Hemodynamics

movement of the blood in the blood vessels outside the heart.

Why?Nutrients,hormones

Rule : NO GRADEINT… NO FLOW.Even the pressure was so high

• pressure gradient is the main force (main factor).

• Other Factors that regulate the flow:1- Diameter of the blood vessel:طردية Q= 2- Length of the blood vessel.عكسية3- Viscosity of the blood.عكسية

100 100

ΔP

ROhm’s law

Polycythemia,Anemia

For example: if you have a vessel of a radius of 1, and the flow is 1 … if you increase the radius to 2 (increased 100%) the flow will increase (2 ^ 4) = 16.

• The cardiac output is distributed in our bodies unequally; this depends on the tissue need of blood. When the tissue is at rest it needs less blood, when the tissue is undergoing metabolism it needs more blood. This is the function of arteries, capillaries and veins.

Differences between arteries and veins:

• Muscle thickness of the blood vessel.• Arteries (pressure reservoirs) high pressure• Veins (blood reservoirs) low pressure

%65 of the blood in our bodies is present in the

veins.

Distensibility:the capability of vessels to stretch, dilate, or swell by pressure from within.

• Veins: (more distensible 8 times than arteries) due to thinner wall than arteries.

A drop of 1-2 liters in the volume of blood inside veins will not cause a great critical effect on the venous blood pressure, whereas blood loss from arteries, even if it was not great in volume, will cause a significant fall in arterial blood pressure with a high risk of patient’s death.

Vascular Compliance (or Vascular Capacitance)

• total quantity of blood that can be stored in a given portion of the circulation for each mmHg

Veins accommodate three times the volume of blood in arteries The arterial system accommodates around 750 ml of blood , the venous system accommodates around 2750-3000 ml of blood

• A small change in the pressure inside veins significantly alters the volume of blood within it.

• - A small change in the volume of blood within arteries significantly alters the pressure inside it.

Critical Closing Pressure

• Critical closing pressure is defined as the pressure at which the vessel collapses.

• seen with increased sympathetic stimulation as it can cause severe vasoconstriction

• happens because vessels are surrounded by tissues which apply external pressure on them leading to their closure.

• The arterial critical closing pressure is normally around 20mmHg.

Physiological relations in Hemodynamics:

• 1- Pressure: (systole and diastole)The pressure in the left ventricle rises to the

maximum during systole and drops to the minimum during diastole . The maximum systolic pressure is 110-130 mmHg and the minimum pressure is 0 mmHg.

The pressure in the aorta will never drop to 0 as in the left ventricle, because before the pressure in the aorta decreases from 80 mmHg the next heart beat(systole) will occur.

• If there is no systole (heart beat) the pressure in the aorta will reduce and the patient will lose consciousness due to the lack of blood reaching the brain.

• من الدم قياسضغط ناخذ احنا جذي aorta منnot from left ventricle due to diastolyic pressure=0

• M.A.P= (average) =93 =DBP+1/ 3pulse pressure- Pulse pressure : diffrence b\w syst and DBP

What is wrong ?

Laminar flow and Turbulent flow:

• Laminar flow: (normally in our body)• fluid flows near a wall, it will have friction with that

wall.(resistance that will cause the velocity of the blood near the wall to decrease.

• The maximum velocity of the blood is found in the center of the vessel which has no friction.

You don’t hear any sound during this flow.

turbulent flow: (ATH,stenosis,…..)• squeezing this vessel (constriction), cause the

blood to flow in different directions.• You will hear sounds during this flow like

murmurs.(Anemic patients)

• What causes the tendency to develop turbulent flow?

• - Diameter of the vessel (constriction).• - Velocity of the blood: higher velocity higher

tendency, this is related to something called Reynold’s number.

• Reynold’s Number: = vpD/u > 400• measures the tendency to develop turbulent

flow. It depends on the velocity, diameter, viscosity and the density.

density viscosity

there is a possibility to develop turbulent flow

Reynold number reaches 4000 sever aortic stenosis.

Where does the maximum resistance occur?

• Arterioles• Capillaries :so there is no resistance at all• Veins : There is resistance

• The peripheral resistance is nearly to 1 (0.93), we don’t use a unit for peripheral resistance we just say it’s 1.

• pressure gradient=93• Flow (cardiac output) = volume / time = (6*1000)/60 =

100 milliliter / sec

3- Velocity :distance/time.• the bigger the surface area, the less velocity,

which is found in the capillaries for better exchange (very huge surface area). The less surface area, the higher the velocity which is found in the aorta.

4-flow:volume/time.• identical everywhere• The same amount of volume will go to all the

areas in the body; the cardiac output will go to aorta, to the large arteries, to the small arteries and arterioles. BUT the velocity is different in these areas.

Measuring Systolic and Diastolic Pressures

• directly measured by inserting a cannula into an artery and connecting a manometer to it, but this method is inconvenient and can be uncomfortable or painful to the patient.

• indirect means, usually by the auscultatory method using a sphygmomanometer.

• inflatable rubber cuff connected to an air valve and a mercury manometer (due to its high density)

• the cuff is placed at the level of the heart on the brachial artery slightly above the cubital fossa, and then the cuff is inflated.

• The cuff applies a pressure on brachial artery causing the blood flow to stop when the pressure in the cuff is higher than the pressure in the artery.

• the next step : gradually and slowly decrease the pressure in the cuff to permit the blood to flow

tracking the pulse by:

• Palpation method; feeling the pulse by pressing on the radial artery. When there is no flow there will be no pulse. The blood pressure at which the first pulse is felt is the systolic pressure. The diastolic pressure cannot be measured by palpation.

• Auscultation method; using a stethoscope • The pressure exerted by the cuff creates a turbulent flow of

blood in the artery and the pressure at which blood starts flowing (indicated by an audible sound) is the systolic pressure.

• The pressure at which the blood flow becomes laminar and inaudible is the diastolic pressure.

Korotkoff sounds

• The sounds heard during the measurement of blood pressure are called Korotkoff sounds.

• neither related to the sounds of the heart, nor related to the ejection of blood by heart, nor related to the valves.

Heart Sounds • the closure of atrioventricular valves(tricuspid

and mitral valves) creates the first heart sound (S1), closure of the semilunar valves (pulmonary and aortic valves) creates the second heart sound (S2).

• second heart sound (S2) is louder than the first heart sound(S1). because the diameters of semilunar valves are smaller than the diameters of atrioventricular valves,

Cardiac Murmur• A stenosis in the cardiac valve results in a turbulent blood

flow through the valve, which in turn creates an abnormal sound called cardiac murmur. two types of cardiac murmur:

• 1- Systolic cardiac murmur: Occurs between S1-S2 • due to aortic valve stenosis or mitral valve incompetence

results in ejection murmur, which sounds similar to “shh” / ʃ/.

• 2-The diastolic murmur Occurs between S2-S1 • due aortic valve incompetence is called rumbling murmur,

which sounds similar to “rrrrr”.

• The diastolic murmur due to mitral stenosis produces a similar sound to the ejection murmur.