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A patient with decreased respiratory effort

Sleep

Contributed by M. Safwan Badr, MD

What is the finding identified by the arrow?

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REM-related loss of intercostal muscle activity resulting in decreased thoracic effort. The loss of intercostal muscle activity is a characteristic finding during REM sleep and results in a decreased functional residual capacity during REM sleep. In patients with marginal oxyhemoglobin saturation (SaO2) during NREM sleep, the decreased FRC results in SaO2 <90%. The decreased FRC also explains why there are larger decreases in SaO2 with apneas and hypopneas during REM sleep.

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