The Millar MPVS Duo can be used in Admittance Mode or Conductance Mode. In admittance mode, the screen prompts users to enter the calibration parameters for the admittance PV Loop Protocol, as shown below.
The Millar MPVS Duo requires three study parameters when in admittance mode: 1) Muscle, 2) Stroke Volume, and 3) Blood Resistivity. The system provides default values each parameter, but users are encouraged to input known values if available.
- Enter Muscle: To change the default muscle parameter, press 1 on the MPVS Duo's keypad. This parameter represents the electrical properties of heart muscle tissue type relating to the σ/ε ratio. An infarcted heart, for example, exhibits an increased heart type value (σ/ε ratio) due to reduced capacitance. Typically, non-infarcted tissue averages 800 K, while infarcted tissue can return 900 K or higher. If the muscle parameter is unknown, use the values listed in the table below for the type of heart tissue you are working with.
- Enter Stroke Volume: To change the default stroke volume (SV), press 2 on the MPVS Duo's keypad. The SV calibration parameter is used to normalize (scale) the computed volume output from the MPVS Duo. When possible, it is recommended to determine SV for each animal or for a small sample population. The SV values can be averaged and input into the MPVS Duo for subsequent experiments. Some of the common methods of determining SV are echocardiography, Swan-Ganz thermo-dilution catheter, aortic flow probe, etc. Good practice dictates acquiring baseline SV values under conditions that mimic those of the experimental protocol, including anesthesia, heart rate, body temperature, and ventilation.
- Enter Blood Resistivity: To change the default blood resistivity, press 3 on the MPVS Duo's keypad. These values are loaded directly from the attached catheter. Experimental interventions such as the administration of fluid, can change the blood resistivity of the animal model. To compensate, blood resistivity can be measured and adjusted from the default value. Default blood resistivity values are shown in the table below.
The user can additionally restore all system calibrations values to factory defaults by pressing 4 on the MPVS Duo's keypad. This option is only selectable once a parameter has been changed from the default value.
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