2 General Description
Service Manual – Osmetech OPTI™ Analyzer
2-9
The red wavelength is utilized for the SO2 measurement because it is much more
strongly absorbed by deoxyhemoglobin than all other hemoglobins, and is
picked close to the isobestic point for oxy- and carboxyhemglobin. Maintaining
high shear force just prior to measurement minimizes sensitivity to erythrocyte
aggregation (rouleau formation).
The optical signal of the detectors is converted by the microprocessor to a
numerical readout in conventional units of measure and displayed on the front of
the device. Other values commonly used for the assessment of oxygen and acid-
base status are calculated from these measured values.
The entire sample path of the Osmetech OPTI cassette is filled with storage
buffer to keep the sensors stable during storage. In addition, the cassette pouch
is filled with a CO
2
atmosphere, which keeps the pH of the storage buffer stable.
The cassette not only contains the sensors but also houses a distribution valve
(cassette valve), the sample fill port, an input/output port (I/O port), a reservoir
and a vent.
The function of the I/O port is to connect the cassette to the peristaltic pump
allowing sample aspiration and calibration gas to flow through the cassette.
The storage buffer in the reservoir ensures stability over the shelf life of the
cassette.
The distribution valve has 2 functions: its hollow body serves as a waste
container, referred to as “waste”, holding storage buffer and OPTI-trol.
In addition, the cassette valve incorporates small channels, called links that
connect the sensor channel, the fill port, the vent and the I/O port in different
combinations. These different connections are achieved by turning the cassette
valve to different positions. Each valve position has an assigned number. An
unused cassette is set to position 0, the home position. The diagram on page 2-9
shows the valve positions and the connections for each position. E.g., position 2
connects the fill port via the valve link to the sensor channel and the reservoir to
the I/O port.
The Osmetech OPTI 1 and Osmetech OPTI CCA analyzers are microprocessor-
based instruments measuring optical fluorescence. The disposable, single-use
cassette contains all the elements needed for calibration, sample measurement
and waste containment. After reading the calibration information specific to a
cassette into the instrument by 'swiping' the cassette package through a
convenient bar code reader, the cassette is placed in the measurement chamber.
While the analyzer warms the cassette to 37.0 ± 0.1 °C, the cassette valve is
turned to position 5. In this position, the I/O port is connected to the vent
allowing the pump to purge calibration gas. At the same time, readings are
taken from all sensors to ensure proper functioning. In addition, the fluid light
gates L1, L2 and L3 are calibrated.
