Category Archives: 1940s

Helium Dilution Lung Volumes, 1949

Lung_Volumes_1949_Helium_Dilution

From: Meneely GR, Kaltreider NL.  The volume of the lung determined by helium dilution. Description of the method and comparison with other methords.  Journal of Clinical Investigaton, 1949 28(1): 129-139, page 130.

“The spirometer circuit is diagrammed in Figure 1.  The seven-liter cylindrical spirometer with obliterated internal dead space write the respiratory tracing on a kymograph drum. The volume of the spirometer may be read from the scale and pointer and, by transfer, from the respiratory tracing itself. The subject is connected to the circuit through a rubber mouthpiece on a three-way valve. The expired air passes vertically through a soda-lime canister for the most efficient absorption of carbon dioxide. Oxygen may be added at any desired rate through the diaphragm type flow control and meter on a tank of “medical” oxygen. A blower impels the expired air through the water bottle which contains many glass bead to break up the bubbles, and prevent disagreeable bumping due to large bubbles. Provision is made for the introduction of helium at the spirometer outlet. Part of the return flow shunts through the analytical cell and returns via the cell outlet to rejoin the return stream. The pressure differences in different segments of the circuit are small: slight negative pressure obtains between the soda-lime and blower, and positive pressure elsewhere. The soda-lime and the water bottle isolate the the blower to a degree, preventing vibration of the air column at the mouthpiece.”

Valve, Low resistance, 1946

Valve_Low_Resistance_1946

From: A low resistance valve and indicating flowmeter for respiratory measurements.  By Leslie Silverman and Robert C. Lee.  Science 1946; 103: p537.

“It can be noted that the valve flap angle is very low (20 degrees), and thus very little change in direction is necessary in permitting air to pass, once the valve begins to open.  The area of the valve flap surface is large, and hence a low pressure will exert enough force to open it.  The weight of the valve flap is offset by the counterweight.  This counterweight (4 grams) was proportioned to give a low opening pressure and yet allow an adequate amount of of positional movement in the complete valve.  The seating surface of the valve is limited to the small longitudinal braces and edges of the seat periphery.  In order to reduce the adhesive effect of the rubber membrane when wet, the seating surfaces are dusted with talcum powder.  This powder prevents the rubber membrane and Lucite seating surfaces from wetting and also helps preserve the membrane.”