Neonatal flow sensors

Neonatal flow sensor (Dragei) cross section and application two hot wires and a shadow wire to determine flow and flow direction. 

Table 23-5. Typical specifications of neonatal babylog 8000 flow sensor (Drager). ...

Ma, Y., Ma, S., Wang, T., Fang, W., 1995. Air-flow sensor and humidity sensor applications to neonatal infant respiration monitoring. Sens. Actuators A Phys. 49 (1-2), 47-50. 

The value of the partial pressure measured at the skin surface depends in a complex way on blood partial pressure, constitution of the skin, local perfusion, metabolism in the associated tissue, cardiac output, and application temperature. An increased temperature of 43 °C raises the gas permeability and expands the capillary vessels of skin which are filled with more artial blood. The local hyperemia has the disadvantage of limiting the application time at a certain site. Assuming stable circulation conditions, transcutaneously measured values correlate with arterial partial pressure by a factor of 1.2 (neonates) to 1.0 (small children) [1]. The measured value for adults proved to be very unreliable. In the case of unstable conditions or shock with a reduction of peripheral blood flow, the transcutaneous value drops very early. Inconvenience in routine use is caused by long preparation times of the sensor, the need for periodic membrane changes, the long run-in time of freshly prepared sensors, the necessity for periodic calibrations and the slow response time to changes in partial pressure. 

Measurement Type Flow range Accuracy Reproducibility Time resolution Gas mixture Modification flow calibrated disposable sensor 0.2-200 L/min <5% 1% 10 ms compensated flow direction sensitive, for neonatal monitoring... 

To combine the advantages of both types, Nellcor designed a sensor see also Figure 23-20) which uses only 1 m of sample line and an extremely small sample cell and offers the advantage of short delay times of about 1 s, low flows of SO mL/min and short rise times of about S5 ms [23]. These features also offer acceptable monitoring of neonates. In practical use. the features arc slightly influenced by the normal problems in sidestream sensors with condensed water also which arc suposed to be overcome by (he proximal-diverting monitor. 

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