Clinical pulmonary physiology. How to report lung function tests

Transcription

1 Clinical pulmonary physiology or How to report lung function tests

2 Lung function testing A brief history Why measure? What can you measure? Interpretation/ reporting Examples and case histories Exercise tests SCE questions

3 A brief history of spirometry AD Galen got a boy to blow into a bladder 1714 James Jurin measured tidal volume and vital capacity 1840 John Hutchinson measured vital capacity in 4000 people 1947 Robert Tiffineau described FEV1 and FEV1/FVC ratio 1950s-1980s Modern clinical respiratory physiology era

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5 Respiratory physiology hall of fame

6 What are lung function tests for? Diagnosis Disease monitoring Assessment for therapy Therapeutic response Assessment of disability/impairment

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10 What is available? CORE Airway function Spirometry Peak flow f/v loop Raw/SGaw Lung volumes He dilution Plethysmography Radiology Gas exchange TLCO/KCO ABGs SpO 2 EXTENDED Respiratory muscle tests Pi&Pe Max Sniff Supine VC Bronchial challenge testing Sleep SpO 2 Polysomnography Exercise testing EIA Metabolic gas exchange

11 Interpretation of Lung function tests Airway function FEV1 etc Physical description e.g. volumes OPINION Reference values Gas exchange TLCO & ABGs Range % predicted Standardised residual (1.64 SD)

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13 ATS/ERS algorithm for lung function diagnosis

14 ERS/ATS Interpretation strategies Two tasks 1. The classification of derived values with respect to a reference population and assessment of the reliability of the data (laboratory task) 2. The integration of the obtained values into the diagnosis, therapy and prognosis for an individual (physicians task) ATS/ERS task force:standardisation of lung function testing No 1 ERJ 2005: 26:

15 The report structure Technical Simple pattern description Relevant variations Reference values Explain anomalies Poor effort Best loop Mouthpiece leaks Coughing etc Quality control VCs equal VA < TLC Suggestions for further investigation Clinician s Answer the question Values in context Confirm diagnosis Suggest differential diagnosis Further investigation Advice on further management

16 Reference Equations Obtained from healthy subjects Gender, age and height Make your own Use reference equations for local population Use ECCS or ATS Ethnic correction GLI (Global, multi ethnic, all ages)

17 Lung function: categories of interpretation Obstructive FEV1/VC Loop Raw TLC RV/TLC Gas trapping (TLC-VA) COPD, asthma, emphysema Big lungs Restrictive FEV1/VC TLC, RV TLCO (KCO) ILD, sarcoid etc Small lungs Constrictive TLC (n RV) KCO Muscle weakness, obesity, scoliosis Squashed lungs

18 Common requests SOB? Cause (COPD, ILD) Is it asthma or COPD? Upper airway obstruction? Fit for surgery? Disease progression? Confirm diagnosis What is the prognosis?

19 Is it asthma or COPD? Young patient <20 pack year smoking history Airway obstruction PFTS may be normal! Good bronchodilator response (normal or 600ml) May need to suggest Explore the history further Peak flow monitoring PC20 etc FeNO/ Sputum eosinophils

20 Is it upper airway obstruction? Low FEV1/ FVC % ( not helpful ) Shape of spirogram(slow rise) Appearance of flow volume loop Airways resistance (Raw or SGaw) Empey Index (FEV1 ml/pfr L/Min) >8 You can t always tell!

21 Upper airway obstruction

22 Fit for surgery? Beware! The anaesthetist knows best Describe the situation Point out the unusual (UAO etc) Suggest how treatment can be improved Some operations have less effect on lung function than others Eyes and prostate ok Abdominal and thoracic surgery worse Prediction pathways (SWT, V/Q etc) Some surgery can improve lung function Decortication Bullectomy LVRS Transplantation

23 Prevalence of COPD is overestimated > 50years

24 Bronchodilator response Various definitions 12% change in FEV1 >200ml FEV >8% predicted FEV1

25 Miscellaneous reporting pitfalls Look at the loop! (minor abnormalities,site & nature of AO) Bronchodilator response in all? (not just FEV1) What sort of TLC? BOX> He Dilution> VA TLCO ( remember the haemoglobin etc) Reference values (the normal abnormal) Ethnic origin (10%)

26 Case 1 SOBE?

27 Case 1 Report Context Older lady, ex smoker, BMI 33 Airways Unobstructed, restrictive pattern, lower range of normal. Loop unhelpful Lung Volumes TLC 57% predicted, RV <50% predicted Gas transfer Low TLCO, relatively preserved KCO Diagnosis and advice?

28 Case 1 Report Lung function test compatible with a severe restrictive disorder. Low RV suggests intrinsic lung disease e.g IPF. Arterial blood gases would be helpful Suggest repeat PFTs after further investigation to monitor progress or treatment response (VC 68%)

29 Case 2 Previous abnormal CXR Progress?

30 Case Report 2 Context Age 33, BMI 23, Ex smoker, Previous lung function tests. Airways Previous tests shown mild airflow obstruction. Current test shows a restrictive pattern with recent fall in values. Still mild airflow obstruction on loop. Lung Volumes Sudden fall, TLC 60% predicted, RV <50% predicted Gas transfer Low TLCO, preserved KCO. Diagnosis and advice?

31 Case Report 2 Previous PFTs show a mild mixed picture (AO + low RV) No features of upper airway obstruction Significant development of more severe restrictive pattern Mixed picture compatible with ILD and smoking history or sarcoidosis Suggest repeat tests after treatment with corticosteroids (two months)

32 Case 3 Progressive dyspnoea

33 Case Report 3 Context Age 22 BMI 24, never smoked, lung function tests two years previously Airways Previous restrictive pattern worsened over time. FEV1 now 38% pred. Lung Volumes Low TLC (39%Pred), RV/TLC ratio 32% Gas transfer Low TLCO, High KCO. Diagnosis and advice?

34 Case Report 3 Severe restrictive pattern with progressive deterioration Preservation of RV/TLV ratio and KCO suggests external restriction (constrictive pattern) Causes might include muscle weakness, scoliosis etc FEV1< 40% predicted indicates that ventilatory failure may be imminent Suggest muscle studies, ABGs and sleep study as appropriate Why is the TLCO low?

35 Nocturnal hypoventilation

36 Case 4 Suitable for surgery?

37 Case Report 4 Context Age 69, BMI 21, Previous lung function tests. Airways Severe airflow obstruction, FEV1 23% predicted Pressure dependent airway collapse on loop No bronchodilator response performed Lung Volumes Gross hyperinflation on plethysmography RV/TLC ratio 69% TLC-VA > 500ml (3L gas trapping) Gas transfer TLCO 25% predicted, low KCO, ABGs? Diagnosis and advice?

38 Case Report 4 Severe airflow obstruction with features of emphysema (loop and KCO) Gross hyperinflation and gas trapping Progressive deterioration Potentially suitable for LVRS (hyperinflation, FEV1, KCO>20% predicted) Other helpful investigations would include ABGs, SWT and imaging

39 Exercise is good for you

40 The uses of cardiopulmonary exercise testing (performance testing, diagnostic, laboratory and field) The differential diagnosis of breathlessness The objective assessment of impairment/disability Guide to prognosis The assessment of therapeutic intervention (drugs/rehab/lvrs) Preoperative assessment Training prescription

41 Spirometry and exercise performance

42 The context of exercise assessment in lung disease Scientific exploration Functional performance measures Physical (domestic) activity Methods Laboratory (CPET) Laboratory (endurance) ADL Questionnaires Field testing (6MWD, ISWT,ESWT) Physical activity monitors Questionnaires (MRC, PFSS)

43 Methods of objective exercise testing in clinical practice Laboratory (Various platforms) Symptom-limited incremental test Constant workload (power) test Field (walking)tests Six minute walk Incremental shuttle walk test Endurance shuttle walk tests

44 Laboratory based exercise tests (CPET) Gold standard Precise physiological data Expensive

45 Incremental exercise response in health Metabolic threshold VE VO 2 VO 2maximal %VO 2max sustainable HR/CO VT Time/workload t

46 CPET for diagnosis for diagnosis of unexplained breathlessness Heart or lungs? Lack of fitness? Dysfunctional breathing? Obesity? Normal but uncompetitive

47 Interpretation of the Symptom Limited Maximal Incremental Exercise Test Has the subject made a good effort? Have they achieved normal values? Why did they stop? How did they get there? (physiological response)

48 Has the subject made a good effort? Plateau of VO 2 Max Patient exhaustion HR or VE close to predicted maximum Blood lactate > 4 mmol/l Respiratory Exchange Ratio >1.2

49 Reference values for exercise tests (VO 2) E.g. Jones N.L. Am Rev Respir Dis ,700-8 Age and Gender (ht and wt) Mostly USA Nearly all on cycle Small numbers (50) Mixed active and sedentary See Cooper for combined equations

50 Why did they stop? Identification of a ventilatory or cardiac limit to exercise Ventilatory VE max > 80% VE max predicted (MVV) Ventilatoryreserve (VE max pred-ve max) < 11 L/min VT > 50-70% of VC Breathing frequency > 50 min PaCO 2 rise Cardiovascular Chest pain High heart rate (220-age) Low Oxygen pulse Low AT

51 Interpretation Algorithmic (Wasserman) Determined by VO 2 peak and AT Can be computerised Analytical Examination of data Pattern recognition Fixed point comparison (VO L/min, VE 30 L/min)

52 Patterns of exercise abnormality VO 2 PEAK AT VD/VT SaO 2 O 2 pulse VO 2 /HR VE/VO 2 HRR Cardiac Disease (may be limited by chest pain) Low Low Normal Normal Low High Nil Pulmonary vascular disease Low Low High Low Low High Nil Airway Obstruction Low High or absent High Normal Normal High High Interstitial Lung Disease Low High or absent High Low Normal High (High Bf and low VT) High Chest Wall Restriction Low High or absent Normal Normal/low Normal Normal (High Bf and low VT High Poor effort Low High or Absent Normal Normal (or high) Normal Normal High

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