Obstructive sleep apnea (OSA) is a chronic disorder where the muscles in the throat relax during sleep, causing the airway to narrow or completely close off. These repeated episodes of airway blockage interrupt normal breathing patterns, which can last for ten seconds or more. This cycle of breathing cessation and subsequent gasping or waking disrupts sleep quality, often leading to severe daytime exhaustion. Continuous Positive Airway Pressure (CPAP) is the most common and effective therapy used to manage this condition.
Understanding the Apnea-Hypopnea Index (AHI)
The severity of obstructive sleep apnea is quantified using a metric called the Apnea-Hypopnea Index, or AHI. This index is calculated by counting the total number of apnea events (complete breathing cessation) and hypopnea events (partial airflow reduction) that occur during a sleep study. That total number is then divided by the hours of sleep recorded, resulting in a score that represents the average number of breathing interruptions per hour.
The AHI score is the foundational tool used by specialists to categorize the level of sleep apnea. A normal AHI is fewer than five events per hour, meaning a person experiences minimal breathing disruptions during sleep.
Mild sleep apnea is diagnosed when the AHI falls between five and fewer than 15 events per hour. Individuals in this range may experience mild tiredness or snoring.
Moderate sleep apnea is defined by an AHI ranging from 15 to fewer than 30 events per hour. At this stage, the frequent interruptions can lead to more significant symptoms, including difficulty concentrating, headaches, and an increased risk of cardiovascular issues.
Severe sleep apnea is diagnosed when the AHI is 30 or greater events per hour. Patients with severe apnea experience breathing disturbances every two minutes or less, leading to significant drops in blood oxygen levels and extreme daytime sleepiness.
Treatment Thresholds for CPAP Use
The decision to initiate CPAP therapy is directly tied to the AHI score, though it is also heavily influenced by the presence of symptoms and other health factors. For patients diagnosed with moderate sleep apnea (AHI 15 to < 30) or severe sleep apnea (AHI [latex]\ge[/latex] 30), CPAP is considered the standard treatment. The high frequency of breathing events in these categories necessitates intervention to reduce health risks. In these higher severity cases, CPAP is indicated because untreated moderate and severe OSA carries risks, including increased blood pressure and a higher likelihood of cardiovascular events. The goal of therapy is to reduce the AHI to below five events per hour, or at least to a level where symptoms are resolved. For patients with mild sleep apnea (AHI 5 to < 15), the treatment protocol is more nuanced and often depends on clinical presentation. CPAP is considered an option rather than a standard requirement for this group, especially if they are asymptomatic. However, CPAP is strongly recommended for mild cases if the patient reports significant symptoms, such as excessive daytime sleepiness or unrefreshing sleep. The presence of comorbidities also pushes the recommendation toward CPAP use, even in the mild range. These conditions include hypertension or cardiovascular disease. Therefore, the threshold for requiring CPAP is not a single AHI number, but a combination of an AHI of 15 or higher, or an AHI of 5 to 14 when accompanied by significant symptoms or existing health vulnerabilities.
The Mechanism of CPAP Therapy
A CPAP machine works by delivering a continuous stream of pressurized air through a hose and a mask worn over the user’s nose or mouth during sleep. This constant flow of air acts as a pneumatic splint, gently pushing against the soft tissues in the upper airway. By maintaining this positive pressure, the machine prevents the throat from collapsing, which is the physical cause of obstructive sleep apnea.
The pressure setting is carefully determined through a process called titration, which is often conducted during a formal sleep study. This process identifies the minimum effective pressure needed to fully eliminate the apneas and hypopneas.
The pressurized air keeps the airway fully open, ensuring uninterrupted breathing and stable blood oxygen levels throughout the night. This stability prevents the frequent micro-arousals that fragment sleep, restoring restorative sleep. Modern CPAP devices often feature humidifiers and pressure relief settings to make the therapy more comfortable and encourage consistent use.
Non-CPAP Treatment Options
Other options exist for those with milder conditions or individuals who cannot tolerate the machine. Lifestyle modifications are often the first step, including weight loss, which can significantly reduce the AHI, and positional therapy, which involves avoiding sleeping on the back to prevent airway collapse.
Custom oral appliances are typically fitted by a dentist. These devices work by holding the lower jaw and tongue forward, thereby physically opening the airway. Oral appliances are generally recommended for mild to moderate OSA, or for severe cases where CPAP is rejected or unsuccessful; surgical interventions or nerve stimulation devices may also be considered.