Aclient says that when the hospital checked his blood pressure after he lost a lot of blood in a work-related accident, the top number (systolic pressure) was lower than usual but the bottom number (diastolic pressure) was about the same. why is this?

When he lost a lot of blood in the accident, during his recuperation his systemic vasoconstriction maintained the diastolic pressure.

The mean arterial pressure is the average arterial pressure throughout one cardiac cycle: systole and diastole.

The cardiovascular system regulates the mean pressure through cardiac output and systemic vascular resistance. The systemic vascular resistance regulation is done through vasoconstriction and dilation.

When a wound or injury is affecting the vascular system, it leads to loss of blood. In this case, epinephrine and norepinephrine act on vascular smooth muscle cells to induce vasoconstriction of both arteries and veins.