What are the sources of error in measuring blood pressure and plulse?
I was working on a lab to investigate the effects exercise and how it affects the heart rate and blood pressure. We used a blood pressure machine and HR monitor. I was wondering what the potential sources of error could be for this setup.
Blood pressure (BP) is measured by placing an inflatable cuff around the upper arm, inflating the cuff to a pressure higher than the blood pressure, then gradually deflating the cuff as one listens with a stethoscope to the crook of the arm for the pulse. The pressures when the pulse first appears, and when the pulse drops off or changes quality are recorded as the systolic and diastolic pressures, respectively. The pulse can be determined by listening during the blood pressure determination, or by feeling the pulse at the wrist.
A machine can do these functions. The machine inflates and deflates the cuff, and measures the pulses using a Doppler device. The computer also keeps track of the pulse rate.
Since you are using a machine in your study, you should read the manufacturer’s manual to determine the pitfalls and inaccuracies expected. Follow the manufacturer’s instructions exactly to obtain optimal results. Also, repeated measurements are helpful.
An experienced examiner must teach the correct manual technique for BP measurement. It is important to recognize the somewhat subtle pulse change that marks the correct diastolic pressure. The rate and degree of cuff inflation, as well as the bleed-off speed are important.
Other important considerations (and therefore sources of error) are as follows:
Cuff size: A larger patient needs a larger cuff.
Patient position: The patient should be seated comfortably with arm at side in a comfortable, loosely flexed position, free of obstructing clothing.
Clothing: Do not place the cuff over, or listen through clothing.
Multiple readings: Always a good idea to obtain an accurate reading.
Compared to BP, pulse measurement is far less subject to error. Again, repeated measurements (either manually or by machine) are recommended.