Blood Pressure in animals

Blood Pressure in animals

Blood Pressure in animals is the pressure exerted by the circulating blood against any unit area of the blood vessel wall. Stephen Hales (1730) demonstrated the existence of pressure in the blood vessels. Average pressure in the aorta is 98 mm Hg and the mean pressure in veins is 3 mm Hg and this pressure difference (98-3 = 95) moves the through the systemic vessels. This pressure difference between the aorta and veins is the perfusion pressure.

BP is highest in aorta (98 mm Hg), moderate in capillaries and lowest in the vena cava (3 mm Hg). This pressure gradient favours the blood flow through the blood vessels.

During ventricular systole the arteries show the highest pressure, referred to as systolic pressure. It is due to increased blood volume and distension of the arterial walls. During ventricular diastole, blood continues to flow out of the aorta into small arteries, the volume of blood in the large arteries decreases, the arteries become less distended and blood exert less pressure in the arteries. The minimum pressure reached in the blood vessels before each new ventricular ejection is referred to as diastolic pressure.

Pulse pressure = the difference between systolic and diastolic pressure

The pulse pressure increases as the blood flows from aorta to distal arteries and then becomes less and less when the blood moves towards periphery. It disappears in the arterioles and capillaries.

• Systolic pressure: Indicates the total kinetic energy imparted to the blood by the heart.
• Diastolic pressure: Reflects the state of peripheral vessels and load on vascular wall.
• Pulse pressure: Ventricular output and measure the variations of kinetic energy of heart.
• Mean pressure is the average pressure in a blood vessel over a given period of time. This represents potential energy that draws blood through the systemic circulation.

This formula is useful to find out mean pressure in major arteries distal to aorta but not in aorta because the pattern of arterial pressure pulsation change as the pulse moves away from the heart. The pressure pulses are more triangular in large arteries not in aorta.

Arterial BP is always expressed in mm Hg whereas capillary and venous pressure can be expressed as mm H₂O.

Normal BP in animals