Walking Test Can Assess Aerobic Capacity of CMT1A Patients
People with Charcot-Marie-Tooth disease type 1A (CMT1A) show a poorer performance in cardiopulmonary exercise testing using a stationary bicycle relative to healthy individuals, a study shows.
Cardiopulmonary exercise testing (CPET) is a non-invasive assessment of the cardiopulmonary system at rest and during exercise.
Notably, this poorer performance appeared to be unrelated to cardiopulmonary limitations; rather, it was due to peripheral factors such as muscle atrophy (wasting).
Results also showed that the 6-minute walk test was a significant predictor of aerobic capacity, one of CPET’s parameters and a measure of an individual’s level of cardiovascular health.
The study findings suggest that this simple walking test could be used as an indirect measure of aerobic capacity, and thereby cardiopulmonary fitness, in this patient population, the researchers noted.
The study, “Cardiopulmonary exercise performance and factors associated with aerobic capacity in neuromuscular diseases,” was published in the journal Muscle & Nerve.
Muscle deficits that characterize neuromuscular diseases, such as CMT, often impair movement and contribute to lower levels of physical activity that puts these patients at a higher risk of obesity, cardiovascular, and metabolic conditions.
Reduced physical activity can lower an individual’s aerobic capacity, or VO2peak, which then could “impact independence for people with neuromuscular conditions,” the researchers wrote. Aerobic capacity is the maximal amount of oxygen a person’s lungs absorb during an exercise test.
Now, researchers in London, U.K., evaluated the performance of 22 adults with CMT1A and 17 adults with inclusion body myositis (IBM) during CPET using a stationary, seated exercise bicycle.
CMT1A is the most common type of CMT and IBM is a rare neuromuscular condition characterized by progressive muscle weakness and wasting associated with inflammation.
The team also assessed whether measures of physical impairment or of functional performance could be potential predictors of aerobic capacity in patients with these neuromuscular diseases. Functional predictors may be used to measure aerobic capacity indirectly when CPET testing is not available or indicated in a given patient.
All patients participated in a trial (ISRCTN99826269) that tested the safety and benefits of a three-month, seated bike-based aerobic exercise training program.
CPET data were analyzed to determine the aerobic capacity, anaerobic threshold, maximum heart rate, ventilatory drive (which reflects the increase in ventilation in response to CO2 production), and respiratory exchange ratio, an indicator of physical intensity and effort.
Anaerobic threshold is the physiological point during increasing intensity exercise when anaerobic processes, or those that produce energy in the absence of oxygen, become more dominant.
Patients’ data were compared with those predicted for age-, sex-, and weight-matched healthy people (used as controls) based on published data.
Results showed that CMT1A patients had significantly lower CPET performance for all parameters relative to their respective controls. However, these patients performed better than the IBM group, with significantly higher aerobic capacity, maximum heart rate, and anaerobic threshold.
Further analysis showed that CMT1A patients had better motor function, walked significantly faster, and took significantly more steps per day than the IBM group.
Still, the CMT1A group were younger and had less leg/arm muscle wasting, “which could have influenced the cycling task used for testing,” the researchers wrote.
Notably, while both CMT1A and IBM showed high effort levels during CPET, they finished the test with a reserve in heart rate (about 76% of maximum) and ventilation (about 50% of maximum), indicating that cardiopulmonary function did not limit exercise.
The findings suggest that “peripheral factors, such as muscle atrophy, may have limited performance” in the cycling task, the team wrote.
Moreover, body fat percentage and performance in the 6-minute walk test, which measures the distance covered over six minutes, were significant predictors of aerobic capacity in both patient groups.
Disease severity in IBM patients, but not in CMT1A patients, also was a good predictor.
The data suggest that the 6-minute walk test “could be a potential proxy [indirect] measure of cardiopulmonary fitness” in the clinic, the researchers concluded.