Circulation time measurement from sleep studies in patients with obstructive sleep apnea

Automatic detection of respiratory events during sleep from Polysomnography data using Layered Hidden Markov Model

OBJECTIVE

Sleep apnea is a serious respiratory disorder, which is associated with increased risk factors for cardiovascular disease. Many studies in recent years have been focused on automatic detection of sleep apnea from polysomnography (PSG) recordings, however, detection of subtle respiratory events named Respiratory Event Related Arousals (RERAs) that do not meet the criteria for apnea or hypopnea is still challenging. The objective of this study was to develop automatic detection of sleep apnea based on Hidden Markov Models (HMMs) which are probabilistic models with the ability to learn different dynamics of the real time-series such as clinical recordings.

APPROACH

In this study, a hierarchy of HMMs named Layered HMM was presented to detect respiratory events from PSG recordings. The recordings of 210 PSGs from Massachusetts General Hospital's database were used for this study. To develop detection algorithms, extracted feature signals from airflow, movements over the chest and abdomen, and oxygen saturation in blood (SaO2) were chosen as observations. The respiratory disturbance index (RDI) was estimated as the number of apneas, hypopneas, and RERAs per hour of sleep.

MAIN RESULTS

The best F1 score of the event by event detection algorithm was between 0.22±0.16 and 0.70±0.08 for different groups of sleep apnea severity. There was a strong correlation between the estimated and the PSG-derived RDI (R2=0.91, p<0.0001). The best recall of RERA detection was achieved 0.45±0.27.

SIGNIFICANCE

The results showed that the layered structure can improve the performance of the detection of respiratory events during sleep.

Lung to finger circulation time in sleep study and coronary artery calcification: the Multi-Ethnic Study of Atherosclerosis

BACKGROUND

Lung to finger circulation time (LFCT) measured from sleep studies may represent a novel physiologic marker for cardiovascular risk in patients with sleep disordered breathing (SDB). We hypothesized that sleep study-derived LFCT would improve risk classification of markers of subclinical cardiovascular disease.

METHODS

We included participants in the Multi-Ethnic Study of Atherosclerosis (MESA) Sleep cohort with moderate-severe SDB (apnea hypopnea index [AHI] ≥ 15/hr) (N = 598).

RESULTS

Those with average LFCT above the median (19.4 s) (vs. shorter LFCT) tended to be older, more obese and male. In multivariable analysis, no significant associations were found between average LFCT and subclinical cardiovascular markers including coronary artery calcium, carotid intima-media thickness or left ventricular hypertrophy. However, there was modest improvement in risk classification of coronary artery calcification as compared with AHI alone when average LFCT was added to AHI (C statistics 0.53 vs. 0.62, p = 0.0066).

CONCLUSIONS

In conclusion, LFCT may be a useful addition to conventional SDB metrics to improve cardiovascular risk assessment.

Prolonged Circulation Time Is Associated With Mortality Among Older Men With Sleep-Disordered Breathing

BACKGROUND

Conventional metrics to evaluate sleep-disordered breathing (SDB) have many limitations, including their inability to identify subclinical markers of cardiovascular (CV) dysfunction.

RESEARCH QUESTION

Does sleep study-derived circulation time (Ct) predict mortality, independent of CV risks and SDB severity?

STUDY DESIGN AND METHODS

We derived average lung to finger Ct (LFCt) from sleep studies in older men enrolled in the multicenter Osteoporotic Fractures in Men (MrOS) Sleep study. LFCt was defined as the average time between end of scored respiratory events and nadir oxygen desaturations associated with those events. We calculated the hazard ratio (HRs) for the CV and all-cause mortality by LFCt quartiles, adjusting for the demographic characteristics, body habitus, baseline CV risk, and CV disease (CVD). Additional models included apnea-hypopnea index (AHI), time with oxygen saturation as measured by pulse oximetry (SpO₂) < 90% (T90), and hypoxic burden. We also repeated analyses after excluding those with CVD at baseline.

RESULTS

A total of 2,631 men (mean ± SD age, 76.4 ± 5.5 years) were included in this study. LFCt median (interquartile range) was 18 (15-22) s. During an average ± SD follow-up of 9.9 ± 3.5 years, 427 men (16%) and 1,205 men (46%) experienced CV death and all-cause death, respectively. In multivariate analysis, men in the fourth quartile of LFCt (22-52 s) had an HR of 1.36 (95% CI, 1.02-1.81) and 1.35 (95% CI, 1.14-1.60) for CV and all-cause mortality, respectively, when compared with men in the first quartile (4-15 s). The results were similar when additionally adjusting for AHI, T90, or hypoxic burden. Results were stronger among men with no history of CVD at baseline.

INTERPRETATION

LFCt is associated with both CV and all-cause mortality in older men, independent of baseline CV burden and SDB metrics. LFCt may be a novel physiologic marker for subclinical CVD and adverse outcomes in patients with SDB.

Portable diagnosis of sleep apnea with the validation of individual event detection

STUDY OBJECTIVE

To develop an algorithm for improving apnea hypopnea index (AHI) estimation which includes event by event validation and event duration estimation. The algorithm uses breathing sounds, respiratory related movements and blood oxygen saturation (SaO₂).

METHODS

Adults with suspected sleep apnea underwent overnight polysomnography (PSG) at Toronto Rehabilitations Institute. Simultaneously with PSG, breathing sounds and respiratory related movements were recorded over the suprasternal notch using the Patch. The Patch had a microphone and an accelerometer to record respiratory sounds and movement, respectively. First, we calculated the amount of drops in SaO₂ from pulse oximeter. Subsequently, energy of breaths and accelerometer were extracted. Features were normalized, weighted, summed and passed through a threshold to estimate Patch_AHI. Patch_AHI was compared to the AHI obtained from PSG (PSG_AHI). Furthermore, performance of event detection was evaluated using F1-score. Moreover, event duration difference between estimated and PSG-based events was compared.

RESULTS

Data from 69 subjects were investigated. Patch_AHI had high correlation with PSG_AHI (r² = 0.88). Considering a diagnostic AHI cut-off of ≥15, sensitivity and specificity were 91.42 ± 11.92% and 89.29 ± 7.62%, respectively. F1-score for individual event detection increased from 0.22 ± 0.10 for AHI≤5 to 0.72 ± 0.09 for AHI >30. Moreover, event duration difference between estimated events and PSG-based events was 5.33 ± 8.17 sec.

CONCLUSION

Our proposed algorithm had high accuracy in estimating individual respiratory events during sleep. The algorithm can increase reliability of acoustic methods for diagnosis of sleep apnea at home.

Sleep Apnea and Heart

Scientific investigations in the past few decades have supported the important role of sleep in various domains of health. Sleep apnea is a highly prevalent yet underdiagnosed sleep disorder representing a valid cardiovascular risk factor, particularly for hypertension. While several studies have demonstrated the benefits of sleep apnea treatment on subclinical cardiovascular measures, there is a paucity of studies proving reduction of cardiovascular events and mortality. Sufficient and high-quality sleep is also important in the maintenance of cardiovascular health. Future investigations should focus on improving identification of patients at greatest risk of adverse cardiovascular s sequalae of sleep apnea and testing the therapeutic benefit of sleep apnea treatment in this vulnerable group.

Gender differences in severity of desaturation events following hypopnea and obstructive apnea events in adults during sleep

OBJECTIVE

Severity estimation of obstructive sleep apnea (OSA) is currently based on the apnea-hypopnea index (AHI), which ignores individual breathing cessation event characteristics. Gender differences in the relationship between the breathing cessation event duration and the related desaturation event severity could mean that the severity of OSA is different in males and females despite a similar AHI. The aim of this work was to evaluate gender differences in the severity of peripheral oxygen desaturation events following obstructive apneas or hypopneas.

APPROACH

Type I polysomnographic recordings of 220 males and 175 females were analyzed. The obstructive apnea and hypopnea events were divided into eight different durational categories from 10 s to 45 s with 5 s interval and  >45 s. The desaturation event severities following obstructive apneas or hypopneas were compared between genders within these durational categories.

MAIN RESULTS

Desaturations following obstructive apneas with a duration of 30-45 s were substantially more severe (p  <  0.05) in females compared to males. In contrast, areas of desaturations following hypopneas (with related hypopnea event durations  ⩽30 s) were smaller (p  <  0.05) in females compared to males. In general, desaturation events following obstructive apneas were more severe compared to desaturations following hypopneas and the increase in the duration of obstructive apnea and hypopnea events led to an increase in the related desaturation severity in both genders.

SIGNIFICANCE

We found gender differences in the desaturation event severities following obstructive apneas and hypopneas. The results indicate that in females longer obstructive apneas (>30 s) could be more detrimental compared to those of males. As severe health consequences are related to the desaturation severity these aspects should be considered when estimating the severity of OSA.

Usefulness of Low Cardiac Index to Predict Sleep-Disordered Breathing in Chronic Thromboembolic Pulmonary Hypertension

Patients with chronic thromboembolic pulmonary hypertension (CTEPH) often have substantial right ventricular dysfunction. The resulting low cardiac index might predispose to sleep disordered breathing (SDB) by increasing ventilatory instability. The prevalence of SDB and potential association with impaired cardiac index was examined in patients with CTEPH. Patients referred for evaluation for pulmonary thromboendarterectomy surgery were recruited. Subjects underwent a sleep study, unless already using positive airway pressure therapy. Hemodynamic data were obtained from contemporaneous right-sided cardiac catheterization. A total of 49 subjects were included. SDB-defined as ongoing positive airway pressure use or apnea-hypopnea index (AHI) ≥5/h-was found in 57% of subjects. SDB was generally mild in severity, with respiratory events mainly consisting of hypopneas. Cardiac index was found to be significantly lower in subjects with SDB than those without (2.19 vs 2.55 L/min/m(2); p = 0.024), whereas no differences were observed in other characteristics. Additionally, cardiac index was independently predictive of AHI. In a subgroup of subjects with an elevated percentage of central events, both cardiac index and lung to finger circulation time correlated with AHI. In conclusion, SDB is prevalent in patients with CTEPH and might decrease with treatments that improve cardiac index.

A Novel Method for Assessing Cardiac Output With the Use of Oxygen Circulation Time

BACKGROUND

We investigated whether a simple breath hold would yield dynamic oxygen (O₂) saturation change and whether the derived circulation time would be useful in assessing cardiac function.

METHODS AND RESULTS

Patients undergoing right heart catheterization for clinical indications (n = 48), including heart failure (HF; n = 24), were prospectively recruited. Each subject was instructed to hold their breath for 20-40 seconds. Lung to finger circulation time (LFCT), defined as the time from the point of rebreathing to nadir O₂ desaturation, was correlated with cardiac output. Among 48 subjects recruited, 37 manifested ≥3% O₂ desaturation allowing for an LFCT measurement. Mean LFCT was 38.5 ± 17.5 seconds (range 18.9-94.7 s). LFCT in patients with a clinical diagnosis of HF was significantly longer than those without (45.9 ± 19.9 s vs 31.5 ± 11.5 s; P = .01). Overall, the LFCT was inversely correlated with cardiac output (Fick: r = -0.56; P < .001 [n = 37]; thermodilution: r = -0.6; P = .001 [n = 27]).

CONCLUSIONS

LFCT is prolonged in low cardiac output. LFCT is a novel method that may be useful to noninvasively assess cardiac function in HF.