Is loop gain different between Non-Rapid Eye Movement (NREM) and Rapid Eye Movement (REM) sleep?

Loop Gain Differences Between NREM and REM Sleep

Loop gain is significantly lower (more stable) in REM sleep compared to NREM sleep, indicating fundamental differences in ventilatory control stability between these sleep stages. 1

Physiological Differences in Loop Gain Between Sleep Stages

• Loop gain measurements show significantly lower values in REM sleep (mean 0.51 ± 0.04) compared to NREM stage 2 sleep (mean 0.63 ± 0.04), indicating more stable ventilatory control during REM sleep 1
• The differences in loop gain between REM and N3 sleep, as well as between N2 and N3 sleep, are not statistically significant 1
• Loop gain tends to increase over the course of the night, with N2 loop gain being significantly lower in the first third of sleep compared to later sleep periods 1, 2

Clinical Implications of Sleep Stage-Dependent Loop Gain

• Patients with NREM-predominant OSA (NREMOSA) demonstrate significantly worse ventilatory control stability (higher loop gain) in NREM sleep compared to REM sleep 3
• Patients with REM-predominant OSA (REMOSA) show a more collapsible airway (lower Vpassive) in REM compared to NREM sleep, rather than differences in loop gain 3
• The major physiological difference between NREMOSA and REMOSA patients is a significantly higher overall loop gain in the NREMOSA group 3

Stability Characteristics of NREM vs. REM Sleep

• NREM sleep can be categorized into stable (NREMS) and unstable (NREMUS) states, with stable NREM characterized by high delta power, stable breathing, blood pressure dipping, and strong sinus arrhythmia 4
• Unstable NREM sleep features fragmented slow oscillations, non-dipping blood pressure, unstable respiration, and cyclic heart rate variation 4
• Similar bimodality exists in REM sleep (REMS vs. REMUS), though this is more difficult to discern in healthy individuals and becomes more apparent in those with combined obstructive and central sleep apnea 4

Factors Affecting Loop Gain During Sleep

• Time of day significantly affects loop gain during NREM sleep, with higher values observed in the morning compared to evening sessions 2
• The arousal threshold is also higher in the morning during NREM sleep, which may contribute to breathing instability at this time of day 2
• Gender influences the susceptibility to OSA during different sleep stages, with women showing greater differences between REM and slow-wave sleep AHI than men 5

Sleep Stage Classification and Eye Movements

• According to AASM guidelines, eye movements are key physiological parameters used to differentiate between sleep stages 6
• Slow eye movements are most prominent in N1 sleep but can persist into N2 sleep, though with less frequency 6
• N3 sleep is characterized by minimal eye movements and has the highest arousal threshold 6

Understanding these differences in loop gain between sleep stages has important implications for diagnosing and treating sleep-disordered breathing, particularly when tailoring interventions for patients with stage-specific breathing abnormalities.