Novel parameters reflect changes in morphology of respiratory events during weight loss

A Review of Novel Oximetry Parameters for the Prediction of Cardiovascular Disease in Obstructive Sleep Apnoea

Obstructive sleep apnoea (OSA) is a sleep disorder with repetitive collapse of the upper airway during sleep, which leads to intermittent hypoxic events overnight, adverse neurocognitive, metabolic complications, and ultimately an increased risk of cardiovascular disease (CVD). The standard diagnostic parameter for OSA, apnoea-hypopnoea index (AHI), is inadequate to predict CVD morbidity and mortality, because it focuses only on the frequency of apnoea and hypopnoea events, and fails to reveal other physiological information for the prediction of CVD events. Novel parameters have been introduced to compensate for the deficiencies of AHI. However, the calculation methods and criteria for these parameters are unclear, hindering their use in cross-study analysis and studies. This review aims to discuss novel parameters for predicting CVD events from oximetry signals and to summarise the corresponding computational methods.

Duration of respiratory events in obstructive sleep apnea: Factors influencing the duration of respiratory events

Several factors influence respiratory event duration during sleep. In general, women have shorter respiratory events compared to men as it appears that women have a more reactive upper airway contributing to the occurrence of short events. In addition, the increased amount of adipose tissue in the upper airways should make the reopening of the upper airways more difficult, leading to long respiratory events. Nevertheless, an increase in body mass index decreases the median duration of apneas, hypopneas, and desaturations in all OSA severity categories. Also, respiratory events are longer in older adults compared to younger ones, and the most likely mechanism explaining this phenomenon appears to be the increased circulatory delay associated with aging. Several studies have also shown that apnea events are longer in rapid eye movement sleep compared to non-rapid eye movement sleep. The main mechanism behind these differences appears to be the greater pharyngeal muscle relaxation during rapid eye movement sleep. Finally, sleeping position affects the duration of respiratory events; apneas and hypopneas are longer in the supine compared to lateral postures regardless of the severity of OSA. In the present report, we discuss the best-known factors influencing the duration of abnormal breathing events during sleep.

Comparison of the effect of weight change, simulated computational continuous positive airway pressure treatment and positional therapy on severity of sleep apnea

Weight loss, continuous positive airway pressure (CPAP) and positional therapy (PT) are important treatments in obstructive sleep apnea (OSA). Although all of these reduce the apnea-hypopnea index (AHI) effectively, the benefits of these treatments have not been thoroughly investigated in a patient-specific manner. Therefore, clinicians do not have objective means to choose an optimal treatment for each patient. We aim to provide clinicians the possibility for treatment optimization in a patient-specific manner by introducing a computational simulation approach. The effect of actual weight change, computationally simulated CPAP treatment and PT and their combinations on the AHI were compared in 54 OSA patients divided into three equally sized groups (weight loss > 7%, weight loss 0%-7%, and weight gain) after a 5-year follow-up with lifestyle intervention. Weight loss reduced the AHI by 43.5% (p < .05) and 18%, simulated CPAP treatment with 3.3-hr adherence by 42.4% (p < .05) and 35.5% (p < .05), and simulated PT by 13.5% (p < .05) and 30.7% (p < .05) in > 7% and 0%-7% weight loss groups, respectively. Simulated CPAP treatment and PT were able to compensate for the increase in the AHI caused by weight gain. A developed simulation approach could help clinicians to estimate treatment success in advance in order to prescribe the most optimal patient-specific treatment to reduce OSA-related health risks.

A Review of Current Tools Used for Evaluating the Severity of Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is a common and heterogeneous disease characterized by episodic collapse within the upper airways, which leads to reduced ventilation and adverse consequences, including hypoxia, hypercapnia, sleep fragmentation, and long-term effects such as cardiovascular comorbidities. The clinical diagnosis of OSA and its severity classification are often determined based on the apnea-hypopnea index (AHI), defining the number of apneic and hypopnea events per hour of sleep. However, the limitations of the AHI to assess disease severity have necessitated the exploration of other metrics for additional information to reflect the complexity of OSA. Novel parameters such as the hypoxic burden have the potential to better capture the main features of OSA by maximizing the information available from the polysomnogram. These emerging measures have described multidimensional qualities of sleep-disordered breathing events and breathing irregularity and will ultimately result in better management of OSA.

Development of methods for sleep disordered breathing to identify phenotypes

Sleep disordered breathing a very common disorder with prevalence rates of up to 49% in large epidemiological studies on subjects older than 40 years. A recent study showed that applying CPAP treatment to patients with sleep disordered breathing recruited by their number of apnea and hypopnea events alone, does improve sleepiness but does not improve overall cardiovascular mortality. Based on older large studies however it is knownthat sleep disordered breathing is a cardiovascular risk and that treatment lowers mortality and morbidity. These results appear to be contradictory. However, they might be explained if patient population investigated are carefully reviewed further, and if sleep apnea severity metrics are reconsidered. According to this, it appears that studies speak of different populations. Whereas epidemiological studies use sampled subjects willing to participate, earlier studies used patients contacting a sleep center with complaints and symptoms. In this paper two studies are presented with an assessment of anatomical metrics for upper airway morphology in order to derive parameters for better prediction. Different phenotypes can explain why some people benefit from treatment and others do not benefit equally. Therefore more than just counting apnea and hypopnea events is needed in order to identify patients at risk and patients who have a lower risk when treated. This will require large data set evaluations with hard outcome data.

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.