Blood pressure

Blood pressure is the force of blood exerted on the inside walls of blood vessels. Blood pressure is expressed as a ratio (e.g. 190/110) The first number is the systolic pressure, or the pressure when the heart pushed blood out into the arteries. The second number is the diastolic pressure, or the pressure when the heart rests. Systemic arterial pressure is never increased during normal human activity, with the exception of gestation. Ironically, by midpregnancy, a slight decrease in diastolic pressure can be recognized. Pulmonary arterial pressure also maintains a constant level. However, vascular tone is more dependent upon sympathetic control than in the nonpregnant state, so that hypotension develops more readily and more markedly consequent to sympathetic blockade following spinal or extradural anaesthesia.