Why is a persons blood pressure always lots higher when standing?
Normally, upon standing there is a slight decrease in the systolic blood pressure (top number) of 5-10 mmHg and an increase in diastolic blood pressure (bottom number) of 5-10 mmHg. The explanation for this is that when you assume the upright position about 500-1000 mL of blood pools in the blood vessels in the lower extremity and abdominal cavity (splanchnic system.) This results in a rapid decrease in venous return to the heart and filling of the heart chambers. This results in a drop in cardiac output (amount of blood ejected from the heart) and blood pressure. The fall in blood pressure and decreased filling of the heart chambers provokes a compensatory reflex mediated by the central nervous system that increases sympathetic and reduces parasympathetic outflow known as the baroreflexor reflex. The sympathetic nervous system is the “fight or flight system” that results in an increase in heart rate, strength of contraction of the heart and constriction of the arteries(vasoconstrictio
