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3 MEASUREMENT RESULTS
Initial tests were performed by placing the sensors
on the colon after the construction of the
anastomosis. Figure 6 shows the sensors at a
distance of 1 cm away from the anastomosis, while
Figure 7 presents the table and graph with the
measurement results, for different sensor locations
around the anastomosis. The sensors were placed
radial (lateral and antimesenterial) and longitudinal,
at ten different locations on both sides of the
anastomosis, as indicated in Figure 7.
Figure 6: Photograph showing the sensors on the colon,
1 cm away from the anastomosis.
The lowest oxygen-tension values are obtained
on the anastomosis (part 3 and part 8 in Figure 7).
This is an expected effect - due to local cell death,
tissue oxygenation at the site of the anastomosis is
reduced. The farther from the anastomosis we
measure, the better the oxygenation, and the higher
the oxygen-tension values. The spikes on the graph
are artefacts visible only at the moments when the
sensors are moved from one tissue location to
another, because then, for a short period of time, the
fibre is in air. The temperature changes
corresponding to tissue and air are visible on the
temperature graph.
Another series of measurements were performed
with the sensors on the small intestine (Figure 8). In
this case, the blood supply to the central part of the
small intestine was obstructed by two strings that
were fastened for ischemia and released for
reperfusion. The measurement results during the
ischemia-reperfusion experiment are shown in
Figure 9.
At the beginning of the test, the sensors were
placed on the small intestine and by fastening the
strings, the intestine was made ischemic (part 1).
The values readily decreased to 4 mmHg, indicating
total ischemia. Once the strings were released, an
overshoot was noted, showing a maximum at
202 mmHg. Two other cycles were repeated to test
the correctness of the measurement. Also in this
case, the results of the tests met our expectations.
In addition to these measurements, other tests
were performed by changing the levels of inspired
oxygen (33.4 %, 42.8 %, 66.7 % and 91 %). We
noted that the local pO
2
changed accordingly to the
inspired oxygen. For an even better characterisation,
a new series of tests is currently performed, during
which the animals are intubated. In this way, the
inspired oxygen can be accurately controlled, while
the rats are being continuously monitored.
4 CONCLUSIONS
The paper has presented the initial measurements
and results with an optical oxygen-tension sensor
and a temperature sensor. The performed tests have
shown that the principle of optical sensing is suitable
for tissue measurements.
The first series of measurements has shown a
significant decrease (approximately 40 mmHg) in
pO
2
on the anastomosis as compared to the other
measurement sites on the colon. It was also shown
that on two points (lateral and antimesentery) of the
anastomosis, the values for the pO
2
were
approximately the same.
The ischemia and reperfusion experiments have
shown that the sensor system reacted as expected to
the local changes on the small intestine. When the
intestine was made ischemic, the pO
2
decreased and
when the obstruction was removed, the pO
2
increased significantly, with an overshoot.
This cycle was repeated three times to test the
correctness and repeatability of the measurement.
Sensors
Anastomosis
ANIMAL STUDIES USING AN OXYGEN-TENSION SENSOR FOR TISSUE VIABILITY MONITORING
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