1262 
MONITORING 
survival was determined by the needs of the 
particular experimental protocol. A routine au- 
topsy was performed and, in addition to the rel- 
evant pathologic examination, a careful exami- 
nation of instrument location and position was 
determined. 
Instrumentation 
We have found that frequent manipulation of 
the lead wires serves to condition and acclimate 
the animal to the data monitoring process. Irri- 
tation or discomfort to the animal was rare dur- 
ing data collection with a two to seven day re- 
covery period. In some cases, additional time 
was necessary until the animal was symptom 
free. At no time were sedatives necessary. 
Specific care and maintenance of the implant- 
able pressure transducers, arterial catheters 
and flow probes has been previously reported.^ 
All hardware was sterilized with ethylene 
oxide. Cold sterilization with benzalkonium 
chloride (Zephiran) has also been used on occa- 
sion. The arterial catheters were filled with 
pure heparin. Recently, in an attempt to further 
minimize thrombus formation, the catheter 
lumen has been coated with colloidal graphite* 
as described by Folts.^ Arterial pressure was 
monitored with a Statham P23Gb transducer 
positioned at heart level and zeroed. The left 
ventricular implantable pressure transducer 
likewise was coated with colloidal graphite to 
minimize thrombogenecity and tissue over- 
growth. The transducer was calibrated prior to 
surgery by a technique developed by Dennison.* 
Briefly, the basic calibration procedure was car- 
ried out in water at 37° over a pressure range 
of 0-200 mmHg. In an attempt to reduce errors 
inherent with this type of transducer, we 
observe the following rules : (a) excitation at ap- 
proximately 50% of rated voltage," (b) utihza- 
tion of low-drift compensation resistors neces- 
sary only with the DynaSciences model, (c) 
maintenance of a performance log with rejec- 
tion of all transducers demonstrating signifi- 
cant drift, and (d) careful matching of central 
aortic and left ventricular systolic pressure to 
compensate for zero drift. Other techniques 
which were used to optimize performance have 
been discussed under the surgical section. 
• Acheson Colloid Company, Port Huron, Michigan 
The vascular occluders consist of an inflata- 
ble cuff and length of tubing which were filled 
with mercury instead of air or saline. This 
method was chosen in order to minimize stress- 
relaxation of the balloon and uneven inflation 
seen when air alone was used. We feel that oc- 
clusiveness may also be more carefully con- 
trolled with this technique. Left main coronary 
flow is monitored during the occlusion as an aid 
in quantifying reductions in flow. 
All data were recorded at the post-operative 
animal location on a multichannel paper re- 
corder* (see Figures 2 and 3). This serves for 
establishing baselines and zeroes, as well as for 
monitoring basal states and responses to var- 
ious diagnostic and therapeutic interventions. 
All data were simultaneously recorded via cable 
at a distal site on analog tape and converted at 
a rate of 250 samples/second to digital form 
using the PCP7 computer. The animal may be 
left alone while connected to the recording in- 
strument in order to provide a stress-free, quiet 
environment. The analog tape is later edited for 
additional and more specific derivations which 
are enumerated in the hemodynamic section 
below. 
The total data monitoring system thus in- 
cludes the implanted instrumentation in the 
biological system, the paper recorder for imme- 
diate assessment of baselines and specific re- 
• Hewlett Packard 
FiGxmE 2. — Post-operative, instrumented animal in 
metabolic cage. Paper recorder for monitoring also 
shown. 
