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Human baroreflex regulation plays an important role in stabilising blood pressure. Though we have several indices to quantify cardiovagal responses, sympathetic baroreflex gain remains difficult to assess. We investigated how the recently validated pressure recovery time (PRT) and sympathetic baroreflex gain (SBRS) derived from the Valsalva maneuver was influenced by acute blood loss. 26 healthy blood donors were included in the study (age 35±15years; 20 men). SBRS was derived from the blood pressure drop (SAP delta) and pressure recovery time during the Valsalva maneuver. Besides we calculated cardiovagal baroreflex parameters, the Valsalva ratio (VR) and a simplified baroreflex gain (VBRS). We compared these parameters before and after the withdrawal of 350-400ml blood. The baseline systolic blood pressure was the same before and after blood donation (123±17 vs 126±23mm Hg, NS). The minimum systolic pressure (SAP min) during phase III was significantly lower, and the SAP delta significantly greater after blood withdrawal (SAP min 83±24mm Hg vs 69±27mm Hg, p<0.001; SAP delta 41±15mm Hg vs 57±16mm Hg, p<0.001). PRT increased significantly (from 2.0 to 3.6s, p<0.006). SBRS did not change between the study conditions (24±12mm Hg/s vs 22±10mm Hg/s, NS), nor did the VR and the
In conclusion, after the acute loss of approximately 350-400ml blood there was a greater blood pressure drop in phase II and III and a slower blood pressure recovery in phase IV of the Valsalva maneuver that resulted in an unchanged SBRS.
Gottsegen György National Institute of Cardiology, Hungary.
This article was published in the following journal.
Name: Autonomic neuroscience : basic & clinical
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A response by the BARORECEPTORS to increased BLOOD PRESSURE. Increased pressure stretches BLOOD VESSELS which activates the baroreceptors in the vessel walls. The net response of the CENTRAL NERVOUS SYSTEM is a reduction of central sympathetic outflow. This reduces blood pressure both by decreasing peripheral VASCULAR RESISTANCE and by lowering CARDIAC OUTPUT. Because the baroreceptors are tonically active, the baroreflex can compensate rapidly for both increases and decreases in blood pressure.
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PRESSURE of the BLOOD on the ARTERIES and other BLOOD VESSELS.
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