The effects of acute blood loss on blood pressure recovery from the Valsalva maneuver

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 ± 15 years; 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 350-400 ml blood. The baseline systolic blood pressure was the same before and after blood donation (123 ± 17 vs 126 ± 23 mm 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 ± 24 mm Hg vs 69 ± 27 mm Hg, p < 0.001; SAP delta 41 ± 15 mm Hg vs 57 ± 16 mm Hg, p < 0.001). PRT increased significantly (from 2.0 to 3.6 s, p < 0.006). SBRS did not change between the study conditions (24 ± 12 mm Hg/s vs 22 ± 10 mm Hg/s, NS), nor did the VR and the VBRS: In conclusion, after the acute loss of approximately 350-400 ml 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.