01/20/16 Flashcards
Background of Cardiac Output
- Heart pumps blood around the body
- Left heart pumps oxygenated blood
- Right heart pumps deoxygenated blood

Anatomy of the heart

Anatomy of the heart; cartoon illustration

The Cardiac Cycle
- Molecular/electrical/physiologicaleventsthat occur from the start of one heartbeat to the start of the next heartbeat
- Consists of 2 periods:
-
Diastole:
- relaxation,heart fills with blood
- BP~80mmHg
-
Systole:
- contraction, heart ejects blood
- BP~120mmHg
Diastole
- Venous return fills atria
- AV valve opens
- ~75% blood flows directly into ventricles
-
Atrial priming
- pumps remaining 25% blood into ventricles
- AV valve closes

Systole
- Ventricles fill with blood
- Increase in pressure
- Isometric contraction
- Aortic/pulmonary valves open
- Blood ejected
- 70% fast, 30% slow
- Ventricles relax
- Aortic/pulmonary valves close

What is cardiac output?
- Cardiac output=Stroke volume * Heart Rate
- CO=SV*HR
- Stroke Volume
- Blood volume ejected by ventricles/beat
- Heart Rate
- # heart beats/min
Calculating Cardiac Output
- Cardiac output (mL/min)=Stroke volume (mL/beat)*Heart rate (beats/min)
- Average resting heart rate:
- ~70 beats/min
- Average resting stroke volume:
- ~70 mL/beat
- Cardiact output=70*70=4900 mL/min
- or ~5 L/min
- During exercise, CO increases 7 fold
Preload and Afterload
- Determinants of stroke volume
- Preload
- Tension of ventricular muscle before contraction
- Determined by left ventricular end diastolic volume/pressure (LVED/LVEP)
- Afterload
- Pressure against which ventricles pump blood
- Determined by total peripheral resistance
Excitiation-Contraction Coupling
- Generation of electrical impulses:
- Sinus node
- AV node
- Propogation of impulses:
- Internodal pathways
- Bachmann’s bundle
- AV node, Bundle of His
- Purkinje fibers
Cardiac Electrophysiology

Ion Channels Confirmational States
- Resting
- Closed, can be opened
- Activated
- Open, ions flowing
- Inactivated
- Closed, can’t be opened

Generation of Cardiac Rhythmicity
- Sinus (sinoatrial) node
- “Pacemaker region”
- Small specialized muscle
- Located in right atrium
- Controls heart rate
- Origin of spontaneous action potential

Spontaneous Action Potentials
- HCN channels
- hyperpolarization cyclic nucleotide gated
- Phase 0:
- Ca2+ enters: ICa-L
- Phase 3:
- K+ exits: IKS/IKR
- Phase 4:
- Na+ enters: If
- Ca2+ enters: ICa-T/ICa-L
- Key:
- L: long
- S: short
- T: transient
- F: funny
- KS: slow delayed rectifier
- KR: rapid delayed rectifier

Transmission of Cardiac Current
- Internodal pathways/Bachmann’s bundle
- Spread current through atria
- AV node/Bundle of His
- Electrically separate atria and ventricles
- Delays current transmission to ventricles
- Has spontaneous activity
- Ectopic pacemaker
- Purkinje Fibers
- Spreads currents through ventricles
Transmission of Cardiac Impulses

Non-spontaneous action potential
“cardiac action potential”
- Phase 0
- Na+ enters: INa
- Phase 1
- K+/Cl- exits: Ito1/Ito2
- Phase 2
- K+ exits: IKs
- Ca2+ enters: ICa-L
- Phase 3
- K+ exits: IKs/IKR/IK1
- Phase 4
- Resting membrane potential

Cardiomyocyte Contraction
- Increase [Ca2+]i through L-type Ca2+ channels
- Ca2+ spread through transverse T-tubules
- Ca2+ opens rynodine receptors on sarcoplasmic reticulum
- Calcium induced calcium release
- Ca2+ binds troponin-C
- Releases tropomyosin from actin
- Increases actin-myosin cross-bridging
Channels and Proteins in Cardiomyocyte Contraction: Illustration

Troponin and Myosin Chains in Cardiomyocyte Contraction: Illustration

Thick/Thin Filament in Cardiomyocyte Contraction: Illustration

Factors affecting Cardiac Output
- Frank-Starling Mechanism
- Autonomics
- Sympathetic nervous system
- Parasympathetic nervous system
- Renin-Angiotensin-Aldosterone System
Frank-Starling Mechanism
- “Within physiological limits, the heart pumps all the blood that it receives without allowing excessing damming of blood in the veins”
- Increase in venous return
- Cardiomyocyte contractility
- Increase stroke volume

Autonomic Regulation of Cardiac Output
- Parasympathetic Nervous System
- Decrease HR and SV
- Dominant at rest
- Sympathetic Nervous System
- Increase HR and SV
- Dominant during exercise/stress

Autonomic Nervous System: Innervation Illustration

Parasympathetic Effects
- Vagal nerves release acetylcholine
- SA and AV nodes
- Acetylcholine stimulates M2-muscarinic receptors
- Increase K+ channel opening
- Decrease sinoatrial node rhythm
- Decrease AV node transmission

Sympathetic Effects
- Sympathetic nerves release norepinephrine throughout heart
- Stimulates Beta-1-adrenergic receptors
- Increase Ca/Na channel opening
- Increase SA node rhythm
- Increase AV node transmission
- Increase force of atrial/ventricular contraction

Autonomic nervous system regulation of spontaneous action potential
- PSNS→rest
- Decrease AP frequency
- Increase phase 4 duration
- Decrease HR→Decrease CO
- SNS→excercise, stress
- Increase AP frequency
- Decrease phase 4 duration
- Increase HR→Increase CO

Baroreceptor Reflex
- Rapid, fine control of CVS
- Sensory baroreceptors
- Carotid sinus/aortic arch
- Detect BP changes
- Increase BP
- Increase PSNS activity
- Decrease CO
- Decrease BP
- Increase NS activity
- Increase CO

Renin-Angiotensin-Aldosterone System
- Decrease BP in kidney nephron macula densa
- Renin secreted into circulation
- Renin→angiotensin to angiotensin I
- Angiotensin converting enzyme (ACE)
- angiotensin-I to angiotensin-II
- Increase aldosterone
- Increase plasma volume
- Increase BP
- Increase CO
