# LVP Tau Formulas

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.

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