Breathing patterns in patients with a Fontan circulation exposed to high altitude

Abstract

ABSTRACT Aim: To study the effect of simulated acute normobaric hypoxia on the breathing pattern of patients with a Fontan circulation (PwF) during exercise compared to a healthy control group. Methods: This study included 23 PwF and 33 healthy controls between 8-40 years old. Median age 20, interquartile range [12:26]. Participants performed two cardiopulmonary exercise tests (CPET) on a cycle ergometer. One CPET was performed at sea level, the other CPET in a hypoxic tent at a simulated altitude of approximately 2500 metre above sea level. Outcome measures were respiratory minute ventilation, tidal volume, breathing frequency, ventilatory efficiency, ventilatory drive, minute ventilation per Watt and the rapid shallow breathing index. Measurements were compared in both conditions at four timepoints: at rest, ventilatory anaerobic threshold, respiratory compensation point, and peak exercise. Mann-Whitney U test and Wilcoxon signed-ranks test were used for statistical analysis. Results: Statistically significant differences (P<0.05) were found in respiratory minute ventilation, tidal volume and breathing frequency between groups at altitude. Ventilatory efficiency, ventilatory drive and the rapid shallow breathing index showed significant higher values in PwF in both conditions. Conclusion: A more rapid, shallow breathing pattern occurred in PwF during exercise when exposed to acute normobaric hypoxia compared to healthy controls. Clinical Relevance : To overcome the less efficient rapid shallow breathing pattern, PwF might explore the possibilities of respiratory muscle training. This might be useful to improve ventilatory efficiency before high altitude exposure.