| |
The
power within each band is calculated as the area under the respective
frequency portion of the power spectrum density curve. The high
frequency power band is considered to reflect PSNS activity as
mediated through the vagus nerve. Such a rhythm is generated through
intrathoracic pressure changes and mechanical variations associated
with breathing and is therefore synchronous with the respiratory
rate. Although sources contributing to the relative power in the
low frequency range are controversial, it is believed to be a
function of mixed PSNS and SNS activity. An increase in low frequency
power has consistently been observed as a consequence of sympathetic
activation. A ratio of the power in the low to high bands often
is used to infer SNS activity (Akselrod,
1995). A variety of control and noise sources affect ANS-driven
heart rate fluctuations, making data selection and analysis tricky
and controversial, but standardization of data collection, scoring
algorithms and interpretation of the data are increasingly becoming
accepted.
In
a study of heart period and heart rate variability analysis by
group and sleep stage with psychophysiological-type insomnia subjects
matched to control subjects, the following data were graphed (Bonnet
and Arand, 1998)
| Figure
3.3.6: Heart Beat-to-Beat (BB) Intervals in People With
and Without Psychophysiological-type Insomnia by Sleep
Stage
|
|---|
|
|
|
Source:
Bonnet MH, Arand DL. Heart rate variability in insomniacs
and normal sleepers. Psychosomatic Medicine. 1998;
60:610-615. Reprinted with permission from Lippincott
Williams and Wilkinson. http://www.lww.com.
|
|
.
| Figure
3.3.7: Ratio of Low-to-High Frequency Spectral Power
in People With and Without Psychophysiological-type
Insomnia by Sleep Stage
|
|---|
|
|
|
Source:
Bonnet MH, Arand DL. Heart rate variability in insomniacs
and normal sleepers. Psychosomatic Medicine. 1998;
60:610-615. Reprinted with permission from Lippincott
Williams and Wilkinson. http://www.lww.com.
|
|
Question
3.3.1
| The
data from the studies just reviewed (Figures 3.3.1, 3.3.2,
3.3.3, 3.3.6, and 3.3.7) show conflicting results, with heart
rate tending to be both faster and slower in people with insomnia
as compared to those without insomnia. |
|
| True |
|
| False |
Question
3.3.2
| There
tends to be a greater dominance of SNS activity in people
with psychophysiological-type insomnia as compared to those
people without insomnia. |
|
| True |
|
| False |
Question
3.3.3
| The
data from these three studies corroborate the postulate that
stress hyperactivation is a feature of insomnia, at least
in insomnia of the psychophysiological-type. |
|
| True |
|
| False |
|