A Pilot Study of Inspiratory Muscle Training to Improve Exercise Capacity in Patients with Fontan Physiology

Abstract

While the Fontan procedure has improved life expectancy, patients with single ventricle physiology have impaired exercise capacity due to limited increase in pulmonary blood flow during activity. Enhancing the "thoracic pump" using inspiratory muscle training (IMT) may ameliorate this impairment. Adult nonsmokers with Fontan physiology were recruited through Boston Children's Hospital's outpatient clinic. Participants underwent cardiopulmonary exercise testing and pulmonary function testing, followed by 12 weeks of IMT and then repeat testing. The primary endpoint was change in % predicted peak oxygen consumption (VO2). Secondary endpoints were changes in other exercise metrics. Eleven patients (6 male) were enrolled. Median ages at time of enrollment and Fontan completion were 28.8 years (25.7, 45.5) and 7.8 years (3.9, 16.5), respectively. Average baseline maximal inspiratory pressure (MIP) was normal; only 2 patients had MIP <70% predicted. Peak work rate improved significantly from baseline after 12 weeks of IMT (116.5 ± 45.0 to 126.8 ± 47.0W, P = 0.019). Peak VO2 tended to improve (baseline 68.1 ± 14.3, change + 5.3 ± 9.6% predicted, P = 0.12), as did VE/VCO2 slope (34.1 ± 6.7 to 31.4 ± 3.6, P = 0.12). There was no change in peak tidal volume or MIP. In a small cohort of Fontan patients with mostly normal MIP, IMT was associated with significant improvement in peak work rate and a trend toward higher peak VO2 and improved ventilatory efficiency. Larger studies are needed to determine if this reflects true lack of effect or whether this pilot study was underpowered for effect size, and whether IMT is more narrowly useful for patients with impaired MIP.