Principles Of Blood Flow

PRINCIPLES OF BLOOD FLOW

Q. 1 All of the following are important in determining blood viscosity except?
 A Hematocrit
 B Plasma protein concentration
 C Shear rate
 D Systemic arterial blood pressure

Q. 1 All of the following are important in determining blood viscosity except?
 A Hematocrit
 B Plasma protein concentration
 C Shear rate
 D Systemic arterial blood pressure

Ans. D

Explanation:

Blood is a non-Newtonian fluid, that changes viscosity with velocity of blood flow. The major determinants of blood viscosity are hematocrit, plasma protein concentration and shear rate or blood flow velocity. These effects are particularly noticeable when the particle size becomes “large” in relation to the vessel size. Red blood cell-vessel effects become measurable when the lumen diameter drops below 1 mm and become important in the microcirculation when the lumen diameter decreases to 100—200 µm.


Q. 2

The law relating distending pressure and tension in a blood vessel wall is called:

 A

Frank Starling’s law

 B

Einthoven’s law

 C

Law of Laplace

 D

Many’s law

Q. 2

The law relating distending pressure and tension in a blood vessel wall is called:

 A

Frank Starling’s law

 B

Einthoven’s law

 C

Law of Laplace

 D

Many’s law

Ans. C

Explanation:

Law of Laplace states that transluminal pressure varies inversely with vessel radius and is directly proportional to tension that develops in the vessel walls. It means the pressure pushes against the wall causing them to stretch(tension), as the size of the vessels decreases the tension in the wall decreases too.

Law of Laplace states that tension in the wall of a cylinder (T) is equal to the product of the transmural pressure (P) and the radius (r) divided by the wall thickness (w).
 
T  =Pr/w
 
Einthoven’s law The relationships of the bipolar limb leads are such that the sum of the electrical currents recorded in leads I and III equal the sum of the electric current recorded in lead II. This relationship is called Einthoven’s law,
and is expressed mathematically as:
 
Lead I + Lead III = Lead II
 
It follows that if the values for any two of the leads are known, the value for the third.
 
Frank-Starling law of the heart: which states that the ventricular output is proportional to the ventricular end-diastolic volume.
 
Ref: Principles of medical physiology, By Sabyasachi Sicar,Page 212.

Q. 3

Which one of the following is the correct statement regarding coronary food flow?

 A

Coronary blood flow is directly related to perfusion pressure and inversely related to resistance

 B

Coronary blood flow is inversely related to perfusion pressure and inversely related to resistance

 C

Coronary blood flow is directly related to perfusion pressure and also to resistance

 D

Coronary blood flow is inversely related to both pressures and resistance

Q. 3

Which one of the following is the correct statement regarding coronary food flow?

 A

Coronary blood flow is directly related to perfusion pressure and inversely related to resistance

 B

Coronary blood flow is inversely related to perfusion pressure and inversely related to resistance

 C

Coronary blood flow is directly related to perfusion pressure and also to resistance

 D

Coronary blood flow is inversely related to both pressures and resistance

Ans. A

Explanation:

A i.e. Coronary blood flow is directly related to perfusion pressure & inversely related to resistance

Factors regulating Coronary Blood Flow

Need for 02 (i.e. hypoxia) is the most important factor maintaining blood flow (by causing vasodilation) – Metabolites eg adenosine, K+, H+, CO2 causes vasodilation & increase blood flow

Nervous factors: sympathetic stimulation increases and parasympathetic stimulation decreases coronary blood flow.

– Coronary perfusion pressure is the balance between mean arterial pressure & resistance offered to blood flow in heart. The mean arterial pressure particularly in aorta plays an important role in maintaining circulation where as resistence decrease itQ.


Q. 4

Laplace’s law, all except

 A

P=T/r

 B

P = 2T/r

 C

T = WP/r

 D

T = Pr/w

Q. 4

Laplace’s law, all except

 A

P=T/r

 B

P = 2T/r

 C

T = WP/r

 D

T = Pr/w

Ans. D

Explanation:

T = Pr/w

LAW OF LAPLACE:

  • States that tension (T) in wall of a cylinder is equal to product of transmural pressure (P) & radius (r) divided by wall thickness (w).
    • I.e., T = Pr/w.



Q. 5

Poiseuille’s equation states that

 A

Blood flow is directly proportion to 2nd power of radius

 B

Blood flow is directly proportion to 4th power of radius

 C

Blood flow is inversely proportion to 2nd power of radius

 D

Blood flow is inversely proportion to 4th power of radius

Q. 5

Poiseuille’s equation states that

 A

Blood flow is directly proportion to 2nd power of radius

 B

Blood flow is directly proportion to 4th power of radius

 C

Blood flow is inversely proportion to 2nd power of radius

 D

Blood flow is inversely proportion to 4th power of radius

Ans. B

Explanation:

Blood flow is directly proportioned to 4th power of radius.

POISEUILLE’S LAW:

  • Also referred as “Hagen-Poiseille’s Law”.
  • Poiseuille’s equation states, 
    • Q = P1 – P2 * { (Π r4) / (8 η L)}
    • Q – Flow rate
    • (P1 – P2) – Pressure difference across vessel (provided P1 > P2).
    • η – Blood viscosity.
    • r – Radius.
    • L – Tube length.
  • If parameter values remains constant, 
    • Blood flow is directly proportional to 4th power of radius.
  • Resistance of vessel to blood flow can be calculated by combining Ohm’s law with Poiseuille’s equation.
    • By substituting values of Q from Poiseuille’s law in Ohm’s law.
  • Implying, resistance is mainly affected by,
    • Blood vessel radius,
    • Vasodilatation/vasoconstriction.
  • Thus ultimately, if parameter values remain constant, 
    • Resistance to blood flow is inversely proportional to 4th power of radius.


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