BLOOD PRESSURE MONITOR/METER

Typical Number in Hospital:

Cost Bands:

References: 6,9

This may monitor blood pressure in the chambers of the heart, in arteries, veins, or in the capillary bed. The most common pressure to be measured is the arterial pressure, and this can be obtained indirectly (from outside the body), or measured directly through catheters or needles placed within the blood stream.

Indirect blood pressure monitors include the common sphygmomanometer which records the external pressure required to occlude an artery within a limb. Since the arterial blood pressure is pulsatile it is possible to identify the point at which the blood pressure is just able to open the artery (systolic, or peak blood pressure) and the blood pressure at which the artery just closes momentarily at its lowest internal pressure (diastolic blood pressure). These two points may be detected by listening through a stethoscope placed on the skin downstream of the pressure cuff, or it may be detected automatically from the pulse waveform produced in the pressure cuff, by the sounds detected by a microphone on the skin under the pressure cuff, or by an ultrasonic doppler transducer which detects the arterial wall movement. Double cuff methods are used in the oscillometer and haemotonometer. Automated indirect blood pressure recorders are sometimes incorporated into other instruments monitoring temperature, respiration rate, and heart rate.

To record the waveform of the arterial pressure a catheter or needle must be introduced into the artery and connected to an electrical pressure transducer. Such devices must record the waveform faithfully and this requires a frequency response of at least ten times the heart rate (e.g. 15 Hz). Good frequency response is particularly important when recording within the chambers of the heart in the cardiac catheter laboratory and the fidelity of the recording depends on the diameter, length, and compliance of the catheter, and on the exclusion of all air from the system.