 Dr. Jalal Mohsin Uddin  D.T.C.D,  F.C.P.S (Pulmonology)

 Spirometry report interpretation is a basic step to understand aero- dynamics of human lung.  For interpretation we may go through five steps :  Step- 1 : Whether the report is interpretable ? (Is the report is correct ?)  Step-2 : Is the report suggesting normal or obstructive / restrictive disease ?

 Step- 3 : If it is obstructive or restrictive disease than measuring its severity.  Step -4 : Making comment regarding the respiratory diseases by seeing the morphology of flow volume and time volume curve (Gestalt method).  Step -5 : Measuring the changes after challenging the patient with drugs eg. Bronchodilator (salbutamol), bronchoprovocative drugs (methacholine, histamine), allergen, exercise.

 ATS acceptability criteria for FVC 1) Smooth continuous curve ( free from artifacts) 2)Good start of test Extrapolated volume < 5% of FVC or 150 ml whichever is larger and time to peak flow <120 ms 3) Good end of test Reaches plateau in 1s ( no further volume exhaled despite continuous expiratory effort Reasonable duration of effort ( => 6 second).

 At the beginning of the data interpretation, please look at the FEV1 and FVC ratio (FEV1/FVC).  If (FEV1/FVC) < 70% than it is a obstructive disease.  If (FEV1/FVC) >70% than it is normal or it may be restrictive. For removing the confusion we have to look at FVC %. If it is <70%, than it can be consider as restrictive pattern of spirometry tracing. If FVC is normal than it can be consider as normal spirometry tracing.

ObstructiveFEV1 %RestrictiveFVC % Mild70 – 99Mild Moderate Moderate Severe Severe Very severe<34Very severe<34

 We can asses the type of respiratory diseases by seeing the morphology of various type of curves ( Flow volume curve, time volume curve ).  This is a typical flow volume curve of a obstructive air way disease. The later part of the flow volume curve is concave upwards.( <<). eg. COPD, asthma. <<

 This is a typical flow volume curve of a restrictive type of lung disease. It is a small flow volume curve, there is steep rise and steep fall of curve. eg. ILD, fibrosis etc.

 The 1 st flow volume curve showing truncated expiratory loop indicating variable intrathoracic upper airway obstruction eg. Tracheal tumor.  2 nd flow volume curve showing truncated inspiratory loop indicating extrathoracic upper air way obstruction eg. Laryngeal growth.

 In this flow volume curve both inspiratory loop and expiratory loop are truncated indicating fixed upper airway obstruction eg. Tracheal stenosis.

Observed%predictedPost-dilator Spirometry FVC(l) FEV 1 (l) FEV 1 / FVC(%) FEF (L/s) MVV(L/min) Volumes TLC(L) RV/TLC(%) D LCO (mL/min per mm Hg) * 1.03* 53* 0.4* 51* 9.37* 75* 10* A case of obstructive disease can be challenged with Broncho dilator (salbutamol), It is called revesibility test. If there is increase of FEV1 200 ml and 12% than the test Is +ve and patient is suffering from bronchial asthma. But In the present picture FEV1 has increased 220ml but it is only 2%, so here test is negative. So it may be a case of COPD.

 Patient having confusing history of asthma (cough variant, exercise induced or drug induced asthma) with normal spirometry tracing can be diagnosed by broncho provocation test. Here methacholine challenge test is done which is positive.

 Practicing spirometry in patient

 36y, F, Wt 183lb (83kg), Ht64in. (162 cm), BMI 31.6 kg/m 2 normal Observe d %predicte d Post- dilator Spirometry FVC(L) FEV 1 (L) FEV 1 /FVC (%) FEF (L/s) MVV(L/min)

 Does the patient have ventilatory limitation?  Do the test values support your impression?  Is the configuration of the flow-volume curve normal?

 There is no ventilatory limitation.  The test values are all normal.  Over most of the vital capacity, flow decreases in a relatively gradual, steady fashion. However, at 2.4 L of expired volume, there is a “knee” in the curve after which flow decreases rapidly. This is a normal variant that is often found in nonsmokers, especially women. This curve shape is due to the point of critical narrowing staying in the trachea until the “knee” is reached This is called a tracheal plateau.

76y, M, Wt 170lb (77kg), Ht 66 in. (168 cm), BMI 27.3 kg/m 2 SpirometryObserv ed %predicte d FVC(L) FEV 1 (L) FEV 1 /FVC (%) FEF (L/s) MVV(L/min) * 1.33* 55* 0.7* 30*

 Questions  What is your estimate of the degree of limitation?  What is causing the limitation?  Is there anything unusual about the test data?  Is there anything unusual about the flow- volume curve?  Is there any other test that you would order?

 Answers  There is a moderate degree of expiratory flow limitation.  On the basis of the test data, the limitation is obstructive.  The decrease in the MVV to 27% predicted is greater than might be expected from an FEV 1 of 47% predicted. This finding should suggest poor patient effort, a neuromuscular disease, or a major airway lesion.

 There is a plateau in upper 50% of the FVC that is abnormal. It is characteristics of a major airway lesion.  The expiratory curve and the corresponding inspiratory loop are reproduced in the figure as the solid lines. The nearly equal reduction in maximal expiratory and inspiratory flows points indicating fixed airway lesion.

 The patient was found to have Wegener’s granulomatosis. Bronchoscopy showed narrowing of both main stem bronchi and of several lobar bronchi. Ordinarily, single obstructing lesions below the carina cannot be detected. However, because both main stem bronchi were involved, a characteristic abnormality in the flow- volume loop could be detected.  With the patient under general anesthesia, the left main stem bronchus and bronchus intermedius were dilated, and stents were placed in both. The right main stem bronchus was also dilated. The dashed flow-volume loop in the figure above was obtained 1 month after this procedure, and although the flows are not normal, they are much improved.

67y, F, Wt 198lb (90kg), Ht 64 in. (162 cm), BMI 34.3 kg/m 2 Observe%predicted Spirometry FVC(L) FEV 1 (L) FEV 1 /FVC (%) FEF (L/s) MVV(L/min) * 1.68*

 Comments and Questions  The patient is a nonsmoker and complains of shortness of breath at times while hurrying on a level surface. On occasion she has noted some wheezing.  Does the patient have ventilatory limitation? If so, on what basis?  Is there anything unusual about the patient?  Is there any additional study you would want?

 The patient has mild ventilatory limitation. This appears to be nonspecific, with equal reduction in the FEV 1 and FVC and thus a normal ratio. There is possible mild restrictive defect, as there is initial steep slope of the flow-volume curve. In addition, however, the increased curvature of the flow- volume curve raises the possibility of a mild airway obstruction. Thus, the limitation is likely due to a mixed restrictive-obstructive process.  The patient is heavy for her height; the BMI is 34.3kg/m 2. this may contribute to the reduced FVC.

 Due to history of wheezing, a methacholine challenge study is performed. The figure shows a markedly positive result of methacholine challenge with a 41% decrease in the FEV 1. Despite this, the FEV 1 /FVC ratio stayed in the high-normal range.  In summary, this is another case of asthma in an obese subject in whom the FEV 1 /FVC ratio was high-normal on presentation.

 Wish you a healthy and happy life