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Medical Research Society 13. THE ROLE OF LOSS O F LUNG RECOIL I N CHRONIC AIRFLOW OBSTRUCTION D. G. LEAVER, ANNETATTERSFIELD and N. B. PFUDE Department of Medicine, Royal Postgraduate Medical School, London, W.12 Airflow obstruction in chronic pulmonary disease is usually attributed to ‘intrinsic’ disease of the airways. In emphysema, however, there is severe loss of lung recoil pressure which could directly cause considerable airflow obstruction, since recoil pressure has been shown to be an important determinant of airways conductance (Butler et al., 1960, Journal of Clinical Investigation, 39, 524) and of maximum expiratory flow rates (Mead et al., 1967, Journal of Applied Physiology, 22, 95; Pride et al., 1967, Journal of Applied Physiology, 23, 646). In twenty patients with chronic bronchitis and reduction of the 1 s forced expiratory volume we have measured total airways conductance (at an inspiratory flow of 0-5 l/s), lung recoil pressure and maximum expiratory flow rates over a wide range of lung volumes. In seven of the twenty patients the observed reduction in conductance could be accounted for entirely by the loss of lung recoil pressure; in all twenty patients, however, maximum expiratory flow was reduced more than could be accounted for by the changes in lung recoil pressure. In contrast, in five patients whose disability was mainly due to ‘intrinsic’ disease of the airways, conductance at functional residual capacity was greatly reduced and changed very little as lung recoil pressure increased. In these patients the reduction in maximum expiratory flow rates was not as marked as would be anticipated from the severe reduction in conductance at low flows. The relation of these two functional patterns to the ‘emphysematous’ and ‘bronchial‘ types of airways obstruction (Burrows et al., 1966, Lancet, I, 830) was discussed. 1 3 ~ preferential distribution of the bolus to the lower lobes if inspired slowly because the lower lobes are more compliant than the upper as a result of the gradient of pleural pressure. With increasing inspiratory flow rate more of the inspired bolus is distributed to the upper lobes. ‘Cross-over’, where ventilation per alveolus in the upper and lower lobes is equal after a given inspired volume, occurs at approximately 2 l/s when the inspired volume is 400 ml. Above this flow rate there is a preferential distribution of gas to the upper lobes. This cross-over is a direct result of the volume-dependence of resistance, the more expanded upper airways having a lower resistance. The computations are made for a wide range of physiological and anatomical parameters, so that the influence of various factors, such as overall lung volumes, airway resistance, and pressure-volume relations, on the distribution of inspired gas, can be explored. The flow rate at which ‘cross-over’ occurs is influenced to some extent by all parameters but is most sensitive to change in the lung volume at which the bolus of gas is injected. The results are in good agreement with recent experiments on the distribution s f gas using boluses of radioactive xenon and external counters at the chest wall. It is stressed that the theory can readily be extended to calculate the distribution of ventilation in situations other than uniform inspiration, for example during cyclic breathing at high frequency (for example during exercise), if the appropriate anatomical and physiological variables for expiration can be determined. 15. THE EFFECT O F HALOTHANE ON VENTILATORY RESPONSES MEDIATED BY THE PERIPHERAL CHEMORECEPTORS J. G. WHITWAM,J. DUFFIN and A. TRISCOTT Department of Anaesthetics, The Royal Postgraduate Medical School, London, W .12 (Introduced by C. M. Oakley) The peripheral chemoreceptors provide a continuing drive to normal respiration which can be detected by 14. A NON-LINEAR THEORY OF THE observing a transient fall in ventilation following two DISTRlBUTION OF PULMONARY breaths of 100% oxygen (Dejours, 1963, Annals of the VENTILATION New York Academy of Sciences, 109, 682). In addiT. J. PEDLEY, M. F. SUDLOW and J. MILIC-EMILI tion, the peripheral chemoreceptors contribute a fast The Physiological Flow Studies Unit, Imperial College, component to the ventilatory response to carbon London, S. W.7 dioxide during normoxia, but it is eliminated by The theory for the distribution of ventilation in a hyperoxia (Bernards et al., 1966, Respiratory Phytwo-compartment model of the lung is developed, siology, 1, 390; Cunningham et al., 1965, Journal of neglecting inertial forces but allowing resistance and Physiology, 179,68~.)This component can be detected compliance to vary with lung volume and resistance by observing a difference in the timing of the ventilato vary with flow rate, all in a non-linear manner. tory response to Pa,co2, raised by a rapid intravenous Numerical solutions to the basic equation are found injection of sodium bicarbonate, between air and for the distribution of inspired gas between the upper oxygen breathing. Twelve female patients premedicated with atropine and lower lobes of erect human lungs. Results are presented to show how a bolus of (0.6 mg) and pethidine (75-100 mg), were anaesthelabelled gas inspired at various volumes and flow tized with thiopentone (3-4 mg/kg), intubated using rates would be distributed. The theory predicts the suxamethonium chloride (50-75 mg) after spraying