Differentiating obstructive from central and complex sleep apnea using an automated electrocardiogram-based method

Abstract

Study objectives: Complex sleep apnea is defined as sleep disordered breathing secondary to simultaneous upper airway obstruction and respiratory control dysfunction. The objective of this study was to assess the utility of an electrocardiogram (ECG)-based cardiopulmonary coupling technique to distinguish obstructive from central or complex sleep apnea.

Design: Analysis of archived polysomnographic datasets.

Setting: A laboratory for computational signal analysis.

Interventions: None.

Measurements and results: The PhysioNet Sleep Apnea Database, consisting of 70 polysomnograms including single-lead ECG signals of approximately 8 hours duration, was used to train an ECG-based measure of autonomic and respiratory interactions (cardiopulmonary coupling) to detect periods of apnea and hypopnea, based on the presence of elevated low-frequency coupling (e-LFC). In the PhysioNet BIDMC Congestive Heart Failure Database (ECGs of 15 subjects), a pattern of "narrow spectral band" e-LFC was especially common. The algorithm was then applied to the Sleep Heart Health Study-I dataset, to select the 15 records with the highest amounts of broad and narrow spectral band e-LFC. The latter spectral characteristic seemed to detect not only periods of central apnea, but also obstructive hypopneas with a periodic breathing pattern. Applying the algorithm to 77 sleep laboratory split-night studies showed that the presence of narrow band e-LFC predicted an increased sensitivity to induction of central apneas by positive airway pressure.

Conclusions: ECG-based spectral analysis allows automated, operator-independent characterization of probable interactions between respiratory dyscontrol and upper airway anatomical obstruction. The clinical utility of spectrographic phenotyping, especially in predicting failure of positive airway pressure therapy, remains to be more thoroughly tested.

Figure 1

Sleep spectrogram in health. The sleep spectrogram in a 57-year-old male, demonstrating the normal profile of high and low-frequency cardiopulmonary coupling (HFC and LFC, respectively) across a normal night of sleep. The AHI is 5 events per hour of sleep. Top: The all night sleep spectrogram. The spectrographic display of cardiopulmonary coupling shows the bimodal stability states, with health (as in this case) dominated by high-frequency cardiopulmonary coupling. Lower left and right: 90° and 60° rotated views of the low-frequency spectral zone from the same subject showing the spectral dispersion within the sparse periods of low-frequency cardiopulmonary coupling.

Figure 2

Spectrographic obstructive sleep apnea. A 62-year-old man with an AHI of 49 events per hour of sleep. Broad spectral band e-LFC suggests oscillations driven by anatomical abnormality. Top: The all night sleep spectrogram. The upper panel shows nearly complete loss of high frequency coupling. Lower left and right: 90° and 60° rotated views of the low-frequency spectral zone from the same subject showing the spectral dispersion within the low-frequency cardiopulmonary coupling spectrum. This view demonstrates the characteristics of virtually pure elevated broad spectral band LFC. Conventional scoring of the respiratory events in this instance is usually “obstructive”, but may also be “mixed.”

Figure 3

Sleep spectrogram in “complex” sleep apnea - I: A 77-year old-male with an AHI of 65 events per hour of sleep. Continuous narrow spectral band e-LFC suggests oscillations driven by chemoreflexes. Top: The all night sleep spectrogram. The upper panel shows complete loss of high frequency coupling. Lower left and right: 90° and 60° rotated views of the low-frequency spectral zone from the same subject showing the spectral dispersion within the low-frequency cardiopulmonary coupling spectrum. This view demonstrates the characteristics of virtually pure elevated narrow spectral band e-LFC. Conventional scoring of the respiratory events in patients with respiratory dyscontrol may be “central” or have varying degrees of obstruction as determined by visual inspection of the flow signals and respiratory effort. The respiratory events thus could be highly periodic obstructive apneas and hypopneas or classic periodic breathing and central apneas – the spectrographic signatures of all of these types of respiratory abnormalities are indistinguishable by this method.

Figure 4

Sleep spectrogram in complex sleep apnea - II: A 60-year-old male with an AHI of 75 events per hour of sleep. Top: The all night sleep spectrogram. The upper panel shows complete loss of high frequency coupling. Lower left and right: 90° and 60° rotated views of the low-frequency spectral zone from the same subject showing the spectral dispersion within the low-frequency cardiopulmonary coupling spectrum. Alternating narrow and broad spectral band e-LFC is seen, suggesting varying moment to moment predominance of central ventilatory control versus anatomic factors in the pathogenesis of sleep apnea in this subject. Conventional scoring of the respiratory events may be “central,” “obstructive” or “mixed,” often showing significant temporal variability.