Significance of the nitroglycerin-flicker fusion response in normal subjects and patients with cardiovascular disease.

The Krasno-Ivy nitroglycerin-flicker fusion test was carried out in normal persons, and in patients with arterial hypertension and/or coronary disease. A positive test was obtained more often in patients with cardiovascular abnormalities than in normal individuals. In the former group the frequency of negative results and the inconstancy of response to multiple tests indicate the unrelia-bility of this procedure for "the early detection of heart disease tendency." No correlation could be demonstrated between the results of the flicker fusion test, the Master twvo step or the cold pressor test. The evidence does not support the, alleged clinical usefulness of the nitroglycerin-flicker fusion test. T HE flicker fusioIi threshold (FFT) refers to that frequency of successive flashes of light at which the light stimulus appears to be continuous in intensity or free from flicker. It has been alleged that the flicker fusion threshold of a normal subject is rarely less than 2400 flashes per minute or 40 per second as measured by the flicker photometer of Krasno and Ivy .' Ill other words, successive flashes below this critical level should appeal as a flickering light wvheln observed b)y a normal individual according to a prescribeel technic. These authors, furthermore, havte reported that the flicker fusion threshold is lowler than normal or impaired ill patients with a definite hypertension or anemia and improves when these conditions respond to therapeutic ineas-ures. They have devised a nitroglycerin-flicker test which involves the (letermination of the flicker fusion threshold before and at twvo minute intervals after the sublingual administration of nitroglycerin (0.4 mg.). They report that nitroglycerin impaired the threshold ill normal subjects; whereas, in almost all patients with hypertension or corotnary disease under their observation, nitroglycerin improved the flicker fusion threshold. Krasno and Ivy ill-terpret these observations as follows: (1) Im-359 pairmeint of the flicker fusion threshold in normal subjects after nitroglycerin is due to ,vasodilation and resultant passive hyperemia of the visual mechanism. (2) Improvement of the threshold after nitroglycerin is evidence of the relief of vasospasm and conisequent active hyperemia. Iii their opinion the nitroglyceriii-flicker test may prove to be a valuable aid in (a) the detection of anginia pectoris and coronary occlusion where the evidence is equivocal, (b) the ideittification of potential candidates for hypertension and coronary disease, and (c) the evaluation of vasodilator properties of various drugs. The value of any test capable of detecting latent coronary disease without subjecting the …