Interpretation of Spirometry: Selection of Predicted Values and Defining Abnormality.

Spirometry is the most frequently performed investigation to evaluate pulmonary function. It provides clinically useful information on the mechanical properties of the lung and the thoracic cage and aids in taking management-related decisions in a wide spectrum of diseases and disorders. Few measurements in medicine are so dependent on factors related to equipment, operator and the patient. Good spirometry requires quality assured measurements and a systematic approach to interpretation. Standard guidelines on the technical aspects of equipment and their calibration as well as the test procedure have been developed and revised from time-to-time. Strict compliance with standardisation guidelines ensures quality control. Interpretation of spirometry data is based only on two basic measurements — the forced vital capacity (FVC) and the forced expiratory volume in 1 second (FEV1) and their ratio, FEV1/FVC. A meaningful and clinically useful interpretation of the measured data requires a systematic approach and consideration of several important issues. Central to interpretation is the understanding of the development and application of prediction equations. Selection of prediction equations that are appropriate for the ethnic origin of the patient is vital to avoid erroneous interpretation. Defining abnormal values is a debatable but critical aspect of spirometry. A statistically valid definition of the lower limits of normal has been advocated as the better method over the more commonly used approach of defining abnormality as a fixed percentage of the predicted value. Spirometry rarely provides a specific diagnosis. Examination of the flow-volume curve and the measured data provides information to define patterns of ventilatory impairment. Spirometry must be interpreted in conjunction with clinical information including results of other investigations.

Prediction Equations for Spirometry in Adults from Northern India.

Background. Most of the Indian studies on prediction equations for spirometry in adults are several decades old and may have lost their utility as these were carried out with equipment and standardisation protocols that have since changed. Their validity is further questionable as the lung health of the population is likely to have changed over time. Objective. To develop prediction equations for spirometry in adults of north Indian origin using the 2005 American Thoracic Society/European Respiratory Society (ATS/ERS) recommendations on standardisation. Methods. Normal healthy non-smoker subjects, both males and females, aged 18 years and above underwent spirometry using a non-heated Fleisch Pneumotach spirometer calibrated daily. The dataset was randomly divided into training (70%) and test (30%) sets and the former was used to develop the equations. These were validated on the test data set. Prediction equations were developed separately for males and females for forced vital capacity (FVC), forced expiratory volume in first second (FEV1), FEV1/FVC ratio, and instantaneous expiratory flow rates using multiple linear regression procedure with different transformations of dependent and/or independent variables to achieve the best-fitting models for the data. The equations were compared with the previous ones developed in the same population in the 1960s. Results. In all, 685 (489 males, 196 females) subjects performed spirometry that was technically acceptable and repeatable. All the spirometry parameters were significantly higher among males except the FEV1/FVC ratio that was significantly higher in females. Overall, age had a negative relationship with the spirometry parameters while height was positively correlated with each, except for the FEV1/FVC ratio that was related only to age. Weight was included in the models for FVC, forced expiratory flow (FEF75) and FEV1/FVC ratio in males, but its contribution was very small. Standard errors of estimate were provided to enable calculation of the lower limits of normal and standardised residuals for these parameters. The equations were found to be valid on the test dataset, and therefore, may be extended to general population. Comparison with the 1960s equations revealed lack of good agreement, and substantially higher predicted FVC with the current equations, especially in the forty-years-plus age group, in both males and females. Even in the age group upto 40 years, the level of agreement was clinically not acceptable. Conclusions. Validated prediction equations have been developed for spirometry variables in adults of north Indian origin using the current ATS/ERS spirometry standardisation recommendations. The equations suggest an improvement in the lung health of the population over time in the middle-aged and the elderly. These equations should address a long-felt unmet need and enable a more appropriate evaluation of spirometry data in different chest diseases in Indian subjects.

Regression equations for spirometry in children aged 6 to 17 years in Delhi region.

Background. Most of the studies carried out in India to develop regression equations for spirometry in children are now several years-to-decades old and had used equipment and measurement protocols that have since changed. Prediction equations using the current standardisation protocols for spirometry are not available. The lung health of the population may have changed too. Objective. To develop regression equations for spirometry for children aged 6 to 17 years of north Indian origin in Delhi region. Methods. School children of north Indian origin, as determined by mother tongue and parentage, aged 6 to 17 years were screened by a health questionnaire and physical examination and those found “normal” underwent spirometry according to the standardised procedure recommended by the American Thoracic Society/ European Respiratory Society (ATS/ERS) task force in 2005. Pearson’s correlation analysis was carried out to identify the predictor variables for spirometric parameters. Prediction equations were developed using the multiple linear regression procedure. The independent variables were entered in sequence of height, age and weight. R2, adjusted R2 and R2 change, standard errors of the estimate (SEE), and estimates of regression coefficients were obtained and the goodness of fit was examined. Results. Data was obtained in 365 boys and 305 girls. Forced vital capacity (FVC), forced expiratory volume in one second(FEV1), peak expiratory flow rate (PEFR), forced expiratory flow rate at 50% and 75% exhalation of vial capacity (F50 and F75) and mean forced expiratory flow rate over the middle 50% of the vital capacity (F25-75) showed moderate to strong correlations with age, height and weight in both boys and girls. In both genders, the equations explained very high variability of FVC, FEV1 and PEFR as shown by the R2 values. The explained variability for flow rates was lesser, with that for F75 being the least. Conclusions. Regression equations for spirometry variables for children of north Indian origin in Delhi region have been developed. These represent the first such effort from India after the publication of the ATS/ERS task force 2005 guidelines on standardisation of spirometry.

A PHOTOMETRIC STUDY OF MAXILLOFACIAL NORMALS IN 14~15 YEAR-OLD KOREAN

Apoptosis of Peripheral Blood Mononuclear Cells in Different Ages of Normal Children

PURPOSE: To survive in an ecological environment, an individual must develop immunity to various antigens. Therefore, populations of peripheral blood mononuclear cells (PBMC) in humans change continuously with growth. The object of this study is to evaluate the apoptosis of peripheral blood mononuclear cells (PBMC) in normal children of different ages. METHODS: PBMC were isolated from the study groups. Ten cord blood samples of normal babies, 10 blood samples of normal children each from 4 different age groups (0-1, 2-5, 6-10, 11-15 year- old and adult), and 20 from normal adults were included in this study. After 24 and 48 hrs incubation in RPMI1640 media containing 10% fetal calf serum, cells were stained with Annexin V and PI and then analyzed with FACScan flowcytometer. RESULTS: Cord blood mononuclear cells showed the lowest percentage of apoptosis compared to other age groups. PBMC isolated from the 0-1 year-old normal children showed the highest percentage of apoptosis, and the percentage of apoptosis decreased with increase of age. After the age of 10, the percentage of PBMC apoptosis was the same as that of adults. CONCLUSION: The differences in the percentage of PBMC apoptosis with different age groups might be from immunologically different state of the hosts with different age. This result could be a useful reference data for the study of apoptosis in pediatric disease in the future.

Age-related prevalence of antibodies to infective-larvae of Wuchereria bancrofit in normal individuals from a filaria-endemic region.

Antibody isotypic levels (IgM, IgE and IgG subclasses) to infective larvae (L3) of Wuchereria bancrofti were measured in 104 normal individuals from a filaria-endemic region in Orissa. The titres of antibodies were considerably higher in adults (n = 25, 25·1 ± 3·8 year) than in children (n = 52, 7·1 ± 2·1 year). Young children (n = 14) less than four years were seronegative to all isotypes other than IgM, the sero-conversion to which was achieved in the children (n=15) by the age of 7·5±1·2 years. The prevalence of other isotypes increased with age and reached a maximum in early adulthood (18·6 ± 1·6 years), which persisted in older adults (> 30 years). However, the increase in IgG3 prevalence with age was less marked. IgG2 was detected only after 10 years of age. Compared to the high prevalence (100%) of IgM, IgE, IgG1, and IgG2, in adults. IgG3 and IgG4 prevalences were low, 35% and 28% respectively. IgA level to L3 antigen was found to be extremely low even in adults. These data indicate that the prevalence of L3 antibodies was different for different isotypes and the acquisition of antibody response essentially followed an age dependent pattern.