Respiratory sinus arrhythmia and carotid baroreflex control of heart rate in endurance athletes and untrained controls.

The purpose of this study was to compare the magnitude of the respiratory sinus arrhythmia, an index of cardiac vagal tone, and carotid baroreflex control of heart rate in endurance-trained athletes (n = 12, aged 20 +/- 1 years, means +/- SE) and untrained control subjects (n = 12, aged 22 +/- 1 year). Average R-R interval (ECG) and its variability were determined at rest under controlled breathing conditions, and the changes in R-R interval in response to brief applications of suction (-10, -25, -40 mmHg) and pressure (10 and 30 mmHg) to the carotid sinus region of the neck were also measured. The average R-R interval at rest was greater in the athletes vs. controls (1150 +/- 45 vs. 854 +/- 44 ms, P less than 0.001), but the standard deviation of the R-R intervals was similar in the two groups (72 +/- 15 vs. 70 +/- 9 ms). The magnitude of the tachycardia in response to neck pressure was also similar in the athletes and controls. Although the heart rate responses to neck suction were not significantly different between the two groups, there was a strong trend for attenuated bradycardic responses in the athletes at the two highest stimulus levels (70 +/- 14 vs. 97 +/- 25 ms and 86 +/- 14 vs. 145 +/- 38 ms for the -25 and -40 mmHg levels, respectively, P greater than 0.1). The results of this study do not support the postulate that cardiac vagal tone is enhanced in the endurance-trained state.(ABSTRACT TRUNCATED AT 250 WORDS)