Abstract:
In man, breathing in and breathing out are independent skills determined by separate factors and affected differently by various diseases so the three components of the lung function ventilation, perfusion and diffusion are in a balance during normal health. Any imbalance will result in a reduction in effective transfer of gases. Due to the developments of past quarter century, different techniques have been invented for measuring the main subdivision of lungs functions.
To obtain high rate of precision, the test must not only be safe but also relatively free of discomfort for subjects. Test results should not be influenced by subject’s cooperation or observer’s bias. Spirometric tests of ventilatory capacity have been extensively used to give a knowledge of over all ventilatory capacity in subjects of different heights, all age groups and both obtained from healthy subjects with patients suffering from respiratory insufficiency.
Before puberty the lung functions of the two sexes are identical but after puberty the pulmonary functions diverge, as anatomical and physiological changes are taking palace. The vital capacity in males is greater as compared to females due to more muscular strength. Since the lungs of adult men contain less collagen tissue than the women, the airways being less supported, forced expiratory volume in one second is lesser in former than the latter (cotes, 1978). Predicted normal spirometric values have been shown to have significant ethnic variation (Williams, etal.,1978).
Gould (1869), observed that vital capacity in blacks was lesser as compared to white Americans of the same height and age. No satisfactory explanation has been offered for racial variation of lungs volumes. Elebute and pearse (1971), postulated the possibility of racial difference in thoracic cage size or shape. However, the magnitude of difference appears to vary with the respective levels of habitual activity (Lawther et al.,1983). The crossectional studies provide an accurate of the mean rate change in FEV1 and FEV18 with age, wereas in longitudinal studies the indices show a constant decline as a result of reduction in strength of respiratory muscles, increase in stiffness of the thoracic cage or may be augmented by the effect of smoking or recurrent episodes of bronchitis (Cotes, 1978) The standing height is believed to be a good quide to the size of the lungs. However, It is not a reproducible measurement. Body weight provides an alternate index of the lung capacities. Similar consideration apply for the body surface area (Hall et al.,1979; Leech et al .,1983).
