There is difference between the normal adult and paediatric respiratory system with respect to the anatomical and physiological development of lung. The cross-sectional shape of the infant thorax is cylindrical and not elliptical as in adolescents or adults. Cartilaginous and extremely compliant chest wall of newborn allows necessary distortion of the infant’s thorax to travel through the birth canal. The rib cage of an infant has more horizontal alignment of the ribs compared to the oblique configuration of ribs seen in adults leading to a variation in the biomechanics. Normally, the process of inspiration is active and that of expiration is passive. This occurs as the pump handle movement is seen in the upper thorax while bucket handle movement is seen in lower thorax. With inspiration, there is pump handle movement which causes an increase in the antero-posterior diameter of thorax, while in the bucket handle movement there is an increase in the transverse diameter of the lower thorax. Movement of the ribs occur at costotransverse and the costovertebral joints. Orientation of these joints varies in the upper and lower ribs.  The transverse diameter is greater than the antero-posterior diameter giving it an ellipsoid shape with the ratio 7:5. Development of alveoli in lungs continues and is completed by 10 years of age. Most of this development occurs in 1^st 6 months of life. The number of alveoli increases with height. 

Normal chest wall mobility is important for effective lung expansion and subsequent ventilation. Respiratory evaluation is an integral part of chest physiotherapy.

Pulmonary function tests are objectively used to measure an

individual’s ability to breathe and also measures how well the lungs ventilate and exchange gas. It is used to measure forced vital capacity (FVC), Forced expiratory volume(FEV) and some other components. Spirometry is an objective measure to assess or monitor disease progression and deterioration during acute exacerbation, the efficiency of an inhaled drug or its delivery system. It is a procedure that measures the rate of change in lung volumes during forced breathing manoeuvres and is also used to determine diagnosis, prognosis and monitor and manage patients with respiratory diseases. Parameters like age, sex, environmental factors, ethnicity, prematurity, patient cooperation and effort affect the results of spirometry. To arrive at a diagnosis, the result of pft should be combined with patient information and symptoms. A Belgian study demonstrated that expert panels could reach 77% accuracy when predicting diagnosis on clinical history and pft reports alone.

There is no evidence suggesting correlation between chest expansion in adults and pulmonary function testing in healthy adults. Normative values of chest expansion in paediatrics and adults are different. This leads to different results in correlation with other interventions. Therefore, there is a need to study paediatric respiratory system differently. Normative values of chest expansion values in paediatrics were known but there’s no evidence regarding its reliability. Hence aim is to find out correlation of chest expansion with pulmonary function tests especially among young, healthy individuals.