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How It Works

How a CPAP Works

Continuous positive airway pressure

By Jason Tung

Everything Comes Down to Sleep

CPAP My freshman year at college taught me how much I dislike mornings. After a long night of studying (or binge-watching a show on Netflix), I would groggily get up in the morning and rush to my 8:30 chemistry class. Despite studying in Seattle, where a Starbucks is never out of sight, I rarely felt refreshed and ready in the morning. Unfortunately, many other Americans rarely get a good night's sleep. One of the most common sleeping disorders is sleep apnea, a condition where the tongue blocks the airway while sleeping. Sleep apnea can affect anyone, but the risk is much higher for overweight males. While sleeping, patients suffer apneas (cessation of breathing), triggering the brain to wake you up to restore breathing. Victims of sleep apnea can suffer anywhere from 5 to thirty apneas an hour, making it very difficult to feel rested.

CPAP

The Components of a CPAP

For over 28 million Americans, apneas frequently disrupt sleeping and can cause very loud snoring. This lack of proper sleep can cause significant mental (depression, hallucinations, and memory problems) and physical (weakened immune system, heart issues, and weight gain) health damage, along with forcing us to rely on a latte to get through the day.

One of the most popular and effective prescriptions for sleep apnea treatment is a continuous positive airway pressure (CPAP) machine. Air from the room is filtered and then passed through the CPAP machine's blower motor which acts as a compressor. This centrifugal blower, often referred to as a squirrel cage fan, utilizes the kinetic energy of the impellers to increase the pressure of the outside air. In order to deliver the air at the exact pressure required for the patient, a piezoresistive silicon pressure sensor is used. When pressure is applied to the membrane of the sensor, the electrical resistance changes due to the mechanical strain. This change in electrical resistivity is known as the piezoresistive effect.
A typical CPAP setup A typical CPAP setup

Once the air is pressurized to a specific prescribed amount (usually between 6 to 14 cmH20) to consistently keep the airway open. In order to keep CPAPs as silent as possible, the blower is dampened and has bearings to keep it running smoothly and quietly. The air then passes through a humidifier to reduce nasal passage irritation caused by an increase in airflow. In cool passover humidifiers, the air goes over room temperature water while heated humidifiers contain warm water for the air to moisten. The pressurized and humidified air travels through the hose attached to the CPAP and is delivered to a mask worn by the patient throughout the night.

A variety of masks are available in order to minimize CPAP noise and help users sleep comfortably. Nasal masks deliver air to just the nose, and nasal pillows are earbud-shaped prongs that have less facial interference than a mask. In addition, there are full face CPAP masks that bring air to the mouth and nose. Although the sleep masks vary in design, they all serve the same purpose of delivering pressurized air to open blocked airways.

New and Improved

An example of data obtained from CPAP use

CPAP devices are fairly simple yet effective devices, reducing or eliminating disruptive breathing for 99% of patients. Using a CPAP can be uncomfortable in the first few weeks and may have very minor yet rare side effects such as dry mouth, claustrophobia, and runny nose. Side effects are usually resolved by using a different mask style that is ideal for the patient. In order to stop sleep apnea symptoms, CPAPs need to be used every night.

In addition to just opening the airway, many modern CPAPS now use software to analyze breathing and sleeping patterns, giving patients daily reports of their sleep habits. CPAP software can also track therapy progress and the overall effectiveness of the device in reducing apneas.

An increasingly common alternative to the CPAP is automatically-adjusting positive airway pressure (APAP) therapy. As mentioned, CPAPs only deliver air at a specified pressure determined from a CPAP titration study. However, APAPs have specified low and high range pressure settings to maintain an ideal air pressure for each breath. The APAP has a complex algorithm that determines the ideal pressure at any given time. Unlike CPAP, the APAP machine can also adjust the pressure if the patient gains or loses weight. Aside from the fluctuation of pressure, APAP and CPAP machines are essentially the same.

CPAP and APAP devices are prescribed to patients suffering from sleep apnea. Although there are alternative therapies for sleep apnea, CPAP is the most common and effective treatment. When properly used, the machine can help people get the sleep necessary for humans to function.

Note: The CPAP and APAP are medical devices that must be prescribed by a doctor.
Jason is a returning summer intern at Jameco and a sophomore at the University of Washington. He is excited to learn about business and medicine while at Washington. His passions include watching sports, photography, and exploring new places.