Real-time detection of nitric oxide isotopes in lung function tests.

In lung function tests, the determination of the pulmonary diffusing capacity (D) using the single-breath method is a commonly applied technique. The calculation of D is performed on the basis of accurate measurements of indicator gas concentrations. In this chapter, we demonstrate the appropriateness of the stable nitric oxide (NO) isotopes (NO)-N-14 and (NO)-N-15 in revealing reliable data of D. We performed studies on animals ((NO)-N-14) by using respiratory mass spectrometry (M3) and on humans ((NO)-N-15) by applying laser magnetic resonance spectroscopy (LMRS). The equipment was characterized by sufficient detection limits of 70 parts/billion at [(NO)-N-14] = 0.001 % (M3) and 40 parts/billion at [(NO)-N-15] = 0.002 % (LMRS), respectively. Lastly, we were able to show that D-values for (NO)-N-14 indeed reveal the entire diffusive properties of the alveolar-capillary membrane and that (NO)-N-15 is a useful indicator gas for reflecting disturbances of pulmonary gas exchange.