Occurrence Of Arousals Research Articles

Cardiac Variability and Heart-Rate Increment as a Marker of Sleep Fragmentation in Patients With a Sleep Disorder: a Preliminary Study

The ratio between the heart-rate increment to total power spectral density (%VLFI) has been introduced as a sensitive measure of sleep-related breathing disorders (SRBD). Since a complex interaction is present between sleep disorders and occurrence of arousals, we hypothesized that %VLFI and other indexes of heart-rate variability (HRV) measures reflect the degree of sleep fragmentation. The high- and low-frequency peaks from spectral analysis (FFT) of R-R intervals, the HRV changes using wavelet transform (WT), the geometric and time domain HRV, and the %VLFI were measured in 336 sleep studies performed in patients with insomnia, SRBD and restless legs syndrome/periodic limb movement disorder (RLS/PLMD). The ability of HRV measures to assess sleep fragmentation was examined by correlation analysis and from the area under the receiver operating characteristic (ROC) curve. The ratio of low frequency to high frequency (LF/HF ratio) at the FFT and WT and the %VLFI were higher in patients with SRBD and RLS/PLMD, compared with patients with insomnia. These measures were related to the arousal (MA) index as well as to the apnea-hypopnea index, oxygen desaturations, and periodic leg movement index (p < .001). The presence of a sleep fragmentation defined as an MA index > 20 was well detected by the %VLFI (ROC area: 0.66 +/- 0.03) and the LF/HF ratio at WT (ROC area: 0.66 +/- 0.03). The %VLFI and LF/HF ratio provide indirect measures of sleep fragmentation, suggesting that HRV measures during sleep assess more the associated sleep fragmentation than the presence of a specific sleep disorder.

Hibernation in the tropics: lessons from a primate

The Malagasy primate Cheirogaleus medius hibernates in tree holes for 7 months, although ambient temperatures during hibernation rise above 30 degrees C in their natural environment. In a field study we show that during hibernation the body temperature of most lemurs fluctuates between about 10 degrees C and 30 degrees C, closely tracking the diurnal fluctuations of ambient temperature passively. These lemurs do not interrupt hibernation by spontaneous arousals, previously thought to be obligatory for all mammalian hibernators. However, some lemurs hibernate in large trees, which provide better thermal insulation. Their body temperature fluctuates only little around 25 degrees C, but they show regular arousals, as known from temperate and arctic hibernators. The results from this study demonstrate that maximum body temperature is a key factor necessitating the occurrence of arousals. Furthermore, we show that hibernation is not necessarily coupled to low body temperature and, therefore, low body temperature should no longer be included in the definition of hibernation.

Heart rate activation during spontaneous arousals from sleep: effect of sleep deprivation

Objective: Arousal (AR) from sleep is associated with an autonomic reflex activation raising blood pressure and heart rate (HR). Recent studies indicate that sleep deprivation may affect the autonomic system, contributing to high vascular risk. Since in sleep disorders a sleep fragmentation and a partial sleep deprivation occurs, it could be suggested that the cardiovascular effects observed at AR from sleep might be physiologically affected when associated with sleep deprivation. The aim of the study was to examine the effect of sleep deprivation on cardiac arousal response in healthy subjects. Methods: Seven healthy male subjects participated in a 64 h sleep deprivation protocol. Arousals were classified into four groups, i.e. >3<6 s, >6<10 s, >10<15 s and >15 s, according to their duration. Pre-AR HR values were measured during 10 beats preceding the AR onset, and the event-related HR fluctuations were calculated during the 20 beats following AR onset. As an index of cardiac activation, the ratio of highest HR in the post-AR period over the lowest recorded before AR (HR ratio) was calculated. Results: For AR lasting less than 10 s, the occurrence of AR induces typical HR oscillations in a bimodal pattern, tachycardia followed by bradycardia. For AR lasting more than 10 s, i.e. awakenings, the pattern was unimodal with a more marked and sustained HR rise. The HR response was consistently similar across nights, during NREM and REM sleep, without difference between conditions. Conclusions: Overall, total sleep deprivation appeared to have no substantial effect on cardiac response to spontaneous arousals and awakenings from sleep in healthy subjects. Further studies are needed to clarify the role of chronic sleep deprivation on cardiovascular risk in patients with sleep disorders. Significance: In healthy subjects acute prolonged sleep deprivation does not affect the cardiac response to arousal.

Nasal pressure recording in the diagnosis of sleep apnoea hypopnoea syndrome

BACKGROUNDNasal pressure tracing is now being used to measure breathing in ambulatory screening devices for sleep apnoea but it has not been compared with other methods of assessment.METHODSSleep induced breathing...

Effects of prone and supine position on sleep characteristics in preterm infants.

The purpose of this study was to address the influence of sleep position on sleep characteristics in preterm infants. We studied 16 infants at a mean post-conceptional age of 36.5 weeks. Infants were successfully recorded with videopolysomnograph in the supine and prone position. Between the two positions, there were no significant differences in percentage of active sleep and quiet sleep (QS), the occurrence of arousal, and the incidence of apnea. The first QS after the feeding was longer in the prone position. The sleep position could affect sleep characteristics but not respiratory characteristics in preterm infants.

Dynamics of periodic breathing and arousal during sleep at extreme altitude

To determine whether nocturnal periodic breathing (PB) at altitude is due primarily to unstable control of ventilation or the inability to maintain stable sleep states, we performed visual and computer analyses of the electroencephalographic and respiratory records of healthy volunteers at simulated altitudes of 4572, 6100 and 7620 m. Transient arousals were associated with < 52% of the apneas identified; thus, the PB cycle was not always associated with transient arousal. Following the termination of oxygen breathing, the reinitiation of PB was not dependent on the occurrence of arousal as the primary event. The transition from apnea to breathing preceded the appearance of arousal by ∼ 1 to 4 sec. Ventilatory drive in the breaths immediately following arousal was significantly larger than corresponding control breaths, matched for Sa o 2 . Our findings suggest that altitude-induced PB is unlikely to result from primary fluctuations in state. Arousals promote the development of PB with apnea and help to sustain these episodes, but are not necessary for their initiation.

Surges of muscle sympathetic nerve activity during obstructive apnea are linked to hypoxemia

Obstructive sleep apnea (OSA) is associated with oscillations of arterial blood pressure (BP) that occur in phase with irregularities of respiration. To explore the role of the sympathetic nervous system in these responses, we studied muscle sympathetic nerve activity (MSNA; peroneal microneurography), an index of vasoconstrictor nerve traffic, and BP during awake regular breathing and during spontaneous apneas in patients with OSA. To determine the role of the arterial chemoreflex, we also examined the effects of 100% O2 (hyperoxia) on MSNA and BP. In awake regularly breathing patients with OSA (n = 12), resting MSNA was markedly higher than in an age-matched control population (n = 15) [41 +/- 23 (SD) vs. 24 +/- 17 bursts/min; P < 0.05] and was unchanged during hyperoxia (n = 9). Apneas during sleep (n = 8) were associated with surges in MSNA followed by transient rises in BP when breathing resumed. In contrast to room air apneas, hyperoxic apneas of similar duration were associated with attenuated MSNA responses (+82 +/- 84% vs. +5 +/- 25% compared with awake baseline; P < 0.05; n = 6), even though O2 did not affect sleep stage and the occurrence of arousal. Thus the BP oscillations that occur with apnea during sleep may in part be mediated by intermittent surges of sympathetic activity resulting in vasoconstriction. Because the MSNA responses to obstructive apnea are blunted during O2 administration, they appear to be linked to intermittent arterial hypoxemia and stimulation of arterial chemoreceptors.

Hyperbaric oxygenation increases arousal and breathing movements in fetal lambs

Oxygenation produced by distending the lungs with 100% O2 increases the occurrence of arousal and fetal breathing movements (FBM), particularly during non-rapid-eye-movement (NREM) sleep, in fetal sheep of > or = 135 days of gestation. We studied the breathing and behavioral responses to a rise in arterial PO2 (PaO2) without lung distension in fetuses between 128 and 132 days of gestation. Twelve fetuses were chronically instrumented to record FBM, behavioral state, blood pressure, arterial blood gas tensions, and pH. Fetal PaO2 was raised by having the ewe breathe 100% O2 at 3 atmosphere absolute pressure spontaneously (group 1, n = 5, 129 +/- 1 days of gestation) or with mechanical ventilation to control fetal arterial PCO2 (group 2, n = 7, 131 +/- 1 days of gestation). Hyperbaric oxygenation raised fetal PaO2 by 20 Torr in both groups. During hyperbaric oxygenation, the occurrence of arousal increased severalfold in both groups. The occurrence of FBM increased during arousal in both groups, during rapid-eye-movement sleep in group 1, and during NREM sleep in group 2. The timing of diaphragmatic activity during arousal and the variability of diaphragmatic activity during NREM sleep were different than those in rapid-eye-movement sleep. We conclude that oxygenation without lung distension increases the occurrence of arousal and of FBM, principally during arousal and NREM sleep, in fetuses of < or = 135 days of gestation.

Behavioral arousal in newborn infants and its association with termination of apnea

Arousal is an important protective mechanism that aids in the resolution of obstructive sleep apnea in adults and children, but its role in neonatal apnea has not been investigated. The primary aim of the present study was to determine the role of arousal in the termination of apnea in preterm infants. Videorecording was used to identify spontaneous behavioral arousal in a group of healthy full-term (n = 7) and preterm (n = 10) infants before and during polygraphic monitoring of cardiorespiratory variables and in a group of preterm infants with apnea (n = 10) during similar polygraphic monitoring. Spontaneous arousal rates (mean +/- SE) in full-term infants before and during polygraphic monitoring were 0.18 +/- 0.03 and 0.23 +/- 0.07 episodes/min, respectively. Corresponding values in nonapneic preterm infants were 0.24 +/- 0.03 and 0.24 +/- 0.02 episodes/min. In apneic preterm infants, mean spontaneous arousal rate during polygraphic recording was 0.26 +/- 0.02, but it was considerably higher during apneic sleep periods (0.59 +/- 0.17) than during nonapneic sleep periods (0.25 +/- 0.01). The frequency of occurrence of arousal was significantly higher (P less than 0.005) in long vs. short apnea, mixed vs. central apnea, and severe vs. mild apnea. Although a clear association between arousal and apneic resolution was observed in preterm infants, lack of arousal responses in a large number of apneic episodes suggests that behavioral arousal is not essential for the termination of apnea in these infants.

Hibernation in the Western Jumping Mouse (Zapus princeps)

Seasonal activity, fat deposition, and the hibernation cycle of the western jumping mouse (Zapus princeps) were studied at 2,900 m, 2,500 m, and 2,010 m elevation in the Wasatch National Forest, Utah. Laboratory groups established from all three sites were studied for fat deposition and weight gain with respect to diets, photoperiod, and temperature. The hibernation cycle, occurrence of arousals, weight and fat loss were studied in the laboratory and related to field parameters. The hiber-nacula of 26 animals were found at a mean depth of 59 cm. They contained no cached food reserves. The mean soil temperature throughout the hibernation period was 4.6°C. Emergence of Zapus princeps from hibernation is cued by increasing soil temperature. All field and laboratory populations emerged from hibernation when the temperature of the hibernaculum was between 8.0° and 9.5°C. Animals entered hibernation with 55 to 70% of dry body weight in fat. Weight increased prior to hibernation at an average rate of 0.65 g/day with a maximum of 2.1 g/day. Animals hibernating in the laboratory and in the field lost weight at an average rate of 0.07 g/day. Experiments showed that neither photoperiod nor temperature acts to cue fat deposition. The critical factor for fat deposition is the availability of seeds in the diet.