A new study published in Experimental Physiology is providing insights into muscle strength impairment in patients with cystic fibrosis (CF). A joint team of researchers from University of Georgia and Georgia Regents University led by Dr. Melissa Erickson used a novel approach to the study of muscle strength in patients with cystic fibrosis called Near Infrared Spectroscopy (NIRS).
NIRS is a new method to measure muscles’ oxidative capacity, i.e. a muscle’s capacity to use oxygen and produce energy for exercise, by studying the relative signals of hemoglobin and myoglobin, two oxygen-carrying proteins used as proxy for mitochondrial metabolism. The mitochondria are the structures in the cell that are responsible for generating energy and use oxygen in their metabolism.
The researchers used NIRS to compare skeletal muscle (the type of muscle that is used in exercise) oxidative capacity in a group of 13 patients with CF (aged between 7 and 42 years) to a group of 16 healthy individuals. To that end, the NIRS device and a blood pressure-like cuff were placed on the thigh to measure muscle tissue oxygen response over time. The highest skeletal muscle oxygen consumption was significantly lower by around 15% in patients with CF. In addition, the oxidative capacity was even worse in elder individuals.
This method allows investigators a non-invasive and inexpensive measurement of the muscle’s capacity to use oxygen, especially when compared to other techniques such as muscle biopsy or magnetic resonance imaging. This also means that this methodology can be safely applied to children and repeated as many times as needed throughout a study.
As excessive muscle weakness and exercise intolerance are two very frequent symptoms in CF, they can be used to measure disease progression. Previous studies found these characteristics to be related not only to lack of physical activity but other factors as well, and this study clearly shows that CF patients have reduced oxidative capacity caused by defects in the mitochondria.
These findings in CF patients represent one of the first usages of the NIRS technique in humans and can be the first step in the development of treatments that improve muscle function in these individuals. Although CF is associated with a shorter life span, one of the main goals of therapy is to optimize the patient’s quality of life.