Table 1.

Biological manifestations in sleep stages.

Physiological Process	During NREM	During REM
brain activity	decreases from wakefulness	increases in motor and sensory areas, while other areas are similar to NREM
heart rate	slows from wakefulness	increases and varies compared with NREM
blood pressure	decreases from wakefulness	increases (up to 30 percent) and varies from NREM
blood flow to brain	does not change from wakefulness in most regions	increases by 50 to 200 percent from NREM, depending on brain region
respiration	decreases from wakefulness	increases and varies from NREM, but may show brief stoppages (apnea); coughing suppressed
airway resistance	increases from wakefulness	increases and varies from wakefulness
body temperature	is regulated at lower set point than wakefulness; shivering initiated at lower temperature than during wakefulness	is not regulated; no shivering or sweating; temperature drifts toward that of the local environment
muscle tension	decreasing with increase of NREM	increases from NREM