Significance of the Oximetric Rebreath Test as a Pulmonary Function Test : In Pulmonary Tuberculosis.

Abstract

It is a recent trend that pulmonary functions are studied by the ventilation function, alveolar function and pulmonary circulation. When a venous catheterization is used, fine details of the pulmonary function can be obtained. This procedure test, however, is not very suitable for severaly ill patients because of its complicated manipulation and its load on the patients.The Oximetric Rebreath Test (ORT) originated in our clinic, has advantages over other tests that it is technically simple. Also, the test can cath even a relatively slight disturbance of the pulmonary function probably of oxygen intake without any discomfort to the patients. However, the nature of this method has not yet been fully clarified. According to Mito and Saji, the ORT and the vital capacity appear to have a tendency to correlate with eath other in cases of pulmonary tuberculosis, but hardly so in other pulmonary diseases. From this stand point, the significance of the ORT as a pulmonary function test is not yet clear. The author, therefore, attempted to study the correlation between abnormal ORT values and pulmonary functional disturbances found by the spirogram, venous catheterization etc. by the combined use of these tests and to make clear the essential significance of the abnormal ORT values in the pulmonary function test in general.Methods and Subjects : 1) The ORT is done, after application of the Ear-Oximeter to a patient's ear lobe, by having the patient make repeated breathing of the air in a bag of 5 to 6 liters in volume. At the point that arterial O2 saturation begins to drop, the O2 content of the air in the bag is measured by means of the Haldane or Scholander Gas Analyser. This value (O2 vol%) is the ORT value. The grade of disturbance is determined in accordance with the criteria proposed by Saji who had revised somewhat the Mito's criteria. In the paper, however, the ORT value is given in terms of ter partial pressure instead of the volume percent.2) Test for ventilations : For this purpose the Aika-Benedict type respirometor was used, and for the measurement of residual gas volume an apparatus of the Keio University type was used. The expired gas was analysed by the Van Slyke-Neill's apparatus.3) Test for arterial blood gas : Blood samples were taken from the cubital artery. Blood gas analysis was done for O2 and CO2 content and capacity by the Van Slke-Neill's method and for O2 and CO2 partial pressure by a bubble balance method.4) Venous catheterization : In a fasting and resting state, a venous catheter is introduced into the pulmonaly arterial stem through the right ventricle, and the Fick's method was done, Analysis of the expired gas and blood gas was done. Analysis of the expired gas and blood gas was done by the above mentioned apparatus.5) Subjects for the tests consisted of 91 patients with pulmonary tuberculosis (73 males and 18 females) who are hospitalized in our hospital.Among these 91 cases, The ORT, spirometry and gas analysis of arterial blood were done in 51 cases, of which in 15 cases the pulmonary arterial catheterization was performed. In another 29 cases the catheterization and ORT were done. Also in a group of 11 cases the residual gas volume and the ORT were determined.Results and Conclusions 1) The correlation between the ORT and the various test : The ORT showed correlation with various tests. In the test of pulmonary capacity and ventilation it is well correlated with the % vital capacity, the % maximal breathing capacity, the % effective alveolar ventilation and the RV/TLC (residual volume/total lunge capacity) ratio. Concerning the pulmonary blood flow and the systemic arterial blood oxygen, the % of effective pulmonary blod flow, the arterial O2 partial pressure and the alveolar-arterial O2 pressure gradient are correlated well with the ORT values. [the rest omitted]