Nox RIP: The Bedrock of Innovation in Sleep Diagnostics


There are a number of ways to measure nighttime breathing during diagnostic sleep tests, but not all tests have the built-in technology to capture the many physiological nuances of respiration.

An important metric, respiratory effort, is monitored during diagnostic sleep tests by respiratory inductance plethysmography (RIP), which records changes in the volume of the abdomen and chest. While The American Academy of Sleep Medicine’s guidelines specify that the preferred measurement of respiratory effort for diagnostic home sleep tests is RIP with two belts, not all of these tests include this important technology.¹

To maximize the accuracy of diagnostic sleep tests and to spur innovation in the field of sleep medicine, clinical scientists and engineers at Nox Medical, have spent years engineering Nox RIP sensors. This patented technology is now a foundational piece of every Nox diagnostic test and has driven new investigations into population health. Nox RIP technology has also served an integral role in the development of new diagnostic tools and careful assessment of RIP ventilation may provide reliable sleep apnea phenotyping for the clinical setting, according to a joint study between Nox researchers and Harvard Medical School.²

Two Nox RIP belts are incorporated into all Nox Medical’s diagnostic sleep tests, including the Nox A1s, a fully portable polysomnography (PSG) system, and the Nox T3s, a home sleep test.

The single—patient-use belts are made with super stretchable elastic, designed for an adjustable and comfortable fit. One RIP belt is placed around the rib cage under the armpits and a second one is positioned around the abdomen. A simple instructional video is available online to guide research subjects and patients on how to set up the home sleep tests without the help of a sleep technologist. 

The Difference of Calibrated RIP 

Nox devices use a calibrated RIP signal, different from standard RIP signal in that it continuously measures movement over time. A calibration of movement is performed for each 30-second epoch. 

This ongoing calibration helps to correctly determine how the movements of the abdomen and thorax contribute to breathing. The continuous calibration is then able to adjust for body position changes. 

In a white paper, the calibrated RIP method of measuring respiratory flow has been compared to show equivalence to a pneumotach, the “gold standard” of flow measurement. The white paper showed that the calibrated RIP flow signal has a very high correlation to the flow signal from a pneumotach.

Reliable Backup Signal 

Currently, many sleep diagnostic tests rely on nasal cannula sensors to measure respiratory pressure from the patient’s nose, but these signals can become disrupted if the sensors are moved during the night. 

As an additional option, the Nox RIP belts record a signal that may be used as a backup for the cannula flow. ³ ⁴ The calibrated RIP flow derived from the Nox RIP belts can be used as a backup flow signal for the cannula in cases where the cannula drops out or, for some reason, patients cannot wear the cannula. Some patients might find the nasal cannula so uncomfortable that they are unable to wear it throughout the night, so the RIP flow may be used for patients who cannot tolerate a nasal cannula.

The calibrated RIP flow derived from the Nox RIP belts can be used as a backup flow signal for the cannula in cases where the cannula drops out or, for some reason, patients cannot wear the cannula. In recent scientific papers,5, the Nox RIP flow has been used as a surrogate to the main flow input (the cannula) for scoring respiratory events. ³ ⁴ ⁵

Additionally, it is possible for patients to incorrectly set up the nasal cannula during unsupervised home sleep tests. This can corrupt the integrity of many HST tests, leading to unnecessary repeat testing, wasted time, and lost revenue for clinicians. 

If a nasal cannula comes loose during a Nox diagnostic sleep test, specialists can re-reference the study to the calibrated RIP signal. This ultimately saves time and resources for clinical sleep and research laboratories alike while preventing lost or invalid recordings.

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.

In whole, by generating a backup signal, the Nox RIP adds an extra layer of integrity to home sleep testing and can prevent failed diagnostic sleep tests. 

For many physicians, the inability to accurately measure sleep in patients’ homes has prevented them from adopting home sleep testing offerings into their practice. Now, physicians can not only administer at-home sleep tests, they can feel confident in the results and use them to determine the best course of treatment for each unique patient.


  1. Troester MM, Quan SF,  Berry RB, et al; for the American Academy of Sleep Medicine. The AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications. Version 3. Darien, IL: American Academy of Sleep Medicine; 2023.
  2. Finnsson E, Jónsson SÆ, Ragnarsdóttir H, Þráinsson HM, Helgadóttir H, Ágústsson JS, Wellman A, Sands SA. Respiratory inductance plethysmography for the reliable assessment of ventilation and sleep apnea phenotypes in the presence of oral breathing.
  3. Chang Y, Xu L, Han F, Keenan BT, Kneeland-Szanto E, Zhang R, Zhang W, Yu Y, Zuo Y, Pack AI, Kuna ST. Validation of the Nox-T3 portable monitor for diagnosis of obstructive sleep apnea in patients with chronic obstructive pulmonary disease. J Clin Sleep Med. 2019;15(4):587–596. https://doi.org/10.5664/jcsm.7720
  4. Magalang UJ, Johns JN, Wood KA, Mindel JW, Lim DC, Bittencourt LR, Chen NH, Cistulli PA, Gíslason T, Arnardottir ES, Penzel T, Tufik S, Pack AI. Home sleep apnea testing: comparison of manual and automated scoring across international sleep centers. Sleep Breath. 2019 Mar;23(1):25-31. doi: 10.1007/s11325-018-1715-6.
  5. Xu L, Han F, Keenan BT, Kneeland-Szanto E, Yan H, Dong X, Chang Y, Zhao L, Zhang X, Li J, Pack AI, Kuna ST. Validation of the Nox-T3 Portable Monitor for Diagnosis of Obstructive Sleep Apnea in Chinese Adults. J Clin Sleep Med. 2017 May 15;13(5):675-683. doi: 10.5664/jcsm.6582.

Topic: Industry News

Nox Medical
Nox Medical is a global leader in the sleep diagnostic technology space. The company provides sleep specialists with patient-friendly diagnostic devices and robust, reliable data collection. With easy-to-use medical device technology, Nox Medical eliminates common diagnostic pain points by prioritizing patient comfort and reliability of results, allowing providers to better assess, diagnose and treat the entire range of sleep health issues, including sleep apnea, circadian disorders and insomnia.