Abstract
The difficulty of obtaining satisfactory records of the depth and rate of respiration in untrained human subjects is known to all who have attempted to make these measurements. Even training, though it results in regular, quiet breathing, undoubtedly alters the normal, unrecorded respiratory movements. These difficulties are much magnified when dealing with patients who are suffering from embarrassed breathing, such as occurs in pneumonia. The presence of a mask or mouthpiece may alter the depth and rate of breathing profoundly. More important may be the changes brought on by the subject's consciousness of the fact that his respirations are being studied.
To circumvent these sources of error we have constructed a body plethysmograph, by means of which it is possible to record the respiratory movements of a patient sick with pneumonia without further embarrassment to his breathing, and, indeed, without his knowledge that his respirations are being observed. The apparatus consists of an air-tight box in which the subject's body is enclosed, his head projecting out of it through a rubber dam, which makes a tight seal about the neck.
The plethysmograph is not in principle different from ones used in animal experimentation. Since the adaptation of such an apparatus to the human subject required certain changes to meet the needs of comfort and convenience, particularly of temperature regulation, we have thought it worth while to publish a more or less detailed description of it.
The subject is transferred from his bed on to a hair mattress 152 cm. long by 79 cm. wide and 8 cm. thick. This mattress is countersunk into a solid platform which forms the base of the plethysmograph. A pillow is placed under the subject's knees. His neck lies in a semicircular yoke, and his head on an adjustable head rest.
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