The attached Excel workbook has the formulas used in the different calculations of Tau  when using Ponemah's LVP analysis module.

Definition:

• Tau
  Tau is the time constant isovolumic left ventricular pressure decay. It is reported in milliseconds, and can be defined as described in the Attributes window section.

Methods:

• Tau Duration
  Defines the duration over which Tau is to be calculated, starting at ‑dP/dtMAX. Tau Duration is measured in milliseconds. Three methods are used for calculating Tau: Pressure, dP/dt, and DevPressure.
• Pressure:
  Tau is calculated as the negative inverse of the slope of the regression line of the natural logarithm of Left Ventricular Pressure versus time.
• dP/dt:
  Tau is calculated as the negative inverse of the slope of the regression line of the natural log of left ventricular pressure -dP/dt versus time.
• DevPressure:
  Tau is calculated as the negative inverse of the slope of the regression line of the natural log of left ventricular pressure - the previous end diastolic level versus time.
• Tau Method
  Defines which two values are used in the calculation of Tau.  Use different methods for different conditions.  Each method passes the data into the formula that calculates the linear line equation using the least square method.  The three available methods are:  Pressure, dP/dt, and DevPressure.