(4) Hemodynamics - Definitions, Formulas, Values

Answer: The amount of blood ejected by the ventricle with each beat.
Rationale: SV = blood ejected per beat (normal ~50–100 mL).

Stroke volume (SV) is:

Answer: ~70 mL (range 50–100 mL).
Rationale: File notes normal SV 50–100 mL with average ~70 mL.

Normal stroke volume average in your file:

Answer: CO = HR × SV.
Rationale: CO equals number of beats per minute times stroke volume.

Cardiac output (CO) formula:

Answer: 4–8 L/min.
Rationale: Typical resting CO between 4–8 liters per minute.

Normal adult cardiac output range:

Answer: CO divided by body surface area (BSA).
Rationale: CI normalizes CO to body size; normal ~2.5–4 L/min/m².

Cardiac index (CI) is:

Answer: 55–65%.
Rationale: EF is percentage of LV blood ejected each beat; <40% indicates systolic HF.

Ejection fraction (EF) normal range:

Answer: The degree of ventricular stretch at end-diastole.
Rationale: Preload relates to end-diastolic volume/pressure; measured by CVP/PAOP.

Preload is best described as:

Answer: The resistance the ventricle must overcome to eject blood.
Rationale: Afterload influenced by arterial pressure and valve stenosis.

Afterload refers to:

Answer: Greater ventricular stretch (preload) leads to stronger contraction (up to physiologic limit).
Rationale: Increased sarcomere length increases force of contraction within limits.

Frank–Starling law states:

Answer: Contractility.
Rationale: Drugs like digoxin, dobutamine increase contractile strength.

Positive inotropes increase:

Answer: Acidosis and some electrolyte disturbances.
Rationale: Acidosis depresses myocardial function; hypoxia/hyperkalemia also impair contractility.

Factors that decrease contractility include:

Answer: ~800–1200 dynes·sec·cm⁻⁵ (file uses dynes/cm³ wording).
Rationale: SVR is LV afterload; file lists ~800–1200.

Systemic vascular resistance (SVR) normal range (from file):

Answer: ~100–250 dynes·sec·cm⁻⁵.
Rationale: PVR reflects RV afterload; file notes 100–250.

Pulmonary vascular resistance (PVR) normal range:

Answer: MAP ≈ (SBP + 2×DBP) / 3.
Rationale: MAP weighted toward diastolic phase since diastole lasts longer.

Mean arterial pressure (MAP) formula (approx):

Answer: 70–105 mmHg.
Rationale: Minimum ~70 mmHg typically needed for organ perfusion.

Normal MAP range per file:

Answer: Systolic BP − diastolic BP.
Rationale: Difference measures stroke volume/arterial compliance; normal ~40 mmHg.

Pulse pressure equals:

Answer: Increased stroke volume, aortic regurgitation, or increased ICP/Cushing triad context.
Rationale: Widened PP may reflect high systolic or low diastolic pressure.

A widened pulse pressure (>40 mmHg) may indicate:

Answer: 60–80%.
Rationale: Measures residual O₂ after tissue extraction; deviations signal mismatch in supply/demand.

Mixed venous oxygen saturation (SvO₂) normal:

Answer: Decreased tissue extraction (e.g., sepsis) or high CO with poor extraction.
Rationale: High SvO₂ means more O₂ returning unused—seen in some pathologies.

An increase in SvO₂ could indicate:

Answer: Increased O₂ extraction — low delivery states like anemia, low CO, or hypoxia.
Rationale: Lower SvO₂ indicates tissues are extracting more due to decreased delivery.

A decrease in SvO₂ suggests: