The use of Ionized Gas Electric Lamps as Recorders in Measuring the Velocity of the Pulse Wave. ∗

Abstract

Bramwell 1 and his co-workers have devised an accurate method for measuring the velocity of the pulse wave, and have made valuable studies of the factors influencing it. They have shown that the two principal factors causing increased velocity are inelasticity of the arterial walls and a high diastolic blood pressure. That is, there is an organic and a functional cause for increased velocity. The greatest need for such a method is to differentiate between the two. It seems that this might be done by observing the effect on pulse wave velocity of reduction of diastolic pressure by means of drugs. No such study has been made, due to frequent accidents with the fragile instrument used. An instrument is needed which is rugged enough to be quite dependable and yet sensitive to the highest degree.

While working in the laboratory of Dr. E. P. Carter in 1924, I devised a method, as yet unpublished, for recording arterial and venous pulsations in which the string galvanometer was used as the recording instrument. A specially designed microphone, similar to that used in telephone transmitters, was placed directly over the artery so that the pulse wave caused increased pressure on the carbon granules and thus increased the current that might pass through. Fluctuations in the current caused by the pulse were recorded by photographing the oscillations of the galvanometer string, giving an accurate picture of the pulse wave. By the use of two galvanometers focused on the same strip of film, or a galvanometer with two strings, and with two microphones placed over arteries at different and measured distances from their bifurcation, it is possible to measure accurately the velocity of the pulse.