Chapter 2
Using the Controller
23
8.
Measured signals: The basic signals recorded by the ML125 NIBP system
are the cuff pressure and the caudal artery pulse.
Cuff pressure is an accurate high level signal with noise of less than +/– 0.1
mmHg and absolute error of less than +/– 2 mmHg (after calibration).
This data is used in association with the reappearance of the caudal artery
pulse to determine the systolic pressure.
The caudal artery pulse is a low level pulse requiring significant
amplification—this is particularly true of mice. The signal is therefore
mixed with noise, and subject to movement and respiratory artifacts. The
signal amplitude may alter significantly as the animal moves and
repositions the transducer in relation to the caudal artery.
A significant feature of the caudal artery pulse is its frequency. For a
conscious rat this is typically in the range 200–500 BPM. For a given set of
circumstances this frequency is relatively constant. The user should be
aware of this frequency, as it will be useful in later analysis.
A sampling rate in the range of 100 – 1000 samples per second will be
adequate for pulse measurements.
Movement and respiratory artefacts in tail pulse measurements are
particularly disruptive because they often occur at times coincident with
actual measurements. However, it should be noted that the technique is
dependent not on the amplitude of the pulse, but rather its onset.
9.
Systolic measurement: Systolic measurement can normally be made with
relative ease. Systolic blood pressure (SBP) occurs when the cuff pressure
corresponds to the restoration of the first caudal artery pulse. The
presence of noise will inevitably introduce some uncertainty in this
estimate, but typical SBP measurements will be within 5% of direct blood
pressure measurements. Repeat each measurement five to six times to
ensure reproducible results are being obtained.
Although direct observation of the pulse is usually sufficient to determine
the systolic blood pressure point, alternative methods of detecting the
onset of the pulse (by performing certain calculations in LabChart on the
pulse signal) are also available, and may in some circumstances be used
effectively:
a.
RMS measurement of pulse: This can be done using the RMS function in
the Data Pad and can be useful in providing a direct measurement of pulse
energy. An averaging period of about 500 ms to 1 second is useful.
b.
Cyclic height: The Cyclic Measurements ‘Height’ function allows an
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