What is normal blood pressure?

Blood pressure is a measurement of the force applied to the walls of the arteries as the heart pumps blood through the body. The pressure is determined by the force and amount of blood pumped, and the size and flexibility of the arteries. Blood pressure is continually changing depending on activity, temperature, diet, emotional state, posture, physical state, and medication use. The ventricles of heart have two states: systole (contraction) and diastole (relaxation). During diastole 

blood fills the ventricles and during systole the blood is pushed out of the heart into the arteries. The auricles contract anti-phase to the ventricles and chiefly serve to optimally fill the ventricles 

with blood. The corresponding pressure related to these states are referred to as systolic pressure and diastolic pressure The range of systolic pressure can be from 90 mm of Hg to 145mm of Hg with the average being 120 mm of Hg. The diastolic pressure typically varies from 60mm of Hg to 90 mm of Hg and the average being 80 mm of Hg.

'Normal' or 'acceptable' blood pressure varies with age, state of health and clinical situation. At birth, a typical blood pressure is 80/50 mmHg. It rises steadily throughout childhood, so that in a young adult it might be 120/80 mmHg. As we get older, blood pressure continues to rise and a rule of thumb is that normal systolic pressure is age in years + 100. Blood pressure is lower in late pregnancy and during sleep.

From this, you can see that a systolic pressure of 160mmHg for an elderly man or 90 mmHg for a pregnant woman may be quite normal. To judge whether any particular reading is too high or too low, we must compare the reading with the 'normal' for that patient.

This technique involves direct measurement of arterial pressure by placing a cannula needle in an artery (usually radial, femoral, dorsalispedis or brachial). The cannula must be connected to a sterile, fluid-filled system, which is connected to an electronic patient monitor.

The advantage of this system is that pressure is constantly monitored beat-by-beat, and a waveform (a graph of pressure against time) can be displayed.

Patients with invasive arterial monitoring require very close supervision, as there is a danger of severe bleeding if the line becomes disconnected. It is generally reserved for critically ill patients where rapid variations in blood pressure are anticipated.

There are a variety of monitors with invasive blood pressure monitoring for Trauma, critical care and operating room applications. These include single pressure, dual pressure, and multi-parameter (i.e. Pressure / temperature)

Invasive Blood Pressure monitors are pressure monitoring systems designed to acquire pressure information for display and processing. This can be used to monitor arterial, central venous, pulmonary arterial, left atrial, right atrial, femoral arterial, umbilical venous, umbilical arterial and intracranial pressures.

Usually, systolic, diastolic and mean pressures are displayed simultaneously for pulsatile waveforms (i.e. arterial and pulmonary arterial).

Some monitors also calculate and display CPP (cerebral perfusion pressure). Normally, a zero key on the front of the monitor makes pressure zeroing extremely fast and easy. Alarm limits may be set to assist the medical professional responsible for observing the patient.