Assessment of Heart Rate Baroreflex Control during Veloergometric Exercises with Different Intensities

Changes in the baroreflex control of heart rate were studied in male subjects during their aerobic veloergometric exercises, using the phase synchronization index (PSI) of the mean arterial pressure (MAP) and heart rate (HR) oscillations in the frequency range of baroreflex waves (from 0.06 to 0.12 Hz). The protocol of tests included continuous recordings of blood pressure (by the photocompensation method) and ECG in volunteers (young men), with the load intensity specified individually for each subject in reference to his anaerobic threshold (AT). It has been shown in the test with a stepwise change in the load power, at a relatively moderate load (60% AT) PSI did not change compared with the value at rest, but significantly decreased when the load was increased up to 80% AT. To assess the time of the PSI, which can characterize the dynamics in the baroreflex resetting, changes caused by variations in the load we used the test with sinusoidally varying power (the mean value was 50% AT, the amplitude was 30% AT, and the power modulation period varied from 1000 to 100 s), MAP, HR and PSI values were calculated for successive 4-min intervals with 3-min overlapping. Whereas under this test, the PSI modulation, due to load power variations, almost disappeared as the period decreased from 1000 to 500 s, but the MAP and HR modulation was preserved until the 250-s period. Thus, the phase synchronization of MAP and HR oscillations at frequencies of baroreflex waves decreases during intensive aerobic exercise, and the pattern of its changes due to load variations are characterized by a relatively slow temporal dynamics.