Differences in resting sympathetic nervous activity between orthostatic hypertension, conventional hypertension, and healthy individuals

Abstract

Abstract Introduction Standing places a significant hemodynamic burden on the cardiovascular system. In healthy individuals, neurohumoral reflex mechanisms, particularly the arterial baroreflex, maintain blood pressure during standing. However, in some cases, the counterregulatory response can be excessive, resulting in a condition known as orthostatic hypertension (OHT), which appears to be linked to an increased cardiovascular risk. In recent years, OHT has been recognized as an indicator for assessing the effectiveness of renal denervation. It is suggested that abnormalities in sympathetic nervous system regulation, particularly related to the renal sympathetic nerves, may play a role in influencing RDN outcomes, however, the relationship between OHT and sympathetic nerve activity remains poorly understood. This study aims to assess the differences in sympathetic nerve activity between OHT patients, conventional hypertensive(cHT) patients and healthy individuals using muscle sympathetic nerve activity (MSNA) measurements. Methods We conducted an examination of hypertensive patients undergoing drug treatment at our clinic between April 1, 2023, and June 30, 2023, to identify cases of OHT. OHT was defined as a sustained increase in systolic blood pressure ≥20 mmHg and/or diastolic blood pressure ≥10 mmHg within 3 minutes of standing. We measured MSNA in the cases for which consent was obtained. Results Among the 138 cases, 31 were diagnosed with OHT, and 7 of them consented to MSNA measurement. Of the 11 cases of cHT patients who consented, two groups were well age-matched. And it was also compared with 11 cases of healthy individuals who underwent MSNA measurement during the same period. Both of the MSNA burst frequency and burst incidence in OHT (38.4 +/- 12.2 bursts/min, 61.1 +/- 21.3 bursts/100 heartbeats) was significantly greater (p<0.05) than that in cHT (28.3 +/- 5.7 bursts/min, 44.6 +/- 11.1 bursts/100 heartbeats), and all these were significantly greater (p<0.05) than in healthy individuals (21.8 ± 7.3 bursts/min, 35.8 +/- 11.3 bursts/100 heartbeats) at rest. Conclusions OHT is associated with sympathetic hyperactivity compared to normal hypertensive patients, contributing to an increased cardiovascular risk. These results indicate that therapy for OHT in hypertensive patients would be required to prevent sympathetic augmentation.