Sleep, 16:S150-S151
© 1993 American Sleep Disorders Association and Sleep Research Society
Spectral Analysis of Blood Pressure in
Patients With Sleep-Related Breathing Disorders
During NREM and REM Sleep
T. Penzel
Zeitreihenlabor, Medizinische Poliklinik der Philipps- Universitat,
Marburg, Germany
Sleep-related breathing disorders (SRBD) have implications on the cardiovascular system. Influences of
the respiratory system on the cardiovascular system
can be studied using spectral analysis of blood pressure
and heart rate (1-3). Spectral analysis of heart rate and
blood pressure was used in several studies in the past
to investigate their cyclical variations. Three different
frequency ranges were distinguished and related to
physiological changes of the same frequency: 1) low
frequencies: <0.1 Hz (longer than 10 seconds) related
to thermoregulation; 2) mid-range frequencies: 0.1-0.3
Hz (between 3.3 and 10 seconds) synchronous with
respiration and related to sympathetic and vagal activity and 3) high frequencies: 0.3-0.5 Hz (between 3.3
and 2 seconds).
Studies that analyzed the effect of different sleep stages
on the periodicities of cardiovascular variables were
usually limited to heart rate variability. Mid-range frequencies, related to respiration, were the main subject
(4). In this study, the effect ofSRBD on heart rate and
blood pressure was analyzed using spectral analysis to
investigate changes in the periodicities of heart rate
and systolic blood pressure. The analysis focussed on
frequencies below 0.05 Hz because blood pressure
swings (20-60 seconds period duration) occur in parallel with periodic apnea and hypopnea. Therefore the
frequency range 0.016-0.05 Hz was defined as apnea
related frequency band.
METHODS
Fifty patients with SRBD and systemic hypertension
according to World Health Organization criteria were
recorded for two consecutive nights in the sleep laboratory with cardiorespiratory polysomnography and
parallel invasive arterial blood pressure. All signals
were recorded on a chart recorder and an 8-channel
analog FM tape recorder (TI 8, Transinstruments). Sleep
stages were scored according to the rules ofRechtschaf-
fen and Kales. Arterial blood pressure and electrocardiogram (ECG) were replayed from the analog tape to
a signal analysis computer (IN 1200, Intertechnique)
at 16-times real-time to perform analysis. Heart rate
was calculated based on the ECG for every heart beat
detected. Systolic, diastolic and mean blood pressure
were determined for every R-wave detected in the ECG.
The four parameters were stored once per second (1
Hz resolution) for further processing. Spectral analysis
based on fast Fourier transform was applied on consecutive segments of 300 seconds for the entire night
recording to investigate underlying rhythms. Only segments where calibration of blood pressure was performed were discarded. Compressed spectral arrays
(2,5) were plotted for heart rate and systolic pressure
for all patients.
RESULTS
A total of 50 patients were recorded. Mean age was
5l.9 years (range 32-69). Mean number of apneas +
hypopneas per recording were 359 (range 15-876). Midrange frequency components (0.1-0.3 Hz) were found
in heart rate and systolic pressure. The amplitude of
the components increased during episodes of partial
upper airway obstruction as occurs during snoring. The
frequency of the components was stabile but changed
as sleep stages changed. Very high amplitudes were
found in the low-frequency range (0.016-0.05 Hz).
These components were found in parallel with obstructive sleep apnea during NREM sleep. During REM
sleep amplitudes of low-frequency components were
more variable. The frequency was found to be the same
as calculated by apnea + hyperventilation duration
(20-60 seconds). Based on the different patterns of
compressed spectral arrays, it was possible to distinguish four different groups of patients.
Group A had distinct peaks in the apnea-related
frequency band with sharp narrow peaks in respiration
S150
S151
SHORT NOTES
CARDIOVASCULAR SPEKTRA
because he had neither respiration- nor apnea-related
pressure swings. This patient with essential hypertension had neither apneas nor obstructive snoring in the
night of investigation.
Parallel evaluation of sleep stages revealed that during REM, sleep blood pressure variations did not show
periodic behavior. Even if total power of the spectrum
was high during REM sleep, the typical apnea-associated frequency peaks were broadened.
CONCLUSION
FIG. 1. A compressed spectral array of systolic pressure gives the
recording of an entire night. Each single line is the result of a spectral
analysis on a 5-minute segment of systolic pressure. Left-bound
peaks are caused by apnea-related blood pressure variation and the
peaks in the middle (around 0.24 Hz) are related to obstructionrelated pressure swings. The frequency of respiration-related swings
is very stabile throughout time and shows sleep stage dependency
in the frequency itself.
related frequencies. Usually, amplitudes of the apneaassociated frequencies did not exceed the amplitudes
in the respiration-related frequencies. Patients had significantly less apneas and hypopneas compared with
the other groups (p < 0.001). Clinically, patients were
diagnosed as heavy snorers.
Group B had very high amplitudes in the apnearelated frequencies compared with Group A. Amplitudes were dependant on sleep stages.
Group C also had very high amplitudes in the apnea
associated frequencies, but the respiration-related frequencies showed no sharp narrow peaks but were scattered over a broad range of frequencies. These patients
were the most overweight and were the youngest (not
statistically significant).
Group D was the largest and was characterized by
a total loss of respiration-related amplitudes. Only apnea-related amplitudes were present with high amplitudes. These amplitudes were scattered over a broad
band offrequencies, which indicated less regular apnea
duration.
One patient was not assigned to one of the groups
The method of spectral analysis can give new insights on the mechanisms of interactions between blood
pressure, respiration and sleep. Analysis of systolic
blood pressure resulted in less disturbed compressed
spectral arrays for evaluation than compressed spectral
arrays of heart rate. It is possible to distinguish and to
quantify the periodic changes in blood pressure, which
corresponds to respiration-related variations and apnea-related variations. It was shown that amplitude of
pulsus paradoxus increases during episodes of obstructive snoring. Heavy snorer type patients had a relatively stabile respiratory frequency throughout the
night. The analysis of the results together with sleep
shows that there exist different mechanisms in the regulation ofNREM and REM sleep that change the regulation of SRBD from periodic to non periodic and
affect the regulation of heart rate and blood pressure.
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Sleep, Vol. 16, No.8, 1993