Lecture_4_-_Cardiac_Output_and_Blood_Pressure

Cardiac Output and Blood Pressure

• Presented by Dr. Peter McFawn

• Location: Room G.01 Anatomy Building

• Phone: 6488 3341

• Email: peter.mcfawn@uwa.edu.au

• Course: PHYL1001 - Physiology: How Does the Human Body Work, 2023

Lecture Outline

• Overview of circulatory system design

• Vascular compartments

• Arterial blood pressure

• Cardiac output

• Cardiac function curve

Aims I

• Compartments of the Cardiovascular System:

  • List and define the compartments

• Heart Rate (HR), Stroke Volume (SV), Cardiac Output (CO), Venous Return (VR):

  • Define each term and know typical values

• Variables affecting Cardiac Output:

  • Understand and apply the equation CO = HR x SV

• Interactions of VR and CO:

  • Explain for both the left and right heart

Aims II

• Fluid Compartments:

  • Define Total Body Water (TBW), Extracellular Fluid (ECF), Intracellular Fluid (ICF), Interstitial Fluid (IF), Plasma, and Blood

• Volume Calculations:

  • Calculate TBW, ECF, IF, and blood volume

• Circulation Types:

  • Describe systemic and pulmonary circulations; explain differences

• Cardiac Function Law:

  • Describe Frank-Starling law and exhibit the cardiac function curve

• Pressure Definitions:

  • Define systolic, diastolic, mean, and pulse pressure; know typical values

• Calculation Practices:

  • Calculate mean and pulse pressure from systolic and diastolic values

Functions of the Cardiovascular System

• Nutrient Delivery:

  • Transport of O2, Glucose, and other nutrients to tissues

• Waste Removal:

  • Elimination of CO2, Lactate, and other waste from tissues

• Transport of Metabolites:

  • Movement of substances to/from storage sites

• Transport of Regulatory Substances:

  • Delivery of hormones and antibodies to action sites

• Blood Movement:

  • Circulation of blood for nutrient transport

Fluids

• Total Body Water (TBW):

  • Comprises 60% male body weight (~50% for females)

• Fluid Compartment Breakdown:

  • ICF: inside cells (2/3 TBW)

  • ECF: outside cells (1/3 TBW)

• Extracellular Fluid (ECF) Composition:

  • Includes interstitial fluid (IF), plasma, and lymph

Blood Composition

• Definition:

  • Fluid present in blood vessels and heart chambers

• Volume Proportions:

  • 6-8% of body mass; ~5 L for a 70 kg person

  • 55% plasma, 45% cells (with PCV 0.45)

  • Components: Erythrocytes (red), Leukocytes (white), Platelets

Blood Cells Functions

• Red Blood Cells:

  • Role in gas transport

• White Blood Cells:

  • Function in immune response

• Platelets:

  • Involved in blood clotting

• Origin:

  • All cells derived from haematopoietic stem cells in bone marrow

Outline of the Circulation

• Arteries:

  • Carry blood from ventricles

• Arterioles:

  • Small arteries that regulate flow

• Microcirculation:

  • Connects arterioles to venules; includes capillaries for exchange

• Veins:

  • Collect and return blood to heart

• Key Structures:

  • Left heart, right heart, major arteries and veins, lungs

Systemic vs. Pulmonary Circulation

• Pulmonary Circulation:

  • Right side of heart; oxygenates blood in lungs

• Systemic Circulation:

  • Left side of heart; delivers oxygen to body

• Series Connection:

  • Both circulations are connected in series

Blood Composition by Circulation Type

• Oxygenation Status:

  • Systemic arteries: oxygenated

  • Systemic veins: deoxygenated

  • Pulmonary arteries: deoxygenated

  • Pulmonary veins: oxygenated

Blood Pressure Dynamics

• Key Phases:

  • Diastole: heart relaxation

  • Systole: heart contraction

• Pressure Values:

  • Diastolic pressure: 80 mmHg (lowest)

  • Systolic pressure: 120 mmHg (highest)

  • Blood pressure expressed as systolic/diastolic (e.g., 120/80 mmHg)

Advanced Blood Pressure Metrics

• Pulse Pressure:

  • Difference between systolic and diastolic (40 mmHg)

• Mean Arterial Pressure:

  • Averaged arterial pressure (90-95 mmHg)

  • Approximation: MAP = DBP + 1/3(SBP - DBP)

Pressure and Flow Relation

• Flow Dynamics:

  • Blood flows from areas of high to low pressure

• Driving Force:

  • Pressure difference between arterial and venous systems

Cardiac Output Basics

• Definition:

  • Amount of blood pumped by heart per minute (about 5 L/min at rest)

Determining Factors for Cardiac Output

• Heart Rate:

  • Number of contractions per minute (70 beats/min)

• Stroke Volume:

  • Volume of blood pumped by ventricle per contraction (70-80 ml)

• Calculation:

  • Cardiac Output = Heart Rate x Stroke Volume

Cardiac Output and Venous Return

• Equilibrium:

  • Venous return approximates 5-5.5 L/min, matching cardiac output

• Ventricular Volumes:

  • End Diastolic Volume (EDV): ~130 ml

  • End Systolic Volume (ESV): ~50 ml

  • Stroke Volume: ~80 ml

  • Ejection Fraction: ~0.65 (65%)

Series Flow Dynamics

• Principle of Continuity:

  • Inflow equals outflow (Q.in = Q.out)

• Notation:

  • Blood volume (Q)= 5 L/min

  • Blood flow (Q) = 5 L/min

Intrinsic Control of Cardiac Output

• Regulation:

  • Venous return is key to control stroke volume

Cardiac Function Curve

• Mechanism:

  • Increasing venous return boosts end diastolic volume and stretches ventricles

  • Stretch enhances pressure generation, increasing stroke volume

Frank-Starling Law

• Concept:

  • The heart pumps all blood received (within physiological limits)

• Mechanism:

  • Higher venous return stretches ventricles, leading to better force production until output matches return

Summary

• Overall Topics:

  • Anatomy of arteries, microcirculation, veins

  • Understanding systemic vs pulmonary circulation

  • Systemic arterial pressure and relevant equations

  • Key concepts of cardiac output, venous return, and blood flow equations

  • Comprehension of cardiac function curves and the Frank-Starling Law

  • Important numerical values and definitions for cardiovascular physiology