Cath-Lab Hemodynamic Calculations – Key Vocabulary

Vocabulary flashcards cover key terms, formulas, constants, and clinical concepts from the lecture on cardiac calculations used in the cath lab.

Fick Cardiac Output

Gold-standard method for measuring cardiac output based on oxygen consumption and arterial-venous O₂ content differences.

Thermodilution Cardiac Output

Cardiac output obtained by injecting cold saline through a Swan-Ganz catheter and measuring the downstream temperature change.

Oxygen Consumption (VO₂)

The volume of O₂ used by the body per minute (≈ 250 mL / min); entered into computers from height-weight tables for Fick calculations.

Hemoglobin (Hb)

Blood protein that carries O₂; multiplied by 1.36 in the Fick formula to derive O₂ content.

Arterial O₂ Saturation (AO Sat)

Percentage of hemoglobin saturated with O₂ in systemic arterial blood; sampled from the femoral or radial line for Fick CO.

Pulmonary Artery O₂ Saturation (PA Sat)

Mixed-venous O₂ saturation obtained from the PA via Swan-Ganz; represents de-oxygenated blood in Fick CO.

Fick Constant (1.36)

Theoretical mL of O₂ a gram of hemoglobin can bind; built into cath-lab software for Fick calculations.

Fick CO Formula

CO = VO₂ ÷ [(Hb·1.36·AO Sat) – (Hb·1.36·PA Sat)] × 10.

Clinical Situations Favoring Fick

Regurgitant valves, intracardiac shunts, arrhythmias (e.g., AFib), and cardiomyopathies where thermodilution is unreliable.

Arterial O₂ Content (CaO₂)

Hb·1.36·AO Sat; O₂ carried per 100 mL of arterial blood, expressed as volume %.

Venous O₂ Content (CvO₂)

Hb·1.36·PA Sat; O₂ carried per 100 mL of mixed-venous blood.

Cardiac Output (CO)

Volume of blood ejected by the heart per minute; reported in L / min.

Stroke Volume (SV)

Blood volume ejected per beat; SV = EDV – ESV (mL).

End-Diastolic Volume (EDV)

LV volume when completely filled (end of diastole).

End-Systolic Volume (ESV)

LV volume remaining after contraction (end of systole).

SV Formula

SV = EDV – ESV; units in milliliters.

Angiographic Cardiac Output

CO = (HR × SV) ÷ 1000, where SV is derived from LV angiogram volumes.

mL → L Conversion

Divide by 1,000 when converting SV·HR product to liters per minute.

Ejection Fraction (EF)

EF = SV ÷ EDV; expresses percent of LV volume ejected each beat.

Cardiac Index (CI)

CO adjusted for patient size: CI = CO ÷ BSA (L / min / m²).

Body Surface Area (BSA)

Patient size metric (m²) used to normalize CO into Cardiac Index.

Systolic Ejection Period (SEP)

Seconds the aortic valve is open each beat; used in aortic Gorlin calculations.

Mean Gradient

Average pressure difference across a valve throughout flow; computer-derived by overlapping LV and AO (or LA and LV) traces.

Gorlin Constant – Aortic

44.5; built into aortic valve area calculation.

Gorlin Constant – Mitral

37.7; built into mitral valve area calculation.

Diastolic Filling Period (DFP)

Seconds the mitral valve is open each beat; replaces SEP in mitral Gorlin formula.

Hakki Formula

Quick estimate: Valve Area ≈ CO (L/min) ÷ √(Peak-to-Peak Gradient).

Peak-to-Peak Gradient

Difference between peak LV systolic and peak AO systolic pressures across the aortic valve.

Regurgitant Fraction

(Angiographic CO – Fick/Thermo CO) ÷ Angiographic CO; expresses % volume regurgitated.

Normal Aortic Valve Area

3 – 4 cm²; < 1.2 cm² indicates significant stenosis.

Tight Aortic Valve Threshold

Valve area approaching or below 1.0 cm² considered severe stenosis needing intervention.

Inch-to-Centimeter Conversion

1 inch = 2.54 cm; used for height entry and catheter measurements.

Mitral Valve Mean Gradient

Computer-derived average pressure difference between LA and LV during diastole.

Aortic Valve Flow

Step 3 of Gorlin: CO (mL/min) ÷ total SEP seconds per minute to get mL/sec across aortic valve.

Mitral Valve Flow

Step 3 of Gorlin (mitral): CO (mL/min) ÷ total DFP seconds per minute to get mL/sec across mitral valve.

44.5 × √ΔP Term

Denominator component in aortic Gorlin converting flow into area (cm²).

Why Do Calculations?

Provide concrete numbers to trend patient status (e.g., EF rise from 35 % to 45 %).

Average VO₂ Value

Typical adult oxygen consumption ≈ 250 mL / min – supplied on exams.

Purpose of SV Measurement

Determines how much blood the heart pumps per beat, foundational for CO and EF.

Gold Standard

In cath hemodynamics, Fick CO and Gorlin valve areas are considered the reference methods.