Antti Kulkas

The severity of individual obstruction events is related to increased mortality rate in severe obstructive sleep apnea

Obstructive sleep apnea (OSA) is linked to an increased mortality rate. However, the severity of individual obstruction events is rarely considered quantitatively in clinical practice. We hypothesized that OSA with especially severe obstruction events would predispose a patient to greater health risks than OSA with a similar apnea–hypopnea index (AHI), but lower severity of individual events. This hypothesis was tested in a follow‐up (198.2 ± 24.7 months) of a population of 1068 men referred for ambulatory polygraphic recording due to suspected OSA. The recordings were analysed according to the guidelines of the American Academy of Sleep Medicine. Furthermore, a novel obstruction severity parameter was determined; this was defined as the product of duration of the individual obstruction event and area of the related desaturation event. Patients treated with continuous positive airway pressure (CPAP) were omitted. We identified 125 deceased patients from our original population and for 113 of these a matching alive patient with similar AHI, age, body mass index (BMI), smoking habits and follow‐up time could be found. The deceased patients with severe OSA (based on conventional AHI) showed higher obstruction severity values than their AHI‐matched alive controls. Based on the multivariate logistic regression analysis, obstruction severity was the only parameter which was related statistically significantly to mortality in the severe OSA category. Furthermore, 59% of all deceased patients and 83% of those who had severe OSA displayed higher obstruction severity than the AHI‐matched alive counterparts. To conclude, the obstruction severity parameter provided valuable prognostic information supplementing AHI. The obstruction severity parameter might improve recognition of the patients with the highest risk.

Novel parameters for evaluating severity of sleep disordered breathing and for supporting diagnosis of sleep apnea-hypopnea syndrome

Abstract Sleep apnea-hypopnea syndrome (SAHS) is a complex public health problem causing increased risk of cardiovascular diseases. Traditionally, evaluation of the severity of the disease is based on Apnea-Hypopnea Index (AHI). It is defined as the average number of apnea and hypopnea events per hour during sleep. However, e.g. the total duration and the morphology of the recorded events are not considered when evaluating the severity of the disease. This is surprising, as increasing the length of apnea and hypopnea events will most likely lead to longer and deeper oxygen desaturation events. Obviously, this is physiologically more stressful and may have more severe health consequences than shorter and shallower desaturation events. Paradoxically, the lengthening of apnea and hypopnea events may even lead to a decrease in AHI and oxygen desaturation index (ODI). This raises the question of whether additional information is needed besides AHI and ODI for the evaluation of the severity of SAHS and its potential cardiovascular consequences. In the present paper, several novel parameters are introduced to bring additional information for evaluation of the severity of SAHS. Besides the number of events per hour, that AHI and ODI takes into account, the duration of the breathing cessations and the morphology of the oxygen desaturation events are considered as important factors that may influence the daytime fatigue and also the related cardiovascular problems. In this study diagnostic ambulatory polygraphy recordings of 19 male patients were retrospectively analysed. Importantly, the novel parameters showed significant variation amongst patients with similar AHI. For example, the correlation between AHI and the Obstruction severity-parameter was only moderate (r2 = 0.604, p < 0.001). This suggests that patients with similar AHI may exhibit significantly different cardiovascular stress related to the disease. It is suggested that the present novel parameters might provide additional information over the currently used parameters and support the evaluation of the severity of SAHS.

Intelligent methods for identifying respiratory cycle phases from tracheal sound signal during sleep

We present two methods for identifying respiratory cycle phases from tracheal sound signal during sleep. The methods utilize the Hilbert transform in envelope extraction. They determine automatically a patient-specific amplitude threshold to be used in the detection. The core of one method is designed to be amplitude-independent whereas the other method uses solely the amplitude information. The methods provided average sensitivities of 98% and 99%, respectively, and positive prediction values of 100% on the total of 1434 respiratory cycles analysed from six different patients. The developed methods seem promising as such or as tools for analysing sleep disordered breathing.

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

Apnea-hypopnea-index (AHI), disregarding the respiratory event morphology, is currently used in estimation of severity of obstructive sleep apnea (OSA). The purpose of the current study was to evaluate the potential of novel parameters in estimation of changes in severity of OSA during weight loss. Polygraphic data of 67 patients, 37 in the control (no weight loss) and 30 in the weight loss (>5%) groups was evaluated at baseline and after two year follow-up. Changes in the values of novel parameters, incorporating detailed information of respiratory event characteristics, were evaluated and compared with changes in AHI. The median AHI in the weight loss group decreased significantly during the follow-up. The number of shorter respiratory events decreased in the weight loss group, while the longer ones remained, increasing the median durations of the respiratory events by 20-62%. For this reason the decrease of the values of the novel parameters were smaller compared to AHI in the weight loss group. This suggests that the severity of OSA might not fall as linearly during weight loss as AHI suggests. Moreover, the novel parameters containing more detailed information on the morphology characteristics may provide valuable supplementary information for the assessment of the severity of OSA.

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.

Tracheal sound parameters of respiratory cycle phases show differences between flow-limited and normal breathing during sleep

The objective of the present work was to develop new computational parameters to examine the characteristics of respiratory cycle phases from the tracheal breathing sound signal during sleep. Tracheal sound data from 14 patients (10 males and 4 females) were examined. From each patient, a 10 min long section of normal and a 10 min section of flow-limited breathing during sleep were analysed. The computationally determined proportional durations of the respiratory phases were first investigated. Moreover, the phase durations and breathing sound amplitude levels were used to calculate the area under the breathing sound envelope signal during inspiration and expiration phases. An inspiratory sound index was then developed to provide the percentage of this type of area during the inspiratory phase with respect to the combined area of inspiratory and expiratory phases. The proportional duration of the inspiratory phase showed statistically significantly higher values during flow-limited breathing than during normal breathing and inspiratory pause displayed an opposite difference. The inspiratory sound index showed statistically significantly higher values during flow-limited breathing than during normal breathing. The presented novel computational parameters could contribute to the examination of sleep-disordered breathing or as a screening tool.

High frequency components of tracheal sound are emphasized during prolonged flow limitation

A nasal pressure transducer, which is used to study nocturnal airflow, also provides information about the inspiratory flow waveform. A round flow shape is presented during normal breathing. A flattened, non-round shape is found during hypopneas and it can also appear in prolonged episodes. The significance of this prolonged flow limitation is still not established. A tracheal sound spectrum has been analyzed further in order to achieve additional information about breathing during sleep. Increased sound frequencies over 500 Hz have been connected to obstruction of the upper airway. The aim of the present study was to examine the tracheal sound signal content of prolonged flow limitation and to find out whether prolonged flow limitation would consist of abundant high frequency activity. Sleep recordings of 36 consecutive patients were examined. The tracheal sound spectral analysis was performed on 10 min episodes of prolonged flow limitation, normal breathing and periodic apnea-hypopnea breathing. The highest total spectral amplitude, implicating loudest sounds, occurred during flow-limited breathing which also presented loudest sounds in all frequency bands above 100 Hz. In addition, the tracheal sound signal during flow-limited breathing constituted proportionally more high frequency activities compared to normal breathing and even periodic apnea-hypopnea breathing.

Amount of weight loss or gain influences the severity of respiratory events in sleep apnea

Abstract Severity of obstructive sleep apnea (OSA) is estimated based on respiratory events per hour [i.e., apnea–hypopnea index (AHI)]. The aim of this study was to investigate effects of weight change on the severity of respiratory events. Respiratory event severity, including duration and morphology, was estimated by determining parameters quantifying obstruction and desaturation event lengths and areas, respectively. Respiratory events of 54 OSA patients treated with dietary intervention were evaluated at baseline and after 5-year follow-up in subgroups with different levels of weight change. AHI, oxygen desaturation index (ODI) and obstruction event severities decreased during weight loss. In lower level weight loss, the decrease was milder in obstruction severity than in AHI and ODI, indicating that the decrease in the number of events is more focused on less severe events. In weight gain groups, parameters incorporating obstruction event severity, AHI and ODI increased, although increase was greater in parameters incorporating obstruction event severity. The number and severity of respiratory events were modulated differently by the level of weight change. AHI misses this change in the severity of respiratory events. Therefore, parameters incorporating information on the respiratory event severities may bring additional information on the health effects obtained with dietary treatment of OSA.

The AASM 2012 recommended hypopnea criteria increase the incidence of obstructive sleep apnea but not the proportion of positional obstructive sleep apnea

OBJECTIVE/BACKGROUND This study compared the effects of using the 2007 and 2012 American Academy of Sleep Medicine (AASM) recommended hypopnea criteria on the proportion of positional obstructive sleep apnea (pOSA). The effect of modifying the minimum recording time in each sleeping position on the proportion of pOSA was also investigated. PATIENTS/METHODS 207 of 303 consecutive patients (91 of 207 were female) participated in polysomnography (PSG) for the suspicion of OSA met the inclusion criteria for this retrospective investigation. PSGs were scored for both the 2007 AASM recommended hypopnea criteria (AASM2007Rec) and the 2012 AASM recommended hypopnea criteria (AASM2012Rec). For each hypopnea criteria OSA patients were grouped as positional [either supine predominant OSA (spOSA) or supine independent OSA (siOSA)] or non-positional. Outcome measures such as SF-36, FOSQ, PVT, and DASS-21 were compared between groups. RESULTS The AASM2012Rec increased the incidence of OSA compared to AASM2007Rec (84% vs 49% respectively). AASM2012Rec increased the number of patients with supine predominant OSA (spOSA) and supine independent OSA (siOSA) but did not change the proportion (spOSA: 61% AASM2012Rec vs 61% AASM2007Rec, siOSA: 32% AASM2012Rec vs 36% AASM2007Rec). OSA patients diagnosed by AASM2007Rec criteria had similar outcome measures to those diagnosed by the AASM2012Rec criteria. The AASM2012Rec increased the proportion of female OSA patients with spOSA and siOSA. A minimum recording time of 60 minutes in each position decreased the proportion of spOSA, but not siOSA patients when compared to a minimum time of 15 minutes. CONCLUSIONS This study demonstrates that, compared to AASM2007Rec, AASM2012Rec almost doubles the incidence of OSA but does not alter the proportion of OSA patients with pOSA. The proportion of female OSA patients with pOSA however, increases as a result of AASM2012Rec. Furthermore, the use of different minimum recording times in each sleeping position can alter the proportion of spOSA.

Amsterdam positional OSA classification: the AASM 2012 recommended hypopnoea criteria increases the number of positional therapy candidates

PurposeThis study examined the effect of hypopnoea criteria on the prevalence of positional obstructive sleep apnoea (pOSA) identified under the Amsterdam Positional OSA Classification (APOC) system.MethodsThree hundred three consecutive patients undertaking polysomnography (PSG) for the suspicion of OSA were included in this retrospective investigation. PSGs were scored using both the 2007 American Academy of Sleep Medicine (AASM) recommended hypopnoea criteria (AASM2007Rec) and the 2012 AASM recommended hypopnoea criteria (AASM2012Rec). For each hypopnoea criteria, OSA patients were grouped according to the APOC categories (I, II or II) or else deemed non-APOC if they did not meet the APOC criteria. Outcome measures, such as Functional Outcomes of Sleep Questionnaire (FOSQ), MOS 36-item short-form health survey (SF-36) and psychomotor vigilance task (PVT), were also compared between the groups.ResultsThe AASM2012Rec increased the prevalence of OSA compared to AASM2007Rec. The AASM2012Rec trebled the number of APOC I patients compared to AASM2007Rec (297% increase) as well as increased the proportion of females in the APOC I group. AASM2012Rec did not change the number of APOC II and APOC III patients. In fact, the same patients were present in these categories irrespective of hypopnoea criteria. The proportion of non-APOC patients proportionally decreased with the AASM2012Rec criteria. There were no differences in outcome measures between the AASM2012Rec and AASM2007Rec groups.ConclusionsThis study demonstrates that, compared to AASM2007Rec, AASM2012Rec increases the prevalence of who could be successfully treated with positional therapy. The proportion of females with pOSA also increases as a consequence of AASM2012Rec.