Positive airway pressure (PAP) is a type of respiratory ventilation primarily used for sleep apnea treatment. With obstructive sleep apnea, physical blockages occur in a person’s airway while asleep. This obstruction can cause their breathing to stop, which reduces the oxygen in the blood, leading to waking up frequently and feeling tired during the day.
PAP treatment is carried out by applying a stream of compressed room air into the patient’s airway through a tube connected to a mask. The positive air flow keeps the person’s airway open, preventing the collapse/blockage and therefore allowing normal breathing. PAP therapy is the most effective and widely used method for treating sleep apnea.
PAP Machines
PAP machines keep the patient’s airway open using air pressure routed through a nasal mask. It’s the air pressure, not the movement of the air, which prevents apneas from happening. The pressure of the PAP device is set according to the patient’s needs – high enough to make sure the airway is fully open during inhalation, but not so high that the sleeper is disturbed by the pressure. The necessary pressure is usually determined by a sleep physician after an overnight sleep study.
There are several types of machines used for positive airway pressure therapy: CPAPs, BPAPs, and APAPs.
Continuous Positive Airway Pressure (CPAP) machines
CPAP machines deliver a fixed, or stable, pre-determined level of air pressure. There is one set pressure level that remains the same during inhalation and exhalation. Its simple approach to supporting the airway is effective for many sleep apnea patients making CPAPs the mostly widely used machine to treat sleep disordered breathing. Because CPAP machines are the most cost-effective, they are usually the first treatment prescribed for central sleep apnea.
Bi-Level Positive Airway Pressure (BPAP) machines
BPAP machines alternate the delivery of two separate pressure levels. A higher inspiratory pressure is used to keep the airway open as a patient breathes in, while a lower expiratory pressure allows the patient to exhale easily. By alternating the inhalation and exhalation pressures, BPAPs encourage the lungs to operate more efficiently. Patients needing a high pressure (≥ 15 cmH2O) to relieve their apneas may find it difficult to exhale against the pressure of a CPAP and can benefit from using a BPAP machine. A BPAP is also much easier for users with neuromuscular disease as the dual settings allow patients to get more air in and out of the lungs without the natural muscular effort needed to do so.
Automatic Positive Airway Pressure (APAP) machines
APAP machines are set at a variable pressure range and adjust the pressure based on the resistance in a patient’s breathing. Like a BPAP, an APAP machine has a low range setting that delivers air at a lower preset pressure, and a high range setting that delivers air at a higher preset pressure. However, an APAP is a titrating device equipped with technology that measures resistance and automatically adjusts the continuous pressure to the minimum required to maintain an unobstructed airway on a breath-by-breath basis. This enables the APAP to meet a patient’s changing breathing needs as they go through various stages of sleep or sleep positions.
Integrated Humidification Systems
PAP machines with a built-in humidifier add moisture to the air flow in order to ease the breathing process for sleepers receiving CPAP, BPAP, or APAP therapy. The dry air flow from PAP machines could irritate the patient’s airway, especially at higher pressure settings. Without humidified air, PAP recipients may experience a dry mouth or nose, irritated throat and nasal passages, headaches, excessive thirst, etc. which can be extremely uncomfortable and could be a deterrent for using the PAP device. Integrated humidifiers typically come in two different styles: passover (cold) humidifiers or heated humidifiers. Heated humidifiers feature a built-in heating element that warms the water in the chamber. Some humidifiers allow users to adjust the level of humidification, and most models offer customizable temperature settings.
Testing PAP Machines
PAP machines have a number of integrated sensors which ensure a continuous, accurate control of air flow, pressure, vibration, and humidity to keep patients comfortable and safe. To maintain optimal performance, the embedded sensors may need to be calibrated and/or checked periodically – during the design/production of the machine or during service. Reference instruments are used to calibrate flow, pressure, and temperature sensors. When testing a PAP machine, often times back pressure will be applied to place a load on the system. Testing its extremes will reveal any potential deterioration of the blower, motor, etc.
Testing Expiratory Pressure Relief
Some PAP devices include an expiratory pressure relief feature which allows individuals to optimize the air pressure for greater comfort during therapy. When enabled, the PAP device will maintain air pressure during inhalation but reduce the delivered mask pressure during exhalation. Sensors embedded in the PAP machine detect a patient’s breathing, and as an individual exhales the PAP responds by reducing the air pressure delivered by a specific amount. When an inhalation is detected again, the machine raises the pressure back to the prescribed setting. TSI flow meters integrate a high speed differential pressure sensor that can measure the pressure relief on PAP machines with 0.5% of reading accuracy.
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