Dr. Kamla Choudhary

1) State the formula relating flow, pressure difference, and resistance.

2) What are the three determinants of resistance?

3) Which determinant of resistance is varied physiologically to alter blood flow?

4) How does variation in hematocrit influence the hemodynamic of blood flow?

Circulation Time- Time taken by blood to travel through whole circulatory system

Substances used to measure – histamine, ether, florescence dye, radioactive substance etc.

Conditions which alter the circulation time

Increase (Due to blood flow sluggish)1.- Myxedema2.- Polycythemia3.- Cardiac failure

Decrease1.- Exercise2.- Hyperthyrodism3.- Anemia 4.- Decrease PR

Cardiovascular regulatory Mechanisms

Circulatory adjustments affected by altering

Output from Heart (by pumping)

Changing diameter of blood vessels

Altering the amount of blood in Capacitance vessels

All these factors finally control the blood flow

Blood flow is regulated by Various regulatory mechanism-

A.Neural Regulatory Mechanism

B. Humoral Regulatory mechanism

Local Regulatory mechanism

Systemic Regulatory mechanism

A. Neural Regulatory Mechanism

Vasoconstriction

sympathetic innervations (noradernergic)

basal vessel tone is present

Vasodilatation

Parasympathetic innervations

Decrease vascular resistance

B.-Humoral Regulatory Mechanism

Local Regulatory mechanism Systemic Regulatory mechanism AutoregulationMyogenic theory

Metabolic theory

VasodilatorBradykininKalidenVIPANP

VasoconstrictionADHAngiotension IIEpinephrine and Norepineprine

Arterial Blood Pressure

• Pressure is force on an area

• If there is a fluid in a containerwe measure the pressure on the surface area of the container.

• That pressure is related to the number of particles that crash into that surface area per unit time

ORIGINS OF PRESSURE INTHE CIRCULATION

Four factors help generate pressure in the circulation: gravity,compliance of the vessels, viscous resistance, and inertia.

1- Gravity causes a hydrostatic pressure difference when there is a difference in height

Because gravity produces a hydrostatic pressure difference between two points whenever there is a difference in height one must always express pressures relative to some reference h level. In cardiovascular physiology, this reference—zero height—is the level of the heart.

2- Compliance Of The Vessels,

Low compliance of a vessel causes the transmural pressure to increase when the vessel blood volume is increased

Compliance: changes in pressure with vessels of different compliances.

of blood causes an axial pressure difference when there is flow

3- The viscous resistance

of the blood and vessels causes pressure to decrease when the velocity of blood flow increases

4- The inertia

For the most part, we have been assuming that the flow of blood as well as its mean linear velocity is steady,

But , blood flow in the circulation is not

steady; the heart imparts its energy in a

pulsatile manner, with each heartbeat

Therefore, v– in the aorta increases and reaches a maximum during systole and

falls off during diastole.

These changes in velocity lead to compensatory changes in intravascular pressure.

The relation between velocity and pressure reflects the conversion between two forms of energy

“fluids flow from a higher to a lower pressure”

it is more accurate to say that fluids flow from a higher to a lower total energy.

Potential Energy And The Kinetic Energy

The impact of the interconversion between these two forms of energy is

manifested by the familiar Bernoulli effect.

In a tube or a blood vessel the total energy—the sum of the kinetic energy of flow and the potential energy—is constant (Bernoulli's principle).

A1

A2

v1 v2

A1

v1Low speedLow KEHigh pressure

high speedhigh KElow pressure

Low speedLow KEHigh pressure

As fluid flows along a horizontal tube with a narrow central region, which has half the diameter of the two ends, the pressure in the central region is actually lower than the pressure at the distal end of the tube

How can the fluid paradoxically flow against the pressure gradient from the lower pressure central to the higher pressure distal region of the tube?

F low = Area X Velocity

Because the flow is the same in both portions of the tube

but the cross-sectional area in the center is lower by a factor of 4

the velocity in the central region must be 4-fold higher

• There are two types of pressure:

• Static Pressure– Pressure from the blood distending

the vessel against the vascular smooth muscle

– LaPlace: T=Pr (tension, pressure, radius)

Dynamic Pressure Pressure from the movement of particles

along the blood stream P=v2/2 (density, velocity)

v small v smallv large

p large p large

p small

According to the principle, the greater the velocity of flow in a vessel,

the lower the lateral pressure distending its walls.

When a vessel is narrowed, the velocity of flow in the narrowed portion increases and in the distending pressure decreases

Therefore, when a vessel is narrowed by a pathologic process such as an atherosclerotic plaque, the lateral pressure at the constriction is decreased and the narrowing tends to maintain itself.

Bernoulli Pressure Lowering The linear drop in fluid pressure is according to Poiseuille's law, but the constriction produces an extra drop in pressure according to the BernoulliPrinciple

The liquid column height is a measure of the fluid pressure at that point in the flow tube

The vertical tubes act as manometers.

The manometers show that the pressure is lowered at the constriction relative to what it would have been in a uniform tube.

The pressure that drives the fluid through the tube is the static fluid pressure at the bottom of the reservoir.

The resistance to flow represented by the tube causes a drop in pressure as you proceed along the tube.

Blood Pressure

The Total Pressure is the sum of the static and dynamic pressures.

This is much like Total Energy is the sum of the kinetic and potential energies.

Blood Pressure

From a practical standpoint…

THE blood pressure is what we measure if we stick a catheter into the lumen of a vessel and measure the outflow pressure.

If a cannula is inserted into an artery, the arterial pressure can be measured directly with a mercury manometer

Arterial Blood Pressure (BP) = The lateral pressure force generated by the

pumping action of the heart on the wall of aorta & arterial blood vessels per unit area.

■ Measured in (mmHg), & sometimes in (cmH2O), where 1 mmHg = 1.36 cmH2O.

■ Of 2 main components:systolic … (= max press reached) = 110-130

mmHg. (C.O& compliance of arteries)diastolic … (= min press reached) = 70-90 mmHg.

(peripheral resistance)In normal adult 120/80 mmHg.

Arterial Blood Pressure (continued)

■ Diastolic pressure is more important, because diastolic period is longer than the systolic period in the cardiac

cycle.Other components:-

■ Pulse pressure = Systolic BP – Diastolic BP. (20-50 mmHg)

■ Mean arterial pressure = Diastolic BP + 1/3 Pulse press.

In normal adult 120/80 mmHg.

DETERMINANTS OF ARTERIAL BLOODPRESSURE

Physical – Arterial Blood volume and compliance of systemPhysiological- Cardiac output (H.R X S.V) Peripheral Resistance

Blood Pressure: Blood Pressure: Generated by Ventricular ContractionGenerated by Ventricular Contraction

Formation of the blood pressure:Elasticity of Windkessel vessel

① diastolic blood pressure ② continuous blood flow in diastole ③ buffering blood pressure