Background: Nitric oxide has become a vital indicator of health since many cells produce it constitutively. It is present in exhaled breath and can be measured.
Material/Methods: A Kiernan NO Breath analyzer (KNB) was used in the present study to determine nitric oxide (NO) levels in exhaled human breath. The KNB was calibrated via measuring NO gas in O2-free N2 obtained
from Scott Specialty Gases. Human subjects aged 21 to 45 were instructed to place the KNB over their nose and mouth and to breathe normally before and after mild exercise (n=24) and relaxation
(n=20). Mean exhaled NO measurements were compared before and after the protocols using paired t-tests.
Results: Regardless of the test, all subjects exhibited NO in their exhaled breath. Exhaled NO decreased signifi cantly after exercise compared to the fi rst reading just prior to the exercise protocol. The mean ±SE of exhaled NO was 22.8±4 before and 13.0±2 ppb after exercise (n=24, P=0.003). In the
resting experiment, exhaled NO was demonstrated to increase signifi cantly after 10 min compared to the reading taken right after the individuals sat down.
Conclusions: The present study demonstrates NO in exhaled human breath can vary, refl ecting the activity state of the individual. Additionally, the study demonstrates that NO in exhaled human breath can be measured rapidly, with high sensitivity, and in real time via the KNB, representing an affordable
means to achieve this determination.

Keywords: Exercise - physiology, Breath Tests, Exhalation - physiology, Nitric Oxide - analysis, Rest - physiology