The effects of hyperpnea on exhaled nitric oxide synthesis in normal subjects.

STUDY

OBJECTIVES

To determine if the concentration of nitric oxide (NO) in the lungs increases with hyperpnea by contrasting calculated production (ie, the product of the fractional expired NO concentration [FeNO] and minute ventilation [Ve]) [Vno] with the amount of NO in equilibrium with the conducting airways (eNOair) and the amount of NO diffusing from the alveoli (eNOalv).

DESIGN

Observational study.

SETTING

University teaching hospital.

PARTICIPANTS

Normal subjects.

INTERVENTIONS: Measurements were made in 16 healthy people during and after 4 min of tidal breathing (10 L/min) and isocapnic hyperventilation of 60 L/min.

MEASUREMENTS AND

RESULTS

FeNO was measured by collecting the exhaled air during the last minute of each trial and passing it through a chemiluminescence analyzer. The expired NO levels in the plateau phases of slow (30 mL/s) and fast (200 mL/s) single-breath exhalations were also obtained before and after hyperventilation. The Vno (mean +/- SEM) increased from 89.8 +/- 12.3 to 329.1 +/- 36.2 nL/min as Ve rose (p < 0.001). However, neither the quantities of eNOair nor eNOalv changed with hyperventilation (eNOair range before to after, 34.9 +/- 7.7 to 30.9 +/- 6.4 parts per billion [ppb], p = 0.96; eNOalv range before to after, 7.3 +/- 1.5 to 6.5 +/- 1.1 ppb, p = 0.97).

CONCLUSIONS

These data demonstrate that the amount of NO in equilibrium with the airway walls and alveoli are not altered by hyperpnea. Rather, the apparent augmentation in Vno in such circumstances appears to be an arithmetic artifact.