A Rubber-Opposed Haemodromograph Used to Measure Reflux in Aortic Insufficiency.

Abstract

The measurement of blood flow throughout the cardiac cycle has been accomplished by use of instruments of rather low efficiency due to their heavy construction and the use of more sensitive instruments has been restricted by the difficulties attending their use. We have attempted to construct a simple instrument for use in studying reflux. The lever of the aortic haemodromograph is of fine aluminum wire, the fulcrum a water-tight strip of rubber dam fixed between 2 metal plates. An oval aluminum vane, 6×8 mm., fixed at one end of the lever projects into the aorta at right angles to the direction of flow; the connection is made air-tight by an oval shoe and threaded washer (Fig. 1). The length from vane to fulcrum is 2 cm., from fulcrum to the strand of rubber used to damp the lever is 5 cm., and a fine brass wire projects 3 cm. above this, its shadow registering on the moving film. The haemodromograph for the carotid is incorporated in the side of a brass tube, 4.5 mm. in diameter, which is introduced between cut ends of the vessel. The lever is damped 5 mm. from its fulcrum, the vane extends 4 mm. into the blood stream and the fine wire extends 3.5 cm. from the fulcrum. The calibration of the apparatus, by measuring deflection produced by known rates of constant flow, is theoretically simple and accurate. In practice with our rather crude instruments we have found such calibration misleading, as the deflection is not constant from day to day, and small wisps of fibrin deposited on the vane produce a marked deviation. At present it can be used only for studying the shape of the curve of rate of flow. The instruments used have a vibration frequency of 50-80 per second; decrement per beat is from 20-30%. The sensitivity and decrement can be varied by varying the tension of the elastic strand. The relationship between deflection of the lever and rate of flow is not linear. With increasing velocity the sensibility of the instrument for a given increment of speed is increased.