Your breathing is shallow and irregular for 1/3 of your life

Key Points

• Breathing volume decreases between 6% and 16% during sleep

• Breathing is shallow and irregular during sleep

• We experience relative hypoxia and hypercapnia during sleep

The Breathing Diabetic Summary

To understand sleep-related breathing disorders, we first have to understand normal breathing during sleep.  That was the goal of this study.

Experiments were conducted with 19 subjects (8 males, 11 females) that had no history of sleep complaints.  Additionally, they were all nocturnal sleepers.  The researchers studied them between 10 PM and 7 AM.  They studied one subject on 3 nights, 9 subjects on 2 nights, and 9 subjects on 1 night.

Baseline measurements were obtained while the patients were lying in bed either before falling asleep or after waking up (using EEG-confirmed wakefulness).  Theses recordings were subsequently averaged to produce the “awake” value. 

For measurements of breathing during different sleep stages, the subjects had to stay in that sleep stage continuously for at least 2 minutes.  Additionally, there could not be any detectable leaks within the breathing mask they were wearing.

Comparison of the awake versus sleeping parameters revealed that breathing volume reduced significantly during sleep.  For non-REM sleep, breathing volume decreased between 6% and 8%.  During REM sleep, ventilation reduced by ~16%.  Interestingly, the breathing rates of these subjects were slightly faster during sleep than while awake, suggesting that breathing becomes shallower during sleep.

Because the participants were breathing less, they became significantly more hypoxic (low O2) and hypercapnic (high CO2) while asleep compared to while awake.

The researchers used this information, along with assumptions regarding lung dead space and dead space due to the breathing mask, to estimate the change in gas exchange occurring in the lungs.  These calculations revealed a reduction in gas exchange between 19% and 39% during sleep, helping explain why the participants experienced hypoxia and hypercapnia.

Lastly, during non-REM sleep, breathing rates were somewhat regular (although a few patients still showed irregular rates during non-REM).  In REM sleep, all participants exhibited shallow and irregular breathing patterns. 

Overall, these results show that breathing volume is reduced during all stages of sleep. The greatest reductions occur during REM sleep, which is also when breathing rate is the most irregular and unstable. The reduction in breathing leads to relative hypoxia and hypercapnia. Interestingly, these breathing patterns are normal and are part of the natural physiological changes our bodies makes during sleep.

Abstract

Respiratory volumes and timing have been measured in 19 healthy adults during wakefulness and sleep. Minute ventilation was significantly less (p less than 0.05) in all stages of sleep than when the subject was awake (7.66 +/- 0.34(SEM) 1/min), the level in rapid-eye-movement (REM) sleep (6.46 +/- 0.29 1/min) being significantly lower than in non-REM sleep (7.18 +/- 0.39 1/min). The breathing pattern during all stages of sleep was significantly more rapid and shallow than during wakefulness, tidal volume in REM sleep being reduced to 73% of the level during wakefulness. Mean inspiratory flow rate (VT/Ti), an index of inspiratory drive, was significantly lower in REM sleep than during wakefulness or non-REM sleep. Thus ventilation falls during sleep, the greatest reduction occurring during REM sleep, when there is a parallel reduction in inspiratory drive. Similar changes in ventilation may contribute to the REM-associated hypoxaemia observed in normal subjects and in patients with chronic obstructive pulmonary disease.

Journal Reference:

Douglas NJ, White DP, Pickett CK, Weil JV, Zwillich CW.  Respiration during sleep in normal man.  Thorax.  1982;37(11):840-844.

Our somewhat unusual breathing patterns during sleep

Key Points

• Breathing volume is reduced by as much as 16% during sleep

• Breathing rate is variable during sleep, especially in REM

• Hypoxic and hypercapnic responses are reduced by as much as 66% during sleep

The Breathing Diabetic Summary

We spend approximately 1/3 of our life sleeping.  And although sleep science is still relatively new, it’s undeniable that sleep is a key component of achieving optimal health.  Which begs the question, if sleep is so restorative, what is happening to our breath during this time?

Published in 1984, this review study found that breathing is significantly reduced during all stages of sleep.  This reduction can be as great as 16%.

Somewhat surprisingly, our breathing rate is extremely variable during sleep.  I expected that our breathing would become rhythmic and deep.  However, research shows that the opposite is true.  We breathe shallower and our breathing rate remains the same, or even increases slightly.

Additionally, it differs for different stages of sleep.  During non rapid eye movement sleep (non-REM), our breathing volume reduces and we sometimes achieve a steady rhythm.  In REM sleep, however, our breathing volume reduces even more, but our rate becomes more sporadic.

We also experience relative hypoxia (low O2) and hypercapnia (high CO2).  In fact, our tolerance to CO2 increases dramatically.  One study suggested that during non-REM, CO2 tolerance increases by ~33%.  During REM sleep, it increases by about 66%.  That’s fairly remarkable.

So, to summarize, here is what happens to breathing during sleep:

• Breathing volume reduces

• Breathing rate is variable

• Hypoxic and hypercapnic responses are reduced

The processes occurring during sleep clearly serve a purpose in restoring health.  If we interrupt these processes, we will not harness the full power of sleeping.

Therefore, if you are breathing with an open mouth during sleep, you are probably breathing too much and not supporting restorative sleep.Luckily, it’s an easy fix.Simply taping your mouth at night is the first step toward achieving optimal breathing volumes during sleep.

Journal Reference:

Douglas NJ.  Control of Breathing during Sleep.  Clin Sci (Lond).  1984;67(5):465-471.