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.

Mortality in middle-aged men with obstructive sleep apnea in Finland.

INTRODUCTION: Obstructive sleep apnea (OSA) has been associated with an elevated rate of cardiovascular mortality. However, this issue has not been investigated in patients with elevated proneness to cardiovascular diseases. Our hypothesis was that OSA would have an especially adverse effect on the risk of cardiovascular mortality in Finnish individuals exhibiting elevated proneness for coronary heart diseases. METHODS: Ambulatory polygraphic recordings from 405 men having suspected OSA were retrospectively analyzed. The patients were categorized regarding sleep disordered breathing into a normal group (apnea hypopnea index (AHI) < 5, n = 104), mild OSA group (5 ≤ AHI < 15, n = 100), and moderate to severe OSA group (AHI ≥ 15, n = 201). In addition, basic anthropometric and health data were collected. In patients who died during the follow-up period (at least 12 years and 10 months), the primary and secondary causes of death were recorded. RESULTS: After adjustment for age, BMI, and smoking, the patients with moderate to severe OSA suffered significantly (p < 0.05) higher mortality (hazard ratio 3.13) than their counterparts with normal recordings. The overall mortality in the moderate to severe OSA group was 26.4 %, while in the normal group it was 9.7 %. Hazard ratio for cardiovascular mortality was 4.04 in the moderate to severe OSA and 1.87 in the mild OSA group. CONCLUSIONS: OSA seems to have an especially adverse effect on the cardiovascular mortality of patients with an elevated genetic susceptibility to coronary heart diseases. When considering that all our patients had possibility of continuous positive airway pressure treatment and our reference group consisted of patients suffering from daytime somnolence, the hazard ratio of 4.04 for cardiovascular mortality in patients with moderate to severe disease is disturbingly high.

Efficient reduction of stimulus artefact in TMS-EEG by epithelial short-circuiting by mini-punctures.

OBJECTIVE: We aimed at comparing the effects of two different electrode-to-skin contact preparation techniques on the stimulus artefact induced by transcranial magnetic stimulation (TMS) in electroencephalography (EEG) signals. METHODS: Six healthy subjects participated in a combined navigated brain stimulation (NBS) and EEG study. Electrode contacts were first prepared in the standard way of rubbing the skin using a wooden stick with a cotton tip. The location of hand motor area and the motor threshold (MT) was determined for each subject. Then, the TMS-induced artefact was measured at 60%, 80%, 100% and 120% of the MT. Subsequently, the epithelium under the electrode contacts was electrically short-circuited by puncturing with custom-made needles and the stimulation sequences were replicated. The artefact was compared between the preparation techniques. RESULTS: The TMS-induced artefact was significantly reduced after puncturing. In addition, the size and duration of the artefact depended on the applied stimulation intensity. The reduction of the artefact was largest in electrodes at and close to the stimulation site. CONCLUSIONS: Mini-puncturing technique enables more accurate analysis of TMS-induced short-latency phenomena in EEG during NBS, and it may aid in the examination of the short distance neural connectivity beneath and close to the stimulation site. SIGNIFICANCE: This study describes a practical skin preparation method that significantly improves the utility of TMS-EEG method in studying short-latency cortical connectivity.

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

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.

Weight loss alters severity of individual nocturnal respiratory events depending on sleeping position.

Weight loss is an effective treatment for obstructive sleep apnea (OSA). The mechanisms of how weight loss affects nocturnal breathing are not fully understood. The severity of OSA is currently estimated by the number of respiratory events per hour of sleep (i.e. apnea-hypopnea-index, AHI). AHI neglects duration and morphology of individual respiratory events, which describe the severity of individual events. In the current paper, we investigate the novel Adjusted-AHI parameter (incorporating individual event severity) and AHI after weight loss in relation to sleeping position. It was hypothesised that there are positional differences in individual event severity changes during weight loss. Altogether, 32 successful (> 5% of weight) and 34 unsuccessful weight loss patients at baseline and after 1 year follow-up were analysed. The results revealed that individual respiratory event severity was reduced differently in supine and non-supine positions during weight loss. During weight loss, AHI was reduced by 54% (p = 0.004) and 74% (p < 0.001), while Adjusted-AHI was reduced by 14% (p = 0.454) and 48% (p = 0.003) in supine and non-supine positions, respectively. In conclusion, the severity of individual respiratory events decreased more in the non-supine position. The novel Adjusted-AHI parameter takes these changes into account and might therefore contribute additional information to the planning of treatment of OSA patients.

Repetition suppression in the cortical motor and auditory systems resemble each other--a combined TMS and evoked potential study.

Repetition suppression (RS) in cortical sensory systems optimizes the size of neuronal ensemble reacting to repetitive stimuli such as sounds. Recently RS has also been demonstrated to occur with mental imaging of movement. We studied the existence of RS in the motor system using transcranial magnetic stimulation (TMS). Six healthy subjects participated in this study. TMS was focused on the primary motor cortex with neuronavigation and RS was studied by measuring the motor-evoked potentials from the contralateral first dorsal interosseous muscle. At the same time, we measured TMS-induced cortical responses using electroencephalography (EEG). For a comparison baseline, we evaluated RS by recording EEG responses to sounds with the same stimulation protocol as with TMS. Each stimulus train included four identical stimuli repeated at 1-s intervals, and the stimulation trains were repeated at 20-s intervals. The response amplitude was reduced significantly (p<.01) after the first stimulus in all stimulus trains. This suggests that RS may be a general mechanism for adaptation of neuronal population responses in the human cortex.

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

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 (r(2)=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.

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.

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

Obstructive sleep apnea (OSA) is commonly diagnosed based on the apnea-hypopnea index (AHI). Presently, novel indices were introduced for sleep apnea severity: total duration of sleep apnea and hypopnea events (TAHD%) and a combined index including duration and severity of the events (TAHD% × average desaturation). Two hundred and sixty-seven subjects were divided based on their AHI into four categories (normal, mild, moderate, severe OSA). In the most severe cases TAHD% exceeded 70% of the recorded time. This is important as excessive TAHD% may increase mortality and cerebro-vascular complications. Moreover, simultaneous increase in duration and frequency of apnea and hypopnea events leads to a paradoxical situation where AHI cannot increase along severity of the disease. Importantly, the combined index including duration and severity of the events showed significant variation between patients with similar apnea-hypopnea indices. To conclude, the present results suggest that the novel parameters could give supplementary information to AHI when diagnosing the severity of OSA.

Design, construction and evaluation of an ambulatory device for screening of sleep apnea.

Obstructive sleep apnea syndrome (OSAS) is a major public health problem. The golden reference for diagnosing OSAS is the sleep-laboratory based polysomnography (PSG). However, screening of population for OSAS may be practical and cost efficient only through ambulatory home recordings. In this work we aimed to design, construct and evaluate a novel ambulatory device for these recordings. The device was designed to record breathing movements, nasal and oral flow, position, snore, blood oxygen saturation and heart rate. The first part of clinical evaluation was done by recording 19 patients simultaneously with the novel device and with clinical reference instrumentation at a sleep laboratory. In the simultaneous recordings, no statistically significant difference was detected in the apnea-hypopnea index. All patients were correctly diagnosed, as compared to the reference instrumentation, with the novel ambulatory device. The second part of clinical evaluation was conducted through 323 ambulatory home recordings of which 275 (193 males and 82 females) were of diagnostically acceptable quality. A total of 106 and 169 recordings were successfully conducted with the novel device and a commercial ambulatory device, respectively. Both devices showed similar diagnostic capability in detecting sleep apnea. The novel device was found clinically applicable, technically reliable and sensitive for the diagnostics of OSAS.

Accuracy of automatic analysis of ambulatory recordings of nocturnal breathing disorders is significantly instrumentation dependent.

Obstructive sleep apnoea (OSA) is generally diagnosed with ambulatory recordings. Although reliability of automated analysis has been investigated, suitability of one single analysis software for use with different devices is unclear. Here, validity of automatic analysis of recordings with two ambulatory devices and reliability of automatic analysis in detection of mixed and central apnoeas are investigated through 100 and 167 recordings with Venla and Embletta devices, respectively. Recordings were analysed automatically with Somnologica 3.2 and compared to manual analysis. Significant differences were seen between devices in classification of the severity of OSA when automatic analysis was applied. 65.4% and 11.4% of patients with mild obstructive sleep apnoea received false negative diagnosis with Venla and Embletta, respectively. Further, as automatic analysis was seen to have major difficulty in detection and classification of central and mixed apnoeas, manual analysis is suggested when these forms of disease are suspected.

The effects of carbamazepine and sodium valproate on SEPs and BAEPs.

SEPs and BAEPs were studied in 36 previously untreated epileptics receiving either carbamazepine (CBZ) or sodium valproate (VPA) monotherapy. CBZ prolonged central conduction times in SEPs and BAEPs. SEP latency prolongation correlated with serum CBZ levels. VPA had minimal effects on evoked potentials. The present study gives evidence of similar effects of carbamazepine and phenytoin on central neural conduction.