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Jussi Virkkala

Publications and source records attributed to Jussi Virkkala.

16 recordsLinked to original sources
PubMed2006

Automatic detection of slow wave sleep using two channel electro-oculography.

An automatic method was developed for detecting slow wave sleep (SWS). The automatic method is based on a two-channel electro-oculography (EOG) with left mastoid (M1) as reference. Synchronous electroencephalographic (EEG) activity was detected by calculating cross-correlation between the two EOG channels by using 0.5-6 Hz band. An amplitude criterion was used for detecting slow waves and beta power 18-30 Hz was used to exclude artefacts. The automatic scoring was compared to a standard visual sleep scoring based on EOG, central EEG and submental EMG. Sleep EEG and EOG were recorded from 265 subjects. The optimal cross-correlation, amplitude and beta thresholds were derived using data from 133 training subjects and then applied to the data from different 132 validation subjects. Results were most sensitive to the changes in the amplitude criteria. Cohen's Kappa between the visual and the new developed automatic scoring in separating non-SWS and SWS was substantial (0.70) with epoch-by-epoch agreement of 93%. SWS epoch detection sensitivity was 75% and specificity was 96%. Also the total amount of slow waves, slow wave time (SWT), was estimated. The advantage of the automatic method is that it could be applied during online recordings using only four disposable self-adhesive electrodes.

Adult↗
PubMed2005

Automated frequency analysis of synchronous and diffuse sleep spindles.

BACKGROUND: Sleep spindles have different properties in different localizations in the cortex. OBJECTIVES: First main objective was to develop an amplitude-independent multi-channel spindle detection method. Secondly the method was applied to study the anteroposterior frequency differences of pure synchronous (visible bilaterally, either frontopolarly or centrally) and diffuse (visible bilaterally both frontopolarly and centrally) sleep spindles. METHODS: A previously presented spindle detector based on the fuzzy reasoning principle and a level detector were combined to form a multi-channel spindle detector. RESULTS: The spindle detector had a 76.17% true positive rate and 0.93% false-positive rate. Pure central spindles were faster and pure frontal spindles were slower than diffuse spindles measured simultaneously from both locations. CONCLUSIONS: The study of frequency relations of spindles might give new information about thalamocortical sleep spindle generating mechanisms.

Adult↗
PubMed2005

Anteroposterior difference in EEG sleep depth measure is reduced in apnea patients.

In the present work, mean frequencies of FFT amplitude spectra from six EEG derivations were used to provide a frontopolar, a central and an occipital sleep depth measure. Parameters quantifying the anteroposterior differences in these three sleep depth measures during the night were also developed. The method was applied to analysis of 30 all-night recordings from 15 healthy control subjects and 15 apnea patients. Control subjects showed larger differences in sleep depth between frontopolar and central positions than the apnea patients. The relatively reduced frontal sleep depth in apnea patients might reflect the disruption of the dynamic sleep process caused by apneas.

Adult↗
PubMed2005

Sleepiness in various shift combinations of irregular shift systems.

The present study examined the occurrence of sleepiness in various shift combinations ending with a night or morning shift. Three weeks' sleep/work shift diary data, collected from 126 randomly selected train drivers and 104 traffic controllers, were used in statistical analyses. The occurrence of sleepiness at work (i.e., Karolinska Sleepiness Scale 7 or higher) was tested with a generalised linear model with repeated measurements including explanatory factors related to shifts, sleep, and individual characteristics. The prevalence of severe sleepiness varied between 25% and 62% in the combinations ending with a night shift and between 12% and 27% in the combinations ending with a morning shift. The occurrence of sleepiness did not, however, systematically vary between the shift combinations in either case. An increased risk for sleepiness was associated with high sleep need and long shift duration in the night shift and with high sleep need, short main sleep period, long shift duration and an early shift starting time in the morning shift. Also having a child was associated with an increased risk for sleepiness in the night shift. The results suggest that the shift history of 24-36 h prior to the night and the morning shift is not strongly associated with the occurrence of sleepiness at work, but there are other factors, such as shift length and starting time and sleep need, that affect a risk for sleepiness at work.

Adult↗
PubMed2004

The effects of sleep debt and monotonous work on sleepiness and performance during a 12-h dayshift.

The study examined the effects of the amount of preceding sleep and work pace on sleepiness and cognitive performance during a 12-h dayshift. Twelve process operators (aged 28-56 years) completed a study with four single 12-h dayshifts and preceding night sleep in the laboratory. A simulated distillation process served as a work task. The 12-h shifts differed from each other in terms of the amount of preceding night sleep (23:00-06:30 hours or 2:30-6:30 hours) and work pace (slow or fast). All shifts contained four work simulation sessions of 1.5 h, and each of them included a 15-min alarm session. Cognitive performance was also measured with a 10-choice reaction time test and a mental subtraction test. Objective sleepiness was measured with a continuous electroencephalography/electro-oculography (EEG/EOG) recording during the work periods and with a sleep latency test. Subjective sleepiness at work was measured with the Karolinska Sleepiness Scale. Sleep debt increased the proportion of EEG/EOG-defined and subjective sleepiness at work, but did not impair work or test performance. The fatiguing effect of monotonous work as indicated by EEG/EOG-defined sleepiness was comparable with the effect of sleep debt. The alarm epochs in the middle of monotonous work temporarily decreased EEG/EOG-defined sleepiness. Sleep debt or monotonous work did not have a significant effect on the results of the sleep latency test. None of the sleepiness or performance measures indicated the impairment of a subject's functional capacity at the end of the 12-h shift. Our results suggest that monotonous work is at least as harmful as moderate sleep debt for alertness at work. The results support the view that the last hours of a single 12-h dayshift with frequent pauses are not associated with an increase in sleepiness or performance errors.

Adult↗
PubMed2004

Sleep in young adults with Asperger syndrome.

Asperger syndrome (AS) is a neurodevelopmental disorder belonging to autism spectrum disorders. Both children and adults with AS have subjective impairment in the initiation and continuity of sleep, and studies using objective assessment are sparse. Twenty young AS adults with frequent complaints of low sleep quality were compared to 10 age-, gender- and education-matched controls without sleep complaints using polysomnography and spectral power analysis of slow-wave sleep. AS subjects displayed a similar polysomnographic profile as compared with controls. In spectral power analysis, a statistically nonsignificant trend towards decreased relative delta power and increased theta power in slow-wave sleep was found in the AS group. It seems that nonorganic insomnia, due to anxiety inherent in AS, is responsible for the low sleep quality in these subjects.

Adult↗
PubMed2004

Visual assessment of selected high amplitude frontopolar slow waves of sleep: differences between healthy subjects and apnea patients.

Slow wave sequences with individually defined amplitude criterion were selected manually from frontopolar sleep EEG of eight healthy control subjects and eight patients with sleep apnea syndrome. Healthy subjects had clearly more time occupied by slow wave sequences in all night sleep. Closer examination revealed that the difference in the amount of slow wave sequence time between the groups was statistically significant only in the first NREM sleep episode. In other words, healthy subjects had more time with slow wave sequences in the first NREM sleep episode, where sleep pressure is supposed to be highest. The lower amount of slow wave sequences in the apnea patients might reflect the fragmented sleep of the patients, inhibiting cortical synchronization.

Adult↗
PubMed2003

Spindle frequency remains slow in sleep apnea patients throughout the night.

BACKGROUND: Our previous data suggested that in normal sleep the frequency of individual sleep spindles would be related to sleep depth and possibly to sleep pressure. Thus far spindle frequency patterns in patients with sleep disorders have not been studied. It would be expected that the spindle frequencies might be affected by sleep fragmentation disturbing the sleep process. METHODS: Twelve apnea patients with age- and sex-matched control subjects were studied with whole-night sleep recordings. Sleep spindles were visually selected and their frequency was determined by spectral analysis. RESULTS: Sleep spindles of the patients were in general slower than in the control subjects. As in our previous study, the frequency of the spindles in the middle-part of the non-rapid eye movement (NREM) sleep episodes increased towards the end of the night in the control group, whereas in the patient group no such increase was found. CONCLUSIONS: The slow spindle frequencies in apnea patients could indicate disturbed sleep and altered neural mechanisms in the structures regulating sleep spindle activity.

Adult↗
PubMed2003

Spindle frequency remains slow in sleep apnea patients throughout the night.

BACKGROUND: Our previous data suggested that in normal sleep the frequency of individual sleep spindles would be related to sleep depth and possibly to sleep pressure. Thus far spindle frequency patterns in patients with sleep disorders have not been studied. It would be expected that the spindle frequencies might be affected by sleep fragmentation disturbing the sleep process. METHODS: Twelve apnea patients with age- and sex-matched control subjects were studied with whole-night sleep recordings. Sleep spindles were visually selected and their frequency was determined by spectral analysis. RESULTS: Sleep spindles of the patients were in general slower than in the control subjects. As in our previous study, the frequency of the spindles in the middle-part of the non-rapid eye movement (NREM) sleep episodes increased towards the end of the night in the control group, whereas in the patient group no such increase was found. CONCLUSIONS: The slow spindle frequencies in apnea patients could indicate disturbed sleep and altered neural mechanisms in the structures regulating sleep spindle activity.

Adult↗
PubMed2003

Sleep-wake rhythm in an irregular shift system.

Sleep in shift work has been studied extensively in regular shift systems but to a lesser degree in irregular shifts. Our main aim was to examine the sleep-wake rhythm in shift combinations ending with the night or the morning shift in two irregular shift systems. Three weeks' sleep/work shift diary data, collected from 126 randomly selected train drivers and 104 traffic controllers, were used in statistical analyses including a linear mixed model and a generalized linear model for repeated measurements. The results showed that the sleep-wake rhythm was significantly affected by the shift combinations. The main sleep period before the first night shift shortened by about 2 h when the morning shift immediately preceded the night shift as compared with the combination containing at least 36 h of free time before the night shift (reference combination). The main sleep period before the night shift was most curtailed between two night shifts, on average by 2.9 and 3.5 h among the drivers and the controllers, respectively, as compared with the reference combination. Afternoon napping increased when the morning or the day shift immediately preceded the night shift, the odds being 4.35-4.84 in comparison with the reference combination. The main sleep period before the morning shift became 0.5 h shorter when the evening shift preceded the morning shift in comparison with the sleep period after a free day. The risk for dozing off during the shift was associated only with the shift length, increasing by 17 and 35% for each working hour in the morning and the night shift, respectively. The results demonstrate advantageous and disadvantageous shift combinations in relation to sleep and make it possible to improve the ergonomy of irregular shift systems.

Adult↗
PubMed2003

Whole-body impedance recording--a practical method for the diagnosis of sleep apnoea.

The aim of this study was to evaluate the utility of whole-body impedance cardiography (ICGWB) in sleep studies, particularly in sleep apnoea detection. A comparison between simultaneous whole night ICGWB and standard polysomnographic recordings were made in 14 patients with a clinical suspicion of obstructive sleep apnoea, a mean age of 46 years (range 30-63 years) and a mean BMI of 29 kg m-2 (25-47). Obstructive apnoeas, central apnoeas and hypopnoeas all caused characteristic patterns in the ICGWB tracing. For an apnoea-hypopnoea index (AHI) > 15 events h-1, the sensitivity of ICGWB was 89% and the specificity 80%. In conclusion, ICGWB signal includes valuable physiological information that can be effectively used for the detection of sleep apnoea episodes. The method seems promising in cases where the multichannel polysomnography is not applicable or when ICGWB is used for haemodynamic monitoring in seriously ill and postoperative patients.

Adult↗
PubMed2003

Occurrence of periodic sleep spindles within and across non-REM sleep episodes.

Sleep spindles have been reported to occur both as single events and periodically in sequences. However, there is no systematic description about the occurrence of spindles in sequences in relation to time of night. The aim of the present study was to examine the temporal occurrence of periodic sleep spindles during the night. Sleep spindles of 19 healthy subjects were selected visually. A minimum of three consecutive spindles was required to form a spindle sequence. A 5-second upper time interval limit was applied as the longest duration between spindles belonging to a spindle sequence. The number of spindles and time occupied by spindle sequences increased from the first to the fourth non-REM (NREM) sleep episode. Within NREM sleep episodes, the number of spindles and spindle sequences dominated at the beginning. In the first two NREM sleep episodes with high slow-wave activity (SWA), there were few spindle sequences and they decreased with increasing SWA. In the third and fourth NREM sleep episode with less SWA, there were more spindle sequences and they were more evenly distributed. It is possible that in the first NREM sleep episodes, hyperpolarization of the thalamocortical cells deepens so rapidly that the NREM sleep level, where spindle sequences arise, is passed and spindle sequences are not formed. Spindle sequences could be regarded as markers of the evolution of the NREM sleep process and their lack or excess in relation to time of night and NREM sleep episode can hopefully be used to indicate changes in brain mechanisms behind NREM sleep.

Adult↗
PubMed2002

Blockade of c-Jun N-terminal kinase pathway attenuates gentamicin-induced cochlear and vestibular hair cell death.

The ototoxic action of aminoglycoside antibiotics leading to the loss of hair cells of the inner ear is well documented. However, the molecular mechanisms are poorly defined. We have previously shown that in neomycin-exposed organotypic cultures of the cochlea, the c-Jun N-terminal kinase (JNK) pathway--associated with stress, injury and apoptosis--is activated in hair cells and leads to their death. We have also shown that hair cell death can be attenuated by CEP-1347, an inhibitor of JNK signalling [Pirvola et al., J. Neurosci. 20 (2000) 43-50]. In the present study, we demonstrate that gentamicin-induced ototoxicity leads to JNK activation and apoptosis in the inner ear hair cells in vivo. We also show that systemic administration of CEP-1347 attenuates gentamicin-induced decrease of auditory sensitivity and cochlear hair cell damage. In addition, CEP-1347 treatment reduces the extent of hair cell loss in the ampullary cristae after gentamicin intoxication. Particularly, the inner hair cells of the cochlea and type I hair cells of the vestibular organs are protected. We have previously shown that also acoustic overstimulation leads to apoptosis of cochlear hair cells and that CEP-1347 can attenuate noise-induced sensory cell loss. These results suggest that activation of the JNK cascade may be a common molecular outcome of cellular stress in the inner ear sensory epithelia, and that attenuation of the lesion can be provided by inhibiting JNK activation.

Animals↗
PubMed2002

Blockade of c-Jun N-terminal kinase pathway attenuates gentamicin-induced cochlear and vestibular hair cell death.

The ototoxic action of aminoglycoside antibiotics leading to the loss of inner ear hair cells is well documented. However, the molecular mechanisms are poorly defined. We have previously shown that in neomycin-exposed cochlear organotypic cultures, the c-Jun N-terminal kinase (JNK) pathway - associated with stress, injury and apoptosis - is activated in hair cells. We have shown that hair cell death can be attenuated by CEP-1347, an inhibitor of JNK signaling (). In the present study, we demonstrate that gentamicin-induced ototoxicity leads to JNK activation and apoptosis in the inner ear hair cells in vivo. We show that systemic administration of CEP-1347 attenuates gentamicin-induced decrease of auditory sensitivity and cochlear hair cell damage. In addition, CEP-1347 treatment reduces the extent of hair cell loss in the ampullary cristae after gentamicin intoxication. Particularly, the inner hair cells of the cochlea and type I hair cells of the vestibular organs are protected. Our previous data have shown that also acoustic overstimulation can cause apoptotic death of cochlear hair cells and that CEP-1347 can attenuate noise-induced hair cell loss. Thus, our results imply that activation of JNK cascade may be a common molecular outcome of cellular stress in the inner ear sensory epithelia and that attenuation of the lesion can be provided by inhibiting JNK activation.

Animals↗
PubMed2002

Spindle frequencies in sleep EEG show U-shape within first four NREM sleep episodes.

It has been shown in previous studies on sleep electroencephalogram (EEG) that spindles are slower in the beginning of the night fastening towards the end of the night. Corresponding findings have been obtained by spectral analysis. The present study was based on our preliminary observation that slower spindles are found in the middle of the non-rapid eye movement (NREM) sleep episodes as compared with the beginning or the end of the episodes. Eight healthy female and six male subjects were studied. Sleep spindles were visually selected and spindle frequencies calculated for 11 analysis points in each NREM sleep episode. The median spindle frequencies formed a clear U-shape within NREM sleep episodes with an initial decrease and final increase. The decrease was statistically significant within the first four NREM sleep episodes. It is possible that the spindle frequency pattern could be used to reveal variations in sleep depth within sleep stage 2. In animal studies the spindle frequency has been found to be associated to the duration of the hyperpolarization-rebound sequences of the thalamocortical cells. If it is assumed that the same cellular mechanisms are responsible for spindle frequencies in humans then the study of variations in spindle frequency could be used to examine the NREM sleep process in humans.

Adult↗