The Acute Exhaled Nitric Oxide Response and 5km Performance in Normobaric Hypoxia in Highly Trained Athletes

Abstract

Nitric oxide produced in the lung is an important modulator of pulmonary vascular resistance, and may therefore be influenced by hypoxia or hypoxemia, where pulmonary hypertension or ventilation/perfusion mismatching may occur. Little is known about the effect of exercising in acute normobaric hypoxia upon exhaled nitric oxide (eNO) in athletes, or the relationship between eNO changes and performance in acute hypoxia. PURPOSE: To characterise the acute effect of heavy exercise in normobaric hypoxia upon eNO, and the relationship with 5km running performance. METHODS: Twelve highly trained runners and triathletes volunteered to participate in the study (n=12, height:178±9cm, weight: 76±10kg, age:30±6yr). eNO was measured using an online analyser (Sievers NOA-280i, Analytix Ltd, UK) according to American Thoracic Society guidelines, 10 minutes pre- and 10 minutes post-exercise. Treadmill exercise consisted of three, 4-minute sub-maximal exercise bouts, followed by a 5km time trial, completed under controlled hypoxic (F1O2=0.150) or sham (F1O2=0.209) conditions. A randomised, single blind research design was used. Pre-and post-exercise eNO were compared between conditions using repeated measures ANOVA. The relationship between 5km time trial performance and changes in eNO was analysed using a Pearson product-moment correlation. RESULTS: Exercise in normoxia and hypoxia caused a significantly (P < 0.05) reduced eNO (from 44.4±32.4ppb to 35.3±24.7ppb and from 45.2±40.7ppb to 38.5±30.3ppb respectively, with no differences between conditions (P > 0.05). 5km performance was significantly reduced in hypoxia (by 189±59 seconds); however, there was no relationship between this performance decrement and alterations in eNO (r=0.081; P > 0.05). CONCLUSIONS: In agreement with previous research, these findings do not support the hypothesis that exercise in hypoxia leads to an increased eNO, although further research is needed to further understand the relationship between eNO and performance in hypoxia.