Pulmonary Diffusing Capacity in Mitral Valve Disease

While the pulmonary diffusing capacity is now accepted as an important test of lung function, comparatively little application of the test has been made in patients suffering from cardiac dis- orders.Bates, Boucot, and Dormer (1955) were the first to describe a simple and reliable means for estimating gaseous diffusion, using the steady state carbon monoxide technique.MacNamara, Prime, and Sinclair (1959) reported their results with this method in a series of normal subjects, a group of patients with emphysema, and also in a group of patients with chronic interstitial fibrosis.The present study was designed to assess the results of diffusing capacity in patients suffering from mitral valve disease, and to attempt to correlate these results with the severity of their mitral stenosis and the degree of pulmonary hypertension present.These patients were undergoing routine appraisal for surgical treatment and, in most, complete hemodynamic findings were available for study.As an additional measure, tests of ventilatory capacity were performed to gauge if this was impaired.In many patients with mitral stenosis there is a background of chronic bronchitis, and this by itself could interfere with the mechanics of breathing.In some of the patients in the latter part of the investigation, arterial blood gas analysis was undertaken to ascertain whether any changes in gaseous diffusion were reflected in the arterial blood.A small group of normal healthy subjects was used as controls and a further group of patients suffering from pulmonary emphysema was similarly investigated to demonstrate how severely the pulmonary diffusing capacity could be depleted. METHODS AND SUBJECTSA Godart pulmometer was used both for simplicity and convenience to estimate V.C. (vital capacity), M.V.V. (maximum voluntary ventilation), and F.E.V. (forced expiratory volume), while P.E.F.(peak expiratory flow) was measured by the Wright peak flow meter (Wright and McKerrow, 1959).Pul- monary diffusing capacity was assayed by the steady state carbon monoxide method after the method so fully and aptly described by MacNamara et al. (1959), employing a Godart diffusion test.This is a spiro- metric gas analyser system, with a 150-litre gas storage tank equipped with two latex balloons, one of which is inspiratory and the other expiratory.A spirometer and kymograph are connected to the circuit to record the patient's minute ventilation during the course of the test.The percentage of carbon monoxide is re- corded by means of an infra-red analyser.Arterial blood for gas analysis was obtained by direct puncture of the femoral artery.Percentage oxygen saturation was determined by means of a Kipp hmmoreflector, the CO2 content by a manometric Van Slyke method, the pH by a Pye pH meter with a Stadie electrode (manufactured by Cambridge) and the PC02 calculated according to the Henderson-Haselbach equation PC02 = pin mEq/-1)).Normal Controls.Seven patients free from any clinical evidence of either cardiac or respiratory disease were used as controls.The results are shown in Table I and values for the diffusing capacity (Dco) both at rest and following exercise are in close accord with those of MacNamara 741