behaviour are out of scope of the present review.

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2 explained about the test, a trial may be done before recording the results. The maneuver consists initially of normal tidal breathing. The subject then inhales to maximally fill the lungs. This is followed by a maximal expiratory effort and then a return to normal tidal breathing. The test can be performed in sitting or standing position with head in neutral position. Nose clips is not required, as the velum closes voluntarily during forced expiratory maneuvers, preventing losses through the nose. Value of the Forced Expiratory Vital Capacity Test The FVC test is the most important pulmonary function test (PFT) since for any given individual during expiration, there is a unique limit to the maximal flow that can be reached at any lung volume. This limit is reached with moderate expiratory efforts, and increasing the force used during expiration does not increase the flow. Once peak flow has been achieved, the rest of the curve defines the maximal flow that can be achieved at any lung volume. The FVC test is so powerful because there is a limit to maximal expiratory flow at all lung volume after 10 to 15% of FVC has been exhaled. Each individual has a unique maximal expiratory FV curve. Because this curve defines a limit to flow, the curve is highly reproducible in a given subject. Most important, maximal flow is very sensitive to the most common diseases that affect the lung. The physics and aerodynamics causing this flow-limiting behaviour are out of scope of the present review. Within-manoeuvre criteria Acceptability The criteria for acceptable curves are: Good starts: Back extrapolated volume <5% of FVC Free from artifacts- cough, early termination, sub maximal effort, leak, obstructed mouthpiece, glottis closure Satisfactory exhalation: Duration of 3 s or a plateau in the volume time curve. Between-manoeuvre criteria Reproducibility After 3 acceptable spirograms 2 largest values of FVC and FEV1 must be within 5% or 0.150L (150 ml) of each other The differences in the criteria used for acceptability and reproducibility at various age groups are detailed in table 1 2. If both these criteria are met, test session is concluded. The machine should provide a back up to the technician regarding the errors in each maneuver and reproducibility based on the ATS and ERS 2005 criteria. If not met, then testing is continued until both of criteria are met with analysis of additional acceptable spirograms or a total of 8 tests have been performed. It also depends on patient comfort and condition, whether post BD curves are required, exercise testing is done and the values we interested in: FEV1 or FVC etc. Table 1: Differences between quality criteria of school vs. Pre-school spirometry. QC criteria School age children (6-16y) Preschool children (< 6y) Start of test criteria: Back extrapolated volume (VBE) Within test criteria End of test criteria Repeatability: difference between 2 highest values of i) FVC and FEV 1 Maximal Inspiration to TLC, minimal pause. VBE 5% or 150 ml FVC, whichever is greater The FV loop should be free from artefact e.g.: Cough Leak Glottic closure that influences measurement Duration of FE: no specified duration (6s >10y; 3s <10y) End expiratory volume plateau 3 acceptable maneuvers Two largest effort of FVC & FEV1 within 150 ml/5% or within 100 ml if the FVC is <1L. Upper limit: 8 Maximal Inspiration to TLC, minimal pause. VBE 10% or 75 ml FVC, whichever is greater The FV loop should be free from artefact e.g.: Cough Leak Glottic closure that influences measurement Duration of FE: no specified duration 2 acceptable maneuvers Within 100 ml or within 10%, whichever is greater Upper limit: None?10 Vol. 2; No.1; January - March

3 How to make spirometry in kids a success? The presence of a child friendly respiratory technician is very essential. It might be hence difficult to perform these tests in adult labs without any pediatric orientation. All three parts of the maneuver should be taught and time should be spent in explaining. The parents should also be taken into confidence. Encouragement, positive reinforcement and reward increase the chances of a good effort. In case the child refuses to perform, ask parents to perform manoeuvre first. Showing enthusiasm, being a cheerleader, using body language, and observing the patient s body language are highly important to obtain good spirometry results. The use of computer aided animation program with flow and volume incentives greatly helps in getting good quality curves. We should always praise and reward them and re-book an appointment in cases of failures 6. Interpretation of spirometry Prior to attempting to interpret pulmonary function test results in physiologic terms, the quality of the measurements made should be assessed. Tests should be evaluated in terms of patient effort, reproducibility, and freedom from artifacts. Less than optimal measurements should be interpreted with caution. After establishing the quality of the measurements, the interpreter s job is first to establish whether the results are normal or abnormal. If abnormality exists, the type and degree of that abnormality needs to be established. For interpretation of results obtained by spirometry normal values for the population is required. Apart from providing idea about the abnormality and severity; reference values also help by providing an expected increase over time 3. Types of Pulmonary Dysfunction Obstruction: It implies airway narrowing during exhalation and is defined by a reduced FEV1/VC ratio <5th percentile of predicted value. Earliest change associated with airflow obstruction in small airways is thought to be a slowing in terminal portion of spirogram. This is reflected in a concave shape on FV Loop. Case 1 illustrates a typical example of obstruction with reversibility. Normal FVC Lung Volumes and diffusion capacity FEV1/FVC Low FVC Low Normal Reduced Normal Restricted Normal study Mixed Disorder Non Reversible Bronchiectasis, Bronchiolitis obliterans etc Obstruction Bronchodilator Reversibility Reversible Asthma Figure 1: Algorithm showing the approach to the interpretation of spirometry in children. The diagnostic pathway for asthma is shown in bold. Restriction: May be suspected when FVC is reduced and FEV1/VC is increased (>85 90%) and FV curve shows a convex pattern. The definitive test for restriction is the measurement of total lung capacity but that would need the measurement of lung volumes. Case 2 illustrates an example of restriction. The algorithm for diagnosis is shown in figure 1. Degree of Pulmonary Dysfunction Degree of pulmonary dysfunction must necessarily be interpreted in relation to clinical experience. Traditionally values above 80 per cent predicted for FEV 1 are commonly considered to be within the normal range, although recent ATS/ERS guidelines have used values >70% as normal. For pulmonary processes characterized as restrictive, the same limits are useful approximations of the degree of deficit using the percent of predicted value of the FVC rather than the FEV 1 to assess degree of dysfunction. When available, the per cent of predicted value for the TLC provides the best estimate of the degree of volume restriction. As per the recent ATS and ERS criteria using the FEV 1 in per cent of mean predicted value, a rough and arbitrary guide to the degree of obstructive dysfunction is as follows: normal, 70% of predicted Vol. 2; No.1; January - March

4 and above; mild dysfunction 60-79% of predicted; moderate dysfunction 60 to 69 percent of predicted; moderately severe between percent, severe between percent and very severe dysfunction, below 35 percent of predicted 3. Response to Bronchodilators A significant bronchodilator response is defined as increase in FEV 1 or FVC by 12% and 200 ml. What are the cut off s for children? It is common practice to regard 70 or 80% predicted as the Lower limit of normal (LLN). However, the true LLN, expressed as % predicted, varies considerably with age. Hence fixed percentages lead to significant misclassifications. ATS and ERS both recommend the use of 5th centile to define LLN (i.e z-scores). Recent software from the Global Lung Initiative (GLI) can be used to calculate LLN values and can be downloaded on any computer. It must be emphasized that this simplistic approach for estimating the degree of pulmonary dysfunction by any method should serve only as a rough guide. Pulmonary function measures made on each patient must be interpreted individually and should guide patient management only in conjunction with the overall assessment of clinical status. A patient whose per cent of predicted FEV 1 is 80 may have mild or even moderate obstruction if his pre disease FEV 1 was 100 to 120 per cent of predicted. Another individual with an FEV 1 of 80 % of predicted may have just relatively small lungs and be entirely normal. If this latter individual experiences a fall in FEV 1 to 59 per cent of predicted, he or she may have only mild airway obstruction. Rather than relying on a single FEV1 measure to assess severity, serial FEV1 (pre & post BD) should be obtained over time. Serial measurements would provide objective data with respect to current lung function and also determine disease progression by evaluation of change in FEV1 over time. Spirometry should be plotted graphically in a manner analogous to what is done with linear growth. Use of Spirometry Reference values The important prediction variables are the size, sex, and age of the subject. Certain races, African American and Asian, for example, require race-specific values. There are various problems with the current reference equations: based on small sample sizes, secular trends not accounted, absence of longitudinal data, dis-contiguous data (different equations are used over different ages in same patient) and changing relationship between lung function and height during adolescent growth spurt. Most reference equations used to predict normal lung function are derived from American/European subjects and may not be suitable for use in other populations. These equations led to misinterpretation of spirometry data in a significant proportion of patients and this might result in inappropriate diagnosis and/or management 7,8. Utility of Lung function in Childhood Asthma Should all children with asthma undergo a spirometry? EPR-3 guidelines suggests that children with moderate/severe persistent asthma should have their PFT monitored periodically (Evidence B). Children with mild persistent asthma should have a yearly PFT if baseline is normal. Children with intermittent asthma should have an interval PFT (when not having an exacerbation). How does spirometry ADD on to the clinical assessment in management of children with asthma? 1. Diagnosis: Reversible airway obstruction is the hallmark of diagnosis. A clear diagnosis would hence rule out mimickes like bronchiectasis, ciliary dyskinesia etc. It would also help to counsel parents regarding the diagnosis (Case 3). 2. PFT would be especially helpful in certain situations like children presenting with chronic cough who are suspected to have cough variant asthma. 3. Exercise induced bronchoconstriction (EIB): there are two groups of children (a) Child presents with exercise induced symptoms (not a known asthmatic) but unclear finding and is suspected to have exercise induced asthma (b) Children with Vol. 2; No.1; January - March

5 known asthma otherwise well controlled might have only vague exercise induced symptoms. Exercise testing in such settings could be very helpful. The American Academy of Allergy and Immunology has published a practice parameter regarding EIB. 4. Useful for assessing the degree of obstruction: based on the FEV1 values obstruction can be classified as mild, moderate, severe. 5. Useful for assessing the control: follow up PFT would help in defining control. Normal PFT is one of the goals for management of childhood asthma. What are the limitations of spirometry in children? 1. It can be done in children over the age of 6 years. The success rate increases with age upto the age of 10 years there after the success rate is around 70-80%. 2. Pre-school children (4-6y) are now found to perform spirometry well. User should be cautious regarding Differences from school children regarding the quality control criteria Correct reference standards The use of computer based animation programmes is useful. Most good equipment has flow and volume incentives. 3. Children with asthma can have normal PFT. Even children with severe asthma can have a normal pulmonary function. 4. There is a lot of discordance between the common measures of asthma control in children like clinical assessment, asthma control test, PFT and FeNo. Hence it is recommended that most of them should be used in conjunction and followed sequentially than using a single value 9. What is the utility of newer PFT modalities? In children who are uncooperative and in pre-school children modalities like impulse oscillometry and interrupter technique are useful. Impulse oscillometry is now available in India in a few centers. A detailed review on these newer modalities can be found in the ATS/ERS statement on pulmonary function testing in preschool children 10. Office Spirometry Office spirometry refers to spirometry performed in the offices (consulting rooms) of paediatricians. The manoeuvre is supervised by the doctor themselves and not usually by the technicians. An increasing number of peer-reviewed papers tend to support the role of spirometry as a diagnostic and therapeutic tool in primary care in adults and children. Nowadays, number of children with asthma is strongly on the rise, but despite this increase, recognition and diagnosis of the disease and, consequently, proper therapy is still relatively poor. Spirometry is the gold standard for assessing lung function in children with asthma, but the costs of the technician and equipment led to peak flowmeters often being used instead. Although peak expiratory flow monitoring and asthma diaries are useful tools in selected patients, there are major limitations to their widespread use in children with asthma. Portable spirometers are now available with affordable prices, software supporting display on laptops and good incentives. Good quality data suggests that after training with pediatric pulmonologists office spirometry can be reliably performed by paediatricians Training and quality control Proper training for the technician/physician who performs the test is perhaps the most important factor in ensuring good-quality spirometric testing. The largest single source of within-subject variability is improper performance of spirometry; therefore, effective training and quality assurance are vital prerequisites for successful spirometry. After adequate training, it is also important to have continual competence assessments and to review the test results carefully. Conclusions Spirometry is an important diagnostic tool in the diagnosis and follow up for children with respiratory diseases especially in children with asthma. Office Spirometry has shown to be reliable and feasible when used by primary care paediatricians but after adequate training and continued supervision. Regular reappraisal of the acquired skills of the paediatricians and technicians is the key for ensuring quality. Only under these prerequisites, office Spirometry can help Vol. 2; No.1; January - March

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