Ventilation

This rather arcane calculator is for studies of ventilation (breathing dynamics) using open-flow plethysmography systems.  It will compute tidal volume (Vt, the volume of gas inspired with each breath), minute volume (Vmin, the total volume of gas inspired each minute), and oxygen extraction (EO2, the fraction of inspired oxygen that is absorbed from tidal gas).

To support these calculations -- which are largely based on the small pressure fluctuations induced by the warming and wetting of tidal air -- you need to provide a number of variables.  Several of these are self-explanatory (at least if you know something about respiratory physiology).  Abbreviations for some of the more obscure ones are:

  • VO2, the rate of oxygen consumption
  • Tb and Ta (body and air temperature)
  • delta-P (pressure gradient between the metabolism chamber and ambient barometric pressure, in mm of water)
  • RH (relative humidity in the metabolism chamber)
  • calibration vol (the volume of gas injected during system calibrations)
  • calibration volts (mean peak height of calibration deflections)
  • calibration gain (signal amplification during calibrations)
  • sample volts (mean peak height of individual breaths in the breathing record)
  • sample gain (signal amplification when recording breathing).

You can use the 'waveform analysis' routines in the ANALYSIS menu to obtain breathing frequeny, calibration volts, and sample volts from recorded breathing records.

       

In this fairly typical example, the animal (a mouse) breathed about 6.3 times per second (not unusual for a small mammal in cold conditions) and had a tidal volume of 0.256 ml and a minute volume of about 97 ml/min.  The oxygen extraction was about 25.7%.

  • Note that you can use either relative humidity (RH) + measurement temperature (T,RH) or water vapor density to compute the water vapor component of the equations.

            Although there are a lot of data to enter, the program makes it as easy as possible.  Most values are remembered between successive uses of the calculator, so you only have to change a few edit fields (like VO2, frequency, and sample volts).  You can tab (or hit return) to move between successive edit fields.

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