Inspiratory muscle training did not improve exercise capacity and lung function in adult patients with Fontan circulation: A randomized controlled trial.
Fritz C, Müller J, Oberhoffer R, Ewert P, Hager A.
Int J Cardiol. 2020 Jan 9. pii: S0167-5273(19)33852-5. doi: 10.1016/j.ijcard.2020.01.015. [Epub ahead of print]
Take Home Points:
- Daily IMT for a 6 month period did not improve exercise and lung capacity and lung volumes in Fontan patients.
- Daily IMT for 6 months in adult patients with Fontan was associated with an increase in O2 saturation at rest.
- Larger studies are warranted in order to gain more insight into the mechanisms of exercise training and the Fontan physiology.
Commentary from Dr. Soha Romeih (Aswan, Egypt), section editor of ACHD Journal Watch:
In Fontan patients, due to the hemodynamic limitations of an absent sub-pulmonic chamber, pulmonary arterial and systemic venous blood flow are strongly affected by modest intrathoracic pressure shifts, since ± 30% of flow in the systemic venous pathway is driven by respiration. In patients with Fontan circulation, blood flow in the IVC is increased during inspiration, enhancing the systemic venous blood return into the lungs considerably.
Young adults with Fontan circulation show respiratory and skeletal muscle weakness, and higher prevalence of respiratory muscle dysfunction, comparable to adults with advanced heart failure.
In a recent study in children with Fontan circulation, daily inspiratory muscle training (IMT) of six weeks improved inspiratory muscle strength and ventilatory efficiency in a cardiopulmonary exercise test (CPET). It is therefore reasonable that an individually adjusted IMT in adult patients with Fontan circulation improves parameters of ventilation and exercise capacity. The aims of the current study were to investigate the effect of a telephone-supervised, daily inspiratory muscle training for 6 months on exercise capacity and on lung volumes in adult patients with Fontan circulation.
- Study subjects
42 patients (50% female; 30.5 ± 8.1 years; age 18 to 51 years old) out of 209 eligible patients participated from January 2017 until October 2018.
After baseline assessments (visit 1), consisting of a lung function test (LFT) and a CPET, 42 patients were randomized into either an intervention group (IG, n = 20) or control group (CG, n = 22). The IG started performing a telephone-supervised, daily IMT until six months follow-up (visit 2). The daily intervention was performed with an inspiratory resistive training device (POWER breathe International Ltd., Southam, UK).
Within the first six months after baseline evaluation the CG continued their usual activities and did not get any treatment. At the six months follow-up (visit 2) this group started IMT under the same conditions, including weekly telephone supervision till 12 months re-evaluation (visit 3). To assess the sustainability of the training program, the IG was asked to continue performing IMT without weekly telephonic-supervision until 12 months reevaluation (visit 3). This independent six-months IMT period of the CG was performed from 12 months follow-up until 18 months re-evaluation (visit 4). (Figure 1)
The study consisted of three visits for the IG and four visits for the CG, where a CPET and a LFT were performed, respectively. All tests were implemented by the same experienced sports scientist.
- Inspiratory muscle training (IMT)
After baseline evaluation patients were instructed by an experienced sports scientist in term of the IMT. Patients were instructed to begin the inhalation phase with diaphragmatic breathing and to continue inhaling by expanding the rib cage. Incorrect breathing and malposition were corrected immediately. Patients used an inspiratory resistive training device for three sets with 10–30 repetitions once daily. During the second 6 months training period, patients were instructed to continue the IMT independently, since no telephone supervision was implemented. Both groups performed IMT under the same conditions.
- Measurement of exercise capacity
Incremental symptom-limited CPET until exhaustion. Gas exchange and ventilation were measured via a breath-by-breath gas exchange analysis. Peak oxygen uptake (VO2 peak) was calculated as the highest mean O2 consumption obtained during any 30-second time interval. Compliance criteria for a valid CPET were achieved when either respiratory exchange ratio (RER) was ≥1.05, or peak heart rate was ≥85%. Cyanotic patients (oxygen saturation b 90% at rest or at peak exercise) were rarely able to reach the above-mentioned thresholds, however they were included in the study, independent of those criteria.
- Measurement of lung function
Forced vital capacity (FVC), forced expiratory volume in the first second (FEV1) and the FEV1/FVC ratio were performed.
- Exercise capacity
At 6 months re-evaluation both groups had not improved their VO2 peak and VO2 peak predicted, without any significant difference between IG and CG. Additionally, no significant difference was found between the IG and the CG concerning ventilatory efficiency.
The only significant result was an increase of O2 saturation at rest in the IG in comparison to the CG after six months IMT. These results indicate an enhancement of hypoxic pulmonary vasoconstriction resulting in an improvement in ventilation/perfusion matching, which favors systemic oxygen delivery by the constriction of intrapulmonary arteries reacting to alveolar hypoxia. Another plausible mechanism could be a reduction in chronic atelectasis following IMT. Hence IMT may improve blood flow of the lungs.
- Lung function
After 6 months of IMT, no significant changes could be observed between the IG and the CG concerning FVC and FVC predicted. Further, FEV1 and FEV1 predicted did not change significantly after IMT between the IG and CG.
Six months of weekly telephone-supervised, daily IMT could not improve exercise and lung capacity in adult patients with Fontan circulation. According to current evidence, beneficial effects of IMT in adult patients with Fontan circulation cannot be verified. Therefore, larger studies are warranted in order to gain more insight into the mechanisms of exercise training and the Fontan physiology.