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LEA Physiology 2025

Chapter 5: Arterial Physiology

  • Authors: Ann Marie Kupinski, Andrew Stalter, Caryn Souza Rorabaugh, Tara Bartholomay.

Objectives

  • List hemodynamic forces on the arterial system.

  • Describe relationship between pressure, flow, and resistance.

  • Identify factors controlling peripheral blood flow.

  • Define physiological changes with arterial disease.

  • Identify different waveforms in arterial flow.

Terms to Know

Kinetic and Potential Energy

  • Kinetic Energy: Energy of work or motion represented partly by blood flow velocity.

  • Potential Energy: Stored/resting energy; in the vascular system, it relates to intravascular pressure.

    • Sources include blood pressure and arterial wall capacitance.

Other Key Terms

  • Inertia: Tendency of a body to remain in its state of motion or rest.

  • Viscosity: Fluid's resistance to flow; higher viscosity leads to higher resistance (e.g. polycythemia vera).

  • Laminar Flow: Flow where liquid moves in smooth parallel layers.

Blood Circulation Overview

  • Right atrium receives deoxygenated blood from the superior venacava (from brain and arms) and inferior vena cava (from lower body).

  • Blood flows through pulmonary artery to pick up oxygen before returning to the left atrium.

Fluid Energy Components

Total Fluid Energy

  • Made up of:

    • Kinetic Energy: Energy of work or motion.

    • Potential Energy: Supplied by heart contraction.

  • Gravitational Potential Energy: Related to the force of gravity.

  • Hydrostatic Pressure: Related to blood column weight within vessels.

  • Bernoulli Principle: Total energy remains constant if the fluid flows without velocity change, barring frictional losses.

Bernoulli Principle

  • Key Concepts:

    • As fluid velocity increases, pressure decreases (inverse relationship).

    • Fluids at higher velocities exert less pressure.

    • Used to explain energy balance in fluid motion and vascular dynamics.

Viscosity and Inertia

Viscosity

  • Increases with elevated hematocrit, affecting flow rates.

Inertia

  • Causes energy losses where blood changes direction or velocity, especially due to stenosis (narrowing).

Velocity and Flow

Definitions

  • Velocity: Rate of movement (cm/s).

  • Volume Flow: Volume moved/time (ml/min).

Relationship with Cross-Sectional Area

  • Smaller cross-sectional areas result in higher velocities (e.g., aorta vs capillaries).

Flow Dynamics in Vessels

  • Total vascular cross-sectional area affects blood flow velocity.

  • Decreased area due to stenosis increases flow velocity to maintain volume.

Poiseuille’s Law

  • Describes steady laminar flow of fluids and pressure/flow relationships emphasizing radius as a critical factor affecting resistance.

    • Formula: Q = (πr^4(P))/(8nl)

    • Small radius changes significantly impact resistance and flow rates.

Resistance to Flow

Key Concepts

  • Resistance analogous to electrical resistance (Ohm's Law).

    • Resistance (R) = Pressure Drop (P) / Flow (Q)

  • Changes in blood vessel radius primarily affect resistance.

Arrangement of Vessels

Series Arrangement

  • Total resistance = sum of individual resistances.

Parallel Arrangement

  • Reciprocal of total resistance = sum of reciprocals of individual resistances, reducing overall resistance in networks.

Peripheral Resistance Types

Low Resistance

  • Occurs with vasodilation; typically found in organs (e.g., kidneys, liver).

High Resistance

  • Seen in resting peripheral arteries (e.g., extremities), often with retrograde flow.

Flow Dynamics

  • Laminar Flow: Streamlined flow with uniform velocity.

  • Turbulent Flow: Irregular motion requiring greater pressure leading to energy losses.

  • Reynolds Number: Calculates flow behavior; turbulence proportionate to velocity, density, radius and inversely to viscosity.

Hydraulic Filtering

  • Converts pulsatile heart output to steady capillary flow for effective nutrient exchange.

  • Compliance: Changes with age; higher in youth leads to better blood handling.

Arterial Waveforms

  • Interpretation of waveforms such as triphasic, biphasic, and monophasic is vital for assessing arterial health.

  • Dampened Waveform: Indicates stenosis, altered velocities.

Peripheral Artery Disease (PAD)

  • Characterized by plaque and impaired blood flow; critical stenosis begins when cross-sectional area is reduced significantly.

  • Flow dynamics change in diseased vessels, affecting hemodynamics.

Effects of Exercise on Flow

  • Exercise increases blood flow significantly; patients with arterial disease may experience claudication due to insufficient adaptation.

Summary of Key Points

  • Understanding hemodynamics provides insights into arterial conditions, influencing Doppler ultrasound interpretation and clinical approaches.