Researchers also found that a method called transcutaneous capnography is able to reliably detect nocturnal hypoventilation, or insufficient breathing, in ALS patients.
Researchers investigated the prevalence of sleep disturbances in ALS patients and how they might correlate with patients’ overall neurological status, including disease duration, progression rate, and respiratory muscle function.
They also tested if overnight oxymetry — a test that records a patient’s breathing during sleep — and early morning blood gas analysis could predict nocturnal hypoventilation, which is characterized by lower levels of oxygen during the night due to respiratory muscle weakness.
They performed a retrospective analysis of 250 patients with nonventilated ALS, of whom 123 were female and 127 male, with a mean age 63.4 years. Disease onset was non-bulbar in 166 patients, and bulbar in 84.
Patients’ oxygen status was assessed with a technique called transcutaneous capnometry, a continuous and noninvasive method of monitoring oxygenation and ventilation. The transcutaneous sensor is placed on the skin and causes an increase in the body temperature of the underlying tissue. The body reacts by allowing gas diffusion through the skin, which is then captured by the sensor.
Results showed that the prevalence of sleep apnea was markedly increased in ALS patients compared with the general population, with 40% of the patients experiencing nocturnal hypoventilation. In addition, 45.6% of them had more than five apneas, a complete loss of breathing, or hypopneas, a partial loss of breathing, per hour, according to the apnoea–hypopnoea index (AHI).
AHI categorizes the severity of sleep apnea in four different stages by the number of apneas or hypopneas per hour: minimal (less than five), mild (between five and 14), moderate (15 to 29), and severe (more than 30).
In 22.3% of the ALS patients, sleep apnea and nocturnal hypoventilation coincided.
Sleep apnea and nocturnal hypoventilation were significantly more common in male than in female patients, but researchers found no differences between genders in regard to age, disease duration, vital capacity (the amount of air that the lungs can expel after having been filled completely), and ALS Functional Rating Scale scores.
“Our study strongly confirms a previous report showing that oxymetry alone is insufficient to diagnose NH [nocturnal hypoventilation] in patients with neuromuscular disorders,” the researchers wrote. The pulse oxymetry is a non-invasive monitoring tool that uses a medical device that indirectly monitors the oxygen saturation of a patient’s blood.
Instead, “transcutaneous capnography is strongly recommended for reliable detection of NH [nocturnal hypoventilation] in patients with ALS,” the study concluded.