Significance of the Oximetric Rebreath Test as a Pulmonary Function Test : In Various Cardiac and Pulmonary Diseases.

Abstract

The oximetric rebreath test (ORT) has proven to be an useful method in the physiological studies of pulmonary functions in our laboratory, since Hara and Mito originated it in 1952. The studies involving the ORT have been reported in detail by Mito and Saji.The present study was designed to recomfirm the significance of this test by comparing it with other pulmonary function tests in 103 cases of various cardiac and pulmonary diseases, such as pulmonary tuberculosis, acute pneumonia, bronchial asthma, pulmonary emphysema, pleuritis, various heart diseases and epidemic hepatitis. Especially, correlations between the ORT values and other pulmonary function values, such as ventilation volume, oxygen partial pressure in arterial blood (Pao2) and its related alveolar oxygen pressure (PAO2), were studied by performing these tests in the same patient, while they were breathing air in a resting state.Results 1. The correlation between the ORT value and arterial oxygen partial pressur : A significant negative correlation between the ORT value and the Pao2 was recognized in the total number of cases (r=-0.573, p<0.01). The details concerning different disease groups are as follows : Pneumonia : in this disease, the ORT values were from 117 to 132 mmHg. (in normal subject, below 115 mm Hg.) and the Pao2 were from 92 to 40 mmHg. The two has a highly significant negative correlation between each other (r=-0.948, p<0.01).Pulmonary tuberculosis : in this disease, the ORT values were from 110 to 135 mmHg. and the Pao2 were from 99 to 75 mmHg. The two had a significant negative correlation between each other (r=-0.809, p<0.01).Heart diseases : in these cases, the ORT values were from 114 to 126 mmHg. and the Pao2 were from 98 to 73 mmHg. The two had a significant negative correlation between each other (r=-0.656, 0.02<p<0.05).Epidemic hepatitis : in this disease, the ORT values were from 108 to 125 mmHg. and the Pao2 were from 98 to 85 mmHg. The two had a significant negative correlation between each other (r=-0.618, 0.02<p<0.05).Further studies are required in bronchial asthma, pulmonary emphysema and pleuritis, to increase the number of cases.2. The significance of the elevation of the ORT value (oxygen partial pressure in the rebreath bag) : The ORT values were higher in the group of patients who have reduced arterial oxygen partial pressures than in normal subjects.The reason for this can be explained with Bohr's oxyhemoglobin dissociation curve as follows : When an initial decrease in the Pao2 is present, an additional decrerse in the Pao2 will cause more decrease in the SaO2 than in subjects who have a normal, i.e., a higher Pao2 in the beginning, due to the nature of the curve. Since the ORT value, i.e., O2 partial pressure in the rebreath bag, is measured when the Sao2 begins to fall (actually when it falls about 4 %), subjects with the initial decrease in the Pao2 will register this fall more easily than those who have a normal Pao2 in the beginning.From the above explanation, it can be understood why the group of patients with a normal PAO2 and a normal Pao2 have low ORT values (below 115 mmHg.), and in the group of patients with functional disturbances of the lung, i.e., in the cases in which the Pao2 were reduced or in the cases where the Pao2 was close to normal but the PAO2 was elevated, the ORT values tend to be elevated. 3. [the rest omitted]