A 0.5 litre blood loss in 30 minutes will lead to which of the following changes?

Loss of 0.5 liter blood means loss of about 10% of the total blood volume. This is associated with a little change in mean aerial blood pressure. The compensatory mechanism begin to operate almost immediately. Since it has occurred over period of 30 minutes, it will give enough time for the compensatory mechanism to maintain BP near normal level. The first response would be baroreflex mechanism. Blood removal causes a fall in pressure, baroroeceptor discharge to vasomotor center will decrease. The resultant stimulation of sympathetic vasoconstrictor and cardioaccelerator fibers will cause normalization of BP and some increase in hea rate. Ref: Guyton and Hall Medical Physiology, 10th Edition, Page 7; Cardiovascular Physiology : Mosby Physiology Monograph Series, 9th Edition, Page 247-52.