The flexibility of the BIS-T1 software is demonstrated by this suggested highly distorted "breathing pattern" suitable for MDI instruction. Note that there are four available components to the creation of a respiratory pattern:
The visual analogs created by defining this components are straight lines (the commercial version of BIStm has curvilinear waveform options for more definitive waveform generation). This is not a limitation in this MDI application, as the critical times here involve constant inspiratory flow rates and breath holding.
The following settings are suggested for a large adult:
Adjustment of this trial model is, unfortunately, very awkward. While it is possible to calculate the various parameters, it is easiest to simply use a stop watch to time Inspiration and Inspiration Hold.
You will note in this example the Inspiration Time is approximately 9 seconds, and the Inspiration Hold time is approximately 7 seconds. As the Inspiratory Tidal Volume is 3000 cc, the Inspiratory Flow is 0.33 L/sec. (3 L. / 9 sec = 0.33 L/sec.) This Inspiratory flow at a constant flow rate, Inspiration Volume and Breath Hold time would be appropriate for a large adult.
© April 10, 2000
Adjustment for the correct Tidal Volume for smaller patients is easy. Adjusting the Inspiratory Flow rate to about 0.2 to 0.4 L/sec. is more difficult. Adjust the Respiratory Rate first (note that the Rate may be fine adjusted, e.g. 4.75 bpm). Then, to adjust the Breath Hold time, adjust the Inspiration Hold time accordingly. Note this will change the Inspiratory Flow rate. With a little practice you will soon be able to make accurate adjustments easily.
Attach the flowmeter outside of the MDI (or powdered inhaler device) if possible (i.e. air is drawn through the flowmeter, to the MDI, and then to the patient). If the flowmeter is between the MDI and patient there will be some "rain-out" of aerosol in the flowmeter.
To use the training system, have the patient exhale down to a desired starting volume below Functional Residual Capacity, and then tell the patient to inhale. Simultaneously press the "Esc" key. This will re-set the system and synchronize the device to the patient effort. Thereafter the patient has a visual biofeedback prompt to inspire at the correct flow rate, to the desired inhalation volume, and thereafter breath hold for the programmed interval of time. Exhalation may be passive and non-controlled.
The following illustrates a patient making the common mistake of inhaling too rapidly. Also, not inhaling a sufficiently large breath, and not breath holding for an adequate time.
The following illustrates a patient inhaling at the proper flow rate, but not inhaling the desired deep breath, or breath holding long enough.
The following illustrates proper MDI use. Inspiratory flow is linear and maintained at the proper flow rate. The inspired breath is to the programmed full capacity, and the breath hold time is to the desired interval.
For further details, see the section Metered Dose Inhaler Trainer