Cardiac Cycle

Blood Distribution

5-7% in heart; 11-13% Arteries; 7% arterioles and capillaries; 60-70% venous system

Capacitance originates from Venous system – change volume by changing capacitance

Blood Flow

FLUID MECHANICS: Fluid flow comparable to current flow; i.e. Ohm’s Law

V=IR » D P= Flow X Resistance P=pressure

In a vessel R µ 1/r⁴ so D P µ Flow x l/r⁴

R µ length

Clinical Note: Short, large bore angio-catheters canulated in an antecubital or femoral vein deliver volume faster than a narrow long central line to a central venous site.

CARDIAC CHAMBERS: Pressure and Flow

Venous System: 5-10 mmHg, muscle contraction moves blood, SVC (superior vena cava) and IVC (inferior)

Right Atrium: 5-10 mmHg, thin wall contains SA node (pace maker) on lateral wall (medial aspect of contains the AV node)

Tricuspid valve: three leaflets: septal, anteriosuperior (or superior or anterior), mural (or inferior or posterior)

Right Ventricle: 20/5-10 mmHg, wraps anterior to LV in banana shape

Pulmonic Valve: three leaflets

Pulmonary Artery: 20/10 mmHg

Pulmonary Veins

Left Atrium: 5-10mmHg

Mitral Valve: 2 leaflets, anterior and posterior

Left Ventricle: 120/5-10 mmHg, thick walled muscular chamber, pumps against peripheral vascular R and P

Aortic Valve: three leaflets –right coronary –left coronary –non coronary cusps

Aorta: 120/80 mmHg – to arterioles, capillaries, venules, veins, and finally returning to the Central Venous System (IVC and SVC)

NOTE: CO_L = CO_R because:

CO = Cardiac Output = MAP/TPR

CO = HR X SV and HR_R = HR_L and SV_R= SV_L

HR = Heart Rate SV = stroke Volume

however: Ejection Fraction _R¹ Ejection Fraction_L EF = SV/EDV = EDV – ESV

Surface Electrocardiogram (EKG OR ECG)

Reflects A/P generated in atrial and ventricular tissue

P-wave: reflects atrial depolarization

QRS complex: represents depolarization of the ventricles (hides atrial repolarization which happens concurrently)

T-wave-:represents repolarization of the ventricles movement to right = ventricular tachicardia (Arithrimyacin)

P to P interval: = atrial rate

R to R interval: = ventricular rate

PR interval: = conduction from SA node to AV node

QT interval = time for ventricular repolarization

Conduction System of the Heart

specialized pacemaker cells exhibit slow diastolic depolarization; membrane slowly reaches E_Th producing A/P

rate of diastolic depolarization: SA node > AV node > HIS purkinje system

HR set by fastest pacemaker due electrical syncitium of cardiac tissue

Timing of Cardiac Events

Systole = contraction Diastole = relaxation generally referring to ventricular

Atrial depolarization (P-wave) produces Atrial contraction which allows Ventricular filling (most filling has already occurred)

QRS complex = Ventricular Systole, T-wave = Ventricular Diastole; Both phases have isovolumic periods

Passive forces in cardiac tissue are high due to properties of titin: realigns sarcomere for optimal contractility

Mitral Valve = open when P_LA > P_LV = closed when P_LA< P_LV

Aortic Valve = open when P_LV > P_Aorta = closed when P_LV < P_Aorta

Mitral Stenosis (calcification of mitral valve-sticky) Þ P_LA increased Þ mitral valve opens sooner

Heart Sounds: S₁ = mitral valve closing S₂ = aortic valve closing OS (opening snap) = stenoic mitral valve opening

LV Pressure Volume relationship

A-C LV filling without change in pressure

C-D LV contraction Þ mitral valve closure Þ isovolumic contraction until P_LV>P_Aorta Þ aortic valve opening

D-E = rapid ventricular ejection

E-F = reduced ventricular ejection until P_LV< P_AortaÞ aortic valve closure

F-A = LV isovolumic relaxation until P_LV< P_LA Þ mitral valve opens

stroke volume = AF - CD