An orthostatic load of 1/4G and 1/3G differentially activates vascular and cardiac components of cardiopulmonary reflexes

Abstract

Introduction – Orthostatic load of varying degree affects cardiopulmonary reflexes and baroreflex. Cardiopulmonary reflexes initiate even before the baroreflex activation in response to volume changes in body caused by changed G load. The cardiopulmonary reflex has two effector components i.e., Heart and Vasculature. Lower body negative pressure (LBNP) is a non-invasive tool used to study the physiological effects of varying G loads. Aim & Objective - The study was designed to explore the varying orthostatic load triggering cardiopulmonary reflexes. Material & Methods - 33 healthy human volunteers were recruited. Continuous heart rate and blood pressure – Systolic, diastolic and mean blood pressure (measured as the area under curve of the pulse waveform) were recorded. Orthostatic load of 1/4G and 1/3G were chosen in order to prevent fall in blood pressure and baroreflex activation. The measurements were taken in supine resting state (0 mmHg), at -10 mmHg (1/4 G) and -15 mmHg (1/3G). Heart rate variability was calculated from the Lead II ECG with the help of Labchart Pro 8 ® software. Peripheral vascular resistance (PVR) was estimated indirectly from arterial pressure waveform. Statistical analysis was performed using Graphpad Prism. Results – At 1/4G of orthostatic load (-10 mmHg of oscillatory LBNP) activation of vascular component (PVR) of cardiopulmonary reflex was found with no changes in the cardiac component (HRV). At 1/3G of orthostatic load (-15 mmHg of oscillatory LBNP), there were activation of the cardiac component (LF:HRV, LF/HF:HRV) associated with further increase in the vascular component (PVR). Conclusion – Data suggests that 1/3G and 1/4G orthostatic load applied using LBNP despite no change in blood pressure, causes differential activation of vasculature and cardiac effector components of cardiopulmonary reflexes No funding received for carrying out the study This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.