Positive airway pressure (PAP) therapy is the gold standard and most widely used treatment for obstructive sleep apnea (OSA). PAP therapy is recommended by the American Academy of Sleep Medicine (AASM) in the treatment of moderate-to-severe OSA in adults and as an option for the treatment of mild OSA (1). PAP is a generic term applied to all therapies that use air pressure delivered through the upper airway of patients with sleep-related breathing disorders (SRBDs) with the purpose of creating a “pneumatic splint” to support the anatomic structures of the upper airway by opening and thus allowing an uninterrupted flow of air to the lungs during sleep.

In this chapter, we will establish a framework for how the anatomy of the upper airway contributes to SRBDs and introduce the different types of PAP therapy that have been developed to restore normal breathing. We will also provide an understanding of how these devices interact with the upper airway to produce salutary health benefits on sleep apnea and diseases comorbid with the disorder.

The term Apnea is derived from the ancient Greek etymology meaning “absence of breathing,” and results in cessation of breathing due to closure of the upper airway. Hypopnea, from the Greek for “under breathing”, refers
to a reduction in breathing due to a narrowing of the upper airway. Both apneas and hypopneas are breathing events that result from obstruction of the airway and can be treated safely using PAP therapy. Snoring is also an obstructive breathing event that can have clinical implications. It is associated with OSA but can occur independently as a result of airway vibrations that typically range from 60 to 80 dB in intensity. As a point of reference, a vacuum cleaner typically emits a decibel level of 70 and a chainsaw, 100. Hearing damage can result from prolonged exposures greater than 80 dB. A grandmother of four in the United Kingdom was recently recorded with a snoring level of 111.6 dB!

Respiratory effort-related arousals (RERAs) are another important clinical manifestation of obstructive sleep-disordered breathing (SDB) that are treated with PAP therapy. These events, like snoring events, don’t rise to the level to meet the clinical definition of an apnea or hypopnea, but are characterized by a reduction in airflow that leads to a pattern of arousals from sleep, which mean they are significant for sleep disturbances. Central apneas and central hypopneas are events that can be differentiated from obstructive apneas and obstructive hypopneas in their cause: Central events originate not because of a narrowing or obstruction in the upper airway, but instead result from a neurologic signal from the central nervous system to stop breathing or reduce breathing that can occur in coordination with conditions like heart failure and stroke, and involves an area of the brain called the “brainstem” that triggers breathing. Sleeping at altitude can also cause central events in a breathing pattern called “periodic breathing.” The use of opioid-based medications can also trigger central events and a “crescendo-decrescendo” pattern of central events called Cheyne-Stokes respiration.

Although the first modern use of the word “apnea” can be traced to 1719, and the symptoms of the disease first appeared in a fictional description of a Charles Dickens character in the Pickwick Papers in 1836 (2), it was not until 1965 that sleep apnea was first documented in the medical literature and it was another 16 years (1980) until the first noninvasive ventilation device, a positive-pressure breathing circuit connected to the nose using plastic tubing and silicone sealant, was used on a patient by Dr. Colin Sullivan. By the end of the 1980s, continuous positive airway pressure (CPAP) had been developed into a more sophisticated treatment for sleep apnea, and by the 1990s, bilevel positive airway pressure (BPAP) had been in use (3), followed by auto-titrating devices that are continuing to evolve and use more sophisticated treatment algorithms to respond to breath-by-breath changes in patient respiration (Fig. 46-1).

A classification system for sleep apnea is used in the diagnosis and is useful in guiding treatment through the clinical pathway: Mild sleep apnea is defined as the occurrence of 5 to 14 respiratory events per hour, on average, throughout the sleep period; moderate sleep apnea is defined as 15 to 30 events per hour; severe sleep apnea is defined as greater than 30 events per hour (Fig. 46-2).

It is not unusual for a sleep technologist to observe hundreds of respiratory events during a single night of sleep. Typically, the total number of obstructive and central apneas and hypopneas is combined to yield an apnea-hypopnea “index” (AHI), which is the average number of events per hour during a sleep period based on a polysomnography (PSG) recording. For patients with a high pretest probability of sleep apnea as a result of associated subjective and objective sleep-related symptoms, but who do not reach the clinically defined minimum for diagnosis by AHI, RERAs are often scored and added to the index to yield a respiratory disturbance index (RDI). RDI can be utilized to make a diagnosis of sleep apnea and qualify some patients for related
follow-up care. For insurance reimbursement purposes, an AHI or RDI greater than or equal to 15 events per hour is required. However, criteria for reimbursement coverage also extend to an AHI or RDI between 5 and 14 events per hour if a patient demonstrates documented objective or subjective sleepiness symptoms or suffers from comorbid conditions such as hypertension, stroke, or heart disease. PAP therapy has been shown to have good clinical outcomes in patients with moderate-to-severe sleep apnea or in patients with mild sleep apnea with associated comorbidities or disorders.

During therapeutic PSG, a sleep technologist fits a mask to the nose and/or mouth of a patient with known sleep apnea and uses it in concert with a medical PAP device that delivers room air at a pressure set by the technologist or determined through an internal device algorithm using the appropriate mode and settings to normalize a patient’s breathing. Picture a box with a fan inside: On one end of this box is an opening covered by a filter that draws in room air from the outside. Inside this box is also a chamber filled with heated water through which the air travels before being sent through plastic tubing to a mask interface and ultimately to the lungs where oxygen enters the blood through sacs called “alveoli.”

Depending on the physiologic, logistic, and psychological needs of the patient, there are a variety of PAP therapy modes to choose from. Most populations with SRBDs experience a reduced or blocked flow of air because of an obstruction by muscles and tissues of the upper airway behind the mouth and throat. For these patients, a fixed flow of positive air, called CPAP, is typically applied. Alternatively, a PAP device with independently fixed inspiratory and expiratory positive airway pressures (IPAP and EPAP, respectively), known as BPAP, can also be effective. BPAP uses two pressures, and IPAP is applied during inhalation and is higher than the EPAP, which is applied during exhalation. In a version called auto-CPAP or auto bilevel, an internal algorithm within the machine can be used to “auto-titrate” effective pressures.

More advanced titration approaches are needed to treat more complex forms of sleep apnea that involve a reduced airflow as a result of underlying neurologic conditions, lung disease, chronic obstructive pulmonary disease (COPD), or medication effect. Adaptive servo-ventilation (ASV) and volume-assured pressure support (VAPS) are two primary examples. The ASV device algorithm automatically adjusts IPAP, EPAP, and pressure support (PS), which is the difference in pressure between IPAP and EPAP (i.e., IPAP minus EPAP equals PS) settings in response to patient breathing within a set range which is established by a technologist on the basis of a physician’s order. The aim of VAPS is to maintain an optimal level of the patient’s tidal volume (VT), which is the volume of air displaced through normal inhalation and exhalation. This value is approximately 400 to 500 mL for a normal adult but must be calculated on the basis of the patient’s actual height that is used to approximate ideal body weight. The appropriate VAPS setting for VT is equal to 7 mL per kg of ideal body weight. With VAPS, the inspiratory phase switches to exhalation settings only after a preset VT is delivered to the patient (4).

SDB has a significant impact on society. The AASM recently contracted a global research and consulting firm to uncover the economic costs of untreated sleep apnea for payers, employers, and patients (5). Their report estimates that undiagnosed OSA cost the United States approximately $149.6 billion in 2015 alone. Between 2% and 4% of the adult US population is affected by sleep apnea, but of the estimated 22 million with the disorder, 80% are undiagnosed and of those that are diagnosed and treated, compliance on PAP therapy is approximately 50%. This means that less than 10% of those suffering from sleep apnea are being effectively treated! This has significant implications for society because of the known, wide-reaching effects that sleep deprivation, or the lack of quality sleep, has on public health, workplace productivity, and safety. A case can be made that sleep apnea is a hidden health crisis of our time.

The upper airway is quite complex (see Fig. 46-3). For the sleep technologist, the most important areas are the nasopharynx, the oropharynx, and the laryngeal pharynx. In terms of preventing snoring, hypopnea, and
OSA, the goal of PAP therapy is to prevent collapse at any point in these three areas of the upper airway.