N1. Cardiac Physiology III: Wigger's Diagram - Notes

I. Wigger's Diagram

  • Graph of electrical and mechanical events during one cardiac cycle.
  • Includes ECG, pressure, left ventricular volume.
  • Key events:
    • A/E – aortic valve opens (minimum P_{aorta} = DBP)
    • B – aortic valve closes
    • C – mitral valve closes
    • D/F – mitral valve opens
    • A/E – ejection begins
    • D/F – passive filling begins
    • IVC – isovolumetric contraction
    • IVR – isovolumetric relaxation

A. Atrial Systole

  • EKG: P wave precedes atrial systole.
  • Pressure:
    • Left atrial pressure increases.
    • Aortic pressure at diastolic blood pressure (DBP).
  • LV Volume: Increases to EDV (End Diastolic Volume).

B. Isovolumic Ventricular Contraction (IVC)

  • EKG: QRS complex precedes ventricular systole.
  • Pressure:
    • Bicuspid (mitral) valve closes [C].
    • Ventricular pressure increases.
  • LV Volume: No change.

C. Ventricular Ejection

  • EKG: S-T segment (ventricles in Ca^{2+} plateau phase).
  • Pressure:
    • Ventricular pressure > Aortic pressure.
    • Aortic valve opens [A].
    • Aortic pressure increases to systolic blood pressure (SBP).
    • Ventricular pressure increases then decreases.
  • LV Volume: Ejection leads to volume decrease to ESV (End Systolic Volume).

D. Early Ventricular Diastole

  • EKG: T-wave precedes diastole.
  • Pressure:
    • Aortic valve closes [B].
    • Dicrotic notch.
    • Ventricular pressure decreases.
  • LV Volume: Isovolumic diastole.

E. Late Ventricular Diastole

  • EKG: T-P segment.
  • Pressure:
    • Ventricular pressure < Atrial pressure.
    • AV valves open.
  • LV Volume: Increases, passive filling of ventricles.

II. Cardiac Output

A. Cardiac Output (CO)

  • Volume of blood pumped by one ventricle in a period of time.
  • Units: mL/min.
  • Measure of total blood flow throughout the body.
  • Increases with exertion and O_2 requirements.
  • Calculated as: CO = HR \,(heart \, rate) \times SV \,(stroke \, volume).
  • Average CO = 5040 mL/min (72 bpm * 70 mL/beat).

B. Blood Flow

  • Q = V \times A
    • Q = flow (cm^3/sec)
    • V = velocity (cm/sec)
    • A = cross-sectional area (cm^2)
  • Aorta and large arteries: 5 – 35 cm/sec (fast to distribute blood quickly to the tissues – “distribution vessels”).
  • Capillaries: ~ 0.05 cm/sec (slow to allow time to exchange with tissues – “exchange vessels”).
  • Ohm’s Law:
    • Q = [Delta]Pressure / Resistance
      • Q = cardiac output (CO) amount of blood pumped by the left ventricle (= amount pumped by right ventricle) 3000 – 25,000 ml/min
      • [Delta]P = pressure difference between the beginning and the end of the tube for the systemic circulation
        • leaves LV pressure = P_{aorta} mean arterial pressure (MAP)
        • returns to RA pressure = P_{vena \, cava} very low (~ 0 mmHg)
        • [Delta]P = P{aorta} - P{vena \, cava} = MAP

C. Resistance (R)

  • R = (8 \eta L) / (\pi r^4)
    • \eta = viscosity
    • L = length
    • r = radius
  • Small vasoconstriction of arterioles = big increase in resistance.
  • Small vasodilation of arterioles = big decrease in resistance.
  • Total Peripheral Resistance (TPR) – total resistance through the systemic circulation
    • arteriolar tone
    • viscosity
    • # of open capillary beds etc.
  • CO = MAP / TPR
  • TPR also called “Systemic Vascular Resistance” (SVR).
  • Effect of Hematocrit on viscosity:

D. Blood Pressure

  • Systolic Blood Pressure (SBP) – maximum P_{aorta} (systole = contraction).
  • Diastolic Blood Pressure (DBP) – minimum P_{aorta} (diastole = relaxation) a good indicator of changes in TPR.
  • Pulse Pressure (PP) = SBP - DBP a good indicator of cardiac contractility.
  • Mean Arterial Pressure (MAP) – “average” pressure in the aorta/large arteries
    • MAP = DBP + (1/3) \times (SBP - DBP)

E. Muscle Tension

Strip of Cardiac Muscle Tensions

  • Passive Tension
  • Active Tension
  • Total Tension
  • Inotropic State: Shifts active (and total) tension curve. Doesn’t change passive tension curve.

III. Regulation of Stroke Volume

  • SV is a measure of ventricular contraction force, which is dependent on:

A. Preload

  • Degree of myocardial stretch before contraction begins.
  • Determined by end-diastolic volume (EDV).
  • High EDV → high myocardial stretch → more cross bridges → greater tension → greater contractile force.
  • Frank-Starling Law of the Heart: within physiological limits, the heart will pump all of the blood that returns to it.
    • Venous return: amount of blood entering heart from venous circulation
      • Determined by respiratory rate, skeletal muscle activity, sympathetic control of veins
      • Determines EDV

B. Afterload

  • Ventricular wall tension during contraction; inversely proportional to CO.
  • Resistance created by arterial blood already in the system and the EDV
    • Aortic pressure holds aortic valve closed
    • Must build pressure to open valve
  • Increased diastolic blood pressure → increased afterload

IV. Cardiac Cycle

A. Phases

  • Filling phase.
  • Isovolumetric contraction phase (IVC).
  • Ejection phase.
  • Isovolumetric relaxation phase (IVR).
  • Diastole (includes atrial systole).
  • Systole (ventricular).
  • At 2: preload (EDV), end diastolic pressure (EDP).
  • At 3: afterload (DBP).
  • At 3 to 4: peak pressure - maximum LV contraction pressure and maximum P_{Ao} (SBP).
  • 3 to 4 volume: Stroke Volume (SV).
  • Ejection \, Fraction = SV / EDV

V. Blood

A. Volume

  • ~ 8% of body weight (60 kg person has about 5 liters of blood).

B. Composition (if centrifuge anticoagulated blood)

  • Plasma
    • H_2O (~ 90%)
    • electrolytes (salts)
    • glucose, other water solubles
    • proteins
      • albumin made by liver t_{1/2} ~ 19 days functions: blood oncotic pressure , carrier protein (lipid solubles)
      • immunoglobulins (antibodies)
      • fibrinogen/clotting factors made by liver t_{1/2} ~ hours to days
  • Buffy coat
    • WBCs (leukocytes) made in bone marrow part of immune system infections WBC count
    • Platelets made in bone marrow initial plug to stop bleeding triggers clotting
  • RBCs (erythrocytes)
    • made in bone marrow (erythropoiesis)
    • carry O_2 (using hemoglobin)
    • Hematocrit (Hct) = RBC volume / total volume
      • normal Hct: women 38% - 46% men 42% - 54%
      • anemia = low Hct
      • polycythemia = high Hct
  • If allow clotting and then centrifuge
    • Serum like plasma (similar concentrations for most things)
    • lacks fibrinogen/clotting factors (and other [proteins] get affected too)

VI. Circulation

A. General

  • Right Ventricle → Lungs → Left Atrium
  • Left Ventricle → Body → Right Atrium

B. Blood Vessels

  • Artery (carries blood away from the heart) vein (carries blood towards the heart)
  • Pulmonary circulation (pulmonary artery → lungs → pulmonary veins)
  • Systemic circulation (aorta → vena cava) (left ventricle → right atrium)
  • Coronary circulation (carries blood to heart muscle)

C. Distribution of Blood (at rest)

  • Venous System - 66%
  • Arterial System - 11%
  • Pulmonary Circulation - 12%
  • Heart – 6%
  • Capillaries – 5%
  • “Capacitance Vessels” venous constriction venous return to the heart shifts blood to the arterial system low arterial pressure increases arterial filling pressure Venous System Arterial System blood vasoconstriction

D. Control of Vascular Smooth Muscle

  • Local factors – stretch, O2, CO2, pH, etc.
  • Hormones/NTs

VII. Blood Pressure/Cardiac Output Control

A. Control Systems

  • Bainbridge reflex – stretch receptors in atrial walls (mostly RA)
    • atrial stretch/filling Vagal (CN-X) afferents (+)
    • (+) HR
    • HRparasympathetic system (-)
  • Stretch activated mixed cation channels (mostly on SAN)
    • atrial stretch/filling (+)
    • activation of cation channels in SAN (+)
    • SAN phase 4 slope (+)
    • sympathetic system (+)

B. Baroreceptors

  • Measure pressure (MAP)
  • baroreceptors in wall of aortic arch CN-X afferents
  • baroreceptors at each carotid sinus CN-IX afferents
  • maximum baroreceptor responsiveness is from ~ 40 – 160 mmHg
  • carotid baroreceptors are dominant over the aortic baroreceptors (though normally they see the same pressure)

C. Chemoreceptors

  • Near baroreceptors use CN-X and CN-IX afferents
  • O2, pH, CO2

D. Blood Volume/Blood Pressure

  • ADH
    • control increased [osm]plasma decreased BP ADH release
    • actions increases H_2O reabsorption by the kidney (receptor = V2 (Gs)) BV vasoconstriction of arterioles/venules (receptor = V1 (Gq)) BP increases thirst (a CNS effect)
  • Renin-Angiotensin-Aldosterone System (RAAS)
    • control sympathetic (\beta1 on the kidney) decreased BP at kidney decreased Na^+ at kidney increase renin release by the kidney
    • actions renin (an enzyme) Angiotensin II (AII) (receptor = Gq and Gi) vasoconstriction of arterioles/venules BP Aldosterone release (from adrenal cortex) kidney Na^+ reabsorption
  • Atrial Natriuretic Peptide (ANP)
    • control increased blood volume or decreased ability of the heart to pump blood atrial stretch stretch atria release of ANP from atrial cells
    • actions decreases H_2O and Na^+ reabsorption by the kidney decreases ADH release and activity decreases RAAS activity vasodilation decrease BV decrease BP

E. Timing

  • Instant: Starling’s Law of the Heart (works on the next contraction).
  • Seconds to minutes: ANS responses hormones.
  • Hours to days: volume control (kidney).
  • Months to years: anatomy changes (blood vessels, heart).