The Effect of Exercise on Left to Right Shunt of Blood Through a Ventricular Septal Defect

Abstract

The effect of exercise on the pulmonary circulation has been studied in normal patients, but hemodynamic changes which occur with exercise in patients with acyanotic congenital heart disease associated with a left to right shunt have not been adequately studied. A left to right intracardiac shunt is well shown by dye dilution techniques.1 The contour of the curve obtained on the degree of shunting, and a measure of this is the ratio of built-up (BT) : disappearance time (DT). When this is above 1 :2-2.1 a left to right shunt is present, as shown by Broadbent et al,1 and this has also been our experience. As the degree of shunting increases, the BT :DT ratio decreases. The ratio is often expressed DT :BT, when this will increase with shunting. For qualitative clinical purposes the former representation has proven simpler and will be used. Changes in left to right shunt with exercise were studied by comparing dye dilution curves done on patients at rest and when exercising. The results were interpreted in relation to pressures recorded during cardiac catheterization. Method The tests were done with the patient in the supine position. A direct writing oximeter, a modification of the Millikan ear oximeter3 was fitted on the left ear, and 100 per cent oxygen administered for 5 minutes before the injection of dye. Evans Blue dye (T 1824) in dosage of 0.2 mgrn. per Kg. body weight was injected rapidly into a right antecubital vein.4 Care was taken to avoid any constriction above the site of injection. The patient exercised in the recumbent position by moving a pair of roller skates up and down inclined wooden ramps for a minimum of 4 minutes. The slope of the ramps and the weights attached to the skates were varied to suit the strength of the patient. The same amount of dye was again injected during the period of exercise. The amount of work done varied widely, depending on the strength of the patient, but averaged 1.7 ft. lbs./sec. (range from 1.2-2.4). A normal dye dilution curve is demonstrated by Figure 1, and a typical left to right shunt by Figure 2.