Albrecht Vorster of the University of Bern, Switzerland has written an article on continuous pulse oximetry and its relevance for CPAP therapy. The article has been published in the Sleep Magazine and describes the latest scientific findings on this topic.
Albrecht Vorster, born in Cologne in 1985, studied biology and philosophy at the University of Freiburg. He holds a doctorate from the Institute of Medical Psychology at the University of Tübingen on memory formation in the sleep of the sea snail Aplysia. He has also won the Science Slam several times. When he is not working or sleeping at night, Albrecht Vorster makes music, for example in the neuroscientist band ‘Hippocamblues’.
Controlled nights – Track and improve treatment through continuous pulse oximetry
Patients with high blood pressure measure their blood pressure, patients with diabetes measure their blood sugar and patients with sleep apnea measure their blood pressure…. Yes, what? How does a sleep apnea patient measure their therapy success without visiting a sleep lab each time? Well, newer CPAP devices sometimes provide information about mask seat and air flow. But how do CPAP-intolerant patients control their apnea, which is about 30% of patients? How can the many patients who rely on a different treatment method, i.e. on the jaw line, nasal stent, palate brace, position ality trainer, tongues and throat muscle training…? The simplest and most effective way of monitoring is by means of pulse oximetry. These devices are now getting smaller and cheaper, so you can control your sleep at home. One reason to take a look at this measurement method.
Continuous pulse oximetry
A classic pulse oximeter, which is worn on the wrist and finger, is familiar to most of the examination in the sleep laboratory or a respiratory polygraph performed at home. If the airway is completely or partially closed at night (apnea / hypopnea), there is a temporary drop in oxygen concentration. It is these changes in oxygen concentration that trigger oxidative stress in the body and promote inflammatory reactions. A drop in oxygen concentration also causes an increase in blood pressure, so blood vessel walls are affected. The risk of heart attack and stroke increases.
The measurement of oxygen saturation at night by means of a pulse oximeter is therefore a direct indication of whether therapy is effective. The real goal of sleep apnea treatment is to ensure a permanently uniformly good oxygen supply throughout the body during sleep. Measuring blood-oxygen concentration for sleep apnea patients is like measuring blood pressure for high blood pressure patients. Three key figures have proved to be particularly important in recent years:
- ODI (Oxygenation Desaturation Index): The number of episodes per hour in which oxygen concentration swells by more than 3%. It correlates quite well with the AHI in studies. If the ODI is 15, that’s roughly equivalent to an apnea-hypopnea index (AHI) of 15.
- T90: The proportion of bedtime in which blood oxygen saturation is below 90%. If this time is over 20% of the night, an increased risk of cardiovascular disease is to be expected. This value is more meaningful than the AHI.
- Low point of oxygen saturation at night: Studies suggest that an oxygen saturation low below 75% is associated with an increased risk of high blood pressure, type 2 diabetes and 5-year mortality, comparable to a T90 above 20%
Will the AHI be replaced by the ODI?
Meanwhile, sleep physicians agree that the mere number of respiratory interruptions (apnea-hypopnea index, AHI) is insufficient. Especially in the case of how serious and dangerous a sleep apnea disease is. The AHI is a historically grown metric with a freely defined cut-off value. Only now does research become aware that other values would have to be used to measure therapeutic success.
The reason is quite simple: Many short breathdropers in which the oxygen concentration drops only slightly are sometimes less problematic for the body than few, but longer breathing pauses, in which the oxygen concentration drops menacingly low. It is even sometimes the case that as the depth and duration of the apnea attacks increases, the AHI paradoxically decreases. Therefore, it has been clear to experts for some time that the AHI is not a good knife value to estimate the severity of AN OSAS and the health risks. The actual danger to the body comes from periods of low oxygen saturation, and the AHI measures this only indirectly.
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The benefits of continuous pulse oximetry
Long-term control of oxygen levels offers many advantages for sleep apnea patients: A visit to the sleep laboratory only offers a snapshot of the state of health at night. But the number of breathdropers varies greatly from night to night. Sometimes the sleep laboratory is much more frequent or rarer than usual. Mean values of oxygen saturation over weeks give a more reliable picture of the state of therapy. Above all, oxygen concentrations are measured even when the mask is deposited at night. This is important because the majority of patients wear the mask only for a few hours per night. Leaks or errors in device adjustment can also be detected quickly while viewing oxygen values.
But most importantly, a permanent measurement of oxygen saturation levels gives the patient back control of his disease. It gives you the opportunity to experiment: How did weight loss affect sleep apnea? What is the effect of evening beer? My medication, smoking or a back-position avoidance pillow? You get the opportunity to improve your own treatment and become an expert in your own cause.
If you as a patient can check the consequences of his actions for your own (invisible) illness, it gives you additional motivation to train and change his behavior. Studies clearly show that high blood pressure patients who regularly measure their blood pressure themselves improve their blood pressure significantly more strongly and show a higher adherence to therapy than those who only follow the prescribed therapy without controlling themselves.
Previous pulse oximeters were quite chunky: as an oversized wristwatch with a fingerattachment. The CIRCUL ring has recently been released. A simple black finger ring that can record movement, oxygen saturation and pulse all night long and transmits to the smartphone via Bluetooth. The data of several days can be stored and compared in the smartphone and, if necessary, even forwarded directly to your treating doctor by e-mail. A good investment for those who want to optimize their treatment in order to improve their health.
The CIRCUL ring can be found here:
With the voucher code SHG10 you also get 10% discount on the purchase of a ring
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