Effects of pneumotachographic recording of breathing on sleep and respiration during sleep

Pneumotachographic recording of ventilation requires an air-tight nasobuccal face-mask which might disturb the subjects' sleep and modify their breathing patterns. In a cross-over randomized study, we compared recordings obtained with and without a face-mask in 20 healthy normal volunteers (10 males, 10 females, mean age: 21.7 +/- SEM 0.5 years). The sleep modifications that resulted from the presence of the face-mask were a lengthening of the REM-sleep latency (+ 38%, p less than 0.01), an increase in intrasleep waking-time (+ 55%, p less than 0.05), an increase in sleep stage-1 duration (+ 40%, p less than 0.02), and a decrease in REM-sleep duration (-20%, p less than 0.01), resulting in a decrease in total sleep duration (-9%, p less than 0.05). The sleep-latency, the number of awakenings, the sleep stage-2 duration, the deep slow wave sleep duration, the sleep stability and the number of sleep cycles were not significantly modified. The respiratory frequency was unchanged in any of the sleep stages. No obstructive or mixed apnoea was observed during the nights when the subjects wore the face-mask. The apnoea index for central apnoeas was low and remained unchanged with and without the face-mask (0.30 +/- 0.10 and 0.35 +/- 0.10 respectively). Thus the observed modifications do not rule out the basic advantage of the pneumotachographic method, that of being the only method to-date providing a direct quantitative measurement of respiratory flow and flow rate during sleep.     

Nonrandom variability of respiration during sleep in healthy humans

STUDY OBJECTIVES: Breath-to-breath variability is not purely random but is, instead, characterized by correlations on short- and long-term scales. Short-term correlations might reflect intact metabolic-control mechanisms. To investigate whether the higher variability of breathing during rapid eye movement (REM) compared to non-REM (NREM) sleep is of random or nonrandom nature--reflecting an altered respiratory control--short-term and long-term correlations of respiratory drive and timing were determined. DESIGN: A full-night polysomnogram with a pneumotachograph attached to a full-face mask was performed. For each breath during NREM and REM sleep, respiratory components were analyzed based on the quantitative airflow. SETTING: Data collection took place in the sleep laboratory. PARTICIPANTS: Twenty-nine healthy subjects (age, 25.8 +/- 3.1 years). MEASUREMENTS AND RESULTS: Long-term correlations are practically absent in respiratory timing and drive components during NREM sleep, whereas they are present during REM sleep. Short-term correlations are present in respiratory drive, tidal volume, and minute ventilation during both NREM and REM sleep. In all timing components, additional short-term correlations are absent. CONCLUSION: We conclude that from NREM to REM sleep, short-term regulation of respiratory drive remains strongly metabolically controlled and clearly different from the short-term regulation of the rhythm-generating function. Regulation of respiratory timing and drive during REM sleep is characterized by additional long-term correlations. We speculate that this is the result of cortical influences during phasic REM sleep. Thus, the variability of breathing during REM sleep contains a nonrandom component, such that breathing components remain dependent upon each other even with large time lags between components.     

Spectral analysis of heart rate variability and respiration during sleep in cocaine-exposed neonates.

This study's objective was to examine the autonomic control of heart rate and respiration during the neonatal period in human infants with prenatal exposure to cocaine. Four-hour daytime recordings of the electrocardiogram (ECG) were obtained from 15 cocaine-exposed and 13 non-exposed full-term neonates at 2 weeks of age during quiet sleep (QS) and active sleep (AS). For each 1-min epoch of sleep, the power spectrum of the R-R intervals was computed from the ECG to obtain the total power (0-2 Hz), and spectral power in the high-frequency (HFP, 0.3-2 Hz), mid-frequency (MFP, 0.1-0.2 Hz), and low-frequency (LFP, 0.03-0.1 Hz) bands. Respiration was also monitored and processed using similar spectral analysis procedures. Cocaine-exposed neonates showed enhanced heart rate variability reflected by an increase in spectral power across all frequency bands. Spectral power in LFP and MFP was higher in cocaine-exposed neonates during both sleep states, but only in HFP during QS. There were no respiratory patterning differences between the groups to account for these findings. The index of sympathovagal balance (LFP + MFP)/HFP, showed no differences between the groups. We conclude that infants exposed to cocaine in utero show differences in the modulation of heart rate reflecting an increase in both vagal and sympathetic influences.     

Cardiac changes during sleep in sleep-deprived infants

OBJECTIVE: To evaluate the influence of a brief period of sleep deprivation on cardiac autonomic controls during sleep in healthy infants. DESIGN: Twelve healthy infants with a median age of 8 weeks (range, 7 to 18 weeks) were recorded polygraphically during a morning and an afternoon nap in a sleep laboratory. They were sleep deprived for approximately 2 hours, either in the morning or in the afternoon, before being allowed to fall asleep. Six infants were sleep deprived before the morning nap, and 6 before the afternoon nap. During both naps, their sleep, breathing, and heart-rate characteristics were continuously recorded. Spectral analysis of heart rate was evaluated as a function of sleep stages. Two major peaks were recognizable: a low-frequency component related to sympathetic and parasympathetic activities and a high-frequency component reflecting parasympathetic tonus. The ratio of low-frequency to high-frequency powers was calculated as an index of sympathovagal interaction. RESULTS: When sleep deprived, the infants had an increase in basal heart rate during non-rapid eye movement sleep (P=.021). With sleep deprivation, the ratio of low-frequency to high-frequency powers increased in non-rapid eye movement sleep (P=.005). These findings were consistent with an increase in sympathetic tone. CONCLUSION: Infants exposed to short-term sleep deprivation manifest changes in cardiac autonomic controls during sleep. These findings could be relevant to mechanisms associated with the sudden infant death syndrome.     

Transepidermal water loss during sleep in infants

Transepidermal water evaporation rate (ER) was measured in 207 infants with a mean postnatal age of 12.7 +/- 10.6 weeks. Measurements were made from the forehead with the use of an Evaporimeter during polygraphic sleep recordings performed under standard conditions. ER values were computed in g/m2 X h. Evaporation rates were significantly lower during rapid eye movement (REM) sleep (8.5 +/- 4.4 g/m2 X h), compared to values measured during quiet wakefulness (11.6 +/- 7.4) or non-REM (NREM) sleep (11.2 +/- 7.6). The differences were not related to age, sex, weight, or rectal temperature, as shown by a covariance analysis. These data, recorded in normal infants, indicate the need to consider the state of sleep or wakefulness of the subjects when comparing results of water evaporation studies.     

Spontaneous arousal activity in infants during NREM and REM sleep

The infant arousal response involves subcortical and cortical responses occurring as a sequence of stereotyped behaviour regardless of the eliciting stimulus. The spontaneous activity of these responses during sleep, however, is uncertain. We examined the spontaneous arousal pattern in normal infants to determine the sequence of responses, and to examine their periodicity and the effects of sleep state. We performed a nap polysomnographic study on 10 normal infants between 2 and 10 weeks of age. Electroencephalographic and electro-oculographic activity, and respiratory airflow and movements were measured, and video recordings were made throughout each study. Different levels of arousal behaviour were examined. We found that spontaneous arousal activity occurred frequently and the majority of responses occurred as a sequence involving an augmented breath followed by a startle and then cortical arousal. Subcortical arousals as reflected by augmented breaths and startles were more common than cortical arousals. Additionally, augmented breaths followed by apnoea were recorded and were not usually associated with other arousal responses. All of the responses occurred periodically either as bursts of activity or as isolated responses. Each of the responses occurred more frequently during rapid eye movement (REM) sleep than during non-rapid eye movement (NREM) sleep. We conclude that there is an endogenous rhythm of spontaneous activity in infants involving excitatory processes from the brainstem, which may or may not be closely followed by cortical excitation. The spontaneous arousal responses occur periodically but with a high level of irregularity and the level of activity is affected by sleep state.     

Respiratory-swallowing interactions during sleep in premature infants at term

Non-nutritive swallowing occurs frequently during sleep in infants and is vital for fluid clearance and airway protection. Swallowing has also been shown to be associated with prolonged apnea in some clinical populations. What is not known is whether swallowing contributes to apnea or may instead help resolve these clinically significant events. We studied the temporal relationships between swallowing, respiratory pauses and arousal in six preterm infants at term using multi-channel polysomnography and a pharyngeal pressure transducer. Results revealed that swallows occurred more frequently during respiratory pauses and arousal than during control periods. They did not trigger the respiratory pause, however, as most swallows (66%) occurred after respiratory pause onset and were often tightly linked to arousal from sleep. Swallows not associated with respiratory pauses (other than the respiratory inhibition to accommodate swallowing) and arousal occurred consistently during the expiratory phase of the breathing cycle. Results suggest that swallowing and associated arousal serve an airway protective role during sleep and medically stable preterm infants exhibit the mature pattern of respiratory-swallowing coordination by the time they reach term.     

Impedance pneumography for long-term monitoring of respiration during sleep in adult males

Impedance pneumography is based on the relationship between respired volume (delta V) and changes of transthoracic impedance (delta/Z/) during breathing. The impedance signal, the relationship between delta V and delta/Z/ and the success rate during long-term recording was studied in 11 healthy adult males, aged 21-46, by a portable tape recorder (Oxford Medilog 4-24). The signals from the tape recorder (delta/Z/), and from a spirometer (delta V) were recorded simultaneously on a mingograph during normal breathing, apnoea, deep sighs, and coughs. The relationship between delta V and delta/Z/ was also analysed on an X-Y recorder. Delta/Z/ was delayed in relation to delta V and during one respiratory cycle the relationship was not linear. The time constant of delta/Z/ was 6 s. A significant correlation was found between peak values of delta V and delta/Z/ for 0 less than delta V less than 2.5 litres. Long-term recording of delta/Z/ during one night's sleep resulted in a success rate of 63-100%, mean 90%. Invalidation of the impedance signal was caused by overloading (81%) and interference (19%). It is concluded that the Medilog respiratory recorder enables determination of respiratory frequency, periods of apnoea and a semiquantitative estimate of volume, but artifacts may invalidate the signal.     

Maternal smoking during pregnancy and sleep problems in 2-month-old infants

Objective

The study aimed to assess possible association between maternal smoking during pregnancy and sleep disturbances in 2-month-old infants.

Subjects and methods

The study comprised 200 apparently healthy infants from community settings selected by chance (88 boys, 112 girls), aged 2 months, who were singletons born in St. Petersburg in 2007. The mothers were asked to complete the questionnaires addressing major infant, maternal and demographic characteristics with particular emphasis on maternal smoking during pregnancy. As a part of the interview, the mothers were requested to describe possible sleep disturbances in their infants, divided into five major sleep domains: bedtime problems, excessive daytime sleepiness, awakenings, regularity and duration of sleep as well as snoring.

Results

Of 200 mothers, 63 (31.5%) smoked during pregnancy. The babies born to smoking mothers more commonly were reported as having bedtime problems [odds ratio (OR)=2.75; 95% confidence interval (CI)=1.15–6.58], and this association remained significant after adjustment was made for major potential confounders. Maternal smoking after delivery did not significantly add to the risk. Babies born to smoking mothers more often had irregular sleep, but this association was markedly influenced by the confounding effect of maternal education. No statistically significant differences were found for total night time sleep duration, the frequency of night time awakenings, excessive night time waking and daytime sleepiness as well as for snoring and noisy breathing during sleep.

Conclusion

Maternal smoking during pregnancy should be considered as a risk factor for infant bedtime problems, emerging as early as 2 months of age.     

Short-term variability of respiration and sleep during unattended nonlaboratory polysomnography--the Sleep Heart Health Study. [corrected

STUDY OBJECTIVES: To determine the short-term variability of indices of disturbed respiration and sleep during 2 nights of unattended nonlaboratory polysomnography conducted several months apart. DESIGN: Participants were randomly selected using a block design with stratification on preliminary estimates of 2 criteria: respiratory disturbance index [RDI3% (apnea or hypopnea events associated with > or = 3% O2 desaturation): < 15/hour total sleep time, > or = 15/hour total sleep time] and sleep efficiency (SEff: < 85% and > or = 85%). The RDI and sleep data from initial and repeated polysomnography were compared. SETTING: NA. PARTICIPANTS: A subset of 99 participants in the Sleep Heart Health Study who agreed to have a repeat polysomnogram within 4 months of their original study. INTERVENTIONS: NA. MEASUREMENTS AND RESULTS: Acceptable repeat polysomnograms were obtained in 91 subjects (mean study interval: 77 +/- 18 [sd] days; range: 31-112 days). There was no significant bias in RDI between study nights using several different RDI definitions including RDI3% and RDI4% (apnea or hypopnea events associated with > or = 4% O2 desaturation). Variability between studies estimated using intraclass correlations (ICC) ranged from 0.77 to 0.81. For subjects with a RDI3% < 15, variability increased as a function of increasing RDI, but for those with a RDI3% > or = 15, variability was constant. Body mass index, SEff, gender, or age did not directly predict RDI variability. Using RDI4% cutpoints of < or = 5, < or = 10 and < or = 15 events per hour of sleep demonstrated that 79.1%, 85.7%, and 87.9% of subjects, respectively, had the same classification of SDB status on both nights of study. There also was no significant bias in sleep staging, sleep efficiency, or arousal index between studies. However, variability was greater with ICC values ranging from 0.37 (% time in REM) to 0.76 (arousal index). CONCLUSION: In the Sleep Heart Health Study, accurate estimates of the severity of sleep-disordered breathing and the quality of sleep were obtained from a single night of unattended nonlaboratory polysomnography. These findings may be applicable to other large epidemiologic studies provided that similar recording techniques and quality-assurance procedures are followed.     

Phasic changes in heart rate and respiration correlated with PGO-spike activity during REM sleep

Summary The correlation between PGO-spike activity and phasic changes in heart rate and respiration during REM sleep has been studied in unrestrained cats.PGO spiking is in 95% of the cases associated with phasic changes in heart rate. Different types of reactions in heart rate were observed. The type of reaction depends on the initial level of heart rate. A correlation between the type of reaction and the duration of spike group, or the number of spikes per polyspike, or the distance of the preceding or following spike did not exist. The changes in heart rate precede the spike by about one second.If a spike discharge occurs in the first half of a respiratory period; the duration of the latter is increased in most of the cases. The interaction between phasic events with particular respect to a possible common pacemaker is discussed.This work was supported by grants from Deutsche Forschungsgemeinschaft.     

Contactless respiration monitoring of infants

Five alternative contactless methods for monitoring respiration in infants during the first year of life are evaluated. The methods are: (i) an air-filled mattress system, (ii) an under-mattress pressure sensor, (iii) a magnetometer and magnet, (iv) a capacitance-change detector and (v) a radar reflection system. A battery-powered 2-channel radar system is described in detail and some results are given of information obtained from overnight recordings in infants.     

Behavioural and EEG responses to auditory stimuli during sleep in newborn infants and in infants aged 3 months

Two studies were conducted in order to assess EEG and behavioural responsiveness to auditory stimuli as a function of sleep state in infants. The subjects in the first experiment were 11 infants aged 3 months, and in the second study the responsiveness of 8 infants aged 3 months was compared with that of 8 newborn infants. The stimuli ranged in intensity from 36 to 90 dB and were presented using a modification of the method of constant stimuli. The occurrence and intensity of behavioural responses were recorded by a trained observer. Electroencephalogram (EEG) responses were defined as EEG desynchronization and were identified by a Fast Fourier Transform algorithm. The results of the two studies showed that infants were more responsive during active sleep (AS) than during quiet sleep (QS) and gave behavioural responses at lower stimulus intensities than EEG responses. Behavioural responsiveness and EEG responsiveness during AS increased as a function of age, while EEG responsiveness during QS decreased. The marked suppression of EEG responsiveness during QS at 3 months of age is thought to be a consequence of developmental changes in sleep mechanisms--an effect which may have clinical implications.     

Unconstrained detection of respiration rhythm and pulse rate with one under-pillow sensor during sleep

A completely non-invasive and unconstrained method is proposed to detect respiration rhythm and pulse rate during sleep. By employing wavelet transformation (WT), waveforms corresponding to the respiration rhythm and pulse rate can be extracted from a pulsatile pressure signal acquired by a pressure sensor under a pillow. The respiration rhythm was obtained by an upward zero-crossing point detection algorithm from the respiration-related waveform reconstructed from the WT 2⁶ scale approximation, and the pulse rate was estimated by a peak point detection algorithm from the pulse-related waveform reconstructed from the WT 2⁴ and 2⁵ scale details. The finger photo-electric plethysmogram (FPP) and nasal thermistor signals were recorded simultaneously as reference signals. The reference pulse rate and respiration rhythm were detected with the peak and upward zero-crossing point detection algorithm. This method was verified using about 24 h of data collected from 13 healthy subjects. The results showed that, compared with the reference data, the average error rates were 3.03% false negative and 1.47% false positive for pulse rate detection in the extracted pulse waveform. Similarly, 4.58% false negative and 3.07% false positive were obtained for respiration rhythm detection in the extracted respiration waveform. This study suggests that the proposed method is suitable, in sleep monitoring, for the diagnosis of sleep apnoea or sudden death syndrome.     

Common slow modulation of respiration, arterial blood pressure and cortical activity during sleep onset while napping.

Using healthy subjects, concomitant 30- to 60-s modulations of respiration, arterial blood pressure and EEG activity were found in 21 experiments about napping. Although mean arterial pressure (MAP) modulations above and below 1/30 Hz increased, in respiratory amplitude (RA) only the lower frequency components augmented significantly. This slow modulation of RA was found to be asymmetrical in time, the duration of RA decreasing parts in the modulation waves being 42% longer than the duration of RA increasing parts. The concomitance of the slow modulations in the different organ systems is accounted for by the influence of the common brainstem system (CBS), which regulates and integrates respiratory, cardiovascular and somatomotor systems and the adjustment of central nervous activity (vigilance). The described common, slow modulations outline the importance of dampening influences during sleep onset. They may provide an important tool for the investigation of the regulatory systems during sleep onset, as well as for investigations about sleep apnoea syndrome and Cheyne-Stokes breathing.     

Nasal occlusion during sleep in normal and near-miss for sudden death syndrome infants

Obligatory nasal breathing has been suggested in the past as a contributor to sudden infant death syndrome (SIDS): nasal obstruction would result in death as infants were unable to breathe orally. To test this hypothesis, we studied 55 normal and 14 near-miss for SIDS infants during a whole-night polysomnography. On several occasions, the infant nares were gently occluded by the fingertips of the investigator. Infants continued to make respiratory efforts against the occluded nose for a variable time (apnoea time), then opened the mouth and started to breathe through it. Mean apnoea time in normal infants was 4.76 +/- 3.41 s (means +/- SD), and 6.54 +/- 4.25 s in near-miss for SIDS ones. These figures were not significantly different. Analysis according to sleep stage (quiet sleep: 4.08 +/- 3.24 s in normals and 6.50 +/- 4.18 s in near-miss for SIDS ones; active sleep: 6.54 +/- 3.67 s in normals and 6.58 +/- 4.76 s in near-miss for SIDS ones) did not disclose any significant difference between groups. There was no significant relationship between apnoea time and age in either group. In many cases, an arousal preceded the resumption of (oral) flow. However, in almost half of the occlusions, oral breathing was initiated during continuing sleep. We conclude: 1) infants are not obligatory nasal breathers, and 2) the nasal obstruction hypothesis should be discarded in the etiology of SIDS.     

Sleep and respiration of rats during hypoxia.

1. The effects of hypoxia on slow-wave sleep (SWS) and of SWS on respiratory responses to hypoxia were investigated on rats provided with chronically implanted cortical electrodes. 2. During the daytime (5-7 hr periods) the proportion of time spent in SWS was 45% (S.E. +/- 1.0%) when the rats breathed air. Exposure to 10% O2 (equivalent to 18,000 ft.) reduced this proportion to 27% (S.E. +/- 2.5%). During hypoxia the intensity of e.e.g. activity in SWS (mean, rectified slow-wave voltage) rarely equalled the normal values characteristic of the same rats in fully developed SWS breathing air. The normal pattern of 5-15 min episodes of SWS was changed by hypoxia to a series of brief (2-3 min) incompletely developed episodes. 3. Addition of CO2 to inspired gas failed to prevent the reduction of SWS during hypoxia. CO2 in normal O2 did not alter sleep significantly. The effects of hypoxia on sleep therefore depend upon changes in O2 pressure rather than upon changes in CO2. 4. The effect of SWS on respiration of rats breathing air was to decrease frequency and minute volume by 10-20%. In hypoxia, however, the frequency increased markedly when the animals entered SWS ; minute volume was not significantly changed. It follows that stimulation of breathing by hypoxia is greater during SWS than during wakefulness. 5. The anomalous increase of respiratory frequency when hypoxic rats entered SWS was abolished by addition of CO2 to the hypoxic gas mixture. 6. Steady-state gaseous metabolism (Vo2 Vco2) was decreased 18 +/- 3% during hypoxia and was increased 31 +/- 4% during exposure to 5% CO2. The implications of these changes for interpretation of respiratory responses to O2 and CO2 are discussed.