As part of a comprehensive evaluation of lung function in Hong Kong Chinese children and adolescents, over a thousand healthy subjects aged 7-19 yr from seven schools were recruited for lung function testing that included spirometry and, in many cases, lung subdivision measurements. Lung function tests were performed using SensorMedics Automated Body Plethysmograph according to published standards. Of these, 551 subjects (219 males), aged 8-19 yr, had satisfactory lung subdivision indices recorded. Analysis for the values of lung subdivisions including total lung capacity (TLC), residual volume (RV), and functional residual capacity (FRC) demonstrated that standing height and sitting height were the best predictors of lung volumes. After allowing for standing height or sitting height in the regression models for lung volumes, age at examination was the second best parameter, although its inclusion into the equations contributed to less than 1% of explained variance for boys and 3% for girls. These are the first reported data in international literature on reference values for lung subdivisions in Chinese children and adolescents.

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Eight cases have been studied in which both lung function and histological morphometric data was available on divers' lungs. A correlation was found between the increase in forced vital capacity measured at routine annual medical examination and the morphometric measurement of alveoli by mean cord length. The results suggest that reduction of forced expiratory volume in one second may be due to narrowing of small airways by distention of the alveoli. Materials and methodsIn a series of necropsies on professional divers 37 cases were suitable for detailed examination of the lungs. Of these, it was possible to obtain the details of the clinical history, including lung function, in only eight. These have been used as the basis of the present study and the data, together with causes of death, are recorded in table 1. LUNG MORPHOMETRYAll the lungs were inflated through the trachea at a standard pressure of 25-30cm water from 10% formal saline using the technique described by Heard et al.4 As part of the routine necropsy protocol the fixed lungs were sliced into sections about 1-5 cm Accepted 29 September 1986 thick by the method of Kleinerman and Cowdrey.s Whole lung sections were randomly selected from each of the eight cases and laid flat. On the upper cut surface of the slice a transparent plastic sheet was laid on which was superimposed a rectangular lattice 15 x 2-5 cm, a method employed by Weibel.6 Each field was numbered consecutively and continuously over all the slices and the fields for sampling were selected by a method of random numbers. This fixed the location of the blocks which were marked on the lung tissue by inserting headless pins through the perforated corners of the squares. The blocks were paraffin wax embedded, cut at 5-7 gm, and stained with retriculin.The histological preparations were examined through a Vickers binocular microscope, fitted with an image splitter, that was coupled to a Cambridge Instruments model 720 Quantimet image analysis system. This gave a display of the histological image on a monitor screen and allowed the electronic image to be definitively identified by independent observation through the light microscope. An electronic pencil allowed each alveolus to be accurately outlined. The quantimet program could then resolve from the area of the individual alveoli the mean cord length. The machine was calibrated to resolve this into micrometres.