THE NATURE OF THE CARDIOPNEUMATIC CHANGE IN THE LUNG GAS VOLUME

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1. The cardiopneumatic volume change in the lung (IP) and that in the body (EP) were measured separately by using a dual plethysmographic method. An averaging technique was adopted for cancelling noises arising in-and outside of the plethysmographs.
2. Inspiratory gas flow of 2 to 9ml was observed at the cardiac systole, and almost the same amount of volume change was observed in the body.
3. There were considerable individual variations in IP and EP, but the time relation between those curves and ECG was rather constant among different individuals.
4. The pulsations of the chest and abdominal walls were also measured simultaneously with IP and EP. They showed an inward movement at the systole, but the commencement of its downward movement occurred earlier by about 50 msec than the change of EP.
5. The cardiopneumatic change in the airflow velocity was measured through a pneumotachograph, and the output was converted into a volume change through an electronic integrator. A close resemblance was seen between the integrated patterns and those of IP and EP.
6. The amplitude of IP, EP and the chest wall pulsation increased sigmoidally with the inflation of the lung. On the other hand, when the airway was obstructed, the pulsations of IP and EP decreased while those of the chest wall showed a slight increase.
7. From the observations mentioned above the following conclusion was derived. When the heart contracts, the thoracic and abdominal walls move inward, and at the same time the blood volume in the thorax is reduced. From the time relation of both changes, however, it seems to be clear that in the normal lung the former change is not caused by the negative pressure generated by the latter change but caused directly by the heart or deformation of pericardium. The origin of the cardiopneumatic change, i. e. IP and EP, therefore, may be ascribed to the difference of the above two volume changes.