THE HEMODYNAMICS OF THE PERIPHERAL CIRCULATION

Dr. Mariano J. Rey

1. To understand how the anatomy and circuitry of the peripheral circulation influence cardiovascular hemodynamics.

2. To learn the relationships among pressure, flow, and resistance that govern cardio vascular hemodynamics.

3. To comprehend the factors that determine arterial blood pressure.

1. Historical background
• A. Harvey - a closed circulation - De Motu Cordis (1628)
• B. Malpighi - blood through capillaries - De Pulmonibus (1661)
2. The Peripheral Circulation
• A. Functional Anatomy of Blood Vessels
• B. Cross-Sectional Area and Velocity Relations
• C. Arrangement in Series and in Parallel
3. Hemodynamics
• A. Velocity
• B. Pressure
• C. Flow
• (1) Laminar Flow
• (2) Turbulent Flow
• D. Resistance
• (1) In Series
• (2) In Parallel
4. Arterial Blood Pressure
• A. Mean Pressure
• B. Pulse Pressure
• C. Determinants of Pressure
• (1) Compliance
• (2) Resistance
• (3) Volume
• (4) 4th Power Law
For Review
Important Equations:
A. OhmÕs Law:

Q =delta P/R or R = delta P/Q or delta P = QR

delta P = Pressure difference between two ends of a vessel
R = resistance
Q = flow

B. PoiseuilleÕs Law:

Q = delta Pn r⁴/8nL or R = 8nL/nr⁴

Q = Flow
R = Resistance
n = viscosity
r = radius of vessel
L = length of vessel
P = pressure difference between two ends of a vessel

C. ReynoldsÕ Number:

N = Vdp/n V = mean velocity
d = tube diameter
p = fluid density
n = viscosity

D. LaplaceÕs Law:

(1) for blood vessels: T = Pr

(2) for cardiac chambers: T = Pr/2h

T = tension in the vessel wall (force per unit length tangential to the vessel wall)
P = tranmural pressure
r = radius of the vessel or of the cardiac chamber
h = chamber wall thickness

Define or Explain
• viscosity
• shear stress
• non-newtonian fluid

Case Studies

The case in Chapter 22 (page 41) - The Circuitry - is that of a bleeding man after an auto accident. The discussion of the case (page 147) shows how the particular circuitry of the arterial system influences the peripheral circulation. Case 1 (page 51) in Chapter 27 - Atherosclerosis - and its discussion (pages 156-157) deal with the concept of arterial compliance. Hypertension - Case 2 - in the same chapter and page, with discussion in pages 157-158 addresses the topic of blood volume and arterial compliance as determinants of blood pressure.

Computer Module
Use the A.D.A.M. Cardiovascular Module to better appreciate vascular hemodynamics. As a review, work through Section 6 - Blood Vessel Structure and Function. Then do Sections 7, 8, and 9 - Measuring Blood Pressure; Factors that Affect Blood Pressure; and Blood Pressure Regulation.

Return to the Slide List

---