To start, let's take a look at a widely accepted definition of sleep apnea. If a person stops breathing for at least ten seconds five different times during an hour, or thirty times during a seven-hour night, then the person is said to suffer from sleep apnea. This means that when a person doesn't breathe for about 1 minute per hour, or 5 minutes per night he is said to have symptoms that constitute the mildest form of sleep apnea. Using this definition of sleep apnea is a good way to begin to think about the severity of the disease. You can see by the definition that factors like CPAP pressure and snoring don't indicate whether a person has sleep apnea. Likewise, they don't indicate a severity level of sleep apnea. Let's take a look at snoring first.
Snoring is caused by turbulent airflow in the airway. The turbulence is generally caused by the relaxation of soft tissue at the back of the throat. When air passes over the soft tissue, the tissue vibrates, and a sound is created. Since snoring does not necessarily result in a cessation of breathing, it follows then that snoring is not necessarily indicative of sleep apnea. You can snore like crazy and not have sleep apnea. In fact, if you're snoring it means air is flowing and you're breathing. Breathing is the exact opposite of apnea. Now, you're probably thinking, "Wait a minute. I thought snoring was a sure sign of sleep apnea". Snoring may be a sign of the potential for sleep apnea, because if you snore you may just have what it takes for a good case of sleep apnea. Specifically, you have soft tissue in your airway that may collapse and block your airway completely. Also, your soft tissue may collapse enough for you to experience hypopneas, or shallow breathing. Shallow breathing can lead to lower levels of oxygen in your blood, and it can lead to high blood pressure, and it can prevent normal sleep architecture (for example, it can prevent REM sleep). So, hypopneas aren't good. Some people may experience far more hypopneas than apneas and still have a dreadful night of sleep (or no sleep).
The surest sign of sleep apnea is snoring followed by no sound at all followed by a gasp for air. This is the typical manifestation of sleep apnea. The period of no sound coincides with the period of no breathing or very shallow breathing. If that period of no breathing lasts for more than ten seconds it's considered an apneic event. Again, snoring without the apneic event does not constitute sleep apnea.
The purpose of a sleep study is two-fold. First, the study is used to determine whether a person has sleep apnea. Second, the study is used to determine the appropriate CPAP pressure setting to be used with CPAP therapy. The pressure setting simply reflects the amount of air pressure required to keep the airway open. The air being delivered by the CPAP machine acts as a splint. The air splint prevents the soft tissues from relaxing and collapsing and closing off the airway. In some people, the air pressure needs to be relatively high to keep the airway open. This is likely due to the architecture of the airway. Someone who needs a high pressure may have a lot of tissue that needs to be held open. More tissue, means more weight, which generally means a higher pressure setting. This same person who needs a higher pressure setting might very well barely meet the minimum requirements to be diagnosed with sleep apnea. In this case, we would have a person with a high pressure setting, with mild sleep apnea. The prescribed pressure, therefore, is not necessarily indicative of the severity of the disorder.
During a sleep study a technician will monitor several "channels" of information. For example, heart rate, blood pressure, blood oxygen level, and brain activity are other important factors. When a person experiences apneic events the heart rate and blood pressure generally increase, while the oxygen level in the blood decreases. This is all bad news. The way in which a person reacts physiologically to this bad news can also indicate the severity of sleep apnea in that individual. For example, if two people have similar apneic events and one of those individuals responds with a greater drop in O2 and gets no REM sleep at all, then it could be argued that that individual has more severe sleep apnea simply because the result of the sleep apnea is more severe. In other words, it would be more critical for this individual to seek therapy.
There's a metric called the AHI, or Apnea Hypopnea Index, that is widely used to determine the severity of sleep apnea. The AHI is a number that corresponds to the number of apneas and hypopneas a person experiences per hour. If the AHI is below 5, then sleep apnea is unlikely to be diagnosed. If the AHI is between 5 and 20, then mild sleep apnea is indicated. AHI between 21 and 50 reflects moderate sleep apnea, and above 50 indicates severe sleep apnea.
There's also a metric called the RDI, or Respiratory Disturbance Index, that includes all respiratory disturbances including snoring events. The RDI and AHI are often equal or similar, although the RDI can be much higher because it includes snoring events. The RDI is not generally used to determine the severity of sleep apnea.
As always, we look forward to your input. If you have any comments or questions about the severity of sleep apnea, feel free to give us a call or send us an email.
CPAP-Supply.com is a leading online retailer of CPAP equipment. Located in Spokane, WA CPAP-Supply.com has been serving thousands of customers around the world since 2001. Founded on a belief that patients are their own best primary care providers, CPAP-Supply.com understands the importance of educating patients and customers on both the effects of and treatment for obstructive sleep apnea. For more information visit CPAP-Supply.com or call toll free 1-888-955-2727.