|
To review,
several indicators of increased SNS-driven catabolic activation
are evident in people with psychophysiological-type insomnia as
compared to people with no insomnia. These include higher metabolic
and heart rates, SNS dominant heart rate variability, body temperature
(Munroe, 1967), and stress
hormones, all indicative of relative SNS activity dominance and
excess stress arousal and activation.
It was noted
previously that insomnia as a symptom can exist in the face of
normal PSG findings and most studies have not differentiated between
these two variants. So a follow-up question is whether excess
stress activation is evident in people with sleep state misperception
(no PSG evidence of insomnia).
The data are
sparse but in a matched control analysis by Bonnet and colleagues,
a group of people with sleep state misperception-type insomnia
was found to have a higher mean overall metabolic rate than their
matched controls of good sleepers (Bonnet
and Arand, 1997). The overall increase was of less magnitude
than seen in people with psychophysiological-type insomnia and
in-between the values for them and controls. This led the investigators
to postulate that sleep state misperception-type insomnia might
be a less severe version or a precursor to psychophysiological-type
insomnia. This remains to be validated.
Consider the
following chart summarizing some PSG sleep features from two of
the aforementioned studies: (Bonnet
and Arand, 1995; Bonnet
and Arand, 1997)
| Table
3.4.1: Comparison PSG SLeep Variables (mean +/- SD)
|
|---|
|
| Insomnia
PP-type
| No
Insomnia
| P
Value
| Insomnia
SSM-type
| No
Insomnia
| P
Value
|
|---|
| Total
Sleep (min)
|
342
(75)
|
442
(23)
|
0.001
|
451
(30)
|
433
(30)
|
NS
|
|---|
| Sleep
efficiency
|
75
(14)
|
94
(3.4)
|
0.0001
|
95(3.0)
|
94
(2.9)
|
NS
|
|---|
| %
NREM stage 2
|
32.8
(14)
|
45.1
(11)
|
0.03
|
48(8.5)
|
42
(9.8)
|
NS
|
|---|
| %
REM
|
14.4
(5.4)
|
20.5
(4.6)
|
0.02
|
21 (6.0)
|
20
(5.3)
|
NS
|
|---|
| %
wake
|
25
(14)
|
5.9 (4.5)
|
0.001
|
5.5
(6.6)
|
5.7
(4.5)
|
NS
|
|---|
| Sleep
latency (min)
|
20.5
(13)
|
5.8
(0.3)
|
0.01
|
10
(7.2)
|
7.9
(5.5)
|
NS
|
|---|
|
PP-type = psychophysiological-type
insomnia
SSM-type = sleep state misperception-type insomnia
Subjects
with the psychophysiological-type insomnia have significantly
fewer minutes of sleep compared to subjects with sleep state misperception-type
insomnia or subjects without insomnia. Sleep loss, including partial
sleep loss, in healthy subjects leads to an increased drive to
sleep that is typically manifested in increased daytime sleepiness.
Furthermore, mental and physical performance often is shown to
deteriorate. Conceivably, people with psychophysiological-type
insomnia, because of documented sleep loss, would be sleepier
in the daytime and do less well on mental or physical performance
tests.
A
commonly used test for estimating sleepiness is the Multiple Sleep
Latency test (MSLT). It consists of providing 4 or 5 opportunities
to nap in 20-min. episodes that are spaced at 2-hour intervals
during the day. Individuals have electrodes applied for PSG sleep
and are asked to assume a sleeping posture and try to sleep in
a darkened bedroom. The faster they fall asleep, the more sleepiness
is inferred to exist. Typically, latencies of < 5 min are considered
to indicate pathological sleepiness and values of more than 10
min. are considered normal and likely indicative of adequate daily
(mostly nighttime) sleep.
The
following table shows the comparison results between people with
and without insomnia (determined by self-report) as summarized
from 2 publications (Edinger
et al., 1997; Lichstein
et al., 1994).
| Table
3.4.2: Comparison of MSLT Results Between People With
and Without Insomnia
|
|---|
| Study
| People
with InsomniaMean + SD (min.)
| People
with no insomniaMean + SD (min)
|
|---|
| Edinger
et al. (1997) |
11.6
+ 6.6
|
10.5+
6.6
|
| Edinger
et al. (1997) |
9.6
+ 5.4
|
11.0+
6.1
|
| Lichstein
et al. (1994) |
10.0
+ 6.2
|
10.9
+ 6.2
|
|
|