Total duration of apnea and hypopnea events and average desaturation show significant variation in patients with a similar apnea-hypopnea index

Hypoxic indices for obstructive sleep apnoea severity and cardiovascular disease risk prediction: A comparison and application in a community population

BACKGROUND AND OBJECTIVE

The apnoea-hypopnoea index (AHI) and oxygen desaturation index (ODI) encounter challenges in capturing the intricate relationship between obstructive sleep apnoea (OSA) and cardiovascular disease (CVD) risks. Although novel hypoxic indices have been proposed to tackle these limitations, there remains a gap in comprehensive validation and comparisons across a unified dataset.

METHODS

Samples were derived from the Sleep Heart Health Study (SHHS), involving 4485 participants aged over 40 years after data quality screening. The study compared several key indices, including AHI, ODI, the reconstructed hypoxic burden (rHB), the percentage of sleep time with the duration of respiratory events causing desaturation (pRED_3p) and the sleep breathing impairment index (SBII), in relation to CVD mortality and morbidity risks. Adjusted Cox proportional models were employed to calculate hazard ratios (HRs) for each index, and comparisons were performed.

RESULTS

SBII and pRED_3p exhibited significant correlations with both CVD mortality and morbidity, with SBII showing the highest adjusted HR (95% confidence interval) for mortality (2.04 [1.25, 3.34]) and pRED_3p for morbidity (1.43 [1.09-1.88]). In contrast, rHB was only significant in predicting CVD mortality (1.63 [1.05-2.53]), while AHI and ODI did not show significant correlations with CVD outcomes. The adjusted models based on SBII and pRED_3p exhibited optimal performance in the CVD mortality and morbidity datasets, respectively.

CONCLUSION

This study identified the optimal indices for OSA-related CVD risks prediction, SBII for mortality and pRED_3p for morbidity. The open-source online platform provides the computation of the indices.

Long-term effects on clinical event, mental health, and related outcomes of CPAP for obstructive sleep apnea: a systematic review

STUDY OBJECTIVES

We performed a systematic review of long-term health outcomes of continuous positive airway pressure (CPAP) use in adults with obstructive sleep apnea.

METHODS

We updated prior systematic reviews with searches in multiple databases through January 3, 2023. We included randomized controlled trials (RCTs) and adjusted nonrandomized comparative studies that reported prespecified long-term (mostly > 1 year) health outcomes. We assessed risk of bias, conducted meta-analyses, and evaluated strength of evidence.

RESULTS

We found 38 eligible studies (16 trials, 22 observational). All conclusions were of low strength of evidence given study and data limitations. RCTs found no evidence of effect of CPAP on mortality (summary effect size [ES] 0.89; 95% confidence interval [CI] 0.66, 1.21); inclusion of adjusted nonrandomized comparative studies yields an association with reduced risk of death (ES 0.57; 95% CI 0.44, 0.73). RCTs found no evidence of effects of CPAP for cardiovascular death (ES 0.99; 95% CI 0.64, 1.53), stroke (ES 0.99; 95% CI 0.73, 1.35), myocardial infarction (ES 1.05; 95% CI 0.78, 1.41), incident atrial fibrillation (ES 0.89; 95% CI 0.48, 1.63), or composite cardiovascular outcomes (all statistically nonsignificant). RCTs found no evidence of effects for incident diabetes (ES 1.02; 95% CI 0.69, 1.51) or accidents (all nonsignificant) and no clinically significant effects on depressive symptoms, anxiety symptoms, or cognitive function.

CONCLUSIONS

Whether CPAP use for obstructive sleep apnea affects long-term health outcomes remains largely unanswered. RCTs and nonrandomized comparative studies are inconsistent regarding the effect of CPAP on mortality. Current studies are underpowered, with relatively short duration follow-up and methodological limitations.

CITATION

Balk EM, Adam GP, Cao W, Bhuma MR, D'Ambrosio C, Trikalinos TA. Long-term effects on clinical event, mental health, and related outcomes of CPAP for obstructive sleep apnea: a systematic review. J Clin Sleep Med. 2024;20(6):895-909.

Reaction time in psychomotor vigilance task is related to hypoxic load in males with sleep apnea

Oxygen saturation (SpO2 )-based parameters are more strongly linked to impaired daytime vigilance than the conventional diagnostic metrics in patients with obstructive sleep apnea (OSA). However, whether the association between SpO2 -based parameters and impaired daytime vigilance is modulated by sex, remains unknown. Hence, we investigated the interplay between sex and detailed SpO2 -based metrics and their association with impaired vigilance in patients with OSA. The study population consisted of 855 (473 males, 382 females) patients with suspected OSA who underwent overnight polysomnography and psychomotor vigilance task (PVT). The population was grouped by sex and divided into quartiles (Q1-Q4) based on median reaction times (RTs) in the PVT. In addition to conventional diagnostic metrics, desaturation severity (DesSev), fall severity (FallSev), and recovery severity (RecovSev) were compared between the sexes and between the best (Q1) and worst (Q4) performing quartiles by using cumulative distribution functions (CDFs). Additionally, sex-specific covariate-adjusted linear regression models were used to investigate the connection between the parameters and RTs. The CDFs showed significantly higher hypoxic load in Q4 in males compared to females. In addition, the DesSev (β = 8.05, p < 0.01), FallSev (β = 6.48, p = 0.02), RecovSev (β = 9.13, p < 0.01), and Oxygen Desaturation Index (β = 12.29, p < 0.01) were associated with increased RTs only in males. Conversely, the Arousal Index (β = 10.75-11.04, p < 0.01) was associated with impaired vigilance in females. The severity of intermittent hypoxaemia was strongly associated with longer RTs in males whereas the Arousal Index had the strongest association in females. Thus, the impact of hypoxic load on impaired vigilance seems to be stronger in males than females.

Long-term health outcomes for patients with obstructive sleep apnea: placing the Agency for Healthcare Research and Quality report in context-a multisociety commentary

This multisociety commentary critically examines the Agency for Healthcare Research and Quality (AHRQ) final report and systematic review on long-term health outcomes in obstructive sleep apnea. The AHRQ report was commissioned by the Centers for Medicare & Medicaid Services and particularly focused on the long-term patient-centered outcomes of continuous positive airway pressure, the variability of sleep-disordered breathing metrics, and the validity of these metrics as surrogate outcomes. This commentary raises concerns regarding the AHRQ report conclusions and their potential implications for policy decisions. A major concern expressed in this commentary is that the AHRQ report inadequately acknowledges the benefits of continuous positive airway pressure for several established, long-term clinically important outcomes including excessive sleepiness, motor vehicle accidents, and blood pressure. While acknowledging the limited evidence for the long-term benefits of continuous positive airway pressure treatment, especially cardiovascular outcomes, as summarized by the AHRQ report, this commentary reviews the limitations of recent randomized controlled trials and nonrandomized controlled studies and the challenges of conducting future randomized controlled trials. A research agenda to address these challenges is proposed including study designs that may include both high quality randomized controlled trials and nonrandomized controlled studies. This commentary concludes by highlighting implications for the safety and quality of life for the millions of people living with obstructive sleep apnea if the AHRQ report alone was used by payers to limit coverage for the treatment of obstructive sleep apnea while not considering the totality of available evidence.

CITATION

Patil SP, Billings ME, Bourjeily G, et al. Long-term health outcomes for patients with obstructive sleep apnea: placing the Agency for Healthcare Research and Quality report in context-a multisociety commentary. J Clin Sleep Med. 2024;20(1):135-149.

Ventilatory Burden as a Measure of Obstructive Sleep Apnea Severity Is Predictive of Cardiovascular and All-Cause Mortality

Rationale: The apnea-hypopnea index (AHI), used for the diagnosis of obstructive sleep apnea, captures only the frequency of respiratory events and has demonstrable limitations. Objectives: We propose a novel automated measure, termed "ventilatory burden" (VB), that represents the proportion of overnight breaths with less than 50% normalized amplitude, and we show its ability to overcome limitations of AHI. Methods: Data from two epidemiological cohorts (EPISONO [Sao Paolo Epidemiological Study] and SHHS [Sleep Heart Health Study]) and two retrospective clinical cohorts (DAYFUN; New York University Center for Brain Health) were used in this study to 1) derive the normative range of VB, 2) assess the relationship between degree of upper airway obstruction and VB, and 3) assess the relationship between VB and all-cause and cardiovascular disease (CVD) mortality with and without hypoxic burden that was derived using an in-house automated algorithm. Measurements and Main Results: The 95th percentiles of VB in asymptomatic healthy subjects across the EPISONO and the DAYFUN cohorts were 25.2% and 26.7%, respectively (median [interquartile range], VBEPISONO, 5.5 [3.5-9.7]%; VBDAYFUN, 9.8 [6.4-15.6]%). VB was associated with the degree of upper airway obstruction in a dose-response manner (VBuntreated, 31.6 [27.1]%; VBtreated, 7.2 [4.7]%; VBsuboptimally treated, 17.6 [18.7]%; VBoff-treatment, 41.6 [18.1]%) and exhibited low night-to-night variability (intraclass correlation coefficient [2,1], 0.89). VB was predictive of all-cause and CVD mortality in the SHHS cohort before and after adjusting for covariates including hypoxic burden. Although AHI was predictive of all-cause mortality, it was not associated with CVD mortality in the SHHS cohort. Conclusions: Automated VB can effectively assess obstructive sleep apnea severity, is predictive of all-cause and CVD mortality, and may be a viable alternative to the AHI.

A mathematical model to serve as a clinical tool for assessing obstructive sleep apnea severity

Obstructive sleep apnea (OSA) is a sleep disorder caused by periodic airway obstructions and has been associated with numerous health consequences, which are thought to result from tissue hypoxia. However, challenges in the direct measurement of tissue-level oxygenation make it difficult to analyze the hypoxia exposure pattern in patients. Furthermore, current clinical practice relies on the apnea-hypopnea index (AHI) and pulse oximetry to assess OSA severity, both of which have limitations. To overcome this, we developed a clinically deployable mathematical model, which outputs tissue-level oxygenation. The model incorporates spatial pulmonary oxygen uptake, considers dissolved oxygen, and can use time-dependent patient inputs. It was applied to explore a series of breathing patterns that are clinically differentiated. Supporting previous studies, the result of this analysis indicated that the AHI is an unreliable indicator of hypoxia burden. As a proof of principle, polysomnography data from two patients was analyzed with this model. The model showed greater sensitivity to breathing in comparison with pulse oximetry and provided systemic venous oxygenation, which is absent from clinical measurements. In addition, the dissolved oxygen output was used to calculate hypoxia burden scores for each patient and compared to the clinical assessment, highlighting the importance of event length and cumulative impact of obstructions. Furthermore, an intra-patient statistical analysis was used to underscore the significance of closely occurring obstructive events and to highlight the utility of the model for quantitative data processing. Looking ahead, our model can be used with polysomnography data to predict hypoxic burden on the tissues and help guide patient treatment decisions.

Factors determining the therapeutic level of positive airway pressure in patients with obstructive sleep apnea syndrome

Objectives

In daily practice, we encounter with obstructive sleep apnoea syndrome (OSAS) patients who require different levels of positive airway pressure (PAP) despite having a similar apnoea-hypopnea index (AHI). We aimed to determine the parameters contributing to the determination of the therapeutic level of PAP.

Methods

Data on 548 patients who underwent polysomnography and PAP titration were analysed retrospectively. Patients were divided into groups according to OSAS severity (mild, moderate, and severe) and the mean pressure in each group was determined, after which patients were further divided into those who required a PAP below the mean and those who required a PAP above the mean.

Results

The mean optimal PAP level in the mild, moderate, and severe OSAS groups was 7.4 ± 2.3, 8.6 ± 2.4, and 9.8 ± 2.9 cm H2O, respectively. In the moderate and severe OSAS group, the subgroup that needed high pressure had a higher supine AHI, a longer apnoea time, and a longer SaO2 <90% time as compared with the subgroup that needed low pressure.

Conclusion

A longer apnoea duration and a higher supine AHI are associated with a higher PAP level in patients with moderate and severe OSAS.

Relationships between brain tissue damage, oxygen desaturation, and disease severity in obstructive sleep apnea evaluated by diffusion tensor imaging

STUDY OBJECTIVES

Patients with obstructive sleep apnea (OSA) show brain injury in sites responsible for autonomic, cognitive, and respiratory functions. Brain changes in OSA may vary with disease severity as assessed by the apnea-hypopnea index (AHI), which does not provide information about the apnea depth and length in contrast to oxygen desaturation. Although significant associations with brain injury and AHI are known in OSA, it is unclear whether AHI or the extent of oxygen desaturations better correlate with brain damage. We evaluated associations between brain changes, AHI, and oxygen desaturation using diffusion tensor imaging-based measures.

METHODS

We acquired diffusion tensor imaging data from 19 patients with OSA using a 3.0-Tesla MRI scanner and calculated, normalized, and smoothed mean, axial, and radial diffusivity maps that were used for correlations between brain changes, oxygen desaturation, and AHI values.

RESULTS

Positive correlations with extent of injury (mean, axial, and radial diffusivity values) and AHI appeared in the frontal areas, cingulate and insula, amygdala, hippocampus, and basal pons, and negative associations emerged in the putamen, internal-capsule, globus-pallidus, and cerebellar cortices. Regional diffusivity values and oxygen desaturation showed positive correlations in the cingulate, frontal, putamen, and cerebellar sites, and negative relationships in several areas, including the occipital cortex.

CONCLUSIONS

Patients with OSA show negative and positive correlations, indicated by increased and decreased diffusivity values, resulting from chronic and acute changes in those areas. The extent of injury in OSA partially depends on the extent of AHI and oxygen desaturation, with the effects representing continued development from acute to chronic processes.

CITATION

Sahib A, Roy B, Kang D, Aysola RS, Wen E, Kumar R. Relationships between brain tissue damage, oxygen desaturation, and disease severity in obstructive sleep apnea evaluated by diffusion tensor imaging. J Clin Sleep Med. 2022;18(12):2713-2721.

Duration of respiratory events in obstructive sleep apnea: In search of paradoxical results

Research related to the duration of respiratory events in obstructive sleep apnea (OSA) has been scarce, perhaps due to the dominant role played by the apnea-hypopnea index (AHI) in the diagnosis and severity estimation of OSA. Lately, however, researchers and clinicians have started to acknowledge the importance of this overlooked parameter. Intuitively, 40-s-long apneas have more harmful physiological and health consequences than 10-s-long apneas. But is this the case? Here, we review the research-based evidence showing physiological, hemodynamic, clinical, sleep quality, and health consequences of long vs. short respiratory events. Most of the reviewed studies support the idea that longer respiratory events have more severe physiological and clinical consequences than shorter events, most probably due to the higher hypoxic burden associated with longer respiratory events. However, a few but highly qualified studies provide clear evidence that short respiratory events have also a deleterious effect on sleep and the physiological and clinical aspects of OSA. The somewhat paradoxical findings that short respiratory events are also associated with a high risk of all-cause mortality is a serious concern. From these results, it is therefore evident that the duration of respiratory events should be quantified when diagnosing and assessing the severity of OSA.

Non-REM Apnea and Hypopnea Duration Varies across Population Groups and Physiologic Traits

Rationale: Symptoms and morbidities associated with obstructive sleep apnea (OSA) vary across individuals and are not predicted by the apnea-hypopnea index (AHI). Respiratory event duration is a heritable trait associated with mortality that may further characterize OSA.Objectives: We evaluated how hypopnea and apnea durations in non-REM (NREM) sleep vary across demographic groups and quantified their associations with physiological traits (loop gain, arousal threshold, circulatory delay, and pharyngeal collapsibility).Methods: Data were analyzed from 1,546 participants from the Multi-Ethnic Study of Atherosclerosis with an AHI ≥5. Physiological traits were derived using a validated model fit to the polysomnographic airflow signal. Multiple linear regression models were used to evaluate associations of event duration with demographic and physiological factors.Measurements and Main Results: Participants had a mean age ± SD of 68.9 ± 9.2 years, mean NREM hypopnea duration of 21.73 ± 5.60, and mean NREM apnea duration of 23.87 ± 7.44 seconds. In adjusted analyses, shorter events were associated with younger age, female sex, higher body mass index (P < 0.01, all), and Black race (P < 0.05). Longer events were associated with Asian race (P < 0.01). Shorter event durations were associated with lower circulatory delay (2.53 ± 0.13 s, P < 0.01), lower arousal threshold (1.39 ± 0.15 s, P < 0.01), reduced collapsibility (-0.71 ± 0.16 s, P < 0.01), and higher loop gain (-0.27 ± 0.11 s, P < 0.05) per SD change. Adjustment for physiological traits attenuated age, sex, and obesity associations and eliminated racial differences in event duration.Conclusions: Average event duration varies across population groups and provides information on ventilatory features and airway collapsibility not captured by the AHI.

Severity of Desaturations Reflects OSA-Related Daytime Sleepiness Better Than AHI

STUDY OBJECTIVES

The aim was to investigate how the severity of apneas, hypopneas, and related desaturations is associated with obstructive sleep apnea (OSA)-related daytime sleepiness.

METHODS

Multiple Sleep Latency Tests and polysomnographic recordings of 362 patients with OSA were retrospectively analyzed and novel diagnostic parameters (eg, obstruction severity and desaturation severity), incorporating severity of apneas, hypopneas, and desaturations, were computed. Conventional statistical analysis and multivariate analyses were utilized to investigate connection of apnea-hypopnea index (AHI), oxygen desaturation index (ODI), conventional hypoxemia parameters, and novel diagnostic parameters with mean daytime sleep latency (MSL).

RESULTS

In the whole population, 10% increase in values of desaturation severity (risk ratio = 2.01, P < .001), obstruction severity (risk ratio = 2.18, P < .001) and time below 90% saturation (t_90%) (risk ratio = 2.05, P < .001) induced significantly higher risk of having mean daytime sleep latency ≤ 5 minutes compared to 10% increase in AHI (risk ratio = 1.63, P < .05). In severe OSA, desaturation severity had significantly (P < .02) stronger negative correlation (ρ = -.489, P < .001) with mean daytime sleep latency compared to AHI (ρ = -.402, P < 0.001) and ODI (ρ = -.393, P < .001). Based on general regression model, desaturation severity and male sex were the most significant factors predicting daytime sleep latency.

CONCLUSIONS

Severity of sleep-related breathing cessations and desaturations is a stronger contributor to daytime sleepiness than AHI or ODI and therefore should be included in the diagnostics and severity assessment of OSA.

CITATION

Kainulainen S, Töyräs J, Oksenberg A, Korkalainen H, Sefa S, Kulkas A, Leppänen T. Severity of desaturations reflects OSA-related daytime sleepiness better than AHI. J Clin Sleep Med. 2019;15(8):1135-1142.

New Indices from Polysomnographic Measures for the Severity of Obstructive Sleep Apnea Syndrome -A Different Look at Obstructive Sleep Apnea Syndrome

Introduction

Obstructive sleep apnea syndrome (OSAS) is characterized by recurrent abnormal respiratory events during sleep and causes oxidative stress which is reported as a major pathogenic mechanism for the development of various cardiovascular disorders. For the diagnosis and management of treatment, disease-related symptoms and the Apnea-Hypopnea Index (AHI) measured from polysomnographic (PSG) recordings are taken together. However, AHI do not sufficiently represent the total hypoxic load, and other indices related to apnea frequency, apnea duration, and desaturation degree should be investigated.

Methods

In this study, 317 polysomnographic recordings were retrospectively evaluated. Apart from the conventional AHI, apnea and/or hypopnea duration percentage (AHDP) and desaturation area (DesatArea) were calculated using PSG data.

Results

According to the AHI, 21.8%, 32.8% and 45.4% of cases were grouped as mild, moderate and severe OSAS, respectively. When AHDP was taken into account, 10.4%, 22.1% and 67.5% of the cases were regrouped as mild, moderate or severe OSAS, respectively. When the DesatArea calculation was used, the grouping of cases as mild, moderate or severe OSAS changed in value to 10.7%, 21.1% and 68.1%, respectively. The total group change was found to be 58.4% for both the AHDP and DesatArea formulation. With the AHDP formulation, regrouping was made in 52.2% of the mild OSAS cases and 62.5% of the moderate OSAS cases; by using the DesatArea calculation, 50.7% of mild OSAS cases and 63% of moderate OSAS cases were regrouped.

Conclusion

Our results show that when another parameters related to abnormal respiratory events are used, the same patients within the same group of disease severity are heterogeneously separated according to severity of hypoxia. It is suggested that grouping the patients based on AHI is insufficient and that using other polysomnographic measurements along with AHI should be considered to represent the severity of the disease.

Polysomnographic phenotyping of obstructive sleep apnea and its implications in mortality in Korea

Conventionally, apnea–hypopnea index (AHI) is used to define and categorize the severity of obstructive sleep apnea. However, routine polysomnography (PSG) includes multiple parameters for assessing the severity of obstructive sleep apnea. The goal of this study is to identify and categorize obstructive sleep apnea phenotypes using unsupervised learning methods from routine PSG data. We identified four clusters from 4,603 patients by using 29 PSG variable and arranged according to their mean AHI. Cluster 1, spontaneous arousal (mean AHI = 8.52/h); cluster 2, poor sleep and periodic limb movements (mean AHI = 12.16/h); cluster 3, hypopnea (mean AHI = 38.60/h); and cluster 4, hypoxia (mean AHI = 69.66/h). Conventional obstructive sleep apnea classification based on apnea–hypopnea index severity showed no significant difference in cardiovascular or cerebrovascular mortality (Log rank P = 0.331), while 4 clusters showed an overall significant difference (Log rank P = 0.009). The risk of cardiovascular or cerebrovascular mortality was significantly increased in cluster 2 (hazard ratio = 6.460, 95% confidence interval 1.734–24.073) and cluster 4 (hazard ratio = 4.844, 95% confidence interval 1.300–18.047) compared to cluster 1, which demonstrated the lowest mortality. After adjustment for age, sex, body mass index, and underlying medical condition, only cluster 4 showed significantly increased risk of mortality compared to cluster 1 (hazard ratio = 7.580, 95% confidence interval 2.104–34.620). Phenotyping based on numerous PSG parameters gives additional information on patients’ risk evaluation. Physicians should be aware of PSG features for further understanding the pathophysiology and personalized treatment.

Severe desaturations increase psychomotor vigilance task-based median reaction time and number of lapses in obstructive sleep apnoea patients

Current diagnostic parameters estimating obstructive sleep apnoea (OSA) severity have a poor connection to the psychomotor vigilance of OSA patients. Thus, we aimed to investigate how the severity of apnoeas, hypopnoeas and intermittent hypoxaemia is associated with impaired vigilance.

We retrospectively examined type I polysomnography data and corresponding psychomotor vigilance tasks (PVTs) of 743 consecutive OSA patients (apnoea–hypopnoea index (AHI) ≥5 events·h⁻¹). Conventional diagnostic parameters (e.g. AHI and oxygen desaturation index (ODI)) and novel parameters (e.g. desaturation severity and obstruction severity) incorporating duration of apnoeas and hypopnoeas as well as depth and duration of desaturations were assessed. Patients were grouped into quartiles based on PVT outcome variables. The odds of belonging to the worst-performing quartile were assessed. Analyses were performed for all PVT outcome variables using binomial logistic regression.

A relative 10% increase in median depth of desaturations elevated the odds (OR_range 1.20–1.37, p<0.05) of prolonged mean and median reaction times as well as increased lapse count. Similarly, an increase in desaturation severity (OR_range 1.26–1.52, p<0.05) associated with prolonged median reaction time. Female sex (OR_range 2.21–6.02, p<0.01), Epworth Sleepiness Scale score (OR_range 1.05–1.07, p<0.01) and older age (OR_range 1.01–1.05, p<0.05) were significant risk factors in all analyses. In contrast, increases in conventional AHI, ODI and arousal index were not associated with deteriorated PVT performance.

These results show that our novel parameters describing the severity of intermittent hypoxaemia are significantly associated with increased risk of impaired PVT performance, whereas conventional OSA severity and sleep fragmentation metrics are not. These results underline the importance of developing the assessment of OSA severity beyond the AHI.

Parameters considering characteristic properties of desaturations have a significant association with impaired vigilance, highlighting the importance of developing methods beyond the AHI for a more detailed assessment of OSA severityhttp://bit.ly/2veqxD9

The correlation between oxygen saturation indices and the standard obstructive sleep apnea severity

OBJECTIVE:

Currently accepted guidelines categorize obstructive sleep apnea (OSA) severity according to the Apnea–Hypopnea Index (AHI). However, it is unclear how to best define OSA severity. The present study sought to evaluate the concurrent validity of the widely accepted AHI by correlating it with various oxygen saturation (SpO₂) and polysomnographic parameters.

METHODS:

The study utilized the data of a previous survey concerning the prevalence of OSA among a middle-aged Saudi population (n = 2682). Among the 346 individuals who underwent polysomnography, 178 had total sleep times of at least 240 min with rapid eye movement (REM) sleep and were included in the study. The standard classification of OSA severity was compared with different SpO₂ and polysomnographic parameters.

RESULTS:

The study found that there were correlations between the standard OSA severity based on AHI severity classification and different SpO₂ and polysomnographic parameters, including the desaturation index (DI), the sum of all desaturations, desaturation below 90%, the average duration of respiratory events, and indices of total arousals and respiratory arousals. All of these parameters correlated directly with OSA severity classification (P < 0.001 for each). However, REM sleep duration and SpO₂ nadir were inversely correlated with OSA severity (P < 0.003 and < 0.001, respectively). In addition, only the DI, SpO₂ nadir, and respiratory arousal index were predictors of OSA severity, as determined through a multiple logistic regression analysis.

CONCLUSION:

Our findings support the clinical reliability of the currently used standard classification of OSA severity based on the AHI.

Feature Extraction of Upper Airway Dynamics during Sleep Apnea using Electrical Impedance Tomography

Characterizing upper airway occlusion during natural sleep could be instrumental for studying the dynamics of sleep apnea and designing an individualized treatment plan. In recent years, obstructive sleep apnea (OSA) phenotyping has gained attention to classify OSA patients into relevant therapeutic categories. Electrical impedance tomography (EIT) has been lately suggested as a technique for noninvasive continuous monitoring of the upper airway during natural sleep. In this paper, we developed the automatic data processing and feature extract methods to handle acquired EIT data for several hours. Removing ventilation and blood flow artifacts, EIT images were reconstructed to visualize how the upper airway collapsed and reopened during the respiratory event. From the time series of reconstructed EIT images, we extracted the upper airway closure signal providing quantitative information about how much the upper airway was closed during collapse and reopening. Features of the upper airway dynamics were defined from the extracted upper airway closure signal and statistical analyses of ten OSA patients’ data were conducted. The results showed the feasibility of the new method to describe the upper airway dynamics during sleep apnea, which could be a new step towards OSA phenotyping and treatment planning.

Linear Mixed Effects Modelling of Oxygen Desaturation after Sleep Apneas and Hypopneas: A Pilot Study

Obstructive Sleep Apnea severity is commonly determined after a sleep polysomnographic study by the Apnea-Hypopnea Index (AHI). This index does not contain information about the duration of events, and weights apneas and hypopneas alike. Significant differences in disease severity have been reported in patients with the same AHI. The aim of this work was to study the effect of obstructive event type and duration on the subsequent oxygen desaturation (SaO₂) by mixed-effects models. These models allow continuous and categorical independent variables and can model within-subject variability through random effects. The desaturation depth dSaO₂, desaturation duration dtSaO₂ and desaturation area dSaO₂A were analyzed in the 2022 apneas and hypopneas of eight severe patients. A mixed-effects model was defined to account for the influence of event duration (AD), event type, and their interaction on SaO₂ parameters. A two-step backward model reduction process was applied for random and fixed effects optimization. The optimum model obtained for dtSaO₂ suggests an almost subject-independent proportion increase with AD, which did not significantly change in apneas as compared to hypopneas. The optimum model for dSaO₂ reveals a significantly higher increase as a function of AD in apneas than hypopneas. Dependence of on event type and duration was different in every subject, and a subject-specific model could be obtained. The optimum model for SaO₂A combines the effects of the other two. In conclusion, the proposed mixed-effects models for SaO₂ parameters allow to study the effect of respiratory event duration and type, and to include repeated events within each subject. This simple model can be easily extended to include the contribution of other important factors such as patient severity, sleep stage, sleeping position, or the presence of arousals.

Intra-night variation in apnea-hypopnea index affects diagnostics and prognostics of obstructive sleep apnea

Background

Diagnostics of obstructive sleep apnea (OSA) is based on apnea-hypopnea index (AHI) determined as full-night average of occurred events. We investigate our hypothesis that intra-night variation in the frequency of obstructive events affects diagnostics and prognostics of OSA and should therefore be considered in clinical practice.

Methods

Polygraphic recordings of 1989 patients (mean follow-up 18.3 years) with suspected OSA were analyzed. Number and severity of individual obstructive events were calculated hourly for the first 6 h of sleep. OSA severity was determined based on the full-night AHI and AHI for the 2 h when the obstructive event frequency was highest (AHI_2h). Hazard ratios for all-cause, cardiovascular, and non-cardiovascular mortalities were calculated for different OSA severity categories based on the full-night AHI and AHI_2h.

Results

Frequency and duration of obstructive events varied hour-by-hour increasing towards morning. Using AHI_2h led to a statistically significant rearrangement of patients between the OSA severity categories. The use of AHI_2h for severity classification showed clearer relationship between the OSA severity and mortality than the full-night AHI.

Conclusions

Currently, the intra-night variation in frequency and severity of obstructive events is completely ignored by conventional, full-night AHI and considering this information could improve the diagnostics of OSA.

Sleep Study and Oximetry Parameters for Predicting Postoperative Complications in Patients With OSA

In the surgical setting, OSA is associated with an increased risk of postoperative complications. At present, risk stratification using OSA-associated parameters derived from polysomnography (PSG) or overnight oximetry to predict postoperative complications has not been established. The objective of this narrative review is to evaluate the literature to determine the association between parameters extracted from in-laboratory PSG, portable PSG, or overnight oximetry and postoperative adverse events. We obtained pertinent articles from Ovid MEDLINE, Ovid MEDLINE In-Process & Other Non-Indexed Citations, and Embase (2008 to December 2017). The search included studies with adult patients undergoing surgery who had OSA diagnosed with portable PSG, in-laboratory PSG, or overnight oximetry that reported on specific sleep parameters and at least one adverse outcome. The search was restricted to English-language articles. The search yielded 1,810 articles, of which 21 were included in the review. Preoperative apnea-hypopnea index (AHI) and measurements of nocturnal hypoxemia such as oxygen desaturation index (ODI), cumulative sleep time percentage with oxyhemoglobin saturation (Spo₂) < 90% (CT90), minimum Spo₂, mean Spo₂, and longest apnea duration were associated with postoperative complications. OSA is associated with postoperative complications in the population undergoing surgery. Clinically and statistically significant associations between AHI and postoperative adverse events exists. Complications may be more likely to occur in the category of moderate to severe OSA (AHI ≥ 15). Other parameters from PSG or overnight oximetry such as ODI, CT90, mean and minimal Spo₂, and longest apnea duration can be associated with postoperative complications and may provide additional value in risk stratification and minimization.

Breathing Disturbances Without Hypoxia Are Associated With Objective Sleepiness in Sleep Apnea

Study Objectives

To determine whether defining two subtypes of sleep-disordered breathing (SDB) events-with or without hypoxia-results in measures that are more strongly associated with hypertension and sleepiness.

Methods

A total of 1022 participants with 2112 nocturnal polysomnograms from the Wisconsin Sleep Cohort were analyzed with our automated algorithm, developed to detect breathing disturbances and desaturations. Breathing events were time-locked to desaturations, resulting in two indices-desaturating (hypoxia-breathing disturbance index [H-BDI]) and nondesaturating (nonhypoxia-breathing disturbance index [NH-BDI]) events-regardless of arousals. Measures of subjective (Epworth Sleepiness Scale) and objective (2981 multiple sleep latency tests from a subset of 865 participants) sleepiness were analyzed, in addition to clinically relevant clinicodemographic variables. Hypertension was defined as BP ≥ 140/90 or antihypertensive use.

Results

H-BDI, but not NH-BDI, correlated strongly with SDB severity indices that included hypoxia (r ≥ 0.89, p ≤ .001 with 3% oxygen-desaturation index [ODI] and apnea hypopnea index with 4% desaturations). A doubling of desaturation-associated events was associated with hypertension prevalence, which was significant for ODI but not H-BDI (3% ODI OR = 1.06, 95% CI = 1.00-1.12, p < .05; H-BDI OR 1.04, 95% CI = 0.98-1.10) and daytime sleepiness (β = 0.20 Epworth Sleepiness Scale [ESS] score, p < .0001; β = -0.20 minutes in MSL on multiple sleep latency test [MSLT], p < .01). Independently, nondesaturating event doubling was associated with more objective sleepiness (β = -0.52 minutes in MSL on MSLT, p < .001), but had less association with subjective sleepiness (β = 0.12 ESS score, p = .10). In longitudinal analyses, baseline nondesaturating events were associated with worsening of H-BDI over a 4-year follow-up, suggesting evolution in severity.

Conclusions

In SDB, nondesaturating events are independently associated with objective daytime sleepiness, beyond the effect of desaturating events.

Phenotyping the pathophysiology of obstructive sleep apnea using polygraphy/polysomnography: a review of the literature

Continuous positive airway pressure (CPAP) is the first-line treatment for the majority of patients affected by obstructive sleep apnea syndrome (OSA). However, long-term compliance with CPAP therapy may result limited and alternatives to CPAP therapy are required to address the increasing need to provide tailored therapeutic options. Understanding the pathophysiological traits (PTs) of OSA patients [upper airway (UA) anatomical collapsibility, loop gain (LG), arousal threshold (AT), and UA gain (UAG)] lies at the heart of the customized OSA treatment. However, sleep research laboratories capable to phenotype OSA patients are sparse and the diagnostic procedures time-consuming, costly, and requiring significant expertise. The question arises whether the use of routine clinical polysomnography or nocturnal portable multi-channel monitoring (PSG/PM) can provide sufficient information to characterize the above traits. The aim of the present review is to deduce if the information obtainable from the clinical PSG/PM analysis, independently of the scope and context of the original studies, is clinically useful to define qualitatively the PTs of individual OSA patients. In summary, it is possible to identify four patterns using PSG/PM that are consistent with an altered UA collapsibility, three that are consistent with altered LG, two with altered AT, and three consistent with flow limitation/UA muscle response. Furthermore, some PSG/PM indexes and patterns, useful for the suitable management of OSA patient, have been discussed. The delivery of this clinical approach to phenotype pathophysiological traits will allow patients to benefit in a wider range of sleep services by facilitating tailored therapeutic options.

Obstructive sleep apnea: current perspectives

The prevalence of obstructive sleep apnea (OSA) continues to rise. So too do the health, safety, and economic consequences. On an individual level, the causes and consequences of OSA can vary substantially between patients. In recent years, four key contributors to OSA pathogenesis or "phenotypes" have been characterized. These include a narrow, crowded, or collapsible upper airway "anatomical compromise" and "non-anatomical" contributors such as ineffective pharyngeal dilator muscle function during sleep, a low threshold for arousal to airway narrowing during sleep, and unstable control of breathing (high loop gain). Each of these phenotypes is a target for therapy. This review summarizes the latest knowledge on the different contributors to OSA with a focus on measurement techniques including emerging clinical tools designed to facilitate translation of new cause-driven targeted approaches to treat OSA. The potential for some of the specific pathophysiological causes of OSA to drive some of the key symptoms and consequences of OSA is also highlighted.

Relationship between heart rate excursion and apnea duration in patients with Obstructive Sleep Apnea

Obstructive Sleep Apnea (OSA) is a sleep disorder with a high prevalence in the general population. It is a risk factor for many cardiovascular diseases, and an independent risk factor for cerebrovascular diseases such as stroke. After an apnea episode, both arterial blood pressure and cerebral blood flow velocity change in function of the apnea duration (AD). We hypothesized that the relative excursion in heart rate (AHR), defined as the percentage difference between the maximum and the minimum heart rate values associated to an obstructive apnea event, is also related to AD. In this work we studied the relationship between apnea-related AHR and AD in a population of eight patients with severe OSA. AHR and AD showed a moderate but statistically significant correlation (p <; 0.0001) in a total of 1454 obstructive apneas analyzed. The average heart rate excursion for apneas with AD ≥ 30s (ΔHR = 31.29 ± 6.64%) was significantly greater (p = 0.0002) than for apneas with AD ∈ [10,20)s (ΔHR = 18.14±3.08%). We also observed that patients with similar Apnea-Hypopnea Index (AHI) may exhibit remarkably different distributions of AHR and AD, and that patients with a high AHI need not have a higher average AHR than others with a lower severity index. We conclude that the overall apnea-induced heart rate excursion is partially explained by the duration of apnoeic episodes, and it may be a simple measure of the cardiovascular stress associated with OSA that is not directly reflected in the AHI.

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.

Frequency and magnitude of intermittent hypoxia modulate endothelial wound healing in a cell culture model of sleep apnea

Intermittent hypoxia (IH) has been implicated in the cardiovascular consequences of obstructive sleep apnea (OSA). However, the lack of suitable experimental systems has precluded assessment as to whether IH is detrimental, protective, or both for the endothelium. The aim of the work was to determine the effects of frequency and amplitude of IH oxygenation swings on aortic endothelial wound healing. Monolayers of human primary endothelial cells were wounded and subjected to constant oxygenation (1%, 4%, 13%, or 20% O₂) or IH at different frequencies (0.6, 6, or 60 cycles/h) and magnitude ranges (13-4% O₂ or 20-1% O₂), using a novel well-controlled system, with wound healing being measured after 24 h. Cell monolayer repair was similar at 20% O₂ and 13% O₂, but was considerably increased (approximately twofold) in constant hypoxia at 4% O₂ The magnitude and frequency of IH considerably modulated wound healing. Cycles ranging 13-4% O₂ at the lowest frequency (0.6 cycles/h) accelerated endothelial wound healing by 102%. However, for IH exposures consisting of 20% to 1% O₂ oscillations, wound closure was reduced compared with oscillation in the 13-4% range (by 74% and 44% at 6 cycles/h and 0.6 cycles/h, respectively). High-frequency IH patterns simulating severe OSA (60 cycles/h) did not significantly modify endothelial wound closure, regardless of the oxygenation cycle amplitude. In conclusion, the frequency and magnitude of hypoxia cycling in IH markedly alter wound healing responses and emerge as key factors determining how cells will respond in OSA.NEW & NOTEWORTHY Intermittent hypoxia (IH) induces cardiovascular consequences in obstructive sleep apnea (OSA) patients. However, the vast array of frequencies and severities of IH previously employed in OSA-related experimental studies has led to controversial results on the effects of IH. By employing an optimized IH experimental system here, we provide evidence that the frequency and magnitude of IH markedly alter human aortic endothelial wound healing, emerging as key factors determining how cells respond in OSA.

Severity of desaturation events differs between hypopnea and obstructive apnea events and is modulated by their duration in obstructive sleep apnea

PURPOSE

Frequency of apnea and hypopnea events is used to estimate the severity of obstructive sleep apnea (OSA). However, comprehensive information on whether apneas and hypopneas cause an equal biological effect is not available. The purpose of the present work was to evaluate the effect of the breathing cessation event type (i.e., obstructive apnea or hypopnea) and duration on the severity of related SpO₂ desaturation events.

METHODS

Type 1 polysomnographies of 395 patients (220 males and 175 females) examined for suspected OSA were analyzed. Desaturation severity related to hypopnea and obstructive apnea events were compared and comparison was controlled for gender, sleep stage, sleeping position, age, and body mass index. Hypopneas and obstructive apneas were further divided into eight different durational categories and related desaturation event characteristics were compared between the categories.

RESULTS

SpO₂ desaturation events caused by obstructive apneas were statistically significantly (p ≤ 0.004) longer, greater in area, and deeper compared to the SpO₂ desaturations caused by hypopneas. The increase in the duration of hypopnea and obstructive apnea events led to increase in the duration and area of related SpO₂ desaturations. The increase in the obstructive apnea event duration also led to increase in the depth of related desaturation event.

CONCLUSIONS

Obstructive apneas led to more severe SpO₂ desaturation compared to hypopneas. Increased event duration led to increase in the severity of the related SpO₂ desaturation. In addition to considering event duration, obstructive apneas should have more weight than hypopneas when estimating severity of OSA and associated long-term cardiovascular risk.

Peri-apneic hemodynamic reactions in obstructive sleep apnea

Obstructive sleep apnea (OSA) increases cardiovascular morbidity and mortality. Little is known on acute peri-apneic hemodynamic alterations due to apneas. We assessed these rapid changes and how duration of apnea might contribute to them. Eight patients with severe OSA were studied with polysomnography including continuous blood pressure monitoring. Peri-apneic hemodynamic alterations, heart rate, blood pressure, stroke volume, cardiac output and peripheral resistance, were assessed in short (<20s) and long (>27s) apneas. Systolic and diastolic blood pressure along with heart rate elevated significantly in both apneas. These changes occurred within first 10 beats immediately after apnea. In contrast to short apneas long apneas caused sudden increase of 0.7l in cardiac output. Acute and pronounced peri-apneic hemodynamic alterations were seen during both short and long apneas. These described rapid hemodynamic changes might escape autoregulatory mechanisms of several organs, thus making OSA patients vulnerable to acute cardiovascular events.

Clinical and polysomnographic predictors of severe obstructive sleep apnea in the South Indian population

Background:

With the emergence of lifestyle diseases in epidemic proportions, obstructive sleep apnea (OSA) is being increasingly recognized in less developed countries as well.

Aim:

We sought to study the demographic, clinical, and polysomnographic (PSG) predictors of OSA severity in a cohort of South Indian patients.

Materials and Methods:

Consecutive patients with PSG proven OSA [apnea hypopnea index (AHI) ≥5/h] were prospectively recruited. The study period was from January 2012 to December 2012. Demographic data, history of vascular risk factors, substance abuse, sleep quality, snoring, and witnessed apneas were collected using a structured pro forma. In addition, PSG variables such as AHI, sleep latency and efficiency, duration of slow wave and rapid eye movement (REM) sleep, and other parameters were collected. Correlations between AHI severity and clinical and PSG parameters were done.

Results:

There were 152 (119 males and 33 females) subjects with a mean age of 53.8 years and body mass index (BMI) of 29.31. Mean AHI was 36.2/h (range: 5.1-110) and 66 subjects had severe OSA. Around 12% had the presenting complaint as insomnia, mainly of sleep maintenance. Of the subjects, 35% had witnessed apneas and 67% had excessive daytime sleepiness (EDS); 40% of patients had ≥2 risk factors. PSG parameters showed short sleep onset latency with a high arousal index. Mean apnea duration was 24.92 s. We found that age >55 years, BMI >25 kg/m², witnessed apneas, EDS, hypertension, dyslipidemia, reduced slow wave sleep duration, mean apnea duration >20 s, and desaturation index >10/h correlated well with OSA severity while the arousal index, sleep latency and efficiency, and exposure to smoking and alcohol showed no association.

Conclusions:

Older subjects with witnessed apneas are likely to have more severe OSA. Even though overall sleep architecture was similar between the groups, severe OSA had shorter slow wave sleep, longer apneas, and higher nocturnal hypoxemia.

RemLogic plug-in enables clinical application of apnea-hypopnea index adjusted for severity of individual obstruction events

Obstructive sleep apnea (OSA) is diagnosed based on obstruction event incidence, albeit individual obstruction event severity is connected to increased mortality rate. Adjusted-AHI parameter, incorporating number and severity of obstruction events, has shown good potential, but is calculated using custom-made MATLAB(®) functions. To allow its clinical use, this study introduces the RemLogic™ plug-in. It is tested comparing adjusted-AHI values calculated with the plug-in and MATLAB(®) with a hundred patients. Furthermore, retrospective follow-up (mean ± SD = 194.1 ± 54.0 months) of 1128 working-age men was conducted to evaluate potential of adjusted-AHI to enhance diagnostic of OSA. Adjusted-AHI values were strongly correlated (r = 1.000, p < 0.001) and their average difference (mean ± SD) was minimal (0.08 ± 0.19%). Using adjusted-AHI to define OSA severity resulted in a higher hazard ratio of mortality in the severe OSA group and, for the first time, adjusted-AHI was found to explain independently the overall mortality and non-fatal cardiovascular events. Importantly, the present plug-in enables clinical use of adjusted-AHI, enhancing assessment of OSA severity.

Length of Individual Apnea Events Is Increased by Supine Position and Modulated by Severity of Obstructive Sleep Apnea

Positional obstructive sleep apnea (OSA) is common among OSA patients. In severe OSA, the obstruction events are longer in supine compared to nonsupine positions. Corresponding scientific information on mild and moderate OSA is lacking. We studied whether individual obstruction and desaturation event severity is increased in supine position in all OSA severity categories and whether the severity of individual events is linked to OSA severity categories. Polygraphic recordings of 2026 patients were retrospectively analyzed. The individual apnea, and hypopnea durations and desaturation event depth, duration, and area of 526 included patients were compared between supine and nonsupine positions in different OSA severity categories. Apnea events were 6.3%, 12.5%, and 11.1% longer (p < 0.001) in supine compared to nonsupine position in mild, moderate, and severe OSA categories, respectively. In moderate and severe OSA categories desaturation areas were 5.7% and 25.5% larger (p < 0.001) in supine position. In both positions the individual event severity was elevated along increasing OSA severity category (p < 0.05). Supine position elevates apnea duration in all and desaturation area in moderate and severe OSA severity categories. This might be more hazardous for supine OSA patients and therefore, estimation of clinical severity of OSA should incorporate also information about individual event characteristics besides AHI.

Morbidity and mortality risk ratios are elevated in severe supine dominant OSA: a long-term follow-up study

PURPOSE

Obstructive sleep apnoea (OSA) is a common public health problem. Sleeping position dependency has been related to OSA, and around half of OSA patients suffer from positional OSA where majority of the respiratory events occur in supine position. The consequences of supine dominant OSA have not been thoroughly investigated in long-term follow-up studies. The aim of the study was to retrospectively investigate the effects of supine dominant OSA on morbidity and mortality risk ratios during long-term follow-up and compare the findings with a non-supine OSA group at different OSA severities.

METHODS

Ambulatory polygraphic recordings of 793 patients with median follow-up time of 194.5 months were retrospectively analysed. The risk ratios of morbidity and mortality of supine dominant OSA and non-supine OSA patients were compared.

RESULTS

Supine dominant OSA patients, having majority of the obstruction events occurring in supine position, showed higher mortality and morbidity risk ratios in severe OSA category than the non-supine OSA patients. In severe category, the observed risk ratios were statistically significant.

CONCLUSIONS

The increased risk ratios of mortality and morbidity found further emphasises that supine OSA might have more severe health consequences than non-positional OSA especially in severe OSA. Severe OSA occurring in supine position was shown to be more deleterious than non-supine OSA based on long-term mortality and morbidity evidence.

Adjustment of apnea-hypopnea index with severity of obstruction events enhances detection of sleep apnea patients with the highest risk of severe health consequences

INTRODUCTION

Presently, the severity of obstructive sleep apnea (OSA) is estimated based on the apnea-hypopnea index (AHI). Unfortunately, AHI does not provide information on the severity of individual obstruction events. Previously, the severity of individual obstruction events has been suggested to be related to the outcome of the disease. In this study, we incorporate this information into AHI and test whether this novel approach would aid in discriminating patients with the highest risk. We hypothesize that the introduced adjusted AHI parameter provides a valuable supplement to AHI in the diagnosis of the severity of OSA.

METHODS

This hypothesis was tested by means of retrospective follow-up (mean ± sd follow-up time 198.2 ± 24.7 months) of 1,068 men originally referred to night polygraphy due to suspected OSA. After exclusion of the 264 patients using CPAP, the remaining 804 patients were divided into normal (AHI < 5) and OSA (AHI ≥ 5) categories based on conventional AHI and adjusted AHI. For a more detailed analysis, the patients were divided into normal, mild, moderate, and severe OSA categories based on conventional AHI and adjusted AHI. Subsequently, the mortality and cardiovascular morbidity in these groups were determined.

RESULTS

Use of the severity of individual obstruction events for adjustment of AHI led to a significant rearrangement of patients between severity categories. Due to this rearrangement, the number of deceased patients diagnosed to have OSA was increased when adjusted AHI was used as the diagnostic index. Importantly, risk ratios of all-cause mortality and cardiovascular morbidity were higher in moderate and severe OSA groups formed based on the adjusted AHI parameter than in those formed based on conventional AHI.

CONCLUSIONS

The adjusted AHI parameter was found to give valuable supplementary information to AHI and to potentially improve the recognition of OSA patients with the highest risk of mortality or cardiovascular morbidity.

Apnea-hypopnea index: time to wake up

Despite the widespread use of the apnea-hypopnea index in research, its scientific and statistical properties have not been examined thoroughly. The index may be viewed either as a rate (number of events per hour of sleep) or as a ratio of two variables (number of events/number of hours of sleep). When considered as a rate, the apnea-hypopnea index may be modeled as the dependent variable, provided that researchers explicitly state which physical property they assume to be measuring. On the other hand, the index is rarely, if ever, the preferred model of exposure to sleep-disordered breathing (an independent variable), regardless of whether it is considered a rate or a ratio variable. Continued indiscriminate use of the apnea-hypopnea index in sleep research should be discouraged.