Reference
Plain-language terms, and the definition of every number the simulator shows.
Terms
- Preload · also end-diastolic volume as preload
- How far the ventricle is stretched at the end of filling, best described by end-diastolic volume. Filling pressure is related to it but is not the same thing.
- Afterload
- The load the ventricle ejects against: arterial pressure, vascular resistance and compliance together.
- Contractility · also inotropy
- How strongly the muscle can generate pressure at a given volume. In the model it is the end-systolic elastance, Ees.
- Ees · also end-systolic elastance
- Slope of the end-systolic pressure–volume line. Higher means stiffer, stronger contraction. Exact definition
- Ea · also arterial elastance
- Effective arterial elastance: end-systolic pressure divided by stroke volume, a lumped description of afterload. Exact definition
- ESPVR · also end-systolic pressure–volume relationship
- The line joining end-systolic points of loops made under different loading.
- EDPVR · also end-diastolic pressure–volume relationship
- The curve of passive filling pressure against volume. It steepens as the ventricle fills, so the last mL of filling costs the most pressure.
- LVEDV · also EDV, end-diastolic volume
- Left ventricular volume at the end of filling. The best simple picture of preload. Exact definition
- LVESV · also ESV, end-systolic volume
- Left ventricular volume at the end of ejection. Exact definition
- Stroke volume · also SV, LV SV
- Blood ejected per beat: end-diastolic minus end-systolic volume (net of any regurgitation). Exact definition
- Ejection fraction · also EF, LVEF
- Stroke volume as a percentage of end-diastolic volume. It depends on loading as well as contractility. Exact definition
- Filling pressure (LVEDP) · also LVEDP, filling pressure
- Left ventricular pressure at the start of ventricular contraction: the pressure cost of the volume the ventricle holds. Exact definition
- Wedge pressure (PAWP) · also PAWP, PCWP, wedge
- Pressure recorded with a balloon catheter wedged in a pulmonary artery branch, an estimate of left atrial pressure when the wedge is complete. Exact definition
- Right atrial pressure (RAP) · also RAP, CVP, central venous pressure
- Mean pressure in the right atrium, a downstream pressure for venous return. Exact definition
- Mean arterial pressure (MAP) · also MAP
- Average aortic pressure over the beat. Exact definition
- Cardiac output · also CO
- Net flow per minute into the systemic arteries: stroke volume times heart rate. Exact definition
- Cardiac index · also CI
- Cardiac output divided by body surface area. Exact definition
- SVR · also systemic vascular resistance
- Pressure drop across the systemic circulation divided by flow. A calculated number, not a measurement of the arterioles themselves. Exact definition
- PVR · also pulmonary vascular resistance
- Pressure drop across the lungs divided by flow. Exact definition
- Stressed volume · also unstressed volume
- The part of blood volume that stretches the vessel walls and generates pressure. Unstressed volume only fills the space.
- Mean systemic filling pressure · also MSFP
- The pressure in the systemic circulation if the heart stopped and flow equalised. It drives venous return.
- Venous return
- Flow from the systemic veins back to the right atrium. At steady state it equals cardiac output.
- Frank–Starling relationship · also Starling
- A fuller ventricle ejects a larger stroke volume, up to a point.
- Elastance · also time-varying elastance
- Pressure per unit of volume above the chamber's unstressed volume. It rises and falls through each beat.
- Compliance
- Volume change per unit of pressure change: the inverse of stiffness.
- Transmural pressure · also distending pressure
- Pressure inside a chamber minus the pressure outside it. This is what stretches the chamber, not the measured pressure alone.
- Pulse pressure variation · also PPV, SVV
- Breath-to-breath swing in pulse pressure on a ventilator. It is only interpretable under specific conditions.
- Qp/Qs · also shunt ratio
- Pulmonary flow divided by systemic flow. Above 1 means net left-to-right shunting. Exact definition
- Fick method · also thermodilution
- Cardiac output from oxygen consumption divided by the arteriovenous oxygen difference.
- Baseline
- The state you compare against. Here it is the starting patient and stays fixed until you replace it.
Measurements
Rhythm
- Heart rate (bpm)
- 60 / RR interval of the displayed beat.
- Instantaneous rate of one beat; irregular rhythms vary beat to beat.
Left ventricle
- LV end-diastolic volume (mL)
- Maximum LV volume in the beat.
- Chamber volume is a model state, not an imaging estimate.
- LV end-systolic volume (mL)
- Minimum LV volume in the beat.Model-derived (not directly measurable in a patient) · validity: Always defined.
- LV total stroke volume (mL)
- LVEDV − LVESV. Total chamber excursion, which includes any regurgitant volume.
- Not equal to forward stroke volume when the aortic or mitral valve leaks.
- LV ejection fraction (%)
- 100 × (LVEDV − LVESV) / LVEDV.
- Total ejection fraction, not effective forward EF.
- EF is load dependent and is not a measure of contractility (Ees).
Flow and output
- Forward aortic stroke volume (mL)
- Net aortic valve flow per beat: ejected volume minus aortic regurgitant volume (effective forward stroke volume).
- Net flow through the aortic valve only; device flow is reported separately.
- Volume ejected through the aortic valve (mL)
- Integral of positive aortic valve flow. Exceeds the effective forward volume in aortic regurgitation.Calculated from signals · validity: Always defined.
- Forward pulmonic stroke volume (mL)
- Net pulmonic valve flow per beat (ejected minus pulmonic regurgitant volume).Calculated from signals · validity: Always defined.
- Systemic cardiac output (L/min)
- Effective forward (net aortic) stroke volume × heart rate / 1000.
- In an unsupported circulation without shunts this equals systemic flow.
- During MCS, device flow is reported separately and not added here.
- Pulmonary blood flow (L/min)
- Net pulmonic stroke volume × heart rate / 1000.
- Equals systemic flow in steady state without shunts.
- Mitral regurgitant volume (mL)
- Integral of negative (retrograde) mitral flow over the beat.Calculated from signals · validity: Reported as 0 when the valve is competent.
- Aortic regurgitant volume (mL)
- Integral of negative (retrograde) aortic valve flow over the beat.Calculated from signals · validity: Reported as 0 when the valve is competent.
- Tricuspid regurgitant volume (mL)
- Integral of negative tricuspid flow over the beat.Calculated from signals · validity: Reported as 0 when the valve is competent.
- Mitral regurgitant fraction (%)
- 100 × MR volume / total LV stroke volume.
- Model flow fraction; not a clinical severity grade without a reviewed mapping.
- Aortic regurgitant fraction (%)
- 100 × AR volume / volume ejected through the aortic valve.
- Model flow fraction; not a clinical severity grade without a reviewed mapping.
- Native aortic output (L/min)
- Net aortic valve flow × heart rate / 1000 (blood ejected by the LV through its own valve).
- Excludes device flow; see co.impella, co.ecmo and co.total.
- Microaxial pump flow (L/min)
- Mean LV-to-aorta pump flow over the beat (parallel to the aortic valve).
- Pressure–flow characteristic is a placeholder until manufacturer curves are mapped (device record).
- VA-ECMO circuit flow (L/min)
- Mean RA-to-arterial circuit flow over the beat (parallel to the whole heart).
- Set flow reduced by arterial afterload sensitivity and RA drainage limits (placeholder circuit).
- Total systemic output (L/min)
- Native aortic + microaxial + ECMO flow: these are parallel paths into the systemic arteries, so they add. Serial segments are never added.
- Cross-checked against mean systemic arteriolar flow (co.systemicCheck).
- Mean systemic arteriolar flow (conservation check) (L/min)
- Mean flow through the systemic arterioles; equals total output at steady state if the circuit conserves flow.Model-derived (not directly measurable in a patient) · validity: Always defined.
- Aortic valve open fraction (%)
- Percentage of the beat during which the aortic valve is open (0 = the valve never opens, as under high VA-ECMO flow).Model-derived (not directly measurable in a patient) · validity: Always defined.
- Pump suction present (% of beat)
- Percentage of the beat in which microaxial inflow is limited by a small LV cavity.
- Suction is modelled as a smooth flow limit below the suction volume; no alarm logic.
- Pulmonary-to-systemic flow ratio (unitless)
- Net pulmonic flow divided by net systemic (aortic) flow.
- Equals 1 without shunts; > 1 for left-to-right shunting.
- Net shunt flow (ASD + VSD, left-to-right positive) (L/min)
- Mean net flow across the modelled defects per minute.Model-derived (not directly measurable in a patient) · validity: Zero without defects.
Pressures
- LV end-diastolic pressure (mmHg)
- LV pressure at the onset of ventricular activation (QRS-equivalent).
- End-diastole defined by activation onset; in aortic regurgitation this precedes the maximal-volume sample.
- LV peak systolic pressure (mmHg)
- Maximum LV pressure in the beat.Model-derived (not directly measurable in a patient) · validity: Always defined.
- Aortic systolic pressure (mmHg)
- Maximum central aortic root pressure in the beat.
- Central aortic, not peripheral cuff or radial pressure.
- Aortic diastolic pressure (mmHg)
- Minimum central aortic root pressure in the beat.Model-derived (not directly measurable in a patient) · validity: Always defined.
- Mean arterial pressure (mmHg)
- Time average of central aortic root pressure over the beat.
- True time average, not the 1/3 pulse pressure estimate.
- Aortic pulse pressure (mmHg)
- Ao sys − Ao dia.Calculated from signals · validity: Always defined.
- PA systolic pressure (mmHg)
- Maximum proximal pulmonary artery pressure in the beat.Model-derived (not directly measurable in a patient) · validity: Always defined.
- PA diastolic pressure (mmHg)
- Minimum proximal pulmonary artery pressure in the beat.Model-derived (not directly measurable in a patient) · validity: Always defined.
- Mean PA pressure (mmHg)
- Time average of proximal PA pressure over the beat.Model-derived (not directly measurable in a patient) · validity: Always defined.
- Mean pulmonary artery wedge pressure (model) (mmHg)
- Time average of the pulmonary venous compartment pressure. Stands in for the wedge pressure a catheter would record; the observation layer (M11) adds catheter artifacts separately.
- Equals mean pulmonary venous pressure in the model; a real wedge includes catheter position and damping effects.
- No respiratory gating applied (respiratory swing is zero unless enabled).
- Mean left atrial pressure (mmHg)
- Time average of LA pressure over the beat.Model-derived (not directly measurable in a patient) · validity: Always defined.
- Mean right atrial pressure (mmHg)
- Time average of RA pressure over the beat. Equivalent to CVP in the model.
- No respiratory gating applied.
- LV–aortic instantaneous peak gradient (mmHg)
- Maximum of (LV − aortic root pressure) while the aortic valve is open.
- True-signal gradient; the cath lab recomputes it from recorded signals.
- Includes any dynamic LVOT gradient.
- LV–aortic mean gradient (mmHg)
- Mean of (LV − aortic root pressure) over the ejection period.
- Gradient rises with flow² for a fixed orifice.
- Transmitral mean diastolic gradient (mmHg)
- Mean of (LA − LV pressure) while the mitral valve is open.
- Rises with flow and with shorter diastole (rate).
- Transtricuspid mean diastolic gradient (mmHg)
- Mean of (RA − RV pressure) while the tricuspid valve is open.Model-derived (not directly measurable in a patient) · validity: Not applicable if the valve never opens.
- Dynamic LVOT peak gradient (mmHg)
- Maximum pressure drop across the dynamic outflow-tract orifice (area falls as the LV empties).
- Volume-dependent orifice model; provocation changes it through preload, afterload and contractility.
- LA v wave (peak) (mmHg)
- Peak LA pressure while the mitral valve is closed.
- A large v wave is not a stand-alone MR severity classifier; it depends on LA compliance.
- LA a wave (peak) (mmHg)
- Peak LA pressure in the 150 ms before mitral closure (atrial contraction).Model-derived (not directly measurable in a patient) · validity: Not applicable without organised atrial contraction.
- RA v wave (peak) (mmHg)
- Peak RA pressure while the tricuspid valve is closed.
- Prominent in TR; also raised by cannon waves in AV dissociation.
- RA a wave (peak) (mmHg)
- Peak RA pressure in the 150 ms before tricuspid closure.Model-derived (not directly measurable in a patient) · validity: Not applicable without organised atrial contraction.
- Mean pericardial pressure (model) (mmHg)
- Time average of the modelled pericardial pressure.
- Exponential pericardial relation of total heart volume plus effusion.
- LV end-diastolic transmural pressure (mmHg)
- LV pressure minus external (transmitted pleural + pericardial) pressure at end-diastole: the pressure that actually distends the chamber.
- Differs from the measured LVEDP whenever pleural or pericardial pressure is not zero.
- Mean RA transmural pressure (mmHg)
- Mean RA pressure minus transmitted pleural and pericardial pressure.Model-derived (not directly measurable in a patient) · validity: Always defined.
- IABP diastolic augmentation (mmHg)
- Peak aortic pressure while the balloon is inflated minus the unassisted systolic peak.
- Depends on balloon volume, arterial compliance and timing.
- Assisted aortic end-diastolic pressure (mmHg)
- Aortic pressure at ventricular activation onset (the pressure the LV must exceed to eject).Model-derived (not directly measurable in a patient) · validity: Always defined.
Right ventricle
- RV end-diastolic volume (mL)
- Maximum RV volume in the beat.Model-derived (not directly measurable in a patient) · validity: Always defined.
- RV end-systolic volume (mL)
- Minimum RV volume in the beat.Model-derived (not directly measurable in a patient) · validity: Always defined.
- RV total stroke volume (mL)
- RVEDV − RVESV.
- Includes regurgitant volume when the tricuspid or pulmonic valve leaks.
- RV ejection fraction (%)
- 100 × (RVEDV − RVESV) / RVEDV.
- Load dependent; not contractility.
Indices
- Cardiac index (L/min/m²)
- CO / body surface area.
- BSA is a scenario parameter.
- Cardiac power output (W)
- MAP × CO / 451.
- No universal threshold is implied.
- Pulmonary artery pulsatility index (unitless)
- (PA sys − PA dia) / RAP.
- Context dependent; no universal threshold implied.
Resistance
- Systemic vascular resistance (WU)
- (MAP − RAP) / CO in Wood units (mmHg·min/L). Multiply by 80 for dyn·s·cm⁻⁵.
- Uses systemic forward flow.
- SVR (dyn·s·cm⁻⁵) (dyn·s·cm⁻⁵)
- SVR in Wood units × 80.Calculated from signals · validity: Same as SVR.
- Pulmonary vascular resistance (WU)
- (mPAP − PAWP) / pulmonary flow in Wood units.
- Uses pulmonary (not systemic) flow and the model wedge pressure.
Coupling
- LV end-systolic pressure (mmHg)
- LV pressure at aortic valve closure (last open→closed transition); falls back to the minimum-volume sample if the valve never opened.
- End-systole defined by aortic valve closure.
- Effective arterial elastance (mmHg/mL)
- LVESP / total LV stroke volume.
- Ea is a lumped afterload index, not SVR.
- Standard unsupported-circulation definition; not valid with major regurgitation or MCS.
- LV end-systolic elastance (model parameter) (mmHg/mL)
- The model's contractility parameter. Known exactly because it is set, not identified from a single loop.
- A single ordinary loop cannot identify Ees; this value is the model parameter.
- Ventricular-arterial coupling ratio (unitless)
- Ea / Ees using the model Ees.
- Interpretation assumes an unsupported circulation without major regurgitation.
Work
- LV stroke work (J)
- Net loop integral ∮P dV of the LV pressure–volume trajectory; 1 mmHg·mL = 1.333×10⁻⁴ J.
- Counter-clockwise loop positive. For a transient beat the loop is closed artificially and the value is an estimate.
- RV stroke work (J)
- Net loop integral ∮P dV of the RV pressure–volume trajectory.
- Same conventions as LV stroke work.
- LV pressure–volume area (model estimate) (J)
- Stroke work plus the potential energy between the model ESPVR and EDPVR from V0 to ESV.
- Uses the model-known relations; not identifiable from one clinical loop.
- No myocardial oxygen consumption or efficiency is derived from it.
Oxygen
- Pulmonary artery saturation (mixing teaching model) (%)
- Flow-weighted mixture of systemic venous blood (Fick SvO₂ on systemic flow) and left-to-right shunted arterial blood.
- Single systemic venous saturation (no SVC/IVC difference); right-to-left shunting lowers arterial saturation, which is not fed back to SaO₂.
- Oxygen saturation step-up (PA minus systemic venous) (% points)
- PA saturation minus systemic venous saturation; positive with left-to-right shunting.
- No threshold for significance is applied without its source.
- Arterial oxygen content (mL/dL)
- 1.34 × Hb × SaO₂ (dissolved oxygen neglected).
- Dissolved O₂ (0.003 × PaO₂) omitted; Hb and SaO₂ are scenario inputs.
- Oxygen delivery (mL/min)
- CaO₂ × CO × 10.
- Uses systemic forward flow of the displayed beat.
- Mixed venous oxygen saturation (steady-state Fick) (%)
- SaO₂ − VO₂ / (1.34 × Hb × CO × 10), i.e. the saturation at which the Fick principle balances consumption against delivery.
- Steady-state oxygen balance with a single systemic compartment; no regional extraction differences, so ScvO₂ is NOT derived from it.
- VO₂ is a scenario input, not measured; organ injury, lactate and urine output are not deterministic readouts of this value.
- Oxygen extraction ratio (%)
- 100 × VO₂ / DO₂.
- Same steady-state assumptions as SvO₂.
- Central venous oxygen saturation (%)
- Would require a regional mixing model (SVC vs IVC extraction); not derived from SvO₂.
- Kept distinct from SvO₂ by design (spec M12).
Volume
- Total blood volume (model) (mL)
- Sum of all compartment volumes at the beat start.
- Conserved except for explicit fluid or blood-loss interventions.
- Volume exchanged with external reservoir (mL)
- Net volume that left the circulation into clamp reservoirs during the beat (positive = removed). Zero unless a clamp is active.
- Only non-zero in isolated-physiology mode; shows that volume is not conserved while clamps are active.
- Stressed systemic venous volume (mL)
- Mean systemic venous volume − unstressed volume.
- Model construct; not clinically measurable directly.
See a number in the simulator? Open the full laboratory and choose All measurements to see it for the displayed beat.