Effect of hypovolemia on efficacy of reflex maintenance of blood pressure on orthostatic challenge.

Blood volume is an important determinant of the efficacy of the negative feedback mechanisms that maintain blood pressure. However, its effect on time profile and magnitude of the responses remain unstudied.,To study the effect of mild hypovolemia on time profiles and magnitude of changes in blood pressure and heart rate in healthy subjects before and after blood donation.,Fifty six healthy volunteer donors who signed up for blood donation were recruited (age 35 ± 7 years; weight 75 ± 9 Kg). Baseline beat to beat blood pressure and Lead II ECG was recorded for 5 min followed by orthostatic challenge for 3 min before and after blood donation.,The donation of 450 ml of blood did not lead to any changes in the resting systolic, diastolic or mean blood pressure. However, there was a significant decrease in pulse pressure after blood donation along with an increase in the heart rate. During orthostatic challenge, after blood donation there was a greater fall in systolic, diastolic, mean and pulse pressure along with a greater increase in heart rate as compared to before the blood donation. The latency to response and the total time to recovery of blood pressure and heart rate increased significantly after blood donation.,Maintenance of blood pressure after orthostatic challenge is not compromised after mild hypovolemia produced by donation of 450 ml of blood. However, mild hypovolemia results in increase in latency of response and is accompanied with larger magnitude of fall in blood pressure during orthostatic challenge.