Cardiac function 2
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Ventricular Pressure Volume Loop
Venous return/CO curves
- Venous return must equal CO on average
- There is only one value for MRAP at which venous return is equal to CO. This is the steady state equilibrium at which the heart operates
Ventricular Function curves
Stroke volume or stroke work against preload?
- Stroke work is better as SV is suseptable to changes in afterload (if MAP increases, SV decreases and SW stays the same)
- SW vs. LVEDP (preload) as easy to measure
- Family of curves for different inotropic states
- Can use to analyze the changes in contractility of a heart
Measurement of Pressure
- Use a fluid filled catheter connected to a pressure transducer
- LA pressure can be measured usinf the pulmonary artery wedge pressure method:
- Catheter passed via veins>RA>RV>Pumonary artery, inflated balloon get left atrial pressure, deflated ballon get pulmonary artery pressure.
Measurement of CO
- Uses the Fick Method based on conservation of mass:
- A1 + A2 = A3
- Where A1 equals the O2 entering the lungs via PA
- A2 = O2 addition in the lungs
- A3 = O2 leaving lungs in PV
- this method can be used using a bolus of dye-rate of dilution used to calculate flow rate.
Based of Fick method but uses cold saline as the indicator and rate of change in temp to calculate flow rate. advantages include in arterial puncture, no toxicity and recirculation is negligible.
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