Measuring exhaled nitric oxide at high altitude.

Area of Science:

• Respiratory Physiology
• Medical Instrumentation
• Environmental Health

Background:

• Nitric oxide (NO) plays a crucial role in respiratory health and disease.
• Accurate measurement of exhaled NO is vital for clinical diagnosis and monitoring.
• Altitude-induced environmental changes can impact the performance of medical devices.

Purpose of the Study:

• To evaluate the performance of two nitric oxide (NO) analysers at high altitude.
• To investigate the effects of altitude on volume and mass flow rates in NO analysers.
• To identify sources of error in exhaled NO measurements at varying altitudes.

Main Methods:

• Two NO analysers with different NO detectors were tested.
• Simulated exhalations of reference gases were used to assess analyser performance.
• Instrument performance was evaluated at simulated altitudes, specifically at 4000 m.

Main Results:

• At 4000 m, both analysers exhibited a +35% increase in volume flow and a -24% decrease in mass flow.
• Reduced mass flow led to a 26% increase in the exhaled NO fraction for a given NO excretion rate.
• An electrochemical NO detector showed an increased signal, resulting in a combined 60% signal output increase relative to NO partial pressure.

Conclusions:

• Altitude significantly impacts the accuracy of exhaled NO measurements due to flow regulation and detector response errors.
• Recommendations include readjusting flow regulators and recalibrating analysers for specific operational altitudes.
• Reporting exhaled NO as partial pressure, not volume fraction, is crucial for consistent and comparable measurements across different altitudes.