Catheter calibrated

The wireless pH capsule (Medtronic Inc.) is oblong in shape and contains an antimony pH electrode, a reference electrode at its distal tip, a battery, and a RF transmitter. The whole device is encapsulated in epoxy. The capsule is introduced into the esophagus on a catheter through the nose or mouth and is attached to the lining of the esophagus with a clip. The probe monitors the pH in the esophagus and transmits the information via RF telemetry at a rate of 6 per second (0.17 Hz) to a pager-sized receiver that is worn by the patient on a belt. Prior to implantation, the capsule is calibrated with its receiver in pH buffer solutions of pH 1.07 and pH 7.01 [168],... 

Strindberg L, Lonnroth P. Validation of an endogenous reference technique for the calibration of microdialysis catheters. Scandinavian Journal of Clinical and Laboratory Investigation 2000, 60, 205-212. 

The aneurysm and aorta are assessed with a 3D reconstruction CT scan or aortography with a calibrated catheter (Table I, Fig, I). The fitness of the femoral arteries is evaluated as the access route. They should be greater than 7 mm in diameter and free from extensive atherosclerotic or stenotic disease. 

The Nijmegen group of Kreuzer merits special mention [50-53]. The so-called catheter oxygen electrode constructed in Nijmegen has the following characteristics. The calibration curve is linear up to 100% O2 and is reproducible within 1% (relative). The current output is of the order... 

Figure 3. Net platelet retention behavior on polyethylene catheters in four goats. Thrombus platelet concentration catheter length was used to calibrate externally detected platelet retention curves. The repeatability of the initial slope ana the variable times to peak are shown. Key I, Goat 32 2, Goat 36 ...

A standard calibration curve is prepared by subsequent addition of small volumes of standard aqueous saturated NO solution (concentration 1.74 mM) into a constant volume of freshly boiled and deoxygenated buffer (pH 7.4 at 37 C). -The current generated after each addition of NO is measured, and the resulting plot of current versus concentration should be linear. The detection limit of a correctly prepared sensor should be about 10 nM for a single-fiber sensor, and 1 to 5 nM for multifiber catheter-protected sensors for in vivo measurement. The detection limit of die cell-culture macrosensor is 5 nM. The response time (time for signal increase from 10-75%) of porphyrinic. sensors is 0.1 ms for micromolar NO concentrations, and 10 ms for nanomolar concentrations. 

With the development of stable, energy dense, isotonic lipid emulsions for intravenous use (Table IV), the use of concentrated glucose solutions which have to be infused through large calibre central veins has decreased. Administration of nutrients by peripheral vein eliminates the complications associated with central catheter placement and use (Jako-bowski et al., 1979). Intravenous fat emulsions are manufactured from either soyabean or safflower oil, stabilized with 1.2% egg phospholipid, and made isotonic with 2.5% glycerol. Formulations are rich in essential fatty acids, yield 1.1 kcal/ml, and have a metabolic fate which is similar to that of naturally occurring chylomicrons. Liposyn, however, has only trace amounts of linolenic acid compared to the two other emulsions. In addition, carnitine is absent from all of the lipid emulsions. 

These microspheres are precisely calibrated, spherical, hydrophilic, microporous beads made of tris-acryl co-polymer coated with gelatin. They come in defined range of sizes, ranging from 40 to 1200 pm in diameter. Their smooth hydrophilic surface, deformability and minimal aggregation tendency have been shown to result in a lower rate of catheter occlusion and more distal penetration into the small vessels [32]. Their efficacy has been evaluated in several conditions, and vdien compared to the standard polyvinyl alcohol particles (PVA) particles, a deeper penetration and embolization of smaller and more peripheral vessels may be achieved. This distal embolization may limit the development of any collateral blood supply. Also, in a study where PVA particles and tris-acryl microspheres of similar size were compared, the level of vascular occlusion with calibrated tris-acryl microspheres precisely correlated with particle size whereas the level of vascular occlusion with PVA particles did not. Another study has demonstrated that in embolized tumors. 

In spile of the case of construction, robustness, and high sensitivity, the lack of a truly static response of a ferroelectric polymer pressure transducer represents a serious limitation to widespread use of this type of device. Several techniques can be conceived in order to overcome this drawback [21] (such as the parallel use of a strain gauge sensor and the use of this transducer to calibrate at intervals the signal detected by the PVDF sensor), but excessive complexity and costs are usually added to the originally simple and cheap design of the piezoelectric polymer catheter-tip sensor. 

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