Biomedical subjects

J P Libert

Publications and source records attributed to J P Libert.

At least 19 recordsLinked to original sources

PubMed2001

Measurement of functional residual capacity through the transient phase of He dilution in newborns.

Helium dilution maneuver is used to determine the functional residual capacity (FRC) 14 newborns ages 1-5 mo. The model equation describes the changing alveolar fractions of He and the ventilation promoted by a rebreathing procedure that does not exceed 40 s. The model does not involve the volume of the rebreathing bag usually needed when applying rebreathing technique and which is a source of error. The equation is discretized and solved for recorded data obtained with equipment adapted to newborns. Results show a strong relationship between FRC and the biometrical indexes, and confirm those found in the literature featuring that the measurement duration of FRC can be considerably shortened.

Body Surface Area↗

PubMed2001

Assessment of dry heat exchanges in newborns: influence of body position and clothing in SIDS.

A dramatic decrease of sudden infant death syndrome (SIDS) has been noted following the issuance of recommendations to adopt the supine sleeping position for infants. It has been suggested that the increased risk could be related to heat stress associated with body position. In the present study, the dry heat losses of small-for-gestational-age newborns nude or clothed were assessed and compared to see whether there is a difference in the ability to lose heat between the prone and supine positions. An anthropomorphic thermal mannequin was exposed to six environmental temperatures, ranging between 25 and 37 degrees C, in a single-walled, air-heated incubator. The magnitudes of heat losses did not significantly differ between the two body positions for the nude (supine 103.46 +/- 29.67 vs. prone 85.78 +/- 34.91 W/m(2)) and clothed mannequin (supine 59.35 +/- 21.51 vs. prone 63.17 +/- 23.06 W/m(2)). With regard to dry heat exchanges recorded under steady-state conditions, the results show that there is no association between body position and body overheating.

Body Temperature Regulation↗

PubMed2000

Interindividual differences in the thermoregulatory response to cool exposure in sleeping neonates.

The responses of the thermoregulatory effectors vary greatly among neonates. Therefore, we assume that a small decrease in air temperature from thermoneutrality induces various thermoregulatory responses within neonates that represent an energy cost due to the cold defence processes. To determine the importance of this variability in nursing, 26 neonates were explored at thermoneutrality and in a cool environment (-1.5 degrees C from thermoneutrality) similar to that which occurs currently in clinical procedure. Oxygen consumption (VO2), oesophageal and skin temperatures, as well as sleep parameters were recorded continuously in both conditions. Analysis of all of the data from all of the neonates revealed that the cool exposure induced thermal and sleep disturbances, but VO2 did not increase and was not negatively correlated to body temperature (as might be expected). Analyses of individual data showed large variability in body temperature regulation: the neonates could be assigned to one of three groups according to the direction of the individual slopes of VO2 versus oesophageal or skin temperature. The groups also differed according to the sleep changes recorded in the cool condition. The results show that the definition of thermoneutrality should be revised by incorporating non only changes in the body temperature, but also the sleep disturbances (increased wakefulness and active sleep, decreased quiet sleep), which are criteria that are more sensitive to mild cool exposure. Thermoneutrality should be defined for each individual, since the results stress that the variability does not help to predict a general pattern of thermoregulatory responses in cool-exposed neonates.

Body Temperature↗

PubMed2000

Gender-related sleep differences in neonates in thermoneutral and cool environments.

Although thermoregulation and sleep exhibit gender differences in adults, the question is still debated in neonates. The aim of this study was to examine the relationship between gender-related sleep differences and cool defence mechanisms in neonates. Sleep and thermoregulation were recorded in healthy preterm neonates (21 boys and 17 girls, 37 +/- 2 weeks post-conceptional age) exposed to thermoneutral and cool conditions. Sleep was analysed for continuity and structure. Although the cool exposure did not strongly impair body homeothermia, sleep was altered but without any significant gender difference. However, when data recorded under each of the thermal conditions were pooled, some gender differences emerged: boys slept less, with more wakefulness after sleep onset, more active sleep and less quiet sleep than girls. In contrast to sleep architecture, most of the sleep continuity parameters exhibited greater variability in boys than in girls. This variability may bias the statistical analyses and probably explains the varying conclusions reported in the literature regarding gender-specific sleep-related differences.

Body Temperature Regulation↗

PubMed1999

Reliability of a new device to assess the oxygen consumption of human respiratory muscles.

PURPOSE: This study tests the reliability of a new device for assessing the oxygen consumption of the respiratory muscles (VO2 resp.). METHODS: Fourteen healthy male volunteers participated in the study. The device consists of an expandable external ventilatory dead space created with pieces of plastic tubing and a spirometer filled with 100% oxygen. It also incorporates a carbon dioxide absorber. Total VO2 (VO2 tot.) was recorded from the spirometric closed circuit and ventilation (V(E)), from the spirometer tracing. For each subject the test procedure was carried out in duplicate (T1 and T2) after an overnight fast. The dead space was increased at a constant rate of 260 mL every 90 s, and VO2 tot. and V(E) increased progressively. Because log VO2 tot. was linearly related to V(E), we calculated the slope value (log VO2-V(E)) and the Y-intercept (VE = 0) of the semilog regression representing, respectively, VO2 resp. and metabolic VO2 (VO2 met.). RESULTS: When compared with values in the literature, these values did not differ from those recorded in subjects of a similar age group. The VO2 resp. and VO2 met. calculated in T1 and T2 were not different (VO2 resp. = 0.0066 +/- 0.0005 for T1 vs 0.0067 +/- 0.0005 log mL x min(-1)/L x min(-1) for T2 and VO2 met. = 269.3 +/- 28.6 for T1 vs 281.9 +/- 24.1 mL x min(-1) for T2). The coefficients of variation were: 25% at T1 and 23% at T2 for VO2 resp. and 34% at T1 and 29% at T2 for VO2 met. Moreover, significant correlations (r = 0.96, P < 0.001 for VO2 resp., r = 0.95, P < 0.001 for VO2 met.), high coefficients of determination (r2 = 0.92 for VO2 resp., r2 = 0.90 for VO2 met.) and negligible SEE (0.0005 for VO2 resp., 0.2 mL x min(-1) for VO2 met.) were found between the two tests. When we plotted the mean values of VO2 resp. and VO2 met. measured at T1 and T2 against their respective differences, more than 95% of the slight differences ranged between the limits defined by mean value +/- 2 SD, reflecting the small discrepancy between duplicate measurements. CONCLUSION: The results confirm that the test performed with this device is useful and reliable for assessing the VO2 resp. in healthy subjects.

Adult↗

PubMed1999

Biological monitoring exposure of workers from plant producing carbon electrodes: quantification of benzo[a]pyrene DNA-adducts in leukocytes, by a 32P-postlabelling method and an immunoassay.

The levels of benzo[a]pyrene were monitored for blood DNA-benzo[a]pyrene adducts in 17 workers from a plant producing carbon electrodes, with high exposure to benzo[a]pyrene (575-902-1149 ng m(-3)). Two different techniques, a 32P-postlabelling method and a competitive immunoassay using polyclonal antibodies obtained from rabbits immunised with DNA modified by benzo[a]pyrene-trans-7,8-dihydrodiol-9,10-epoxide were used. For each worker, urinary 1-hydroxypyrene, a potential indicator of exposure to polycyclic aromatic hydrocarbons, was measured. The effect of tobacco by urinary cotinine measurement was also considered. The postlabelling and immunoassay detection limits for DNA-benzo[a]pyrene adducts were respectively 0.15 and 10 fmol 50 microg(-1) of DNA. The results obtained by the two methods demonstrated a good detection of DNA-benzo[a]pyrene adducts, but no direct relationship between the quantity of adducts and the concentration of benzo[a]pyrene in air-borne was noted in the studied plant. The levels of DNA-benzo[a]pyrene adducts obtained by immunoassay were significantly higher than those obtained by the 32P-postlabelling (P < 0.001). For several workers, variations due to professional or non professional factors must be taken into account in interpreting the results. In conclusion, the two methods used proved very efficient in determining DNA-benzo[a]pyrene adducts, and may be useful in monitoring human exposure to known and previously unidentified environmental genotoxic agents.

Adult↗

PubMed1998

Sleep modifications during cool acclimation in human neonates.

The present study aimed at testing in human neonates whether the thermal acclimation could reduce the sleep disturbances induced by brief cool exposure. Six neonates were exposed in incubator to a standardised cool thermal load of 75 h duration. The results show an increase of the metabolic heat production (VO2: +25% reaching 5.68 ml/min per kg) during cool acclimation which is not associated with a reduction of the sleep modifications observed on the first cool exposure: the increase of active sleep (+15%, +2 min) and the decrease of quiet sleep (-15%, -11 min) persist and wakefulness after sleep onset increases (+12%, +10 min). In conclusion, there is no sleep adaptation as cool acclimation progressed.

Acclimatization↗

PubMed1998

Humidity control tool for neonatal incubator.

In the first days of life, the daily evaporative loss from premature neonates can reach up to 20% of body mass. Such loss can be reduced by increasing the air humidity inside the incubator. Neither passive humidification nor open loop systems allow high humidity rates to be maintained or easily controlled: at 34 degrees C, the maximum levels vary with the system from 40% to 77% of relative humidity. The skin evaporative exchanges between the neonate and the environment are directly proportional to the water vapour partial pressure difference between the neonate's skin and the air. An active closed loop system has been designed, which permits reliable and accurate control of humidity according to the water vapour partial pressure set, between 1 and 6 kPa, in an air temperature range of 28-39 degrees C. It is characterised by variations of about 0.05 kPa around the set value and a maximum humidification speed of 0.25 kPa min-1. The algorithm is based on optimal control and the dynamic programming principles. Test results place this active system above usual systems for its power, precision and adaptability. It is an exploitable tool in fundamental and clinical research, to precisely study the humidity effects on neonatal comfort and thermo-regulation evolution.

Algorithms↗

PubMed1998

Effects of interval training at the ventilatory threshold on clinical and cardiorespiratory responses in elderly humans.

This study assessed clinical and cardiorespiratory responses after an interval training programme in sedentary elderly adults using the ventilatory threshold (Vth) as the index of exercise training intensity. A selection of 22 subjects were randomized into two groups: 11 subjects served as the training group (TG) and the others as controls (CG). Maximal exercise tests were performed on a treadmill before (T0), each month (T1, T2) and after the 3-month interval training programme period (T3). The TG subjects were individually trained at the heart rate corresponding to Vth measured at T0, T1 and T2 as the breakpoint in the oxygen uptake-carbon dioxide production relationship. Their training programme consisted of walking/jogging sessions on a running track twice a week. The sessions consisted of varying durations of exercise alternating with active recovery in such a way that the subjects slowly increased their total exercise time from an initial duration of 30 min to a final duration of 1 h. During training the heart rate was continuously monitored by a cardiofrequency meter. Compared with the daily activities of the controls, no training programme-related injuries were observed in TG. Moreover, programme adherence (73%) and attendance (97.3%) were high. The maximal oxygen uptake and Vth were increased in TG, by 20% (P<0.05) and 26% (P<0.01), respectively. Interval training at Vth also significantly increased maximal O2 pulse (P<0.05) and maximal ventilation (P<0.01). A significant decrease in submaximal ventilation (P<0.05) and heart rate (P<0.01) was also noted. These results would suggest that for untrained elderly adults, an interval training programme at the intensity of Vth may be well-tolerated clinically and may significantly improve both maximal aerobic power and submaximal exercise tolerance.

Adaptation, Physiological↗

PubMed1998

Effects of medium- and long-chain triglycerides on sleep and thermoregulatory processes in neonates.

Sleep processes and body temperature regulation of neonates are never taken into account in the evaluation of nutrients, although these functions are implicated in the regulation of energy metabolism and are influenced by the nutritional state and its metabolic consequences. Medium-chain triglycerides (MCT) are currently used in paediatric units during the first weeks of because they are considered to be a rapid source of energy, easy to assimilate for growing premature infants, whose digestive function is immature. However, no study has described the thermic effect of these nutrients on body temperature regulation and sleep. The present study aimed at analysing the influence of three feeding formulas with different content of MCT on sleep processes and on thermoregulation of neonates fed until desired intake was reached. Whatever the thermal conditions (thermal equilibrium or cool environment), the MCT-fed groups had higher body temperatures and than groups fed without MCT, for whom total sleep time was reduced at thermal equilibrium. In this group, the large amount of quiet sleep seems to favour a strategy of conserving energy. Higher energy expenditure in MCT-fed groups is not harmful to growth rate since nutritional efficiency is even better reflected by a larger body mass gain. The thermic effect of MCT contributes to lessening the vulnerability of neonates exposed to low incubator temperatures.

Body Mass Index↗

PubMed1998

Determination of diffusing capacity by modeling the dynamics of C18O uptake in newborns.

Dynamic modeling of lung C18O diffusion is used to measure the C18O transfer factor (TLCO) of 14 newborns aged 1-4 mo. The model equation is based on the alveolar fractions of C18O and on changing alveolar ventilation induced by the rebreathing conditions. The model does not involve the volume of the rebreathing bag which is usually needed when applying rebreathing technique and which is a source of error. The equation is discretized and solved for recorded data obtained with equipment adapted to use in newborns. A least-square parameter calculation technique is applied to estimate TLCO. Results show a strong relationship between this index and the biometrical ones and confirm those found in the literature featuring that the measurement duration can be considerably shortened.

Analysis of Variance↗

PubMed1997

Consequences of a small decrease of air temperature from thermal equilibrium on thermoregulation in sleeping neonates.

A new heating unit (servocontrolled skin temperature derivative system) has been designed to control the thermal environment in closed incubators. This type of control acts to attain and closely maintain a thermal equilibrium between a neonate's skin temperature and the environment. The present study aims to discover if thermal equilibrium is located within a thermoneutral range defined from oxygen consumption VO2 and body temperature, and whether it is more appropriate to define an optimal thermal environment. As regards VO2 and body temperature, results show that the air temperature reached at thermal equilibrium fulfils the definition of thermoneutrality. According to these criteria, a small decrease (1:5 degrees C) from thermal equilibrium also provides a near thermoneutral environment to the neonate but induces sleep disturbances and an increase in body movements. These two additional parameters delineate a narrower thermoneutral zone than does minimal metabolic rate because VO2 can stay constant even when air and body temperatures decrease. The results suggest that thermal equilibrium might be assimilated with a thermal comfort zone.

Automation↗

PubMed1997

Skin derivative control of thermal environment in a closed incubator.

Defining a thermoneutral environment remains difficult because thermoneutrality depends on both physical and physiological factors. A servocontrolled skin temperature derivative (SCS) heating device has been designed to control the thermal environment in closed incubators without the necessity of setting an air or skin reference temperature. The thermal environment obtained with the SCS program is controlled only by the neonate's skin temperature changes. For each neonate, the program allows the attainment of a specific individual thermal equilibrium (Teq). Although the mean value of the thermal equilibrium level measured on 29 neonates does not differ significantly from the neutral air temperature defined from the charts of other researchers, individual values of Teq differed greatly among neonates of similar birthweight and postnatal age. When compared with on/off heating programs, the SCS system permits greater quiet sleep occurrence and seems to provide an optimal thermal environment. The results suggest that the skin temperature derivative heating program takes into account both the ambient and physiological factors affecting body temperature regulation of each neonate.

Automation↗

PubMed1997

A short-term poikilothermic period occurs just after paradoxical sleep onset in humans: characterization changes in sweating effector activity.

We examined the changes in sudorific effector activity in five healthy young (21-23 y) subjects just before, during and just after successive paradoxical sleep (PS) phases. Local sweat rates were evaluated minute by minute over the chest (mcs). Previous observations, showing that mcs levels dropped before paradoxical sleep onset was electrophysiologically scored, were confirmed. At the end of this period of mcs depression, which in the present study coincided with paradoxical sleep onset, we show for the first time a short period (3-7 min) (period I) during which sweat production completely disappeared. A second period then followed (period II), at the very beginning of which mcs was re-elicited and thereafter increased in close correlation with paradoxical sleep duration. During period II, the remaining inhibiting influences (maximal during period I) and their releases could be specified by the successive valleys (indicating mcs inhibition) and peaks (indicating release of the mcs inhibition) drawn by the minute by minute mcs changes. These inhibitions became weaker as paradoxical sleep advanced. Given the strategic position of period I (at paradoxical sleep onset) and the total mcs abolition therein observed, it may be assumed that this poikilothermic state is the re-emergence of the 'ancestral' mode of body temperature regulation. From a thermophysiological point of view, period II may be considered as more 'modern' and directly related to the extension of paradoxical sleep in humans. This extension could be underlain by the unique development of our cognitive and/or learning functions.

Adult↗

PubMed1997

Detection of benzo[a]pyrene-DNA adducts in human placenta and umbilical cord blood.

Placenta constitutes a vital organ of exchange between mother and foetus. In addition to this favourable effect for foetal development, placenta indirectly may allow transfer of several maternal blood xenobiotics. Human placenta and umbilical cord blood are interesting models for investigating maternal environment and the metabolism, the bioactivation and the transfer of carcinogens such as polycyclic aromatic hydrocarbons. We used them to assess the effect of a woman's smoking on the foetus. Few studies cover this subject. In pregnant women who have continued to smoke, benzo[a]pyrene compound of cigarette smoke is metabolically activated to diol-epoxide derivative: benzo[a]pyrene-trans-7,8-dihydrodiol-9,10-epoxide, ultimate carcinogen (BPDE-I). This derivative is covalently fixed on DNA and gives BPDE-I-DNA adducts. By a competitive immunoassay technique, we determined BDPE-I-DNA adducts in 20 samples of placenta and umbilical cord blood from women who smoked (n = 15) and who did not (n = 10). Tobacco consumption was checked by urinary cotinine determination. In the group of smokers levels of adducts were found in 13 specimens of placenta (from 10 to 60 fmol/50 micrograms of DNA) and 12 umbilical cord blood (from 10 to 22.15 fmol/50 micrograms of DNA) samples. These results indicate that a mother's tobacco consumption is linked to the accumulation of BPDE-I-DNA adducts in the placenta, which are seen in smaller quantities in the umbilical cord blood, probably because of the metabolic capacity of the placenta and the transfer of B[a]P from the mother to the foetus.

Adolescent↗

PubMed1997

Neutral temperature range in incubators: performance of equipment in current use and new developments.

Low-birth-weight neonates should be nursed at thermoneutrality inside incubators. Thermoneutrality control is essential to enhance body growth and to reduce neonatal illnesses and mortality. Guidelines have been published to provide the thermoneutral range, but the recommendations did not always take into account all ambient and physiological parameters influencing thermoneutrality. In most marketed incubators, the heat supply is controlled through convective air flow (closed incubators) or through radiant power density (radiant warmer beds). The heating unit (on/off cycling or adjustable proportional control) is activated by an error signal calculated from the difference between a controlled temperature and a reference value preset by the clinician. The controlled variable can be either the incubator air or the skin temperature of the anterior abdominal region of the neonate. The neonate's size, thermal properties of the mattress and of incubator walls, air temperature and humidity, air velocity, incubator wall temperatures all influence the heat exchanges between the neonate and the surroundings, and, consequently, modify the obtention of thermoneutrality. Moreover, studies of the physiological mechanisms by which the neonate regulates body heat storage suggest that metabolic rate, behavior, vigilance level, nursing care, and heater control processes should also be taken into account. Little attention has been paid to these factors, and incubator performances are often disappointing. This article reviews the different factors that modify thermoneutral condition. An attempt is made to suggest new ways to design equipment incorporating these factors in algorithms controlling heater processes in order to reach the optimal thermal environment in which the neonate should be nursed.

Air↗

PubMed1996

[Evolution of the result of respiratory function studies in children with bronchopulmonary dysplasia].

BACKGROUND: Reports of short- and medium-term evolution of Lung Function Tests (LFT) in infants with bronchopulmonary dysplasia (BPD) are still scarce. POPULATION AND METHODS: The results of the first (before 3 months of corrected age) and the second (between 3 and 9 months of corrected age) LFT in 22 premature infants with BPD (gestational age 31 +/- 2.5 weeks; birth weight: 1570 +/- 440 g; duration of mechanical ventilation: 46 +/- 24 days, total duration of oxygen therapy: 88 +/- 47 days) were compared to those obtained in 27 normal infants for the first LEF and 10 normal infants for the second LFT, similar to the patients for birth weight and corporeal index (CI). RESULTS: In the first LFT, major abnormalities were an increased thoracic gaz volume (TGV) (16.5 +/- 42 vs 122 +/- 24 mL; P < 0.001) and TGV CI ratio (1.25 +/- 0.31 vs 0.89 +/- 0.17 ml/kg/m2; P < 0.0001) a decreased pulmonary compliance (2.49 +/- 1.46 vs 11.60 +/- 4.50 mL/cmH2O; P < 0.0001) and specific pulmonary compliance (0.015 +/- 0.10 vs 0.100 +/- 0.042 mL/cmH2O/mL de TGV; P < 0.0001), an increased total pulmonary resistance (20.4 +/- 12.1 vs 10.5 +/- 5.3 cmH2O/L/s; P < 0.001). In the second LFT, an increased TGV (235 +/- 62 vs 166 +/- 28 mL; P < 0.01) and TGV CI ratio (1.64 +/- 0.65 vs 0.98 +/- 0.11 ml/kg/m2; P < 0.05), a decreased pulmonary compliance (2.68 +/- 2.0 vs 15.2 +/- 5.7 mL/cmH2O; P < 0.0001) and specific pulmonary compliance (0.013 +/- 0.010 vs 0.106 +/- 0.050 mL/cmH2O/mL de TGV; P < 0.0001), an increased total pulmonary resistance (17.1 +/- 9.6 vs 8.6 +/- 4.9 cmH2O/L/s; P < 0.05) were noted when compared with the control group results. Major abnormalities of the blood gases were hypoxemia (63 +/- 10 vs 85 +/- 20 mmHg; P < 0.05), hypercapnia (38.5 vs 31 +/- 4 mmHg; P < 0.0001) during the first LFT. Hypoxemia (77 +/- 14 vs 90 +/- 14 mmHg and hypercapnia (37 +/- 4 vs 29 +/- 5 mmHg) continued in the second LFT. Thoracic distention and total pulmonary resistances in infants with BPD did not improve but their pulmonary compliance (P < 0.0001) and PaO2 (P < 0.01) between the first and second LFT did it. Infants who had been ventilated for a hyaline membrane disease (HMD) were more hypoxic on the second LFT (P < 0.05) than those who had been ventilated for other causes. Statistically significant relationships were found between thoracic distention and duration of positive inspiratory pressure (P < 0.05; r = 0.43), duration of positive expiratory pressure (P < 0.05, r = 0.45) total oxygen therapy duration; between total pulmonary resistance and duration of mechanical ventilation with high frequency (P < 0.05; r = 0.52); between hypoxemia and duration of oxygen therapy with FiO2 > or = 60% (P < 0.05; r = 0.54). CONCLUSIONS: This study shows prolonged clinical and functional abnormalities of the respiratory functions requiring longer follow-up.

Blood Gas Analysis↗

PubMed1996

Body temperature regulation in the newborn infant: interaction with sleep and clinical implications.

Thermoregulation in newborn infant differs from that of adult. Comparisons between sleep stages show that, during rapid eye movements (REM) sleep, the impairment of thermoregulatory responses in adult is not observed in newborn. Both behavioral and autonomic temperature regulations are always operative in the range of air temperatures usually imposed. The interaction between sleep and thermoregulation seems to be less important in newborns than in adults, suggesting that sleep processes are well protected, reducing the probability of occurrence of central dysfunction. According to the model describing thermoregulation during sleep on the basis of changes in the hierarchical dominance of brain structures, either the influence of diencephalic structures is never depressed in REM sleep or the functional autonomy of the rhombencephalon is still relevant in the immature encephalon of the newborn. The thermoregulatory model also allows understanding of inter-individual differences in thermoregulation and levels of thermoneutrality. An attempt has also been made to learn the role of heat stroke in the production of sudden infant death syndrome when body heat loss is hampered.

Adaptation, Physiological↗