Ross Hamilton Lei Qu Hanniff Mohd Nor David Lee Introduction Dr Andre Churchwell is our Sponsor Learned about the vagaries of commercial common blood pressure monitors Automatic monitors lost their accuracy over extended periods of time because of a lack of calibration ID: 725278
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Slide1
Automatic Blood Pressure Monitor Calibration
Ross Hamilton
Lei Qu
Hanniff Mohd Nor
David LeeSlide2
Introduction
Dr. Andre Churchwell is our Sponsor
Learned about the vagaries of commercial common blood pressure monitors
Automatic monitors lost their accuracy over extended periods of time because of a lack of calibration
Results in a repurchase of the monitor after a certain period of time and usesSlide3
Goals
Investigate the possible variation from automatic blood pressure monitor that will cause diagnosis problems
Solve the problem of recalibration
Design a “
rezeroing
” device such as a calibration signal circuit to enhance the accuracy of the monitorsSlide4
Discrepancies recorded in the literatureSlide5
Discrepancies continuedSlide6
Conclusions from the literature
Many other literature also indicate a discrepancies between the mean measurements of the BP monitors versus the mercury
sphymanometer
(ranging from 0.1 to 2.5 mm Hg)
Thus, we can sufficiently conclude that there is a discrepancy between the two measuring devices.
However, to further complement our experiment, we have performed the similar statistic comparison ourselvesSlide7
Cause of the discrepancy
Degree of deflation of the arm band
Affect monitors true zero value
Degradation of piezoelectric resistor after usagesSlide8
Mechanism behind the BP monitor
Piezoelectric resistor
As the arm band inflates, it shuts off the blood flow in the valves of the patient’s arm
As the arm band deflates, the blood flow will restart, thus there will be pressure from blood flow to the arm band
Beginning stage of blood flow is turbulence flow, and as arm band releases, flow becomes more laminarSlide9
Mechanism Continued
Pressure goes to piezoelectric resistor which will act as a transducer and give a signal readout
Systolic pressure will be obtained at the highest variance of the pulse wave peaks
the diastolic pressure will be the lowest variance of the pulse wave peaksSlide10
Flow chartSlide11
ADC circuit schematicSlide12
Microcontroller circuit schematicSlide13
Power Source circuit schematicSlide14
Operational flow chartSlide15
The Gold StandardMercury sphymanometer
Uses no electronic transducers
Mercury is extremely pressure-sensitive
From Watson, et al, the accuracy of the mercury sphymanometer is confirmed. Slide16
Progress thus far
The fake arm experiment between the gold standard and the BP monitor
Bandpass
filter on the breadboard (picture included)Slide17
The fake arm experiment
Null hypothesis: the mean of the Omron values are equal to the mean from the
sphymanometer
Assumptions
The data are obtained from the identical sample population (generated fr4om the same BP analyzer)
The gold standard does not have drifting issuesUsed the fake arm blood pressure analyzer to generate the BP
20 trials
The paired two-tail t-test was conducted to determine the validity of the null hypothesis
P value = 6.19 x 10^-15
Null hypothesis rejected
Hypertension case also experimented with a set average BP (150/100)
P value = 1.15 x 10^-15
Null hypothesis rejectedSlide18
Conclusion
The mean of the Omron values are not equal to the mean of the
sphymanometer
We can infer from this conclusion that variation resulted from the Omron
However, the trials are only 20 so this conclusion is statistically insufficientSlide19
Constructing the circuit
Started constructing the
bandpass
filter
The resisters and capacitors will be modified through trial and error to get a desired filtration of the analog input
The circuitry was modified with the help of Dr. GallowayThe analog input will have frequency simulating the actual heart beat (ranging between 1 and 2 Hz) with a signal intensity of 5 volts
The signal will be captured using
Labview
with a sample rate of 1000 Hz for resolution purposesSlide20
Picture of the breadboardSlide21
Problems faced
The ADC element pins are separately too closely for insertion unto the breadboard
MCU programming may be complex
Running out of time so must dedicate more hoursSlide22
Future work
Add a pressure transducer to the input port
Adapt the ADC unto an artificial chip and connect it to
the filter circuit
Connect the port to the pressurizing pad
Construct the MCU unitConnect the compartmentsPerform another experiment between the gold standard and the BP monitor with greater number of trials (~300 trials)Slide23
References
Discrepancies references
de
Greeff
A,
Shennan A. Blood pressure measuring devices: ubiquitous, essential but imprecise. Expert Rev Med Devices. 2008 Sep;5(5):573-9. ReviewEllis C, Gamble G,
Hamer
A, Williams M,
Matsis
P, Elliott J, Devlin G, Richards M, White H; New Zealand Acute Coronary Syndromes (NZACS) Audit Group. Patients admitted with an acute coronary syndrome (ACS) in New Zealand in 2007: results of a second comprehensive nationwide audit and a comparison with the first audit from 2002.
Heinemann M,
Sellick
K, Rickard C, Reynolds P,
McGrail
M. Automated versus manual blood pressure measurement: a randomized crossover trial.
Int
J
Nurs
Pract
. 2008 Aug;14(4):296-302.
Lamb TS,
Thakrar
A,
Ghosh
M, Wilson MP, Wilson TW. Comparison of two
oscillometric
blood pressure monitors in subjects with
atrial
fibrillation.
Clin
Invest Med. 2010 Feb 1;33(1):E54-62.
Landgraf
J,
Wishner
SH,
Kloner
RA. Comparison of automated
oscillometric
versus
auscultatory
blood pressure measurement. Am J
Cardiol
. 2010 Aug 1;106(3):386-8.
Epub
2010 May 22.
PubMed
PMID: 20643251. [
McManus RJ,
Mant
J, Hull MR, Hobbs FD. Does changing from mercury to electronic blood pressure measurement influence recorded blood pressure? An observational study. Br J Gen
Pract
. 2003 Dec;53(497):953-6.
Misc. resources
http://instruct1.cit.cornell.edu/courses/ee476/FinalProjects/s2005/ww56_ws62/Final%20Project%20Web/index.html
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1120346/
Watson, S.; Wenzel, R. R.;
di
Matteo
, C.; Meier, B.; and
Lüscher
, T. F. (1998). "Accuracy of a new wrist cuff
oscillometric
blood pressure device". American Journal of Hypertension 11: 1469-1474 (1998).