrapulmonary or extrapulmonary) Raised TLC – COPD esp. emphysema – Transiently during/recovering from asthma exacerbation Increased RV – Airways disease (air-trapping) – Respiratory muscle weakness (extrapulmonary)

Causes of Abnormal Lung Volumes Raised FRC – COPD incl. emphysema Reduced FRC – Fibrotic lung disease (intrapulmonary) – Obesity(extrapulmonary)

Diffusion Capacity TLCO = transfer factor for the lung for carbon monoxide i.e. Total diffusing capacity for the lung – Same as DLCO KCO = transfer coefficent i.e. Diffusing capacity of the lung per unit volume, standardised for alveolar volume (VA) VA = Lung volume in which carbon monoxide diffuses into during a single breath-hold technique

Diffusion Capacity Technique – Single breath hold methane/helium technique TLCO = KCO x VA Corrected for Hb

Abnormal Diffusion Capacity Low TLC: Low TLCO and low/normal KCO = intrapulmonary restrictive defect – Interstitial lung diseases e.g. Idiopathic pulmonary fibrosis, sarcoidosis, CTD, HP – Cardiac e.g. Pulmonary oedema – Pulmonary vascular disease e.g. Pulmonary hypertension (may have normal TLCO) High TLC: Low TLCO + KCO – emphysema (in the context of obstruction)

Abnormal Diffusion Capacity Low TLCO but high KCO = extrapulmonary restrictive defect – Obesity – Respiratory muscle weakness (neuromusclar) – Pleural disease e.g. effusion, encasement – Skeletal e.g. Ankolysing spond., thoracoplasty, severe kyphoscoliosis – Severe dermatological disease e.g. Scleroderma Also: post pneumonectomy

Abnormal Diffusion Capacity Normal/raised TLCO + raised KCO – Asthma – Pulmonary haemorrhage e.g. vasculitis

Other tests Reversibility testing – Spirometry before and after bronchodilator e.g. Salbutamol – > 12% or 200ml change in either FEV1 or VC provides some evidence of reversibility = possibility of asthma – >20% or 400ml change in either FEV1 or VC provides strong evidence of reversibility = strong possibility of asthma – Absence of reversibility does not rule out asthma

Other tests Erect/supine spirometry – Screening for respiratory muscle weakness Flow/volume loop – Localising large airway obstruction – Respiratory muscle weakness Mouth pressures – Inspiratory muscle weakness vs. expiratory Cardiopulmonary exercise testing

Z scores

95 % of the population should be within a Z score between to Therefore any value is ‘abnormal’ – Although it depends on what Z score they started off with … trends are more important than absolute values if available

Tips Go through the PFT’s systematically – Spirometry -> lung volumes -> diffusing capacities Try and classify the abnormality – Obstructive – Extrapulmonary restrictive defect – Intrapulmonary restrictive defect – Mixed picture Only make a diagnosis if the rest of the clinical picture given is in keeping with the PFT’s

Tips Even if the Z scores do not completely reach significance, if there is a definable pattern then consider PFT’s ‘tending towards’ Don’t be afraid to call it normal if it is! Don’t get confused about spirometry ratio – ≤0.7 is obstructive – There isn’t a ‘restrictive ratio’, if FEV1 and VC are significantly down then spiromety suggests restriction. If they are not significantly down, then a ratio of > 0.7 is normal.

Tips TLC + VA measure the same thing in different ways – TLC measures lung volume incl. non-ventilated areas, VA only measures ventilated areas and therefore TLC should be > VA – Technical issues if TLC < VA – If TLC >> VA – ‘volume gap’ – emphysema in context of obstruction Don’t call it extrapulmonary unless KCO is supranormal (>100% predicted) in restriction

FEV1VCRatioTLCTLCOKCO Asthma (can be normal) ↓ ↔/ ↓ ↓↑↔/ ↑↑ COPD (Emphysema) ↓ ↓↓↑ Intrapulmonary Restrictive Disease ↓↓↓↔/ ↑ ↓↓ ↓/ ↔ Extrapulmonary Restrictive Disease ↓↓↓↔/ ↑ ↓↓↑

Description Already established as a 'classic' in the field, Clinical Tests of Respiratory Function presents an authoritative yet accessible account of this complex area, fusing the basic principles of respiratory physiology with applications in clinical practice across a wide range of disorders. This third edition has been extensively revised to reflect advances in our understanding of respiratory function at rest, on exercise and during sleep, together with technological developments related to investigation and treatment. Now subdivided into four practical sections, users can easily pick their desired topic, from the commonly used tests and their underlying physiological mechanisms to abnormalities of function in both respiratory and non-respiratory diseases. The book concludes with a helpful section on test interpretation, new to this edition. This eagerly awaited revision will quickly find a place on the bookshelves of all practitioners clinicians and laboratory investigators who have an interest in respiratory function. "...a dominating and outstanding reference for students and practitioners in the field of pulmonology and respiratory care."--Doody's About the Author G.J Gibson, Emeritus Professor of Respiratory Medicine, University of Newcastle upon Tyne; and Consultant Respiratory Physician, Freeman Hospital, Newcastle upon Tyne, UK