Lecture 7-Structure and function of the Cardiovascular System (Part 2)

What is one way that influences cardiac output?

blood volume

How does an increase in blood volume lead to an increase in cardiac output?”

• ↑ Blood Volume
  → ↑ Venous Return
  → ↑ Preload
  → ↑ Stroke Volume
  → ↑ Cardiac Output4

Any ↑ or ↓ in blood volume will…

change stroke volume

Venous vs Arterial System

Arteries / Arterioles- Move blood away from the heart under high pressure

• Pressure reservoir

• High pressure

• Less stretch (low compliance)

Veins / Venules-store blood and return it to the heart

• Volume reservoir

• Low pressure (~3–4 mmHg)

• Highly stretchable (high compliance)

• Hold most of the blood

Pressure Gradient

a. What is a “pressure gradient”?

a. what does it drive?

b. give us exactly how it works…

a. It’s just a difference in pressure between two places.

b. It drives blood flow, including venous return (blood coming back to the heart).

b. Overall blood flow through the whole circulation is driven by:

• High arterial pressure (aorta ~120 mmHg) → low pressure at the right atrium (~3 mmHg)

Capillaries

a. where are they found?

b. how are they structurally?

c. how is fluid movement?

a. sit between arterioles and venules and are where exchange occurs

b. Capillaries are porous, not rigid

c.. Fluid movement depends on pressure inside vs outside vessel

Heart Failure

how it happens?

• Blood backs up

• ↑ capillary pressure

• Fluid leaks into tissue

• Gravity → swelling in feet

• Can also cause organ swelling

Osmotic Pressure

a. what does it do?

b. depends on what?

c. used clinically for what?

a. Pulls fluid into vasculature (blood vessels) and away from the tissues.

b. Depends on solute concentration (Na⁺, proteins)

• More solute (Na⁺/proteins) → stronger pull → higher osmotic pressure

c. Used clinically to manage fluid balance

We talk about blood flow redistribution in what 2 situations?

1. cold exposure

2. exercise

Blood Flow Redistribution

Cold Exposure

• Vasoconstriction in fingers/toes

• Blood redirected to core

Blood Flow Redistribution

Exercise

• Blood redirected from gut → muscles, skin, heart

• Cardiac output increases

Blood Flow Redistribution

constants

• Heart always gets 4% of blood flow

• Brain flow is constant ≈ 750 mL/min

What type of control is used in the Regulation of Blood Flood?

Extrinsic and Intrinsic Control

Regulation of Blood Flow

Regulation acts like a… 

 dimmer switch, not on/off

Regulation of Blood Flow

Extrinsic Control

• Sympathetic

  • Vasoconstriction

  • ↑ Pressure

• Parasympathetic

  • Vasodilation

  • ↓ Pressure

• Hormones

  • Epinephrine ↑ HR & force

Heart Rate Response to Exercise

1. Initial HR increase

   • Removal of parasympathetic (vagal) tone

2. Further increase

   • ↑ Sympathetic tone

3. High intensity

   • Epinephrine release

4. Recovery

   • Parasympathetic tone returns

Heart Rate Response to Exercise

Faster recovery

 healthier parasympathetic system

How does heart rate changes during exercise in someone whose heart is denervated (like after a heart transplant or certain procedures)?

• No neural control

• HR depends on epinephrine only

• Slow HR increase

• Slow recovery

define cardiac remodeling

the heart physically changes its size/shape/wall thickness over time in response to different stressors.

Cardiac Remodeling

what are the different stressors?

1. Exercise (Physiologic)

2. Hypertension (Pathologic)

3. Dilated Cardiomyopathy

Cardiac Remodeling

Exercise (Physiologic)

• Bigger chamber

• Same wall thickness

  • ↑ Stroke volume

  • ↓ Resting HR

Cardiac Remodeling

Hypertension (Pathologic)

• Thick walls (hypertrophy)

  • Poor oxygen delivery

  • Risk of ischemia & MI (myocardial infarction)

Cardiac Remodeling

Dilated Cardiomyopathy

• Thin walls

  • Weak contraction

  • ↓ Ejection fraction (30–40%)

What do you call the natural, built-in (intrinsic) mechanism of the heart?

Frank–Starling Mechanism

Frank–Starling Mechanism

how it works?

• ↑ Preload → ↑ Stretch → ↑ Force

• Stretch improves:

  • Actin–myosin overlap

  • Calcium entry

    • Calcium ↑ = Force ↑

• Effective up to ~160 bpm

what is the Ejection Fraction (EF)?

• % of blood ejected from ventricle

• Normal resting EF: 50–70%

• Max with exercise: 80–85%

• Never 100%

Heart Failure Symptoms

• Fatigue

• Shortness of breath

• Swollen feet

Explain Cardiac Cycle (Pressure–Volume Loop)….

Systole

• Isovolumetric contraction

• Ejection (rapid → reduced)

Diastole

• Isovolumetric relaxation

• Filling (rapid → reduced)

Cardiac Cycle (Pressure–Volume Loop)

Key Volumes

• EDV (End-Diastolic Volume) = max ventricular volume

• ESV (End-Systolic Volume) = blood left after contraction

• SV (Stroke Volume) = EDV − ESV

Normal SV ≈

• 70 mL

Electrical Control of Heart Rate

• SA node intrinsic rate: 70–80 bpm

  • heart’s natural pacemaker

• Parasympathetic

  • ↓ excitability

  • Slows HR

• Sympathetic

  • ↑ excitability

  • Faster depolarization

  • ↑ HR

Force–Frequency Relationship

a. main pattern?

b. why it happens?

c. applies to who?

a. ↑ firing frequency → ↑ force

b. Due to calcium accumulation

c. Applies to heart & skeletal muscle

Inotropic Effects

• Positive inotrope → ↑ contraction strength

• Negative inotrope → ↓ contraction strength

• Many cardiac drugs act here

What are Blood Pressure Essentials?

• MAP

• CO

What sets blood pressure?

MAP = CO × TPR

• MAP = mean arterial pressure (average pressure in arteries)

• CO = cardiac output (how much blood the heart pumps per minute)

• TPR = total peripheral resistance (how “tight/narrow” the arterioles are)

What sets cardiac output?

CO = HR × SV

• HR = heart rate

• SV = stroke volume

What is considered an BP emergency?

Dropping diastolic BP

Blood Pressure during excercise?

• Systolic BP ↑

• Diastolic BP stays ~same

• TPR ↓ to balance ↑ CO

Explain Kidney & Blood Pressure Control…

• Kidneys control blood volume fastest

• RAAS

  • Na⁺ + water retention

  • ↑ BP

• ADH (Vasopressin)

  • Vasoconstriction

  • ↓ urine

ACE Inhibitors

• Block compensation - RAAS

• ↑ bleeding occurs, more dangerous