Cardiac Physiology Part 1

Cardiac Physiology Part 1

• Left heart pressures are greater than right heart pressures
• Atrioventricular (AV) valves (mitral and tricuspid) open during diastole
• Semilunar valves (aortic and pulmonary) open during systole
• Blood moves from higher pressure areas to lower pressure areas
• Pressure gradient (PG) drives blood flow
• Normal cardiac pressures are measured in mmHg
  • RAP: 2-8 (mean)
  • RVP: 15-25
  • PAP: 15-25
  • PCWP: 2-12
  • LAP: 2-12
  • LVP: <120
  • Ao: <120
• Cardiac cycle has four phases:
  • Diastole
  • Isovolumic Contraction Time (IVCT)
  • Systole
  • Isovolumic Relaxation Time (IVRT)

Diastole

• Diastole is the period of heart relaxation when the ventricles fill with blood
• Atrial pressure rises as atriums fill
• AV valves open when atrial pressure exceeds ventricular pressure
• Blood flows from high pressure to low pressure
• Three phases of diastole:
  • Early Rapid Filling ("the dump")
  • Diastasis ("the slow down")
  • Atrial Contraction ("the kick")

End-Diastolic Volume (EDV)

• EDV is the largest volume of blood in the heart during the cardiac cycle
• Ventricular pressures are higher than atrial pressures
• Closure of AV Valves signals the end of diastole

Atrioventricular Valves & Diastolic Pressure Gradients

• Pressure from the left atrium (LA) across the mitral valve (MV) to the left ventricle (LV)
• Mean LAP: 2-12 mmHg
• Diastolic LVP: 3-12 mmHg
• Pressure from the right atrium (RA) across the tricuspid valve (TV) to the right ventricle (RV)
• Mean RAP: 2-8 mmHg
• Diastolic RVP: 2-8 mmHg

Semilunar Valves & Diastolic Pressure Gradients

• Diastolic LVP: 3-12 mmHg
• Diastolic (aortic) pressure: ~80 mmHg
• Large pressure gradient (~70 mmHg) keeps the aortic valve (AoV) shut
• Diastolic RVP: 2-8 mmHg
• Diastolic (pulmonary) pressure: 4-12 mmHg
• Sufficient pressure gradient keeps the pulmonary valve (PV) shut

Isovolumic Contraction Time (IVCT)

• Short period immediately preceding systole
• Ventricles are in the process of contracting, but blood has not yet left the ventricles
• Ventricular volumes remain constant.
• All four valves are closed
• Ventricular pressures increase
• Ventricular wall thickness increases
• Atrial filling continues

Systole

• Systole is a period of heart contraction when ventricles eject blood
• Ventricular pressure exceeds great artery pressure; semilunar valves open
• Blood ejects from ventricles to great arteries
• Blood flows from high pressure areas to lower pressure areas
• Semilunar valves close which signals the end of systole.

End-Systolic Volume (ESV)

• ESV is the smallest volume of blood in the heart during the cardiac cycle
• Represents the amount of blood remaining in ventricles at the end of systole

Systolic & Diastolic Function Recap

• Ventricular pressure exceeds great artery pressure
• Cause SL valves to open
• SL valves close (2nd heart sound)
• Systolic function, diastolic function dependent on several components:
  • Contractility
  • Wall thickening & motion
  • Indication of adequate coronary blood flow and oxygen
  • Chamber size
  • Ventricular end-diastolic pressure

Wall Motion Abnormalities (WMA)

• Cardiac walls that do not thicken/contract properly
• May indicate ischemic heart disease
• Can be global (entire chamber) or local (small area)

Wall Motion Terminology

• Hyperkinetic: excessive wall motion (walls squeezing more than normal)
• Hypokinetic: decreased wall motion (walls squeezing less)
• Akinetic: no wall movement or thickening (walls not squeezing)
• Dyskinetic: movement away from the center, or in the opposite direction (may indicate heart attack)

What Causes Wall Motion Abnormalities (WMA)?

• Myocardial ischemia (starvation of blood flow to the heart muscle) can lead to myocardial infarction
• Abnormal relaxation (diastolic dysfunction)
• Reduced systolic function

Heart Sound Recap

• 1st heart sound (S1): AV valve closure ("lub")
• 2nd heart sound (S2): SL valve closure ("dub")
• 3rd heart sound (S3): Early rapid filling ("ventricular dump")
• 4th heart sound (S4): Atrial contraction ("ventricular kick")

Cardiac Function

• Cardiac function relates to the heart's ability to pump oxygenated blood successfully under various circumstances.
• Supply needs to equal demand
• Compensation mechanisms (e.g., increased heart rate, increased force of contraction) adjust during exercise
• Reduced demand during rest leads to slower heart rate and reduced contraction force
• Function is dependent upon systolic and diastolic functions