20 healthy young subjects and 20 healthy older subjects will go through a medical examination. Subjects will be asked for their medical history especially on respiratory and cardiac diseases. All subjects will go through a spirometry test to evaluate their respiratory function. After their medical clearance each subjects will be asked to wear a CBRN respirator for 45 minutes. 15 minutes without filter, 15 minute with 0.8 cmH2O resistance, and 15 minutes with 1.2 cmH2O resistance. Throughout the test, Pco2 AND PO2 will be measured. The investigator will evaluate the effect of resistance (filter resistance) and the age of the subject on CO2 accumulation in the mask.

After signing the consent form, 20 healthy young subjects and 20 healthy older subjects will go through a medical examination. Subjects will be asked for their medical history especially on respiratory and cardiac diseases. All subjects will go through a spirometry test to evaluate their respiratory function. After their medical clearance each subjects will be asked to wear a CBRN respirator for 45 minutes. 15 minutes without filter, 15 minute with 0.8 cmH2O resistance, and 15 minutes with 1.2 cmH2O resistance. Throughout the test, Pco2 AND PO2 will be measured with mass spectrometer. Oxygen saturation, Pulse rate, and minute ventilation will also be monitored. The investigator will evaluate the effect of resistance (filter resistance) and the age of the subject on CO2 accumulation in the mask.

Inclusion Criteria:

Healthy females and males, with no respiratory, cardio vascular diseases, high blood pressure, psychiatric problem, degenerative nervous system problem, and chronic head ache, muscular disease, or severe acute disease within the two weeks before the study. age 18 and 25, and 55 and 70 years old. Who volunteer to the study

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Exclusion Criteria:

Did not pass the Inclusion criteria, pregnant women, O2 saturation lower then 95%, pathological sound from the heart or lungs. Claustrophobia, smoking history more then 2.5 packs years.