320
T. Penzel et al.
Petr Einbrodt, in 1860, was the first to describe this form of cardiorespiratory coupling
[10]. During daytime activity and exercise, RSA is usually not visible, or much attenuated. In contrast, at rest and during sleep, RSA is pronounced and easily recognizable [31]. Early studies were even able to describe correlation between the extent of
coupling and the various sleep stages.
An additional coupling phenomenon was found in the synchronization of heart
beats and respiratory phases. Phase synchronization as the adjustment of the phases of
self-sustained oscillators due to their weak interaction was described for the first time
in the seventeenth century in conjunction with pendulum clocks [16, 30]. In the case
of cardiorespiratory phase synchronization (CRPS), heartbeats occur in increased
numbers during certain phases of the respiratory cycle: e.g., at the beginning of the
inhalation phase, at the end of the inhalation phase, and in the middle of the exhalation
phase [3, 4, 35, 39, 44].
These two coupling phenomena—respiratory sinus arrhythmia (RSA) and phase
synchronization (CRPS)—can occur independently of each other (Fig. 20.3). In addition, the two coupling mechanisms are variously influenced by different physiological
parameters. A prominent example is the respiratory frequency that largely impacts
the extent of RSA but not CRPS [4].
The physical training condition of the persons examined is thought to influence
the extent of CRPS [35]. Athletes have demonstrated pronounced synchronization
between respiration and heartbeat, which led to the conclusion that the occurrence of
CRPS represents ergonomically effective regulation. The influence of the extent and
the effectiveness of this coupling on physical or mental performance have not yet
been determined. In this context, such coupling could also represent a good surrogate
parameter fore recovery after physical exertion.
Further studies have systematically investigated CRPS during sleep for different
age groups of healthy subjects and among sleep-apnea patients [4, 20, 21, 32]. Among
healthy persons, the dependence of the extent of synchronization on the various
sleep stages becomes evident and CRPS is most distinctly pronounced during deep
sleep, and least pronounced in REM sleep [4]. This sleep-stage dependency is many
times greater for phase synchronization than for respiratory sinus arrhythmia and is
likewise much greater than the variations in mean heart rate, HRV, and respiratory
rate. However, as soon as sleep apnea occurs, exertion takes place in the regulation
of the breathing and circulatory system. As a result, the phase relationship between
these two systems is impaired to the extent that CRPS can no longer be detected.
In order to study cardiorespiratory coupling during sleep apnea, cardiorespiratory
coordination was introduced recently [32]. Cardiorespiratory coordination is a time
domain measure quantifying chronological interrelations between respiration and
heartbeat that is not affected even by epochs of hyperventilation following apnea
events [32]. Additionally, cardiorespiratory coordination is less sensitive to cardiorespiratory disturbances in general and therefore may be more suitable for sleep
apnea detection than CRPS. This is also because for CRPS, each respiratory cycle
is transformed into phase space, which means that during apneas (i.e., prolonged
periods of time until the next respiratory onset occurs), many more heartbeats will
fall into the ‘apnea’ respiratory cycle than during ‘normal’ respiration. This results in
T. Penzel et al.
Petr Einbrodt, in 1860, was the first to describe this form of cardiorespiratory coupling
[10]. During daytime activity and exercise, RSA is usually not visible, or much attenuated. In contrast, at rest and during sleep, RSA is pronounced and easily recognizable [31]. Early studies were even able to describe correlation between the extent of
coupling and the various sleep stages.
An additional coupling phenomenon was found in the synchronization of heart
beats and respiratory phases. Phase synchronization as the adjustment of the phases of
self-sustained oscillators due to their weak interaction was described for the first time
in the seventeenth century in conjunction with pendulum clocks [16, 30]. In the case
of cardiorespiratory phase synchronization (CRPS), heartbeats occur in increased
numbers during certain phases of the respiratory cycle: e.g., at the beginning of the
inhalation phase, at the end of the inhalation phase, and in the middle of the exhalation
phase [3, 4, 35, 39, 44].
These two coupling phenomena—respiratory sinus arrhythmia (RSA) and phase
synchronization (CRPS)—can occur independently of each other (Fig. 20.3). In addition, the two coupling mechanisms are variously influenced by different physiological
parameters. A prominent example is the respiratory frequency that largely impacts
the extent of RSA but not CRPS [4].
The physical training condition of the persons examined is thought to influence
the extent of CRPS [35]. Athletes have demonstrated pronounced synchronization
between respiration and heartbeat, which led to the conclusion that the occurrence of
CRPS represents ergonomically effective regulation. The influence of the extent and
the effectiveness of this coupling on physical or mental performance have not yet
been determined. In this context, such coupling could also represent a good surrogate
parameter fore recovery after physical exertion.
Further studies have systematically investigated CRPS during sleep for different
age groups of healthy subjects and among sleep-apnea patients [4, 20, 21, 32]. Among
healthy persons, the dependence of the extent of synchronization on the various
sleep stages becomes evident and CRPS is most distinctly pronounced during deep
sleep, and least pronounced in REM sleep [4]. This sleep-stage dependency is many
times greater for phase synchronization than for respiratory sinus arrhythmia and is
likewise much greater than the variations in mean heart rate, HRV, and respiratory
rate. However, as soon as sleep apnea occurs, exertion takes place in the regulation
of the breathing and circulatory system. As a result, the phase relationship between
these two systems is impaired to the extent that CRPS can no longer be detected.
In order to study cardiorespiratory coupling during sleep apnea, cardiorespiratory
coordination was introduced recently [32]. Cardiorespiratory coordination is a time
domain measure quantifying chronological interrelations between respiration and
heartbeat that is not affected even by epochs of hyperventilation following apnea
events [32]. Additionally, cardiorespiratory coordination is less sensitive to cardiorespiratory disturbances in general and therefore may be more suitable for sleep
apnea detection than CRPS. This is also because for CRPS, each respiratory cycle
is transformed into phase space, which means that during apneas (i.e., prolonged
periods of time until the next respiratory onset occurs), many more heartbeats will
fall into the ‘apnea’ respiratory cycle than during ‘normal’ respiration. This results in