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Cardiovascular Cardiovascular System: The System: The

HeartHeartMary Christenson, PT, PhDMary Christenson, PT, PhD

DPT 732: Management DPT 732: Management ApplicationsApplications

of Physiology IIof Physiology IISpring 2009Spring 2009

http://www.amazon.com/Guinness-World-Records-2004/dp/product-description/0553587129

Did You Know?Did You Know? Coronary circulation is the shortest Coronary circulation is the shortest

circulation in the bodycirculation in the body ““The longest cardiac arrest lasted four The longest cardiac arrest lasted four

hours in the case of fisherman Jan Egil hours in the case of fisherman Jan Egil Refsdahl (Norway), who fell overboard off Refsdahl (Norway), who fell overboard off Bergen, Norway, on December 7, 1987. He Bergen, Norway, on December 7, 1987. He was rushed to Haukeland Hospital after his was rushed to Haukeland Hospital after his body temperature fell to 75° F (24° C), and body temperature fell to 75° F (24° C), and his heart stopped. He made a full recovery his heart stopped. He made a full recovery after being connected to a heart-lung after being connected to a heart-lung machine.”machine.”

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ObjectivesObjectives Describe the physiologic structure and function of Describe the physiologic structure and function of

the heart.the heart. Describe the systemic & pulmonary blood flow Describe the systemic & pulmonary blood flow

circuits of the CV system.circuits of the CV system. Describe the coronary circulation and compare and Describe the coronary circulation and compare and

contrast to the pulmonary/systemic circulation.contrast to the pulmonary/systemic circulation. Describe the function of the different types of Describe the function of the different types of

cardiac muscle and the microanatomy (striated, cardiac muscle and the microanatomy (striated, intercalated discs, gap junctions) of each.intercalated discs, gap junctions) of each.

Describe the energy requirements of the heart.Describe the energy requirements of the heart. Compare/contrast the intrinsic and extrinsic Compare/contrast the intrinsic and extrinsic

regulation of heart pumping.regulation of heart pumping.

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Objectives (continued)Objectives (continued) Describe the cardiac cycle and compare and contrast Describe the cardiac cycle and compare and contrast

the relationship between EKG tracing, heart sounds, the relationship between EKG tracing, heart sounds, atrial and ventricular pressure changes, atrial and atrial and ventricular pressure changes, atrial and ventricular volume changes, and valve actions that ventricular volume changes, and valve actions that occur within the left chambers of the heart during a occur within the left chambers of the heart during a cardiac cycle.cardiac cycle.

Describe the specialized excitatory and conductive Describe the specialized excitatory and conductive system of the heart.system of the heart.

Describe the cellular mechanisms of pacemaker Describe the cellular mechanisms of pacemaker potential and cardiac muscle contraction, and potential and cardiac muscle contraction, and compare with action potentials and skeletal muscle compare with action potentials and skeletal muscle contraction.contraction.

Describe the characteristics and principle features of Describe the characteristics and principle features of a normal EKG (waves, segments, complexes, a normal EKG (waves, segments, complexes, polarization, depolarization, repolarization).polarization, depolarization, repolarization).

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Heart Anatomy: A ReviewHeart Anatomy: A Review Functional anatomyFunctional anatomy

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Heart Anatomy: A ReviewHeart Anatomy: A Review

External anatomy viewExternal anatomy view Membrane coveringsMembrane coverings Heart wallHeart wall Vessels entering/exitingVessels entering/exiting

Blood flow circuits: arteries versus veinsBlood flow circuits: arteries versus veins Pulmonary circuitPulmonary circuit Systemic circuitSystemic circuit

Coronary arteriesCoronary arteries

PericardiumPericardium

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Heart WallHeart Wall

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Heart Anatomy: A ReviewHeart Anatomy: A Review

Internal anatomyInternal anatomy ChambersChambers Structures Structures

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Coronary Blood Flow

Systemic & Pulmonary Blood Flow

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Cardiac Muscle & Cardiac Muscle & MicroanatomyMicroanatomy

MuscleMuscle Atrial muscleAtrial muscle Ventricular muscleVentricular muscle Specialized excitatory and conductive Specialized excitatory and conductive

muscle fibersmuscle fibers Muscle cellsMuscle cells Intercalated discsIntercalated discs Gap junctionsGap junctions

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Electron Micrograph

Cell Connections

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Compare/Contrast Cardiac Compare/Contrast Cardiac and Skeletal Mechanism of and Skeletal Mechanism of

ContractionContraction SimilaritiesSimilarities

Striated – myosin/actin mechanismStriated – myosin/actin mechanism T-tubule mechanism – acting on sarcoplasmic T-tubule mechanism – acting on sarcoplasmic

reticulumreticulum DifferencesDifferences

T-tubule mechanism – direct diffusion of Ca++T-tubule mechanism – direct diffusion of Ca++ Action potentialAction potential

Cardiac muscle “plateau”Cardiac muscle “plateau” Strength of contractionStrength of contraction

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ConductionConduction

Ability of cardiac mm to depolarize Ability of cardiac mm to depolarize and contract is intrinsicand contract is intrinsic

Intrinsic conduction systemIntrinsic conduction system ComponentsComponents

Sinus node = sinoatrial/S-A nodeSinus node = sinoatrial/S-A node Internodal pathwaysInternodal pathways A-V nodeA-V node A-V bundleA-V bundle Left and right bundle branches of Purkinje Left and right bundle branches of Purkinje

fibersfibers

Intrinsic Conduction Intrinsic Conduction SystemSystem

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Features of the S-A Node Smaller diameter muscle fibers Almost no contractile muscle fibers Connect directly with atrial muscle (mm)

fibers Cell membranes naturally “leaky” to Na+

and Ca++ ions – therefore, less negative resting membrane potential than other cardiac mm cells

Fast Na+ channels, at less negative potential, “inactivated”

Self-excitation

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EKGEKG

Electrical impulses passing through the Electrical impulses passing through the heart also spread into adjacent tissues heart also spread into adjacent tissues and some to the surface of the bodyand some to the surface of the body

Can be captured at surface of the body Can be captured at surface of the body using electrodesusing electrodes

EKG TracingEKG Tracing

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Cardiac CycleCardiac Cycle

Events that occur from the beginning of Events that occur from the beginning of one heartbeat to the beginning of the nextone heartbeat to the beginning of the next Chamber and vessel blood volume changesChamber and vessel blood volume changes Chamber and vessel blood pressures changesChamber and vessel blood pressures changes Electrical activity notedElectrical activity noted Heart sounds occurHeart sounds occur Valves open and closeValves open and close

Describe the relationships between the Describe the relationships between the eventsevents

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Cardiac cycle Cardiac cycle

Consists of:Consists of: Diastole: period of relaxation; heart filling with Diastole: period of relaxation; heart filling with

bloodblood Systole: contraction period, heart ejects bloodSystole: contraction period, heart ejects blood

What would be:What would be: the definition of end-diastolic volume (EDV)?the definition of end-diastolic volume (EDV)? the definition of end-systolic volume (ESV)?the definition of end-systolic volume (ESV)?

Ejection fraction: fraction of EDV ejectedEjection fraction: fraction of EDV ejected

Guyton Cardiac Cycle

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Relationship of Cardiac Cycle Relationship of Cardiac Cycle to ECGto ECG

P wave: spread of depolarization P wave: spread of depolarization through atrial tissue followed by through atrial tissue followed by contraction - atrial pressurecontraction - atrial pressure

QRS complex: spread of depolarization QRS complex: spread of depolarization through ventricular tissue followed by through ventricular tissue followed by contraction - ventricular pressurecontraction - ventricular pressure

T wave: repolarization of the ventricles T wave: repolarization of the ventricles which represents ventricular relaxationwhich represents ventricular relaxation

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Atria as “Pumps”Atria as “Pumps”

Majority of returning venous blood Majority of returning venous blood flows directly from atrium to ventricleflows directly from atrium to ventricle

Atrial contraction usually causes an Atrial contraction usually causes an additional 20% ventricle filling; additional 20% ventricle filling; “primer pump”“primer pump”

Atrial function “unnecessary” except Atrial function “unnecessary” except during vigorous exerciseduring vigorous exercise

Atrial pressure changesAtrial pressure changes

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Ventricles as “Pumps”Ventricles as “Pumps”

Ventricular filling: after systole, A-V Ventricular filling: after systole, A-V valves open due to build up of valves open due to build up of pressure in atria during systole: pressure in atria during systole: period of rapid filling of ventricles period of rapid filling of ventricles followed by 2 additional phasesfollowed by 2 additional phases

Period of Isovolumic ContractionPeriod of Isovolumic Contraction Period of EjectionPeriod of Ejection Period of Isovolumic RelaxationPeriod of Isovolumic Relaxation

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Preload and AfterloadPreload and Afterload

Preload – End-diastolic pressure when Preload – End-diastolic pressure when the ventricle is filled; amount of tension the ventricle is filled; amount of tension on the muscle when it begins to contracton the muscle when it begins to contract

Afterload – pressure in the artery leading Afterload – pressure in the artery leading from the ventricle; load against which the from the ventricle; load against which the muscle exerts its contractile forcemuscle exerts its contractile force

Heart and/or circulation pathology can Heart and/or circulation pathology can severely alter preload and/or afterloadseverely alter preload and/or afterload

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Chemical Energy Chemical Energy Requirements for Requirements for

Cardiac ContractionCardiac Contraction Great dependency/almost exclusive reliance Great dependency/almost exclusive reliance

on O2 for energy metabolism (oxidative) on O2 for energy metabolism (oxidative) compared to skeletal muscle which can compared to skeletal muscle which can utilize anaerobic metabolic sources as wellutilize anaerobic metabolic sources as well

Energy derived primarily from oxidative Energy derived primarily from oxidative metabolism of fatty acids (food of choice: metabolism of fatty acids (food of choice: primary oxidative nutrient source), some primary oxidative nutrient source), some lactate, glucoselactate, glucose

Cardiac muscle can also use lactic acid Cardiac muscle can also use lactic acid generated by skeletal muscle activitygenerated by skeletal muscle activity

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Intrinsic Regulation of Intrinsic Regulation of the Cardiac Pumpthe Cardiac Pump

Heart pumps 4-6 liters of blood/minute @ Heart pumps 4-6 liters of blood/minute @ restrest

Frank-Starling MechanismFrank-Starling Mechanism Heart automatically pumps incoming blood; i.e., Heart automatically pumps incoming blood; i.e.,

amount of blood pumped determined primarily amount of blood pumped determined primarily by rate of blood flow into heartby rate of blood flow into heart

As cardiac muscle is stretched with returning As cardiac muscle is stretched with returning blood volume, approach optimal length of actin blood volume, approach optimal length of actin and myosin fibers for contractionand myosin fibers for contraction

Stretch of R atrial wallStretch of R atrial wall Increase HR by 10-20%Increase HR by 10-20%

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Extrinsic Regulation of the Cardiac Pump (ANS)

Sympathetic Nervous System (SNS) Norepinephrine released by

sympathetic nerve fibers in response to stressors such as fright, anxiety, or exercise; threshold reached more quickly Increase cardiac output (CO)

Pacemaker fires more rapidly Enhanced mm contractility

Effects of inhibiting SNS

Extrinsic Regulation of the Cardiac Pump (ANS)

Parasympathetic Nervous System Reduces HR when stressors removed Acetylcholine hyperpolarizes

membranes of cells – opens K+ channels PNS fibers in Vagus nerves to heart can

decrease CO Primarily affects HR rather than contractility

Autonomic Innervation of Autonomic Innervation of the Heartthe Heart

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Resting Conditions

S-A node receives impulses from both autonomic divisions continuously

Dominant influence is inhibitory – heart said to exhibit “vagal tone”

“Disconnect” vagal nerves = HR increases ~25 bpm almost immediately