Why You Can Trust Nox RIP Belts for Your Sleep Diagnostics


When a patient undergoes a sleep study with Nox Medical’s diagnostic equipment, whether at home or in the lab, the patient’s breathing throughout the night is recorded with the patented Nox respiratory inductance plethysmograph (RIP) belts.

The Nox RIP belts are engineered to move in sync with the natural movements of each breath to help clinicians understand the moments during the night when a patient might experience apneas or hypopneas. Respiratory effort and flow are recorded concurrently. Both signals are captured with unparalleled accuracy to also distinguish between central and obstructive sleep apnea.

Prior research has demonstrated that the Nox RIP flow signals have a high correlation to signals taken from pneumotach, the gold standard in respiratory measurements. Researchers at Nox Medical, in collaboration with researchers at Brigham and Women’s Hospital / Harvard Medical School have shown that properly calibrated RIP ventilation could mitigate some of the problems caused by measuring ventilation in the presence of mouth breathing.  This is helpful when patients go into REM sleep since they often start to breathe through their mouth due to the loss of muscle tone.

“We believe that by comparing nasal cannula to RIP flow, we are able to detect periods of mouth breathing and correct for the missing amplitude in the cannula flow signal caused by the oral breathing route,” says Eysteinn Finnsson, research engineer at Nox Medical.

The two belt RIP technology that first became available in the early ‘80’s has proven to be a superior technology for measuring respiration and breathing. The technology is based on the electrical physics of wire-loops that says that the inductance of a wire loop is directly proportional to the area that it encircles. This is particularly beneficial for respiratory measures, as repeated studies have confirmed that the calibrated sum of areal signal of abdomen and thorax movements align closely with the actual respiratory volume and this allows other useful respiratory signals to be derived.

The Nox RIP belts themselves are designed with this principle in mind, they come in pairs, fully encircle the body and are designed to minimize any size adjustment loops that may cause signal distortion. One belt encircles the abdomen, near the belly button. A second belt is strapped around the thorax. 

A thin, metal wire conductor woven into the elastic fabric of each Nox RIP provides the impedance that is used to measure the expansion of the chest and the stomach as the patient breathes. The Nox RIP belts’ qualify to allow the calculation of a calibrated RIP sum signal and this allows other useful respiratory signals to be derived, including the Nox RIP flow signal. 

Sleep lab technologists often find that the Nox RIP flow signal serves as a backup signal for when the nasal cannula falls out during the night or if the patient is unable to tolerate the cannula.

When comparing the Nox RIP flow with the cannula flow, clinicians may experience that the RIP flow signal is reliable and is therefore often used in lieu of the nasal cannula flow signal, says Joel Porquez, RPSGT, RST, CCSH, a member of the technical support team at Nox Medical.

As a testament to the technology’s accuracy, several recent scientific papers have used the Nox RIP flow as a surrogate to the cannula flow signal for scoring respiratory events.

A recent study, published in Sleep Breathing Physiology and Disorders, described that when using disposable Nox RIP belts, the signal reliability was 98.5 to 98.8% on average, surpassing the reliability of the cannula and reusable belts, which was on average 85.5–92.5% in the different datasets.

“It definitely is quite valuable. It has saved us on quite a few home sleep studies that would otherwise be invalid,” says Jay Hemnani, RPSGT, sleep lab manager at FusionSleep in Georgia, where clinicians use Nox equipment. 

The extra RIP flow signal is also essential for the many patient populations who are extra sensitive to the sensations of the nasal cannula, including those with special needs and pediatrics, according to Porquez.

The patented automatic calibration also makes the Nox RIP technology stand out. When the patient moves and shifts throughout the night, the signal amplitudes can change. To maintain accuracy, the Nox RIP belts automatically recalibrate for body position movement. The continuous calibration of the measured signal is performed for each 30-second epoch to determine the contribution of the abdomen and thorax to breathing. 

Using single-use RIP belts has a number of benefits compared with reusable sensors. Due to the nature of the signal, it is for example important that the RIP belt follows the respiratory movements closely but does not behave like a rope that would affect the movements that are being measured. This calls for belts with very high elasticity. The elasticity of the single-use belts can be very high, as they only need to last one study and don’t need to tolerate cleaning, explains Sveinbjorn Hoskuldsson, co-founder and chief technology officer of Nox Medical. 

“I like the fact that they are single-use. That way, you know you are getting a good quality signal right from the beginning, every time,” says Hemnani. 

Designed with a feather-light and breathable material, the belts are worn above the patient’s clothes for optimal comfort. To easily conform to all body types, the belts come in multiple sizes, and are built with an elastic material that doesn’t restrict movement. Approximately an inch in width, each belt is built with a minimal profile, so many patients may barely notice the sensation of wearing them. Overall, the Nox RIP technology accomplishes the dual goals of prioritizing patient comfort and delivering accurate results.


Nox Medical. Calibrated RIP compared to pneumotach – White Paper

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Topic: Industry News