Inspiratory Muscle Training Is Associated With Improved Inspiratory Muscle Strength, Resting Cardiac Output, And The Ventilatory Efficiency Of Exercise In Patients With A Fontan Circulation
Authors: Karina Laohachai, David Winlaw, Hiran Selvadurai, Ganesh Kumar Gnanappa, Yves d'Udekem, David Celermajer, Julian Ayer
DOI / Source: 10.1161/JAHA.117.005750
Date: 21 August 2017
Reading level: Intermediate
Why This Matters for Freedivers
Inspiratory muscle training is one of the few “breathing tools” that has fairly consistent evidence for increasing inspiratory strength. Even though this study is in a medical population (Fontan circulation), it still shows something useful for freedivers: a simple, home-based protocol can measurably strengthen the breathing muscles and slightly improve breathing efficiency during exercise. The big takeaway is not “this will boost your apnea,” but that targeted inspiratory training can create real, trainable changes—so it’s worth treating IMT like any other structured training block, not a vague breathing routine.
Synopsis
This study looked at whether a short, practical block of inspiratory muscle training (IMT) can improve breathing-muscle strength and “breathing efficiency” during exercise. The participants weren’t athletes—they were teenagers with a Fontan circulation (a type of heart surgery where blood flow to the lungs works differently). That matters because these patients often have reduced exercise capacity and weaker breathing muscles, and anything that improves how the body handles breathing during effort could have real benefits.
The setup was straightforward: 23 adolescents followed a 6-week home IMT program, doing 30 minutes per day using a threshold IMT device. The resistance was set at 30% of each person’s maximal inspiratory pressure (MIP) (basically, how hard they can inhale against a blocked mouthpiece). The researchers tested respiratory muscle strength, lung function, and exercise performance before and after the training. A subset of participants also did exercise cardiac MRI scans to see whether there were changes in blood flow and heart pumping performance.
The biggest change was in inspiratory strength: after 6 weeks, MIP increased by about 61% on average. Importantly, this wasn’t just “getting better at the test” for exhaling too—maximal expiratory pressure didn’t change, which supports the idea that the training specifically targeted the inhalation muscles.
They also found a modest improvement in ventilatory efficiency during exercise, measured by the VE/VCO2 slope (in plain terms: how much you have to breathe to get rid of a given amount of CO2). A lower value generally means you’re ventilating more efficiently during exercise. This improved after training. What didn’t clearly change was overall peak exercise capacity—so the training wasn’t a magic upgrade in fitness in just 6 weeks, but it did shift some underlying “how breathing behaves under load” variables in a helpful direction.
The cardiac MRI subgroup adds an extra interesting layer: after IMT, resting cardiac output increased slightly, and ejection fraction improved. That suggests that breathing mechanics and pressures in the chest might influence circulation in this type of heart physiology. For freedivers, the details aren’t directly transferable, but the concept is worth noting: breathing muscle function and chest pressures can interact with circulation, not just airflow.
The overall message is that a simple daily IMT routine can produce real, measurable changes in inspiratory muscle strength, and may improve the efficiency of breathing during exercise—without requiring a complicated lab-based training program.
Abstract
Background—Patients with a Fontan circulation have reduced exercise capacity and respiratory muscle strength. Inspiratory muscle training (IMT) improves exercise capacity and quality of life in adults with heart failure. We assessed whether 6 weeks of a home-based program of IMT improves inspiratory muscle strength and the ventilatory efficiency of exercise in adolescent patients with a Fontan circulation.
Methods and Results—Twenty-three adolescent participants (aged 16±2 years) with a Fontan circulation underwent 6 weeks of IMT for 30 minutes daily. Respiratory muscle strength (maximal inspiratory pressure and expiratory pressure), lung function, and exercise capacity (cardiopulmonary exercise testing) were assessed. Fourteen of 23 participants also underwent exercise cardiac magnetic resonance imaging to examine the effects of IMT on cardiac output and systemic and pulmonary blood flow. Six weeks of IMT improved maximal inspiratory pressure by 36±24 cm H2O (61±46%) with no change in maximal expiratory pressure. Ventilatory efficiency of exercise improved after 6 weeks of IMT (from 34.2±7.8 to 32.2±5.6, P=0.04). In those who underwent exercise cardiac magnetic resonance imaging, IMT increased resting cardiac output (from 4.2±1.2 to 4.5±1.0 L/min, P=0.03) and ejection fraction (from 50.1±4.3 to 52.8±6.1%, P=0.03).
Conclusions—Six weeks of IMT is associated with improved inspiratory muscle strength, ventilatory efficiency of exercise, and resting cardiac output in young Fontan patients. IMT may be a simple beneficial addition to the current management of Fontan patients, potentially reducing exercise intolerance and long-term morbidity and mortality.