Physiological Responses of Baroreflex Sensitivity During Graded Orthostatic Stress in Healthy Young Adults

International Journal of Anatomy and Physiology | Vol. 15, No. 10, October 2026 | pp. 109–117

DOI: 10.46882/2026/IJAP/001013

Research Article

Title: Physiological Responses of Baroreflex Sensitivity During Graded Orthostatic Stress in Healthy Young Adults

Names of Authors: E. M. Lindström¹, R. A. M基础²*

Authors’ Affiliations:
¹ Department of Physiology, Karolinska Institutet, Stockholm, Sweden.
² Department of Medical Physiology, Faculty of Medicine, Alexandria University, Alexandria, Egypt.

Abstract:
Orthostatic stress triggers autonomic compensation mechanisms to maintain cerebral perfusion against gravity-induced blood pooling. This study examined changes in cardiovagal baroreflex sensitivity (BRS) during graded orthostatic stress using a lower body negative pressure (LBNP) model. Twenty-five healthy volunteers (13 males, 12 females; aged 22 ± 3 years) underwent continuous non-invasive measurement of beat-to-beat blood pressure and electrocardiography (ECG). The protocol included a 10-minute baseline period followed by graded stages of LBNP at −15, −30, and −45 mmHg, each lasting 5 minutes. Spontaneous BRS was calculated using the sequence method. At baseline, the mean BRS was 16.4 ± 2.5 ms/mmHg. Graded LBNP induced a significant, stepwise reduction in BRS, falling to 12.1 ± 1.8 ms/mmHg at −15 mmHg, 8.4 ± 1.2 ms/mmHg at −30 mmHg, and 4.2 ± 0.6 ms/mmHg at −45 mmHg (p < 0.01 vs. baseline). This decline in cardiovagal BRS correlated with a progressive shortening of the R-R interval and a rise in diastolic blood pressure, indicating a shift toward sympathetic dominance. Systolic blood pressure was stable up to −30 mmHg but fell significantly at −45 mmHg (p < 0.05), confirming a limitation in baroreflex buffering capacity during severe orthostatic challenges. These quantitative physiological profiles help clarify orthostatic tolerance thresholds, assisting in the diagnosis of clinical autonomic dysfunction and postural orthostatic tachycardia syndrome.

Keywords: Baroreflex sensitivity, Lower body negative pressure, Orthostatic stress, Blood pressure, Autonomic nervous system.

Manuscript Timeline: Received: June 19, 2026; Revised: August 14, 2026; Accepted: September 18, 2026; Published: October 18, 2026.

Citation: Lindström EM, M基础 RA. Physiological Responses of Baroreflex Sensitivity During Graded Orthostatic Stress in Healthy Young Adults. International Journal of Anatomy and Physiology. 2026; 15(10): 109–117. doi:10.46882/2026/IJAP/001013

Subscribe to read the full article: https://mail.internationalscholarsjournals.org/subscribe-to-read