[Cardioinhibitory reflex provoked by stimulation of carotid sinus in normal subjects and those with cardiovascular disease].

The normal range and the reproducibility of the cardioinhibitory carotid sinus reflex were studied in 288 apparently healthy subjects of different ages (aged from 17 to 84 yrs., 156 males, 132 females). In each subject we chose the longest RR interval as an activation index of the reflex obtained by carotid sinus massage; its mean value increased slightly with advancing age. In the were 1, 5, 2, 5, 3, 3 sec. respectively, with a 99% confidence limit. No sex difference was found. We studied also a group of 105 patients (aged from 39 to 82 yrs., 67 males, 38 females) with various types of cardiovascular disorders, without a previous history of spontaneous syncope. Abnormal maximum RR values were found in 18 of them (17%). This percentage was significantly higher than in normals (2%). In 11 patients (10%) the carotid sinus stimulation evoked a syncopal attack. It seems therefore that a statistically abnormal carotid sinus hypersensitivity can occur in a substantial number of cardiovascular patients without necessarily leading to spontaneous syncopal attacks. Finally the reproducibility of the cardioinhibitory reflex was tested in 42 patients with maximum RR interval values ranging from normal to extremely abnormal. In each subject a significant correlation (r = 0.79) was found between the maximum RR interval values tested in two occasions at intervals ranging from 1 hour to 3 months; besides a concordance in normal or abnormal result was present in 93% of the cases.