Abstract
The superficial and total blood flows of the forearm and hand were studied by the use of 4 different methods. Over 100 experiments were performed on 15 healthy adults, including 2 women. Each experiment was preceded by a rest of 15 to 30 minutes, and equally lengthy periods of control observation. The experiments lasted from 1 to 3 hours.
The plethysmograph indicates that a deep breath causes a fall in forearm volume of from 5 to 10 cc. The shrinkage begins near the end of inspiration, and reaches a maximum in from 15 to 30 seconds. Recovery is slower but complete.
The fall in volume may be analyzed further by the discontinuous blood flow method of Hewlett and Zwaluwenberg. 1 While the hand and part of the forearm are in the plethysmograph, the venous outflow is obstructed suddenly by abruptly raising to 70 or 80 mm. Hg. the pressure within a small cuff placed just centrad to the plethysmograph. The resultant changes in forearm volume indicate the rate of inflow of blood through the still open arteries. Although this method of measuring is discontinuous, it has the advantage of indicating the total blood flow through the forearm.
This method shows that on deep inspiration the blood flow begins to slow in mid-inspiration; reaches its maximum at the end of inspiration, and disappears rapidly. A record obtained in mid-expiration shows the flow already partly recovered. On deep inspiration, the blood flow through the forearm is stopped completely, for from 1 to 15 seconds, depending upon the rate and depth of the inspiration and the subject of the experiment. Experiments performed at every phase of the respiratory cycle indicate that the diminished flow is due to the inspiratory movement, for recovery becomes complete even when the breath is held at inspiration.
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