Sleep requirement

SLEEP

Sleep is the natural periodic state of rest for mind and body with closed eyes characterized by partial or

complete loss of consciousness. Loss of consciousness leads to decreased response to external stimuli and decreased body movements. Depth of sleep is not constant throughout the sleeping period. It varies in different stages of sleep.

SLEEP REQUIREMENT

Sleep requirement is not constant. However, average

sleep requirement per day at different age groups is:

1. Newborn infants : 18 to 20 hours

2. Growing children : 12 to 14 hours

3. Adults : 7 to 9 hours

4. Old persons : 5 to 7 hours.

PHYSIOLOGICAL CHANGES DURING SLEEP

During sleep, most of the body functions are reduced to basal level. Following are important changes in the body during sleep:

1. PLASMA VOLUME

Plasma volume decreases by about 10% during sleep.

2. CARDIOVASCULAR SYSTEM

Heart Rate

During sleep, the heart rate reduces. It varies between 45 and 60 beats per minute.

Blood Pressure

Systolic pressure falls to about 90 to 110 mm Hg. Lowest level is reached about 4th hour of sleep and

remains at this level till a short time before waking up. Then, the pressure commences to rise. If sleep is

disturbed by exciting dreams, the pressure is elevated above 130 mm Hg.

3. RESPIRATORY SYSTEM

Rate and force of respiration are decreased. Respiration becomes irregular and Cheyne-Stokes type of

periodic breathing may develop.

4. GASTROINTESTINAL TRACT

Salivary secretion decreases during sleep. Gastric secretion is not altered or may be increased slightly.

Contraction of empty stomach is more vigorous.

5. EXCRETORY SYSTEM

Formation of urine decreases and specific gravity of urine increases.

6. SWEAT SECRETION

Sweat secretion increases during sleep.

7. LACRIMAL SECRETION

Lacrimal secretion decreases during sleep.

8. MUSCLE TONE

Tone in all the muscles of body except ocular muscles decreases very much during sleep. It is called sleep paralysis.

9. REFLEXES

Certain reflexes particularly knee jerk, are abolished. Babinski sign becomes positive during deep sleep.

Threshold for most of the reflexes increases. Pupils are constricted. Light reflex is retained. Eyeballs move up and down.

10. BRAIN

Brain is not inactive during sleep. There is a characteristic cycle of brain wave activity during sleep with

irregular intervals of dreams. Electrical activity in the brain varies with stages of sleep (see below).

TYPES OF SLEEP

Sleep is of two types:

1. Rapid eye movement sleep or REM sleep

2. Non-rapid eye movement sleep, NREM sleep or non-REM sleep.

1. RAPID EYE MOVEMENT SLEEP – REM SLEEP

Rapid eye movement sleep is the type of sleep associated with rapid conjugate movements of the

eyeballs, which occurs frequently. Though the eyeballs move, the sleep is deep.Characteristics REM sleep  doxical sleep. It occupies about 20% to 30% of sleeping period. Functionally, REM sleep is very important because, it plays an important role in consolidation of memory. Dreams occur during this period.

2. NON-RAPID EYE MOVEMENT SLEEP – NREM OR NON-REM SLEEP

Non-rapid eye movement (NREM) sleep is the type of sleep without the movements of eyeballs. It is also called slow-wave sleep. Dreams do not occur in this type of sleep and it occupies about 70% to 80% of total sleeping period. Non-REM sleep is followed by REM sleep.

STAGES OF SLEEP AND EEG PATTERN

RAPID EYE MOVEMENT SLEEP

During REM sleep, electroencephalogram (EEG) shows irregular waves with high frequency and low

amplitude. These waves are desynchronized waves.

NON-RAPID EYE MOVEMENT SLEEP

The NREM sleep is divided into four stages, based on the EEG pattern. During the stage of wakefulness, i.e. while lying down with closed eyes and relaxed mind, the alpha waves of EEG appear. When the person proceeds to drowsy state, the alpha waves diminish.

Stage I: Stage of Drowsiness

Alpha waves are diminished and abolished. EEG shows only low voltage fluctuations and infrequent

delta waves.

Stage II: Stage of Light Sleep

Stage II is characterized by spindle bursts at a frequency of 14 per second, superimposed by low voltage

delta waves.

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