Appendix A
Technical Details
27
Pump Control
Control over the cuff inflation and deflation sequence is achieved using an
internal microprocessor. The microprocessor waits until it detects a start
signal either from the front Start/Stop button or from the external trigger
input. It then turns on the internal pump and starts to fill the cuff. While
pumping, it continuously monitors the cuff pressure and compares it to the
maximum cuff pressure set on the back panel switch (either 200 mmHg or
280 mmHg). When this maximum cuff pressure is reached, the pump is
switched off. The air in the cuff is allowed to escape at a predefined rate
through a small release valve. The pressure will continue to decrease until it
reaches about 35–40 mmHg, at which point a quick release solenoid will be
opened to quickly release the residual air.
The inflation and deflation cycle can be stopped (or reset) at any time by
pressing the Start/Stop button during the cycle. The microprocessor then
opens the quick release valve and the pressure will return quickly to
atmospheric. This takes about a second.
Pressure and Pulse Monitoring
In order to determine the systolic pressure the NIBP system provides two
analog output signals for animal pulse and cuff pressure.
An internal pressure transducer is used to monitor the air pressure in the cuff
air supply line. The output of the transducer is amplified and then provided as
a signal from the rear panel on the controller. The NIBP Controller is factory
calibrated to produce 1 volt output per 300 mmHg, with zero volts
corresponding to zero pressure.
The pulse signal is recorded via the Pulse Input connection on the front panel
of the NIBP Controller. This input connection is designed to allow different
types of pulse transducers to be connected, depending on the application. For
rats and mice the pulse transducer is incorporated with the tail cuff. The
signal from the external pulse transducer is amplified and then band-pass
filtered, before being passed to the pulse output connector on the rear panel.
Pulse signal filtering is achieved using a band-pass filter with preset
frequencies depending on the Pulse Range setting on the front panel. The
band-pass filter consists of an analog, second order (two pole) high-pass filter
followed by an eighth order (switched capacitance) low-pass filter.
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