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NOSE - ONLY, DIRECTED - FLOW SYSTEMS: A FEW PRINCIPLES AND ADVANTAGES

"Why should I choose a nose-only, directed-flow inhalation system instead of a whole body chamber?" This is a question commonly asked by investigators when planning an inhalation exposure experiment. Several reasons are as follows:

1. The dose of the inhaled aerosol (or gas) to the respiratory tract can be more accurately controlled in nose - only exposures than in whole body exposures. The main reason for this greater accuracy is that only the nose and the respiratory tract are exposed to the aerosol or gas in a nose-only chamber. Neither fur nor skin is exposed. Thus, dermal absorption and ingestion of deposited materials via preening are eliminated.

2. The investigator can handle animals more safely during and after an exposure to a hazardous material. This is because a smaller quantity of aerosol or gas is needed for a nose - only exposure, much less than for a whole body exposure. This limits the potential exposure should a leak or other misfortune occur. Further, the fur and skin are relatively free of deposited aerosol or gas, also limiting potential exposure.

3. Under certain conditions, more animals can be exposed simultaneously in a nose - only chamber than in a whole body system. Multiple ports (one animal per port) and compact design allow up to 240 animals to be exposed at once. This design employs a 10 tier by 24 animal per tier system. The radial design of the CH Technologies nose-only chamber with its close stacking and open-air flow for cooling and ventilation reduces chamber volume compared to most whole body chambers. This results in a reduced amount of aerosol or gas for exposure.

4. A single individual can operate the in - hood - based, CH Technologies nose - only system. Most whole body inhalation systems require several operators with complex engineering support.

5. Animals are more easily monitored in the nose - only system because each can be readily observed or removed from the chamber while still in its nose - only restraint tube. Examination or other manipulation is then made simple.

6. It is easier to measure respiratory parameters during exposures with the substitution of sealed plethysmograph tubes for the usual open or closed restraint tubes. This is made "simple" through the use of accompanying plethysmography computing technology such as that available from BUXCO Electronics (http://www.buxco.com).

7. It is acknowledged that the use of nose - only chamber and restraint can cause stress to the animals. This stress differs from that seen in whole - body exposures. In the whole - body case, the animals often sleep through the exposure with a concomitant reduction in exposure dose through fur filtration and reduced minute ventilation. Restraint plus increased temperature in the nose - only restraint tube require that room temperature be reduced during exposure. With this change, the stress of restraint can be accommodated by a control group of restraint only (sham) exposed animals.

8. The preceding list is not exhaustive and both sides may have pro and con views. The bibliography for this field is evolving and future issues will address some of the points raised here. Stayed tuned!

By: Rudolph J. Jaeger, Ph.D, D.A.B.T., Arlene L. Weiss, MS, DABT, and Susan G. Shami, Sc.D.

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