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Figure 2: Simplified Summary of Sleep Apnea Pathophysiology, Including Aspects That Can Be Monitored with
Parameters in a Standard Polysomnogram (Blue Boxes)
ventricular, or atrial
Heart rate variability,
efficiency sympathetic nervous
Oxygen desaturation is often measured as the oxygen desaturation Heart Rate Variability
index, which is the number of times that the oxygen level drops by An important aspect of sleep apnea pathophysiology is chronic
three or four percentage points per hour. While a measure of sympathetic nervous activation to levels above those seen in individuals
oxygenation, it is usually directly correlated with AHI and may not without disturbed sleep. The cascade of problems that develop with
offer additional insight from AHI.
It is possible, however, that new sympathetic activation include systemic hypertension, increased risk for
interventions designed to treat either central or obstructive sleep ventricular arrhythmias, adverse ventricular and vascular remodeling,
apnea may have an impact on overall oxygen saturation with an and renin–angiotensin activation. Changes in autonomic activity can be
avoidance of significant desaturations. The end-point of reducing the measured directly from nerve fiber recordings or indirectly from analysis
deoxygenation burden improves the ‘lesion’ of sleep apnea of heart rate variability. Heart rate variability, especially using the
pathophysiology and should be considered an important effect, even spectral analysis approach, has the benefit of providing complete
if it is independent of the AHI. autonomic information to include cardiac parasympathetic influences.
Sleep Efficiency The importance of cardiac events during sleep apnea was recently
An intervention that increases sleep efficiency, defined as sleep latency as recognized by the AASM with the recommendation to include
well as sleep duration, coupled with improvement in sleep architecture electrocardiogram (ECG) recordings as standard data in a polysomnogram.
may improve clinical outcomes. Short sleep duration predicted the risk of Processing of the ECG signal allows quantification of heart rate variability
hypertension, cardiovascular disease and type II diabetes in the Sleep and ventricular and atrial arrhythmias during apneic periods or
Heart Health Study.
Sleep duration may alter sleep stages achieved, desaturation events. Analyzing and quantifying information from ECG
which may further alter cardiac and systemic autonomic control, likely recordings during polysomnography has not routinely been included in
resulting in increased sympathetic activation with vagal withdrawal.
previous sleep apnea studies, but may provide an excellent means to
Sympathetic activation leads to renin–angiotensin activation and judge successful treatment interventions. Specifically, the variability in
significantly changes vasomotor control, leading to hypertension heart period is directly correlated with vagal control of the heart. Heart rate
and other cardiovascular diseases (see Figure 2). variability can be measured in so-called ‘time–domain’ methods, such as
standard deviation of the inter-beat (RR) intervals, or ‘frequency–domain’
As novel therapies emerge, it will be important to assess the impact on measurements, which identify periodic changes in heart rate.
sleep efficiency, including increased sleep time and acquisition of Frequency–domain measurements can be applied to shorter segments
appropriate sleep stages. This effect would likely be reflected in the AHI of heart rate recordings and offer a more detailed view of specific input to
as fewer arousals are expected, but theoretically could alter sleep the heart from both the parasympathetic nervous system, which exerts
physiology without significant changes in the AHI. Again, if apnea is high-frequency influences (~0.15Hz), and the sympathetic nervous system,
prevented, but replaced by hypopnea, an alteration in the AHI would not which exerts lower-frequency signals (>0.2Hz). Heart rate variability
be seen, but improved sleep efficiency may be present. Improved sleep measurements in either domain correlate with improved morbidity and
efficiency may also affect other symptoms of sleep apnea, including mortality in heart failure patients.
Changes in cardiac autonomic control
daytime sleepiness and fatigue. occur naturally during the transition from non-rapid eye movement (REM)
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