LMR spectroscopy: a new sensitive method for on-line recording of nitric oxide in breath.

Laser magnetic resonance spectroscopy (LMRS) is a sensitive and isotope-selective technique for determining low concentrations of gaseous free radicals with high time resolution. We used this technique to analyze the nitric oxide (NO) concentration profile while simultaneously measuring the flow and expired volume during several single breathing cycles. Eight healthy, nonallergic volunteers were investigated. An initial NO peak was found in all breathing cycles before the NO concentration dropped to a relatively stable plateau in the late phase of expiration. The nasal NO peak was significantly higher than the oral NO peak. The nasal NO plateau was always higher than the oral NO plateau. The height of the initial nasal and oral NO peak rose with increasing duration of breath hold, whereas the late expiratory NO plateau changed only little for either the nasal or the oral breathing cycles. Our findings demonstrate, in line with other reports using other techniques, that the nose is the primary source for NO within the airways.