Hemodynamic Terminology – Study Notes

Preload

• Definition: Volume of blood in ventricles at end-diastole.

• Elevated preload: Seen in CHF (fluid overload).

  • Preload reducers:

    • Diuretics (remove excess fluid).

    • Venous vasodilators (e.g., Nitroglycerin).

    • Morphine (venodilation + pain relief in MI).

• Low preload: Seen in shock states (low-flow).

  • Increase preload: Volume resuscitation (IV fluids, blood products).

• Measurement: Cannot measure volume directly → extrapolate with pressure.

  • Central Venous Pressure (CVP) or Right Atrial Pressure (RAP).

Afterload

• Definition: Resistance ventricles must overcome to eject blood.

• High afterload: Hypertension.

  • Afterload reducers: ACE inhibitors (↓ angiotensin II vasoconstriction).

• Low afterload: Distributive shock (septic, anaphylactic, neurogenic).

  • Increase afterload: Vasopressors (e.g., norepinephrine, vasopressin).

• Measurement:

  • Systemic Vascular Resistance (SVR).

  • Calculated using MAP, CVP, and CO.

  • Obtained via invasive monitoring (PA catheter/Swan-Ganz).

Cardiac Output (CO)

• Definition: Blood pumped per minute (L/min).

• Formula: CO = Stroke Volume (SV) × Heart Rate (HR).

• Normal: 4–8 L/min.

• Limitation: Absolute CO doesn’t account for body size.

Cardiac Index (CI)

• Definition: CO adjusted for Body Surface Area (BSA).

• Normal: 2.5–4 L/min/m².

• Clinical use: More accurate than raw CO.

• Example:

  • Large patient (Arnold) CO = 4 → CI may be low.

  • Smaller patient (Tom) CO = 4 → CI may be normal.

Mean Arterial Pressure (MAP)

• Definition: Average arterial pressure across one cardiac cycle.

• Formula: (SBP + 2×DBP) ÷ 3.

• Goal: ≥ 65 mmHg for organ perfusion.

• Clinical use: Key target in shock management.

Contractility (Inotropy)

• Definition: Force of myocardial contraction.

• Positive inotropes (↑ contractility):

  • Dobutamine (standard inotrope for low CO).

• Positive inotrope + Negative chronotrope:

  • Digoxin (↑ contractility, ↓ HR).

• Negative inotropes (↓ contractility):

  • Beta-blockers → cardioprotective post-MI (↓ oxygen demand, allow myocardium to rest).

Pulmonary Capillary Wedge Pressure (PCWP)

• Also called: Pulmonary artery occlusive pressure (PAOP).

• Obtained via: Swan-Ganz (PA) catheter.

  • Inserted via IJ → RA → RV → PA → wedged in small PA branch.

  • Balloon inflation allows distal lumen to “sense” left atrial pressures.

• Normal: 6–12 mmHg.

• Clinical use: Best indirect measure of left atrial/left ventricular end-diastolic pressure.

• Limitations: In pulmonary hypertension → may need direct LA line.

• Waveforms while threading:

  • RA: low pressure, CVP waveform (2–6 mmHg).

  • RV: higher systolic pressures, spiked waveform.

  • PA: systolic/diastolic pressures, pulmonary artery waveform.

  • Wedged: flat waveform, reflects PCWP.