1146 
MONITORING 
are less often quoted. In a bench test, the fol- 
lowing performance would be expected : 
Parameter Units 
Frequency Response - KHz 
(Defined and Calculated) 
(undamped, in water, 1% flat) 
Volumetric Compliance — mm^ X 10-o/mm Hg 
(Calculated) 
Flow Perturbation Zero Shift, % F.S. 
(at Vi max. excitation) Still/Agitated Water 
Overpressure — Standard 
Arterial Transducer 
Less than 1% Zero Shift ..- mm. Hg 
No Damage _. mm. Hg 
Gage Pressure Reference (to 10 
Atm) 
Line Pressure Error % line pressure 
(Gage Pressure Reference) 
Size — Diameter mm. 
— Thickness mm. 
Range 
1 to 4 
3 to 70 
0.2 to 2 
1000 to 3000 
3000 to 9000 
Yes 
0.1 
3 to 7 
1.0 to 1.2 
We now consider the long term performance 
of transducers. The following tables reflect both 
long term laboratory tests, with transducers 
immersed in water and subject to simulated 
physiological pressure cycling, and in vivo 
experience. 
Considering first the Standard accuracy and 
capabilities criteria, we have found the follow- 
ing figures to be representative : 
Parameter 
Units 
Range 
Non-Linearity 
Hysteresis _ 
Non-Repeatability 
Static Error Band 
Zero Temperature Shift 
(Z shift induced) 
Sensitivity Temperature Shift 
(circuit induced) 
Pressure Range — special _ 
± % F.S., B.S.L. 
% F.S. 
% F.S. 
± % F.S., B.S.L. 
mm. Hg/°C 
% reading/" C 
0.2 to 0.4 
0.1 to 0.2 
0.1 to 0.2 
tO.2 to 0.5 
0.4 to 1.0 
0.3 to 0.4 
50 to ? 
Several items are worthy of note. Non- 
linearity, Hysteresis, Non-Repeatability, and 
their combination. Static Error Band, are al- 
most inevitably improved with in vivo use. In- 
deed we have noted, as transducers come in for 
successive repair, that transducers continue to 
improve up to at least five years of age — figures 
beyond that are scattered, but similar. Second, 
the figures for zero temperature shift and sen- 
sitivity temperature shift are inevitably worse 
than bench test results, but do not represent a 
degradation of the inherent capabilities of the 
transducer. 
As will be noted below, most transducers ex- 
hibit a long term zero shift (and to a lesser 
extent, sensitivity shift) in vivo. The tempera- 
ture compensation network, being adjusted for 
the transducer's initial calibration, becomes less 
and less effective with time, because of this 
shift. If, however, a transducer is recompen- 
sated and recalibrated after prolonged use, its 
temperature characteristics will be comparable 
to, or superior to that of a new transducer ; the 
exercising effect of use tends to make the trans- 
ducer require less temperature compensation 
than a new instrument. 
We now consider long term accuracy and 
capabilities criteria which are not commonly 
specified. The following tabulation represents 
my own judgment of the results of in vitro tests 
conducted in our laboratory and a preliminary 
report of in vivo tests conducted on comparable 
instruments by the Scripps Clinic and Research 
Foundation. 
Parameters Conditions Units Range 
Frequency Response.. Probably only moderately diminished if no thick tissue deposition. No complaints. 
Zero Shift with time _ Initial 1-3 months.- % F.S./mo 2 10 
(in vitro tests) Subsequent months % F.S./mo. — 1 3 
Zero Shift with time _ Initial 1-3 months % F.S./mo. 2 10 
(in vitro tests) Subsequent months % F.S./mo. 1 B 
Predictability of Zero Shift with time_ Any month ± % oi previous month's shift— 10 20 
Sensitivity Shift with time — Initial 1-3 months %/mo. 1 4 
(in vitro tests) Subsequent months %/rao _ 0 2 
Sensitivity Shirt with time — — . Initial 1-3 months %/mo. 3 10 
in vivo tests Subsequent months %/mo. 1 6 
Predictability of sensitivity shift with time — . Any month _ ± ■% of previous month's shift ±10 ±20 
(in vitro test) 
Power Consumption _ Std. 500 ohm fiA — 60 300 
(to generate a 1 mV signal F.S.) Special 5000 ohm yuA 10 16 
Resistance to Ground _ Initial M Ohms _ 100 « 
(Old style designs only) 3-6 months - - M Ohms - 50 >100 
6 mo— 3 yrs M Ohms 20 >100 
