Impaired parasympathetic responses in patients after myocardial infarction.

To assess whether vagal and sympathetic responses are impaired 3 months after myocardial infarction, 27 patients, 15 age-matched control subjects and 13 young normal subjects underwent physiologic stress tests. In patients, facial immersion in water at 25 degrees and 0 degrees C provoked less slowing of heart rate than in age-matched control subjects. Young normal persons responded with the greatest reduction in heart rate. Response to facial immersion decreased linearly with age in normal subjects (Y = -0.97X+86). Isometric handgrip or cold pressor test elicited brisk increases in blood pressure in almost all patients, but the vagal response to facial immersion correlated poorly with such pressor responses. Thus, in the patients studied 3 months after myocardial infarction, the parasympathetic response to facial immersion was significantly impaired whereas sympathetic pressor responses remained intact.