Cardiovascular Physiology Flashcards
CO
(Cardiac Output), L/min [CO = HR x SV]
Volume of blood pumped from each ventricle per minute
Avg at rest: 5L/min
SA Node
(Sinoatrial), 1st step in Impulse Conduction System
- Primary Pacemaker
- Intrinsic Rate: 60-100bpm
- Sends AP to AV Node via Bachman’s and Internodal Bundles
(0. 4sec) - P wave on EKG
*Cardiac Cycle electrical event: slow channel with AV Node
Impulse Conduction System
SA Node* AV Node* Bundle of His Bundle Branches Purkinje Fibers*
*All muscle cells have potential to conduct an impulse
AV Node
(Atrioventricular), 2nd step in Impulse Conduction System
-Secondary Pacemaker
-Intrinsic Rate: 40-60bpm
-Sends AP to Bundle of His (0.11sec - slower for
ventricular filling)
-Delay following P wave on EKG
*Cardiac Cycle electrical event: Slow channel with SA Node
Bundle of His
3rd step in Impulse Conduction System
-Sends AP to Bundle Branches via interventricular septum
HR
(Heart Rate), bpm
Number of cardiac cycles/beats per minute
Avg at rest: 72bpm
- Stronger myocardium & sympathetic drive
- -> lower resting HR
SV
(Stroke Volume), mL/beat [EDV - ESV = SV]
Volume of blood ejected by each ventricle per cycle/beat
Avg at rest: 70mL/beat
3 Physiologic Controls:
Preload
Contractility
Afterload
EF
(Ejection Fraction), % [EF = (SV / EDV) x 100]
Percentage of blood ejected by each ventricle per cycle/beat
-indicator of pump efficiency
-% decline: ^HR and VO2 = heart works harder to deliver same amt of O2
Avg at rest: 55-65%
Critical point: <20%
CI
(Cardiac Index) [CO / Body SA]
Indicator of pump function in clinical units
Avg at rest: 2.8 - 4.2
Cardiac Innervation
Modulation of HR and contractility
- Sensors
- Afferent pathways (Vagus & Glossopharyngeal N)
- Integration center (Medulla/pons)
- Efferent pathways (Symp vs Parasymp)
- Receptors (Myocardium)
Cardiac Innervation:
Efferent Pathways
Sympathetic Parasympathetic
-Cardiac N -Vagus N
-Ventricular myocardium -Atrial myocardium
-Adrenergic (Epi/Norepi) -Cholin / Musc (AcH)
-AMPING: -DAMPENING
Inc HR / AV conduxn / Dec HR / AV conduxn /
Force contraxn Force contraxn
Sensors of Cardiac Innervation
- Baroreceptors - pressure
- Chemoreceptors - Dec O2 / Inc CO2 or H+
- Stretch receptors - venous return
Baroreceptors
Pressure sensors in aortic arch + carotid sinus
Chemoreceptors
Sensors in aortic arch and carotid body that detect decrease in [O2] and increase in [CO2 and H+]
Stretch Receptors
Sensors that detect venous return in junction of great veins and atria
Bundle Branches
4th step of Impulse Conduction System
=Send AP down interventricular septum to Purkinje Fibers in
subendocardium
Purkinje Fibers
5th step of Impulse Conduction System
- Tertiary Pacemaker
- FAST cell to cell AP transmission
- Intrinsic Rate: 20-40bmp
- Synchronous contraction + wringing action
*Cardiac Cycle electrical event: Fast channel
Adrenergic Receptors
Cardiac N
Myocardial receptors of the Sympathetic Pathway
-mediated by epi/norepinephrine
Examples: Beta-1 & 2, Alpha-1
Cholinergic Receptors
(Muscarinic) - Vagal N
Myocardial receptors of the Parasympathetic Pathway
-mediated by ACH
Chronotropic
HR
Dromotropic
AV Conduction Speed
Inotropic
Atrial Contraction
Cardiac Cycle
(Heart Beat)
sequence of simultaneous electrical (depol / repol) and mechanical (systole / diastole) events
Electrical Events of Cardiac Cycle
Depolarization = Inc permeability of pacing cells –> AP
Excitation
Repolarization = Restoration / Recovery / Refractory
periods of cell
Mechanical Events of Cardiac Cycle
Systole
Diastole
Characteristics Common to All Muscle Cells
(CRAE) Conductivity Rhythmicity Automaticity Excitability
Depolarization
Electrical event of Cardiac Cycle:
-Increased membrane permeability of pacing cells (Na, K,
Ca)
–>AP Excitation
Slow Channels: SA/AV Nodes
Fast Channels: Purkinje Fibers + myocytes
Repolarization
Electrical event of Cardiac Cycle:
- Cell restored to negative via Na/K Pump
- -> Recovery
*Refractory periods (ERP / RRP)
Cardiac Electrical Cycle Fast Response
Fast channels: Purkinje + myocytes
Phase 0: Rapid Depol (Na+ IN)
Phase 1: Partial Repol (Cl- IN)
Phase 2: Plateau (No net change) *Not in SA/AV Nodes
Phase 3: Rapid Repol (Na/K Pump restores)
Phase 4: Rest (K+ OUT)
Cardiac Mechanical Cycle
Vent Late Diastole (+ Atrial Sys) = Fast vent filling
Vent Early Diastole (+ Atrial Dia) = Isovolumetric Contraxn
Vent Late Diastole = Vent Ejection
Vent Early Diastole = Isovolumetric Relaxation
Vent Mid Diastole = Slow vent filling
EDV
(End Diastolic Volume)
Volume of blood when ventricles completely filled
Norm: 120-130mL
[EDV - ESV = SV]
Isovolumetric Contraction
Contraction with no blood movement bc Vent Pressure > Atrial Pressure and AV valves close while SL valves do not open immediately
*Ventricular Early Systole
ESV
(End Systolic Volume)
Volume of blood left in ventricles post ejection
Normal: 50-60mL
[EDV - ESV = SV]
Isovolumetric Relaxation
Relaxation with no blood movement bc vent pressures < atrial pressures so SL valves close, and AV valves remain closed until vent pressure < atrial pressure
*Ventricular Early Diastole
Preload
Physiological control of SV
=Degree of stretch prior to contraxn
-dependent on venous return (increase = INC SV)
Drugs that decrease preload:
- Diuretics
- Venous dilators
- Sympathomimetics
Contractility
Phys control of SV
=Force of contraction based on interactions at
crossbridges of myofilaments (Inc = INC SV)
-dependent on Ca avail & increased SNS input
Drugs that affect contractility:
- Adrenergics (INC)
- Beta blockers and Ca Blockers (DEC)
Afterload
Phys control of SV
=amt of aortic/pulmonary pressure the ventricles must
overcome to open SL valves and eject blood
(Inc Arterial Pressure = Inc afterload = DEC SV)
-dependent on pressure, radius and wall
thickness
Drugs that increase afterload:
- Vasodilators - ACE Inhibitors - ACE Receptor blockers - Sympatholytics
Hemodynamics
Relationship b/w blood flow and pump (pressure source)
[R SV = L SV] and [CO = VR]
3 Variables:
- CO
- Perfusion Pressure
- Peripheral Vascular Resistance
Hemodynamic Disorders
- Thrombosis
- Embolism
- MI
- Edema
- Shock
Shock
microcirculation failure and inadequate perfusion of blood to vital organs
–> Peripheral vasodilation: Hypotension
= bad O2 delivery, cap beds close and shunt
blood to major organs, others shut down
Types:
- Cardiogenic
- Hypovolemic
- Neurogenic
- Septic
Albumin
Plasma protein that acts as oncotic pressure that pulls fluid into cells
