Heart rate variability in healthy young adults exposed to global system for mobile communication (GSM) 900-MHz radiofrequency signal from mobile phones.

Given the large number of mobile phone users and the increasing exposure to radiofrequency electromagnetic field (RF-EMF) worldwide, we aimed to study the effect of RF-EMF related to mobile phones on heart rate variability (HRV). Twenty-six healthy young adults participated in two experimental sessions with a double-blind, randomized and counter-balanced crossover design. During each session, participants were exposed for 26 min to a sham or real 900 MHz RF-EMF, generated by a commercial dual-band Global System for Mobile technology (GSM) mobile phone. We recorded an electrocardiogram at rest during the exposure. We evaluated HRV by time- and frequency-domain analysis. Evaluation of time-domain HRV parameters revealed a statistically significant increase of the standard deviation of interbeat intervals (SDNN) during the real exposure. Other time-domain parameters were not affected. Analysis in the frequency-domain demonstrated that total spectral power and low-frequency band (LF) absolute power were significantly increased during exposure (p = .046 and p = .043, respectively). However, other parameters were not affected. In conclusion, it seems that most HRV parameters were not affected by GSM signal exposure in our study. The weak effect observed on HRV frequency-domain is likely to represent a random occurrence rather than a real effect.

Effects of Smoking Exposure in Infants on Gastroesophageal Reflux as a Function of the Sleep-Wakefulness State.

OBJECTIVE: To determine whether perinatal smoking exposure is associated with gastroesophageal reflux (GER)-related changes in sleep-wakefulness states in neonates. STUDY DESIGN: Thirty-one neonates, referred for the investigation of suspected GER, were recruited and underwent multichannel impedance-pH monitoring and synchronized 8- to 12-hour polysomnography. The infants' exposure to tobacco smoke was estimated by means of a urine cotinine assay. The total number, frequency (h-1), and mean duration (minutes) of GER-pH (reflux events detected by the pH electrode only) and GER-imp (reflux events with bolus movement detected by impedance) events were determined. Intergroup differences (smoking-exposed group vs nonexposed group) were probed with nonparametric, unpaired Mann-Whitney U tests. A χ2 test was used to assess a possible intergroup difference in bolus retrograde migration during GER-imp events. RESULTS: According to the urine cotinine assay, 21 of the 31 neonates had been exposed to cigarette smoke during the perinatal period. The number (and frequency) of GER-imp was significantly greater (P = .016) in the exposed group (29 [0-90]) than in the nonexposed group (12 [2-35]). Migration of the esophageal bolus from the distal segment to the most proximal segment was significantly more frequent (P = .016) in the exposed group (83% of GER) than in the nonexposed group (41%). The GER pattern associated with smoking exposure was particularly obvious during Rapid eye movement sleep. CONCLUSIONS: The more frequent occurrence and greater proximal migration of GER-imp in the smoking-exposed group (especially during rapid eye movement sleep) may have clinical relevance. Smoking exposure is a preventable risk factor for limiting the occurrence of GER in neonates.

Occupational Risk Factors for Musculoskeletal Disorders among Workers in Dairy Diversification.

BACKGROUND: In a changing European agricultural context, diversification of dairy farms is gaining attention. This study seeks to (1) assess musculoskeletal pain prevalence associated with tasks such as butter, yogurt, and cheese production; and (2) analyze associated risks. METHODS: Observing 31, mostly female, workers, we utilized the ERGOROM questionnaire, a methodology adapted from the Institut National de Recherche et de Sécurité, and Key Indicator Method forms. RESULTS: Findings revealed that tasks like load carrying (42% of workers), manual work (17%), and awkward postures (14%) resulted in musculoskeletal pain, predominantly in the lower back (65%), neck (39%), and dominant upper limb areas (shoulder: 61%, elbow: 26%, and wrist: 65%). While psychosocial risks remained low, concerns arose from workload, hygiene standards, and resource unpredictability. CONCLUSIONS: As dairy farming evolves from artisanal to semi-industrial, our study emphasizes the importance of ergonomic adaptations to protect farmers' health and prevent musculoskeletal disorders during diversification.

Work-Related, Non-Specific Low Back Pain among Physiotherapists in France: Prevalence and Biomechanical and Psychosocial Risk Factors, as a Function of Practice Pattern.

BACKGROUND: Physiotherapists worldwide experience lower back pain (LBP). Up to 80% of physiotherapists report having experienced an episode of LBP at some point in their career, and LBP is the most common musculoskeletal disorder in this profession. In France, the prevalence of LBP among physiotherapists and associated work-related risk factors have not previously been studied. OBJECTIVE: To determine whether the risk of work-related non-specific LBP among French physiotherapists depends on practice pattern. METHOD: A link to an online self-questionnaire was sent to French physiotherapists. The various practice patterns were compared with regard to the prevalence of LBP, the total number of days with LBP during the previous 12 months, and the degree of exposure to biomechanical, psychosocial and organisational risk factors. RESULTS: Among the 604 physiotherapists included in the study, the prevalence of work-related, non-specific LBP in the previous 12 months was 40.4%. The prevalence was significantly greater among physiotherapists working in geriatrics (p = 0.033) and significantly lower in sports medicine (p = 0.010). Differences in exposure to risk factors were also found. CONCLUSIONS: The risk of non-specific LBP among French physiotherapists appears to depend on the mode of practice. All the various dimensions of risk must be taken into account. The present study could serve as a basis for more targeted research on the most exposed practices.

Low-back related leg pain: is the nerve guilty? How to differentiate the underlying pain mechanism.

Low back pain (LBP) that radiates to the leg is not always related to a lesion or a disease of the nervous system (neuropathic pain): it might be nociceptive (referred) pain. Unfortunately, patients with low-back related leg pain are often given a variety of diagnoses (e.g. 'sciatica'; 'radicular pain'; pseudoradicular pain"). This terminology causes confusion and challenges clinical reasoning. It is essential for clinicians to understand and recognize predominant pain mechanisms. This paper describes pain mechanisms related to low back-related leg pain and helps differentiate these mechanisms in practice using clinical based scenarios. We illustrate this by using two clinical scenarios including patients with the same symptoms in terms of pain localization (i.e. low-back related leg pain) but with different underlying pain mechanisms (i.e. nociceptive versus neuropathic pain).

Relationship between sleep and acid gastro-oesophageal reflux in neonates.

The aim of the present study was to investigate the impact of gastro-oesophageal acid reflux on sleep in neonates and, reciprocally, the influence of wakefulness (W) and sleep stages on the characteristics of the reflux (including the retrograde bolus migration of oesophageal acid contents). The pH and multichannel intraluminal impedance were measured during nocturnal polysomnography in 25 infants hospitalised for suspicion of gastro-oesophageal reflux. Two groups were constituted according to whether or not the infants displayed gastro-oesophageal reflux (i.e. a reflux group and a control group). There were no differences between the reflux and control groups in terms of sleep duration, sleep structure and sleep state change frequency. Vigilance states significantly influenced the gastro-oesophageal reflux pattern: the occurrence of gastro-oesophageal reflux episodes was greater during W (59 ± 32%) and active sleep (AS; 35 ± 30%) than during quiet sleep (QS; 6 ± 11%), whereas the mean duration of gastro-oesophageal reflux episodes was higher in QS than in W and AS. The percentage of retrograde bolus migrations of distal oesophageal acid content was significantly higher in AS (62 ± 26%) than in W (42 ± 26%) and QS (4.5 ± 9%). In neonates, gastro-oesophageal reflux occurred more frequently during W, whereas the physiological changes associated with sleep state increase the physiopathological impact of the gastro-oesophageal reflux. The duration of oesophagus-acid contact was greater during sleep; AS facilitated the retrograde migration of oesophageal acid content, and QS was characterised by the risk of prolonged acid mucosal contact.

Assessment of radiant temperature in a closed incubator.

In closed incubators, radiative heat loss (R) which is assessed from the mean radiant temperature (Tr) accounts for 40-60% of the neonate's total heat loss. In the absence of a benchmark method to calculate Tr--often considered to be the same as the air incubator temperature-errors could have a considerable impact on the thermal management of neonates. We compared Tr using two conventional methods (measurement with a black-globe thermometer and a radiative "view factor" approach) and two methods based on nude thermal manikins (a simple, schematic design from Wheldon and a multisegment, anthropometric device developed in our laboratory). By taking the Tr estimations for each method, we calculated metabolic heat production values by partitional calorimetry and then compared them with the values calculated from V(O2) and V(CO2) measured in 13 preterm neonates. Comparisons between the calculated and measured metabolic heat production values showed that the two conventional methods and Wheldon's manikin underestimated R, whereas when using the anthropomorphic thermal manikin, the simulated versus clinical difference was not statistically significant. In conclusion, there is a need for a safety standard for measuring TR in a closed incubator. This standard should also make available estimating equations for all avenues of the neonate's heat exchange considering the metabolic heat production and the modifying influence of the thermal insulation provided by the diaper and by the mattress. Although thermal manikins appear to be particularly appropriate for measuring Tr, the current lack of standardized procedures limits their widespread use.

Health, Occupational Stress, and Psychosocial Risk Factors in Night Shift Psychiatric Nurses: The Influence of an Unscheduled Night-Time Nap.

BACKGROUND: Occupational stress and shift work (including night shift work) are associated with physical and psychological health consequences in healthcare providers in general and those working in psychiatric establishments in particular. The aim of this study was to assess the impact of occupational risk factors and unscheduled night-time naps on self-reported health disorders among nurses working in a French psychiatric hospital. METHODS: We performed a 12-month observational field study of experienced nurses working at Philippe Pinel Psychiatric Hospital (Amiens, France) between September 2018 and September 2019. A comparative descriptive study of two groups of nurses who filled out a questionnaire on health and occupational stress was performed: nurses working permanently on the night shift (the night shift group, who took unscheduled naps), and nurses rotating weekly between morning and afternoon shifts (the day shift group). RESULTS: The night and day shift groups comprised 53 and 30 nurses, respectively. There were no intergroup differences in health disorders, sleep quality, occupational stress, and risk factor perception. Correlation analyses showed that in the day shift group, a low level of support from supervisors was associated with elevated levels of distress, anxiety, and gastrointestinal disorders. In the night shift group, a greater overall work load was associated with elevated levels of anxiety and distress. These findings indicated that the nurses on the night shift had adapted well to their working conditions. CONCLUSIONS: An organizational strategy including an unscheduled night-time nap might improve health among night shift nurses.

Are benzo[a]pyrene-DNA adducts an accurate biomarker of long-term in utero exposure to smoking?

BACKGROUND: Maternal smoking during pregnancy is associated with adverse perinatal outcomes. In view of concerns about underreporting, benzo[a]pyrene (B[a]P)-DNA adducts could be used to provide information about long-term in utero exposure to smoking but have not previously been used with samples from neonates. This study aimed to verify whether B[a]P-DNA adducts could accurately assess tobacco smoke exposure during fetal life. The objectives were to correlate B[a]P-DNA adduct levels with active maternal and passive smoking and to determine the sensitivity and specificity of smoking and nonsmoking status by comparing neonatal B[a]P-DNA adduct levels with those of maternal self-reports. MATERIALS AND METHODS: B[a]P-DNA adducts in neonatal buccal cell samples were determined by a competitive immunoassay. Three groups of neonates were constituted according to maternal self-reported smoking status during pregnancy: nonsmokers (n=25; control group), <10 cigarettes per day (n=18; S- group), or >10 cigarettes per day (n=21; S+ group). RESULTS: The mean B[a]P-DNA adduct level rose significantly when comparing the controls with the S- and S+ groups. Maternal active smoking had the strongest effect on B[a]P-DNA adduct levels in neonates. A cross analysis between B[a]P-DNA adduct levels and maternal self-reported levels revealed high sensitivity and specificity. CONCLUSIONS: This preliminary study suggests that B[a]P-DNA adducts are reliable biomarkers for the screening of long-term in utero exposure to smoking and are accurate when compared with maternal self-reported levels of active smoking. Detection of B[a]P-DNA adducts in neonates could provide a useful, noninvasive tool in clinical risk assessment studies but would benefit from further confirmation with another validated biomarker.

Perceived Usefulness of Telerehabilitation of Musculoskeletal Disorders: A Belgium-France Pilot Study during Second Wave of COVID-19 Pandemic.

BACKGROUND: COVID-19 has affected the practice of physiotherapy, and telerehabilitation (TR) may be seen as an alternative model of care if it is accepted by patients and physiotherapists. This study investigates the perceived usefulness of TR and the intention to use it among physiotherapists and patients from Belgium and France concerned with musculoskeletal disorders (MSDs) during the pandemic period. METHODS: An online questionnaire based on the technology-acceptance model was designed. Sociodemographic data were collected and Likert scales were proposed to assess perceived ease-of-use, perceived usefulness and intention to use TR. Data were collected between 17 January and 17 March 2021; 68 patients and 107 physiotherapists answered. RESULTS: In total, 88% of patients and 76% physiotherapists had not used TR at the time they answered. Only 12% of patients and 1% of physiotherapists are willing to use TR, and 50% of physiotherapists think they will never use TR compared to 25% of patients. A total of 98% of participants agreed that they had a good mastery of the technological tools requested. CONCLUSIONS: Physiotherapists are more reluctant to use TR than patients, regardless of convincing EBM results. This is related to their own representation of proper MSD management, which must include the use of hands-on techniques.

The influence of in utero exposure to smoking on sleep patterns in preterm neonates.

BACKGROUND: In utero exposure to smoking is known to adversely affect brain regions involved in behavioral state organization and could therefore interact with the neurophysiological development of neonates. STUDY OBJECTIVES: The present study investigated the effects of prenatal smoking exposure on sleep patterns in the preterm neonate. DESIGN: Overnight sleep patterns were polysomnographically assessed at thermoneutrality. Sleep continuity and structure were scored for the respective frequencies, durations and percentages of active, quiet, and indeterminate sleep and wakefulness after sleep onset. The number and duration of body movements were also analyzed. SETTING: The neonatal intensive care unit at Amiens University Medical Center (France). PARTICIPANTS: Healthy preterm neonates (postconceptional age: 33.9 +/- 6.0 weeks) were enrolled according to whether their mothers had not smoked at all during pregnancy (control group, n=19), smoked less during pregnancy (low-smoking group, Slow, n=10), or smoked more (heavy-smoking group, Sheavy n=10) than 10 cigarettes per day throughout pregnancy. MEASUREMENTS AND RESULTS: Neonates born to heavy-smoking mothers had a significantly lower mean birth weight than controls (-21%) and displayed disrupted sleep structure and continuity: they slept less overall (with a higher proportion of active sleep and a lower proportion of quiet sleep) and had more wakefulness after sleep onset. Compared with controls, neonates from both smoking groups displayed more body movements and, as a result, more disturbed sleep. CONCLUSIONS: High prenatal smoking exposure modifies sleep patterns in preterm neonates by disrupting sleep organization and increasing nocturnal body movements. These findings raise the question of the repercussions of these sleep disturbances (at what is a critical stage in brain development) on the child's physiological and neurobehavioral outcomes.

Influence of thermal drive on central sleep apnea in the preterm neonate.

BACKGROUND: The incidence of apnea in neonates depends on a number of factors, including sleep state and thermoregulation. OBJECTIVE: To assess the role of thermal drive (body heat loss [BHL]) in the mechanisms underlying short episodes of central apnea during active and quiet sleep in neonates. MATERIAL AND METHOD: Twenty-two neonates (postconceptional age: 36.3 +/- 0.9 weeks) were exposed at thermoneutral (incubator temperature: 32.5 degrees C), warm (34.2 degrees C), and cool (30.4 degrees C) conditions during 3 consecutive morning naps. Oxygen consumption (VO2), skin and rectal temperatures, and central apnea were scored during active sleep and quiet sleep. The thermal drive was expressed as BHL calculated using indirect partitional calorimetry. RESULTS: As expected, apnea occurred more frequently in active sleep than in quiet sleep (P < 0.001). The frequency of apnea in active sleep was higher in the warm condition (P < 0.05). In contrast, apnea episodes were less frequent (P < 0.05) and shorter (P < 0.05) for cool exposure, during which VO2 and rectal temperature increased. The frequency (P < 0.001, r2 = 0.31), mean (P < 0.05, r2 = 0.06), and maximum (P < 0.001, r2 = 0.19) durations of apnea were correlated with the BHL: the greater the BHL (body cooling), the less frequent and the shorter the apnea episodes. In contrast, no relationship between apnea and mean skin or rectal temperature was observed. CONCLUSION: Apneic events were more closely related to BHL than to body temperatures. In cool exposure, the decreases in the duration and frequency of apneic episodes suggest that these events depend on the metabolic drive (which is proportional to energy expenditure).

A new, transportable ergometer for the measurement of musculotendinous stiffness during wrist flexion.

We present here a new, dedicated mechanical device for monitoring quick-release movements of the wrist. The ergometer was designed to easily assess musculotendinous properties during wrist flexion. Maximal voluntary contractions (MVC) and quick-release (QR) movements during wrist flexion were performed on 14 subjects. A validation of the ergometer, using a test-retest methodology, was performed to assess its reliability and sensitivity. The device has been technically and biomechanically validated in a range of situations, including inertia measurement (mean inertia was found 0.0119+/-0.0012 N m s(2) rad(-1)) and appearance of the unloading reflex. Our results indicate that the device provides highly reliable, sensitive evaluation of wrist muscle stiffness (intraclass correlation coefficient for inertia, maximal voluntary contraction and stiffness index were 0.873, 0.994 and 0.930, respectively). Its portability facilitates measurement of the influence of repetitive, occupational activity on the musculotendinous complex of the wrist flexors.

The hypoxic test in preterm neonates reinvestigated.

AIM: We currently lack a suitable gold-standard method for implementation on modern equipment to assess peripheral chemoreceptor sensitivity. The aim of the present study was to develop an accurate and reproducible method for assessing peripheral chemoreceptors sensitivity in sleeping preterm neonates. METHODS: A poïkilocapnic hypoxic test was performed twice during rapid eye movement sleep (REM sleep) and non-rapid eye movement sleep (nonREM sleep). The infant breathed hypoxic gas (15% O2 ) for 60 s. The ventilatory response to hypoxia was assessed by comparing minute ventilation during the control period (21% O2 ) with successive 4-cycles sequences during hypoxia. We detected the first statistically significant increase in minute ventilation and recorded the corresponding response time. RESULTS: During normoxia, minute ventilation was higher during REM sleep than in nonREM sleep (428.1 mL · min-1 · kg-1 [307.7-633.6]; 388.8 mL · min-1 · kg-1 [264.7-608.0], respectively; P = 0.001). After hypoxia, minute ventilation increased in both REM and nonREM sleep. The response was significantly higher in REM than in nonREM (25.3% [10.8-80.0] and 16.8% [7.5-33.2], respectively; P = 0.005). The intraclass correlation coefficients for all respiratory parameters were above 0.90. CONCLUSION: We have developed a highly reliable method for assessing peripheral chemoreceptors sensitivity at the response time to hypoxia. In the future, researchers could use this method to assess the involvement of peripheral chemoreceptors in infants who experience chronic hypoxia (e.g. in bronchopulmonary dysplasia and recurrent apnea).

An assessment of the autonomic nervous system in the electrohypersensitive population: a heart rate variability and skin conductance study.

The aim of the study was twofold: first, to compare the activity of the autonomic nervous system (ANS) between the population self-declared as electrohypersensitive (EHS) and their matched control individuals without intended exposure to electromagnetic fields (EMF). The second objective was to determine whether acute exposure to different radiofrequency signals modifies ANS activity in EHS. For that purpose, two different experiments were undertaken, in which ANS activity was assessed through heart rate variability (HRV) and skin conductance (SC). In the first experiment, a comparison between the EHS group (n = 30) and the control group (n = 25) showed that the EHS has an increased number of responses to auditory stimuli as measured by skin conductance activity, and that none of the short-term heart rate variability parameters differ between the two matched study groups. The second experiment, performed in a shielded chamber, involved 10 EHS from the first experiment. The volunteers participated in two different sessions (sham and exposure). The participants were consecutively exposed to four EMF signals (GSM 900, GSM 1800, DECT, and Wi-Fi) at environmental level (1 V/m). The experiment was double blinded and counterbalanced. The HRV variables studied did not differ between the two sessions. Concerning electrodermal activity, the data issued from skin conductance and tonic activity did not differ between the sessions, but showed a time variability. In conclusion, the HRV and SC profiles did not significantly differ between the EHS and control populations under no exposure. Exposure did not have an effect on the ANS parameters we have explored.NEW & NOTEWORTHY This study provided analysis on the skin conductance parameters using a newly developed method (peak/min, extraction of skin conductance responses) that had not been performed previously. Additionally, the skin conductance signal was decomposed, considering tonic and phasic activities to be a distinct compound. Moreover, this is the first time a study has been designed into two steps to understand whether the autonomic nervous system is disturbed in the EHS population.

The dynamics of cardiac autonomic control in sleeping preterm neonates exposed in utero to smoking.

OBJECTIVE: We aimed to determine whether in utero exposure to smoking may influence the activity and dynamics of cardiac autonomic control in preterm infants. We hypothesized that cardiac autonomic control is altered in preterm infants exposed prenatally to smoking and that these effects may vary as a function of the sleep state. METHODS: We studied healthy, preterm neonates born to mothers who had smoked throughout pregnancy but not since birth (n=16). In utero-exposed neonates were matched with control preterm neonates born to non-smoking mothers (n=18). Cardiac autonomic control was monitored as a function of the sleep state by assessing heart rate variability with both linear and non-linear methods. RESULTS: Preterm neonates with in utero exposure to smoking displayed alterations (relative to control neonates) in short-term cardiac autonomic control in all sleep states. These alterations included low vagal activity, elevated sympathetic activity, and low complexity and adaptability in heart rate control dynamics. CONCLUSIONS: Our results constitute direct evidence that cardiac autonomic activity and control are altered in sleeping preterm infants exposed to smoking in utero. SIGNIFICANCE: These alterations may place the affected infants at a higher risk of neurological and cardiovascular complications, which could conceivably persist throughout childhood and adulthood.

Feeding behavior in neonates whose diet contained medium-chain triacylglycerols: short-term effects on thermoregulation and sleep.

BACKGROUND: Feeding formulas for premature infants often contain medium-chain triacylglycerols (MCTs). However, previous studies in animals and adults showed that MCTs may decrease food intake. OBJECTIVES: The objectives were to determine in hospitalized premature infants whether food intake is modified by dietary MCT supply and to assess the effects on thermoregulation and sleep, which are involved in the regulation of energy metabolism and in the optimal physiologic development of the neonates. DESIGN: Food intake, body mass, and nutritional efficiency during 3 consecutive days were compared in 2 groups of neonates according to the fat composition of their feeding formula [MCT group: 37% MCT, 63% long-chain triacylglycerols (LCTs); LCT group: 100% LCT]. On the third day, sleep and metabolic rate were recorded in the morning during an interval between meals. RESULTS: Regardless of day, energy intake was greater in the MCT group than in the LCT group (x difference: 67.3 kJ x kg(-1) x d(-1); P = 0.007). Metabolic rate (1.8 mL x min(-1) x kg(-1); P < 0.001), cheek skin temperature (0.31 degrees C; P = 0.04), and total sleep time (52 min; P = 0.01) were also higher in the MCT group. CONCLUSION: The ratio of MCTs to LCTs in neonates' feeding formulas can modify physiologic functions involved in energy-balance regulation.

The interaction between sleep and thermoregulation in adults and neonates.

The interaction between sleep and thermoregulation leads to different thermoregulatory responses depending on the sleep stage and alterations in sleep when in a cool or warm environment. In the human adult, differences in thermoregulatory efficiency during rapid eye movement (REM) sleep and slow wave sleep (SWS) are less pronounced compared to other mammals: although thermoregulatory processes persist in REM sleep, they are less efficient than during SWS. Cold and warm loads disturb the efficiency and structure of sleep. The duration of REM sleep and (to a lesser extent) of SWS decreases. In contrast, pre-sleep warm loads enhance SWS and improve sleep continuity. This procedure may promote and maintain sleep in depressed patients, whose sleep and body temperature rhythms are modified. In contrast to adults, homeothermic processes in neonates are maintained or even enhanced during active sleep (AS) when compared to quiet sleep (QS). Sleeping in a cool environment increases the duration of AS at the expense of QS. As a result, the thermoregulatory function overcomes the need to conserve energy that would otherwise lead to increased QS. An interaction between sleep, respiration, and thermoregulation may be involved in Sudden Infant Death Syndrome: an alteration in the thermal balance may perhaps induce respiration instability, especially during AS.

Effect of caffeine on peripheral chemoreceptor activity in premature neonates: interaction with sleep stages.

Caffeine is widely used for the treatment of apnea in premature neonates. However, the localization of caffeine's target site (central nervous system and/or peripheral chemoreceptors) is not well defined, especially for sleeping neonates whose sleep stages interact with respiratory control. The aim of this study was to assess the activity of the peripheral chemoreceptors in relation to sleep stages in premature neonates treated (or not) with caffeine for idiopathic apnea. Peripheral chemoreceptor activity was assessed in 22 neonates (postconceptional age of 36 +/- 1 wk with birth weights ranging from 790 to 1,910 g) by performing a 30-s hyperoxic test during active and quiet sleep. Eleven neonates received caffeine treatment (4.0 +/- 0.5 mg.kg(-1).day(-1)) and 11 served as controls. For all neonates, the decrease in minute ventilation observed during hyperoxia was greater during active than during quiet sleep. Neonates receiving caffeine showed a significantly greater decrease in ventilation during hyperoxia in both sleep stages, compared with controls (caffeine; -29.7 +/- 12.8% vs. control; -22.0 +/- 7.4%; F(1,15) = 4.6, P = 0.04). We conclude that caffeine administration increases the effectiveness of chemoreceptor activity. Because sleep stage durations were not affected by the treatment, it is likely that the decrease in apneic episodes typically observed with caffeine therapy is only related to respiratory processes and is independent of the sleep stage organization.

Influence of head position on thermal stress in newborns: simulation using a thermal mannequin.

The influence of head position on thermal stress was assessed by using a heavily clothed thermal mannequin in three different body positions [supine, face straight up (FSU); supine, face to the side (FTS); prone, FTS] and with or without the head covered by a bonnet. The mannequin was exposed to air temperatures of 29, 32, 34, and 36 degrees C. When the head is uncovered, body or head position has no impact on heat loss. When the head is covered, dry heat loss from the mannequin as a whole (and that from the head in particular) is lower (-0.35 to -0.40 W) in the FTS position than in the FSU position as a result of decreased heat loss from the surface area of the face in contact with the mattress. In the FTS position and with the head covered, there was no difference in heat loss between the prone and supine positions. The results suggest that in heavily clothed newborns whose head is covered by a bonnet, thermal stress depends on the head position.