Relationship between decreased oxyhaemoglobin saturation and exhaled nitric oxide during exercise

Area of Science:

• Exercise Physiology
• Pulmonary Medicine
• Biochemistry

Background:

• Highly trained male endurance athletes often experience decreased oxyhaemoglobin saturation (SaO2) during intense exercise, known as exercise-induced hypoxaemia (EIH).
• Ventilation-perfusion (VA/Q) mismatching and diffusion limitations are implicated in EIH.
• Nitric oxide (NO), a vasodilator found in exhaled air, may influence VA/Q matching and pulmonary vascular resistance.

Purpose of the Study:

• To investigate the relationship between exhaled nitric oxide (NO) levels and exercise-induced hypoxaemia (EIH) in elite male cyclists.
• To test the hypothesis that athletes with EIH exhibit lower NO levels compared to those without EIH.

Main Methods:

• Eighteen highly trained male cyclists were divided into normal (NORM) and low (LOW) SaO2 groups based on peak exercise SaO2.
• Subjects underwent a ramped cycle test to exhaustion while breathing NO-free gas.
• Exhaled NO concentration (CNO) and production rate (VNO) were measured at rest and during exercise using a chemiluminescent analyser.

Main Results:

• Exhaled NO concentration (CNO) remained stable from rest to maximal exercise in all participants.
• Exhaled NO production rate (VNO) increased significantly during exercise but did not differ between the NORM and LOW SaO2 groups.
• No significant correlation was found between the change in SaO2 and VNO from rest to maximal exercise (r=-0.12, P > 0.05).

Conclusions:

• Exhaled nitric oxide (NO) does not appear to be a significant factor in the development of exercise-induced hypoxaemia (EIH) in highly trained male cyclists.
• The findings suggest that other physiological mechanisms are primarily responsible for decreased SaO2 during heavy exercise in this population.