💓

Hemodynamic Principles Overview

Sep 12, 2025

Overview

This lecture series provides a comprehensive overview of hemodynamic principles, focusing on understanding blood flow, key cardiac anatomy, oxygen delivery, determinants of cardiac output, non-invasive and invasive monitoring techniques, and optimization strategies for patient hemodynamics.

Heart Anatomy and Blood Flow

  • The heart has four chambers: right atrium, right ventricle, left atrium, and left ventricle.
  • Blood flows: right atrium → tricuspid valve → right ventricle → pulmonic valve → pulmonary artery → lungs → pulmonary veins → left atrium → mitral valve → left ventricle → aortic valve → aorta.
  • Main vessels: superior vena cava and inferior vena cava return deoxygenated blood; pulmonary arteries take blood to lungs; pulmonary veins return oxygenated blood.
  • Heart valves: tricuspid, pulmonic, mitral (bicuspid), and aortic.

Oxygen Delivery and Determinants

  • Oxygen delivery (DO2) = cardiac output × arterial oxygen concentration × 10.
  • Arterial oxygen concentration (CaO2) depends mostly on hemoglobin and oxygen saturation, with PaO2 having minor impact.
  • Cardiac output (CO) = heart rate × stroke volume; normal CO is 4–8 L/min.
  • Cardiac index adjusts CO for body surface area; normal is 2.5–4 L/min/m².

Cardiac Output and Influencing Factors

  • Heart rate and stroke volume have inverse compensatory relationship; tachycardia compensates for low stroke volume.
  • Factors influencing HR: hypovolemia, blood pressure changes, SNS activation, fever, exercise, arrhythmias, heart blocks, certain drugs.
  • Stroke volume is determined by preload (volume in ventricle before contraction), contractility (force of contraction), and afterload (resistance to ejection).
  • Frank-Starling law: increased preload stretches the heart, increasing contractility, but overstretching (e.g., CHF) reduces efficiency.
  • Afterload is affected by aortic compliance, vascular resistance, and blood viscosity.

Non-Invasive Hemodynamic Monitoring

  • Assess perfusion by looking for skin changes (cool, clammy, cyanotic), GI changes (decreased bowel sounds), kidney/liver/lung signs (low urine, altered labs), and CNS/cardiac signs (altered LOC, chest pain).
  • Blood pressure reflects CO × systemic vascular resistance (SVR).
  • Mean arterial pressure (MAP) ≈ [2 × diastolic + systolic]/3; essential for organ perfusion, typically aim for MAP > 60.
  • Pulse pressure = systolic – diastolic; indicates arterial tone.

Invasive Hemodynamic Monitoring

  • Central venous pressure (CVP) measures right atrial preload; normal 2–10 mmHg.
  • Arterial line (A-line) gives real-time systolic, diastolic, MAP; more accurate than cuff BP if waveform is optimal.
  • FlowTrac/Vigileo systems analyze A-line waveform for stroke volume, CO/CI, and stroke volume variation (SVV); SVV > 13% suggests low preload.
  • Pulmonary artery (Swan-Ganz) catheter measures: CVP, pulmonary artery pressure (PAP: 20–30/10–20 mmHg), pulmonary capillary wedge pressure (PCWP: 8–12 mmHg), and CO/CI.
  • SVR = 800–1200; low suggests vasodilation, high suggests vasoconstriction.

Optimization of Hemodynamics

  • Heart rate: treat tachyarrhythmias with beta/calcium channel blockers or adenosine; bradycardia with atropine, dopamine, epinephrine, or pacing.
  • Contractility: decrease with beta/calcium channel blockers; increase by fixing underlying cause, giving inotropes (dobutamine, milrinone), or using assist devices.
  • Preload: decrease with diuretics, dialysis, venodilators; increase with fluids/blood, crystalloids, or colloids.
  • Afterload: decrease with vasodilators (nitroprusside, nicardipine) or balloon pump; increase with vasopressors (norepinephrine, epinephrine, vasopressin).

Key Terms & Definitions

  • Hemodynamics — the study of blood movement and forces in the circulatory system.
  • Preload — the volume/pressure in the ventricle before contraction.
  • Contractility — the strength of ventricular contraction.
  • Afterload — resistance the heart must overcome to eject blood.
  • Cardiac output (CO) — total blood pumped by the heart per minute.
  • Cardiac index (CI) — CO corrected for body surface area.
  • Central venous pressure (CVP) — pressure in the right atrium; reflects preload.
  • Mean arterial pressure (MAP) — average pressure in arteries during the cardiac cycle.
  • Systemic vascular resistance (SVR) — resistance blood faces in systemic circulation.

Action Items / Next Steps

  • Review the blood flow pathway through the heart and major vessels.
  • Memorize normal values for CO, CI, CVP, PAP, PCWP, MAP, and SVR.
  • Practice calculating MAP and pulse pressure.
  • Read about drugs and devices used for hemodynamic optimization (beta blockers, inotropes, vasopressors, IABP).

Full transcript