A demand valve device decreases exhaust nitric oxide and nitrogen dioxide by nitric oxide inhalation with a nasal cannula in the human

To improve patients' quality of life and decrease pollution risks to medica l personnel, we tested the usefulness of a nitric oxide (NO) inhalation sys tem consisting of a nasal cannula and a demand valve in an open circuit sys tem. To estimate the content of NO entering the lung with the open system, concentrations of NO and nitrogen dioxide (NO2) were measured in a mechanic al lung model, and then nitrocylhaemoglobin (NO-Hb), methaemoglobin (Met-Hb ), and nitrite (NO2-) + nitrate (NO3-) concentrations in venous blood were measured in eight healthy subjects. Exhaust NO and NO2 in the open system w ere also observed in 14 healthy subjects. In the lung model, NO concentrati on delivered with the open system was approximately 1/11 of that in the gas tank. Increases in Met-Hb and NO2- + NO3- with the open system showed that the concentration of delivered NO was approximately 1/9 of that in the gas tank. The open system reduced exhaust NO to 1/10 in human subjects. These data suggest that this NO inhalation system delivers sufficient NO to spont aneously breathing patients. In addition, these findings indicate that ther e is little environmental toxicity associated with the open circuit system.