Visual and automatic classification of the cyclic alternating pattern in electroencephalography during sleep

Cyclic alternating pattern (CAP) is a neurophysiological pattern that can be visually scored by international criteria. The aim of this study was to verify the feasibility of visual CAP scoring using only one channel of sleep electroencephalogram (EEG) to evaluate the inter-scorer agreement in a variety of recordings, and to compare agreement between visual scoring and automatic scoring systems. Sixteen hours of single-channel European data format recordings from four different sleep laboratories with either C4-A1 or C3-A2 channels and with different sampling frequencies were used in this study. Seven independent scorers applied visual scoring according to international criteria. Two automatic blind scorings were also evaluated. Event-based inter-scorer agreement analysis was performed. The pairwise inter-scorer agreement (PWISA) was between 55.5 and 84.3%. The average PWISA was above 60% for all scorers and the global average was 69.9%. Automatic scoring systems showed similar results to those of visual scoring. The study showed that CAP could be scored using only one EEG channel. Therefore, CAP scoring might also be integrated in sleep scoring features and automatic scoring systems having similar performances to visual sleep scoring systems.

Ankyloglossia as a risk factor for maxillary hypoplasia and soft palate elongation: A functional - morphological study

OBJECTIVES

To characterize associations between restricted tongue mobility and maxillofacial development.

SETTING AND SAMPLE POPULATION

Cross-sectional cohort study of 302 consecutive subjects from an orthodontic practice.

MATERIAL AND METHODS

Tongue mobility (measured with tongue range of motion ratio [TRMR] and Kotlow free tongue measurement) was correlated with measurements of the maxillofacial skeleton obtained from dental casts and cephalometric radiographs.

RESULTS

Tongue range of motion ratio and Kotlow measures of restricted tongue mobility were associated with (i) ratio of maxillary intercanine width to canine arch length, (ii) ratio of maxillary intermolar width to canine arch length and (iii) soft palate length. Restricted tongue mobility was not associated with hyoid bone position or Angle's skeletal classification.

CONCLUSIONS

Restricted tongue mobility was associated with narrowing of the maxillary arch and elongation of the soft palate in this study. These findings suggest that variations in tongue mobility may affect maxillofacial development.

Continuous positive airway pressure therapy in obstuctive sleep apnea: benefits and alternatives

INTRODUCTION

Obstructive sleep apnea (OSA) is a highly prevalent condition affecting persons of all age with an increasing public health burden. It is implicated in cardiovascular disease, metabolic syndrome, neurocognitive impairment, reductions in quality of life, and increased motor vehicle accidents. The goals of OSA treatment are to improve sleep and daytime symptoms, and minimize cardiovascular risks.Areas covered: Continuous positive airway pressure (CPAP) is considered the gold standard therapy that delivers pressurized air into the upper airway to relieve obstruction during sleep. Although CPAP is an effective modality of treatment for OSA, adherence to therapy is highly variable. This article highlights the benefits of CPAP therapy, along with alternative treatment options including oral appliance, implantable and wearable devices, and surgery. Expert commentary: CPAP therapy is the gold standard treatment option and should continue to be offered to those who suffer from OSA. Alternative options are available for those who are unable to adhere to CPAP or choose an alternative treatment modality. The most interesting advances have been incorporating orthodontic procedures in conjunction with myofunctional therapy in prepubertal children, raising the possibility of OSA prevention by initiating treatment early in life.

[Historical review on obstructive sleep apnea in children]

An historical review on the discoveries on pediatric obstructive sleep apnea syndrome and sleep-disordered breathing is outlined. Starting with the description by Dickens of "Joe" the obese, snoring and sleepy individual, the authors trace more than 50 years of questions and research starting with the lean adult to the child and from the recognition of obstructive sleep apnea syndrome to the outline of upper-airway resistance syndrome. The pathophysiological knowledge on sleep-disordered breathing has evolved over time, as have treatment approaches in children, from tracheostomy to positive-airway-pressure therapy, to adenotonsillectomy with and without orthodontic treatments to oral-facial myofunctional therapy. Co-morbidities of sleep-disordered breathing are multiple, involving cognition, behavioral, and mood disorders, cardiovascular impairment, etc. There have been many advances in a short time due to the investigation of OSAS, but many questions still need responses.

Radiofrequency Volumetric Reduction of the Palate: An Extended Follow-Up Study

OBJECTIVE: The goal was to evaluate the effect of radiofrequency (RF) of the palate on speech, swallowing, taste, sleep, and snoring 12 to 18 months after treatment.

METHODS: Twenty-two patients were evaluated by clinical examination, questionnaires, and visual analog scales. The patients with relapse of snoring were offered further RF treatment. RESULTS: After a mean follow-up of 14 months, no adverse effect was reported. Subjective snoring scores relapsed by 29% overall. Nine patients (41%) noted relapse of snoring from 2.1 ± 1.1 to 5.7 ± 2.7 ( P < 0.001). Eight of the patients underwent further RF treatment with a reduction of snoring from 5.8 ± 2.9 to 3.3 ± 3.1 ( P = 0.01).

CONCLUSION: The success of RF volumetric reduction of the palate diminishes with time, as with other surgical procedures of the palate. However, the minimal invasiveness of the RF provided a high patient acceptance for retreatment, and relapse of snoring can be improved.

Delta sleep instability in children with chronic arthritis

The objective of the present study was to evaluate the expression of a cyclic alternating pattern (CAP) in slow wave sleep (SWS) in children with the well-defined chronic syndrome juvenile idiopathic arthritis (JIA). Twelve patients (9-17 years of age), 7 girls, with JIA were compared to matched controls by age, pubertal stage and gender. After one night of habituation in the sleep laboratory, sleep measurements were obtained by standard polysomnography with conventional sleep scoring and additional CAP analyses. The sleep parameters of the JIA and control groups were similar for sleep efficiency (91.1 +/- 6.7 vs 95.8 +/- 4.0), sleep stage in minutes: stage 1 (16.8 +/- 8.5 vs 17.8 +/- 4.0), stage 2 (251.9 +/- 41 vs 262.8 +/- 38.1), stage 3 (17.0 +/- 6.0 vs 15.1 +/- 5.7), stage 4 (61.0 +/- 21.7 vs 77.1 +/- 20.4), and rapid eye movement sleep (82.0 +/- 27.6 vs 99.0 +/- 23.9), respectively. JIA patients presented nocturnal disrupted sleep, with an increase in short awakenings, but CAP analyses showed that sleep disruption was present even during SWS, showing an increase in the overall CAP rate (P < 0.01). Overall CAP rate during non-rapid eye movement sleep was significantly higher in pediatric patients who were in chronic pain. This is the first study of CAP in pediatric patients with chronic arthritis showing that CAP analyses can be a powerful tool for the investigation of disturbance of SWS in children, based on sleep EEG visual analysis.

Comparison of hypopnea definitions in lean patients with known obstructive sleep apnea hypopnea syndrome (OSAHS)

STUDY OBJECTIVES

In the interest of improving inter-rater reliability and standardization between sleep laboratories, hypopnea definitions were recently changed to place less emphasis on arousal scoring and more emphasis on oxygen desaturations. We sought to determine whether these changes would affect detection and treatment of OSAHS in lean patients-a group known to desaturate less-than-obese patients.

METHODS

Thirty-five lean subjects (15 male, 20 women, five post-menopausal) diagnosed OSAHS and a documented benefit from treatment had diagnostic polysomnograms (PSG) originally scored using the American Academy of Sleep Medicine (AASM) rule from 1999 (referred to as "Rule C"). These patients had appropriate clinical care based on those results. PSG records were then re-scored in a randomized and blinded fashion utilizing hypopnea Rule A and B of the 2007 AASM guidelines.

RESULTS

Baseline mean (SD) apnea hypopnea indices (AHI) for rules A, B, and C were 6.4 (3.1), 20.6 (8.2), and 26.9 (7.3), respectively (p < 0.0001). Mean (SD) BMI was 24.4 (1.0). By design, all subjects were treatment responders. Eighty-six percent with CPAP, 83% with oral appliance, and 100% with surgical intervention reported resolution of their initial daytime or sleep complaint. Post-treatment AHIs for rules A, B, and C were 0.8 (0.9), 1.8 (1.2) and 2.3 (1.6; p < 0.001). In all three scoring conditions, the AHI was reduced significantly with treatment (p < 0.001). A repeated measures ANOVA of the difference between scoring methods indicated statistically significant differences between all three strategies at both pre- and post-treatment (p < 0.001). Sleepiness on the Epworth sleepiness scale decreased from a mean of 10.9 (2.3) to 5.7 (1.3) with treatment (p < 0.001). This change in subjective rating of sleepiness was more strongly correlated with rules B and C (r = 0.6) and more modestly correlated with Rule A scoring (r = 0.4).

CONCLUSION

Response to treatment was more tightly correlated with arousal based scoring rules B and C in this group of lean subjects. The1999 hypopnea rule was used at baseline to detect this cohort of patients with OSAHS that ultimately benefitted from treatment. Rule B detected OSAHS and correlated well with response to treatment, but many more were categorized as mild (5 < AHI < 15) at baseline. Since 40% of the subjects had an AHI less than 5 with Rule A, lack of sensitivity should be considered before applying Rule A to the scoring of sleep studies in lean patients.

Sleep-disordered breathing and chronic atrial fibrillation

BACKGROUND

Little has been known about the prevalence of sleep apnea in patients with atrial fibrillation (AF). Studies have suggested that the prevalence of AF is increasing in patients with sleep-disordered breathing. We hypothesize that the prevalence of OSA is higher in chronic persistent and permanent AF patients than a sub-sample of the general population without this arrhythmic disorder.

OBJECTIVE

Evaluate the frequency of Obstructive Sleep Apnea in a sample of chronic AF compared to a sub-sample of the general population.

METHODS

Fifty-two chronic AF patients aged (60.5 +/- 9.5, 33 males) and 32 control (aged 57.3 +/- 9.6, 15 males). All subjects were evaluated by a staff cardiologist for the presence of medical conditions and were referred for polysomnography. The differences between groups were analyzed by ANOVA for continuous variables, and by the Chi-square test for dichotomous variables. Statistical significance was established by alpha=0.05.

RESULTS

There were no differences in age, gender, BMI, sedentarism, presence of hypertension, type 2 diabetes mellitus, abdominal circumference, systolic and diastolic blood pressure, and sleepiness scoring between groups. Despite similar BMI, AF patients had a higher neck circumference compared to control group (39.9cm versus 37.7cm, p=0.01) and the AF group showed higher percentage time of stage 1 NREM sleep (6.4% versus 3.9%, p=0.03). Considering a cut-off value for AHI >= 10 per hour of sleep, the AF group had a higher frequency of OSA compared to the control group (81.6% versus 60%, p=0.03). All the oxygen saturation parameters were significantly worse in the AF group, which had lower SaO(2) nadir (81.9% versus 85.3%, p=0.01) and mean SaO(2) (93.4% versus 94.3%, p=0.02), and a longer period of time below 90% (26.4min versus 6.7min, p=0.05).

CONCLUSION

Sleep-disordered breathing is more frequent in chronic persistent and permanent AF patients than in age-matched community dwelling subjects.

Non-invasive estimation of esophageal pressure based on intercostal EMG monitoring

Recording of esophageal pressure waveform is an important clinical tool to identify patients with sleep-disordered breathing. Commonly, esophageal pressure probes are not tolerated by patients undergoing sleep monitoring. We therefore developed a technique to non-invasively estimate esophageal pressure based on recording of intercostal EMG monitoring. A three step approach to modification of the intercostal EMG signal was created to closely match results obtained from esophageal pressure recording. The algorithm was then tested on 10 subjects with sleep-disordered breathing undergoing full polysomnography with simultaneous monitoring of esophageal pressure and intercostal EMG. Analysis of correlations between esophageal pressure and intercostal EMG were computed by sleep stages. The overall correlation coefficient in all subjects combined was r=0.896, p<0.00001. The results indicate that this method can be used reliably in clinical sleep studies where esophageal pressure recordings cannot be performed.

[Cyclic alternating pattern as a sign of brain instability during sleep]

During the last 20 years, the fact that the role of microarousal arousal is very involved in the pathophysiology of sleep disorders has been widely demonstrated. However, in spite of this, the nature of microarousal is still under debate. The awakening system forms a part of the relationship between activation system and sleep maintenance, thus providing the natural evolution of sleep and defending it from the stimuli of the external world. The awakening system, that includes the concept of microarousal, can appear isolated or periodically, then receiving the name of cyclic alternating pattern (CAP). CAP may be affected by different factors that can alter its periodicity, thus offering quantitative information on sleep instability. It can also serve as another new tool to understand human sleep and as complementary information supplied by the sleep macrostructure and microarousal study. This study aims to explain the concept of CAP and its pathophysiology studied up to the present.

Stroke and treatment with nasal CPAP

Stroke patients present a high prevalence of obstructive sleep apnea (OSA) and those with OSA have a higher mortality after 1 year and poorer functional outcome compared with others. The aim of this study was to prospectively evaluate the acceptance of nasal continuous positive airway pressure (CPAP) by recent stroke patients with OSA. Recruitment of non-comatose stroke patients with sufficient consciousness for diagnostic evaluation of OSA was performed and they were treated at home with nasal CPAP after hospital calibration and training on the usage of CPAP. Initial evaluation and regular follow-up of the home trial of auto-CPAP was carried out for a duration of 8 weeks. Of 50 initially recruited patients, 32 (100%) responded to the minimum cognitive criteria but seven patients (22%) only used nasal CPAP for 8 weeks. Subject dropout was related to difficulties with CPAP usage as perceived by patient and family members, facial weakness, motor impairment and increase difficulties and discomfort with usage of full-face mask. The majority of OSA stroke patients rejected CPAP treatment. Better education and support of patients and families, and special training sessions in rehabilitation services, will be needed to improve compliance.

Erectile dysfunction, obstructive sleep apnea syndrome and nasal CPAP treatment

BACKGROUND AND PURPOSE

To evaluate the effect of one month of continuous positive airway pressure (CPAP) in a subgroup of obstructive sleep apnea (OSA) patients with erectile dysfunction (ED) and compare this subgroup with age- and body mass index (BMI)-matched OSA patients without ED.

PATIENTS AND METHODS

Prospective general, sleep, psychiatric and sexologic evaluations were conducted. Epworth Sleepiness Scale (ESS), Beck Depression Inventory (BDI), Sleep Disorders Questionnaire (SDQ), Quality of Life SF-36, and polysomnography were used. Seventeen OSA patients with ED were compared prior to CPAP treatment and during CPAP treatment with age- and BMI-matched OSA patients without ED. Parametric and non-parametric statistics, chi-square, Fisher exact test and multiple regression analyses were performed.

RESULTS

Ninety-eight men (BMI=28.8 kg/m2, apnea-hypopnea index (AHI)=49.6 events/h, ESS=14.8, BDI=8.4, and lowest SaO2=75.3%) were divided into subgroups of lowest SaO2>80% (A) and lowest SaO2< or =80% (B). (A) Forty-six men had a mean lowest SaO2 of 85.7%+/-2.9, AHI=29.5+/-17.6, age=46.3+/-9.3 years, ESS=13.6+/-4.2, BMI=25.8+/-4.8. Seven of the patients had ED. (B) Fifty-two men had a mean lowest SaO2=60.10+/-10.0%, AHI=67.4+/-24.5, BDI=9.0+/-6.9, age=47.4+/-9.4 years, ESS=16.2+/-4.4, BMI=31.4+/-5.1. Twenty-one of the patients had ED (chi2: P=0.006). Significant variables for ED were lowest SaO2 and age (r=0.17). CPAP-treated subgroup: ED subjects had significantly lower SaO2, ESS, BDI and SF-36 subscale scores than OSA controls. Nasal CPAP eliminated the differences between groups, and ED was resolved in 13 out of 17 cases.

CONCLUSIONS

ED in OSAS is related to nocturnal hypoxemia, and about 75% of OSAS patients with ED treated with nasal CPAP showed remission at one-month follow-up, resulting in significant improvement in quality of life.

An animal model of a spontaneously reversible obstructive sleep apnea syndrome in the monkey

The anatomies of the tongue and uvula in monkeys share many similarities with humans, such that this species has the closest approximation to the human upper airway than any other species. In this study, we investigated the feasibility of using small monkeys as experimental animals for an obstructive sleep apnea model. Monkeys received intradermal injections of liquid collagen in the uvula, tongue, and lateral pharyngeal walls every 2 weeks. Polysomnography was performed bi-monthly in order to control the impact of injections on breathing events, respiratory effort (as measured by esophageal pressure), and sleep. Before injections, the three animals showed normal breathing during sleep with a mean of 4.8 +/- 2.0 events/h. After injections, a mean of 27.9 +/- 19.7 hypopneas/h was recorded (P = 0.023). Total sleep time was significantly reduced, with a decrease of REM sleep and stage II sleep; however, stage I sleep increased. Collagen injections in monkey's upper airways can create sleep-disordered breathing and abnormal sleep, as seen in sleep apneic patients.

[Pediatric autopsy and informed parental consent]

AIM

In French legal terminology, the definition of autopsy is "organs'withholding". This phrase is ambiguous, meaning both removing the organs for their macroscopic exam and their retention for subsequent histology. The autopsy of a child requires an informed consent from both parents. The issue is that the pathologist who performs the autopsy is not the one who delivers the information and gets the parents' consent: therefore, he does not know what they were told and what they actually agreed upon.

MATERIALS AND METHODS

A questionnaire was sent to 3 groups of paediatricians (N=891) to approach their knowledge regarding autopsy.

RESULTS

Among 362 paediatricians who answered the questionnaire, 57.2% never attended an autopsy and procedures were badly known. They did not know whether or not organs, were systematically sampled especially brain. Regarding the possibility of conservation of organs, a majority thought that one should not solely answer to parents'queries (63.8%) but rather that one should point out every possibility, without giving the ins and outs (60.8%). The majority favoured organs retention and use for research.

CONCLUSION

We make 3 suggestions: to register autopsy in the Natioanal Securite Sociale nomenclature, to establish information and consent forms for organs'removal, retention and disposal, and to offer parents the possibility of an interview with the pathologist before and/or after the autopsy, in association with the paediatrician.

Medications for the treatment of narcolepsy

Narcolepsy is a syndrome of unknown aetiology characterised by excessive daytime sleepiness (often severe) usually in association with cataplexy (brief episodes of partial or complete muscle paralysis) and often with other uncommon symptoms. Due to limited disease-specific knowledge, medication treatment for this condition has focussed on specific symptom amelioration rather than improving or eliminating underlying disease mechanisms. Such treatment generally consists of stimulants for daytime sleepiness and anticataplectic medication for cataplexy; hence, both types of agents are reviewed in this article. Recent discoveries, including the finding that canine familial narcolepsy is caused by a single gene defect in the hypocretin receptor, coupled with the findings in human narcoleptics of undetectable hypocretin levels in the CSF and of severe hypocretin-containing neuronal atrophy in brains of deceased narcoleptics, have shifted the focus of narcolepsy treatment research to the hypocretin system. The hope is that a single agent can be developed to provide effective treatment for all symptoms of narcolepsy. While the mechanism of action in narcolepsy is unknown, gamma-hydroxybutyrate (GHB) is proving to be such an agent. Interestingly, GHB is not known to impact hypocretin pathways in the brain, yet specific research exploring this possible interaction has not been performed. The market for medications limited to use by narcoleptics is small because of the relatively low prevalence of narcolepsy; however, the prevalence of clinically important daytime sleepiness and/or fatigue is surprisingly high. New agents that effectively manage the sleepiness of narcolepsy thus have a much larger potential for appropriate use in treating sleepiness and fatigue in the general population. This fact has recently been demonstrated by the tremendous success of modafinil, a drug introduced to the market a little over 2 years ago, which was developed to treat sleepiness in narcolepsy but now is used in a much larger patient population.

HD-16: a new quality of life instrument specifically designed for insomnia

BACKGROUND AND PURPOSE

To design a new quality of life (QoL) instrument specifically for insomnia.

PATIENTS AND METHODS

Based on severe insomniacs' interviews, we have built a new quality of life scale that has been tested in one group of 240 severe insomniacs, in one group of 422 mild insomniacs and in one group of 391 good sleepers. Ten steps led to the construction of a specific QoL scale.

RESULTS

Five dimensions have been validated as both relevant and independent from each other. Sixteen items out of the 43 initially tested were retained and significantly different within the groups in each dimension. Based on the 16 items selected, we called the scale Hotel Dieu 16 (HD-16). We have therefore verified the score's specificity (correlation score of +0.36) and the reliability of the scale (Cronbach coefficient alpha=0.78).

CONCLUSION

HD-16 may be used as a focused instrument to better assess an insomniac's quality of life.

A prospective study of nocturia and the quality of life of elderly patients with obstructive sleep apnea or sleep onset insomnia

OBJECTIVE

To prospectively evaluate the relationship between obstructive sleep apnea syndrome (OSAS), nocturia and quality of life in elderly patients free of the urologic and medical conditions that lead to increased nocturia.

METHODS

Prospective study of nocturia in men 65 years and older with isolated OSAS or sleep onset insomnia. After a 7-day nocturia evaluation and nocturnal polysomnography, Epworth Sleepiness Scale (ESS), Beck Depression Inventory (BDI), Quality of Life (SF-36) were administered.

RESULTS

OSAS patients with frequent nocturia had significantly greater body mass index (BMI), greater apnea-hypopnea index (AHI), lower lowest oxygen saturation and lower SF-36 subscale scores. Treatment with nasal continuous positive airway pressure (CPAP) for OSAS and behavioral techniques for insomnia improved ESS and BDI scores for all three groups. SF-36 subscale scores improved more in subjects with multiple nocturia. AHI and BMI explain 38% of the variance for nocturia.

CONCLUSION

Nasal CPAP reduces OSA and nocturia and improves quality of life of elderly patients.

Twenty minutes versus forty-five minutes morning bright light treatment on sleep onset insomnia in elderly subjects

OBJECTIVE

To compare the efficacy of 20 min versus 45 min light exposure for relieving psychophysiological insomnia in the elderly.

METHODS

Prospective recruitment of subjects 60 years and older with psychophysiological insomnia. Random distribution to 20 or 45 min of daily exposure to 10,000 lux for 60 days. Sleep latency, total sleep time, fatigue and activity were measured at baseline and 3 and 6 months posttreatment. Blind analysis of data and comparison were performed using repeated-measure analysis of variance, independent samples t test and Wilcoxon rank signed test.

RESULTS

At 3 months, improvement was significantly higher in the 45-min versus 20-min condition. At 6 months, variables returned toward baseline in the 20-min but not in the 45-min condition.

CONCLUSIONS

Twenty minutes of bright light treatment leads to a lesser treatment response than 45 min at 3-month follow-up and to a return toward baseline at 6-month follow-up that was not seen with a 45-min exposure.

Work and rest sleep schedules of 227 European truck drivers

OBJECTIVE

To investigate the sleep-wake behavior and performance of a random sample of European truck drivers.

METHODS

The drivers completed a questionnaire concerning sleep-wake habits and disorders experienced during the previous 3 months. In addition, they were asked to complete a sleep and travel log that included their usual work and rest periods during the previous two days. They answered questions concerning working conditions and reported their caffeine and nicotine intake during their trips.

RESULTS

A total of 227 drivers, mean age 37.7+/- 8.4 years (96.2% acceptance rate), participated in the study. The drivers were found to have a fairly consistent total nocturnal sleep time during their work week, but on the last night at home prior to the new work week there was an abrupt earlier wake-up time associated with a decrease in nocturnal sleep time. Of the drivers, 12.3% had slept less than 6 h in the 24 h previous to the interview and 17.1% had been awake more than 16 h.

CONCLUSIONS

Shifting sleep schedules between work and rest periods can generate long episodes of wakefulness. This type of sleep deprivation is rarely investigated. Its is usually not taken into consideration when creating work schedules, but affects the performance of drivers. Unsuspected shifts occur at the onset of a new workweek. Sleep hygiene education for professional drivers is still far from perfect.

Effect of fatigue on performance measured by a driving simulator in automobile drivers

OBJECTIVE

To identify risk factors of performance decrement in automobile drivers.

METHODS

114 drivers (age <30 years, n=57; age > or =30 years, n=57) who stopped at a rest stop area on a freeway were recruited for the study. They filled out a questionnaire on their journey, sleep/wake patterns and performed a 30-min test on a driving simulator. The test evaluates, by computerized analysis, the lateral deviation of a virtual car from an appropriate trajectory on a virtual road. A sex/age matched control group was recruited in the community. Control subjects were studied at the same time of day as the index case driver. Controls had normal sleep wake schedule, absence of long driving and performed the same driving test.

RESULTS

Drivers performed significantly worse than controls on the driving test. Age and duration of driving were the main factors associated with decreased performance.

CONCLUSION

Our driving simulator can identify fatigue generated by driving but results must be considered in relation with age of subjects.