What are Breathing Pauses?

Your "Personal Sleep Summary" included a bar graph showing the average number of breathing pauses per hour of sleep, recorded during the night you wore the sleep recorder. An arrow pointed to your number, anywhere from zero to fifty. The scientific term for this number is the apnea-hypopnea index (AHI). We investigators believe that this number will prove to be the most important measurement made during the sleep study.

The term apnea means a breathing pause, defined as no breathing (inhalation) for ten seconds or more. The term hypopnea (hi-pop-knee-ah) means a shallow breath, defined as an inhalation of less than half of the usual amount of air inhaled during a single breath. The depth of every breath you took during the night was measured by the stretchy black bands placed around your chest and stomach. The AHI was calculated by adding together the average number of apneas and hypopneas measured during each hour of your sleep.

Apneas and hypopneas are almost always caused by a temporary narrowing (obstruction) of the breathing space just above the Adam's apple (pharynx or upper airway in the neck). This narrowing of the airway makes it harder to take a deep breath. Many factors are known to increase the chance that upper airway narrowing will occur during sleep. Some of these factors include a large neck size, being overweight, being a middle-aged man, snoring, having high blood pressure, sleeping on your back, and drinking alcohol at bedtime. However, many persons with a large number of breathing pauses during sleep (a high AHI) have none of these risk factors.

So, is it abnormal to have more than one breathing pause every five minutes of sleep? (an AHI of 12 or higher) If the answer to this question were known, the Sleep Heart Health (SHH) study would not be necessary. However, about half of the 4000 SHH participants tested so far had an AHI of 12 or more, and we doubt that half of you are "abnormal". At the far extreme, sleep specialists worry about patients who are referred to them with complaints of loud snoring, daytime sleepiness for many years, and then AHI levels of more than 40 are measured in a sleep laboratory. Many of these patients are diagnosed as having sleep apnea syndrome. It is not known whether or not this increases the risk of heart disease developing later in life, but the snoring and daytime sleepiness can often be eliminated with treatment.

What is REM Sleep?

Contrary to the personal experience of many people, sleep is not a continuous unchanging state. Through examination of brain wave recordings identical to that obtained as part of the Sleep Heart Health Study, one can see that there are two distinct phases of brain wave activity that occur during sleep. These are known as non rapid eye movement sleep (NREM) and rapid eye movement sleep (REM). These two types of sleep occur in cycles during the night, although periods of REM sleep are longer during the second half of the night than during the first half. REM sleep received its name because early sleep researchers were able to see rapid eye movements underneath the closed eye lids of sleeping subjects. If you want to stay up all night and watch someone you know as he/she sleeps, you too can see the REM, just like these sleep pioneers.

Scientists believe that REM sleep is the time when most people dream. Why do we think this? Because when people are awakened during REM sleep, they recall imagery of dreams. REM sleep also is a state of physiologic activation during sleep. During NREM sleep, blood pressure, pulse and respiratory rate generally decrease. However, during REM sleep these indices tend to increase and fluctuate almost as if the individual was awake. In fact, the brain waves during REM sleep resemble that seen when someone is awake.

Why do we need REM sleep? The answer to this question is not known. Some scientists believe that REM sleep removes uneccessary connections between brain cells and as these connections are deleted, we experience dream imagery. Others believe that REM sleep is a way of sorting out the events of the day--discarding unimportant facts and filing relevant ones. Irrespective of why REM occurs, it is important that we get adequate amounts of it. In normal people, REM sleep occupies 20-25% of ones sleep time. If we don't get this amount, we may display changes in our behavior such as irritability, anxiety and difficulty concentrating. Fortunately, in most people REM sleep occurs naturally and we don't have to do anything for it to occur in the proper amounts. So, for your next night's sleep, have a long and happy REM!!?

Sleep Study Update

Data is being collected for the Sleep Heart Health Study in nine different communities across the United States. As a group, we have completed over 4,500 home sleep studies in a wide variety of physical and geographical locations.

In Tucson, over 725 sleep studies have been performed in the past year. Our goal is to complete 900 high quality studies by November of 1997. We sincerely appreciate the contributions of each and every one of you towards making the Sleep Heart Health Study in Tucson a success.

A critical component of the Sleep Study is the follow-up information required to assess whether or not pauses in breathing during sleep increases the likelihood of heart or other disease. A very brief questionnaire will soon be sent to each of you asking simple questions about your health over the past year. Please take a short moment of your time to provide this vital information. We appreciate it!!