[Atopic dermatitis aggravates the allergic airways inflammation in acute viral bronchiolitis]. / La dermatite atopique aggrave l'inflammation allergique dans la bronchiolite aiguë virale.

INTRODUCTION: Exhaled nitric oxide (FeNO) is a putative non-invasive marker of eosinophilic airway inflammation with a good predictive value for allergic asthma in preschool children. The aim of the present study was to compare FeNO after acute viral bronchiolitis (AVB) in children aged less than 2 years without atopic dermatitis (AD) vs those with atopic dermatitis, as well as children with AD without any history of AVB. METHODS: Forty-two children (mean age +/- SD: 12.3 +/- 5.2 months; range 5.0-23.5; sex-ratio M: F=1.3: 1) were included in this prospective study, > 8 wks after an episode of AVB. The patients' atopic status was assessed both by clinical phenotype and IgE- mediated response to inhaled and/or food allergens. FeNO (ppb) was measured off-line by the chemoluminescence method on samples obtained from gas collected in a balloon during tidal breathing. RESULTS: There was a significant difference between the AVB/AD (23.4 +/- 14.3 ppb, n=15) vs the AVB without AD group (13.5 +/- 10. 1 ppb, n=13) or the AD without AVB group (11.0 +/- 8.3 ppb, n=14). Maternal feeding for more than 2 months decreased FeNO by 50%. CONCLUSION: Atopic children below 2 years with AD produce more NO after AVB than non-atopic children or atopic children without any history of AVB. Maternal feeding decreases FeNO.

Effects of inspiratory flow rate alterations on gas exchange during mechanical ventilation in normal lungs. Efficiency of end-inspiratory pause.

The influence of inspiratory flow rate (TI), without changing respiratory frequency, tidal volume, and FIO2, was investigated in 11 normal lungs in patients undergoing mechanical ventilation because of central respiratory failure due to stable coma. The patients were anesthetized and paralyzed. They first received a conventional ventilation (TI = 25 percent, pause = 10 percent) and then, were submitted to four different TI values, randomly administered without any end-inspiratory pause (EIP) (TI = 20 percent; TI = 33 percent; TI = 50 percent; TI = 67 percent). In the middle and at the end of the procedure, a return to basal conditions was introduced. At each ventilator setting, the following were obtained: respiratory flow (Pneumotachograph Fleish No. 2), airway pressure, FRC changes (inductive plethysmography), arterial and mixed venous blood gases, hemodynamic data, and VA/Q ratios distribution using multiple inert gases technique. EIP suppression provides a significant increase in VA/Q mismatch (until TI = 50 percent) and in shunt effect (between 3 and 9 percent of cardiac output [QT]). The absence of simultaneous PaO2 change is due to increasing PVO2 linked to a higher QT. The shorter the TI, the higher the PaCO2 connected with a relative alveolar hypoventilation. However, increasing TI without EIP significantly decreases ventilation distribution inequalities. This improvement is concomitant with a rise in FRC (FRC67-FRC20 = 0.340 +/- 0.450, p < 0.05) without any change in other variables or auto-PEEP production. In summary, in subjects with very slight mechanical lung impairment (peak inspiratory pressure = 20.5 +/- 5.3 cm H2O at TI = 20 percent and 15.2 +/- 3.3 cm H2O at TI = 67 percent), this study confirms the deleterious effect of EIP suppression and TI decrease. One can compensate for this effect of EIP absence by increasing TI as soon as it reaches TI = 67 percent, ie, inverse ratio ventilation.

Adjustments in oxygen transport during head-out immersion in water at different temperatures.

Respiratory gas exchange was investigated in human subjects immersed up to the shoulders in water at different temperatures (Tw = 25, 34, and 40 degrees C). Cardiac output (Qc) and pulmonary tissue volume (Vti) were measured by a rebreathing technique with the inert gas Freon 22, and O2 consumption (VO2) was determined by the closed-circuit technique. Arterial blood gases (PaO2, PaCO2) were analyzed by a micromethod, and alveolar gas (PAO2) was analyzed during quiet breathing with a mass spectrometer. The findings were as follows. 1) Immersion in a cold bath had no significant effect on Qc compared with the value measured at Tw = 34 degrees C, whereas immersion in a hot bath led to a considerable increase in Qc. Vti was not affected by immersion at any of the temperatures tested. 2) A large rise in metabolic rate VO2 was only observed at Tw = 25 degrees C (P less than 0.001). 3) Arterial blood gases were not significantly affected by immersion, whatever the water temperature. 4) O2 transport during immersion is affected by two main factors: hydrostatic pressure and temperature. Above neutral temperature, O2 transport is improved because of the marked increase in Qc resulting from the combined actions of hydrostatic counter pressure and body heating. Below neutral temperature, O2 transport is altered; an increase in O2 extraction of the tissue is even calculated.

EMG study of respiratory muscles in humans immersed at different water temperatures.

The electromyograms of the rectus abdominis (EMGra) and of the diaphragm (EMGdi) have been recorded on human subjects immersed at two bath temperatures (TW), 25 and 40 degrees C. The recordings were obtained during a calibrated isometric contraction sustained for 20 s against a closed stopcock at functional residual capacity (FRC) level for EMGra (expiratory effort) and at pulmonary volume greater than 90% vital capacity for EMGdi and EMGra (inspiratory effort). After eliminating the electrocardiographic artifact, the EMG signal was processed to obtain its root-mean-square (rms) value and three parameters of its frequency spectrum, total energy (Etot), centroid frequency (fc), and high-to-low ratio (H/L). The results show that EMGdi is not modified by TW. On the other hand rms and Etot of EMGra are always increased at TW = 25 degrees C compared with TW = 40 degrees C, whereas fc and H/L decrease with temperature during the expiratory effort at FRC level but do not vary during inspiratory effort at high pulmonary volume. These results, compared with those previously published for cooled limb muscles, show that TW can elicit EMG alterations on the superficial respiratory muscles through two mechanisms, an intrinsic mechanism due to the local variation in muscle temperature and an extrinsic mechanism acting upon the control system of the muscle contraction. Linked alterations of the muscular mechanical activity probably account for the observed effects of TW on the statics and the dynamics of the pulmonary volumes.

Solubility of Freon 22 in human blood and lung tissue.

The solubility of Freon 22 in human blood and lung tissue was determined using the chromatographic method of Wagner et al. (J. Appl. Physiol. 36: 600-605, 1974). In normal human blood, the mean Bunsen coefficient of solubility (alpha B) was 0.804 cm3 STPD.cm-3.ATA-1 at 37 degrees C. It increased with hematocrit (Hct) according to the equation alpha B = 0.274 Hct + 0.691. Tissue homogenates were prepared from macroscopically normal lung pieces obtained at thoracotomy from eight patients undergoing resection for lung carcinoma. The Bunsen solubility coefficients were 0.537 +/- 0.068 and 0.635 +/- 0.091 in washed and unwashed lung, respectively. These values can be used in the determination of both cardiac output and pulmonary tissue volume in humans by use of the rebreathing technique.

Pulmonary mechanics in ventilated preterm infants with respiratory distress syndrome after exogenous surfactant administration: a comparison between two surfactant preparations.

The effects of two surfactant preparations on lung mechanics have been studied on 24 ventilated premature infants with respiratory distress syndrome (RDS): 13 were given artificial surfactant (Exosurf Neonatal, Burroughs-Wellcome) and 11 natural porcine surfactant (Curosurf, Laboratoire Serono France). Measurements of respiratory system compliance (Cdyn, Crs) and resistance (Rrs) were performed immediately before surfactant administration and repeated 6, 18, 24, 48, and 72 hours later. With Exosurf treatment, 6 hours after surfactant administration inhaled O2 concentration (FlO2) could be lowered from (0.72 +/- 0.20, to 0.62 +/- 0.33; P < 0.05), whereas Crs did not change (0.37 mL/cmH2O/kg, +/- 0.14 vs. 0.39 +/- 0.12, NS). After 24 hours and during the following days a significant increase in Crs occurred (24 hours post-Exosurf: 0.51 +/- 0.18, P < 0.05). With Curosurf treatment, the improvement in oxygenation was greater and FlO2 could be lowered much more after 6 hours (from FlO2, 0.78 +/- 0.23 to 0.34 +/- 0.11, P < 0.01). This was associated with an increase in Crs (from 0.39 +/- 0.09 to 0.59 +/- 0.17, P < 0.05). During the following days, Crs was significantly higher in the group treated with Curosurf. Resistance was not altered by the type of surfactant preparation used except after 72 hours, when Rrs increased in the group treated with Exosurf. In conclusion, Curosurf appears to be more effective than Exosurf with regard to immediate pulmonary changes in ventilator treated premature infants with RDS. A rapid increase in Crs after Curosurf treatment indicates that recruitment of new functional areas of the lung is likely to be associated with a stabilization of small airways and alveolar units.

Optimal pressure support level for beginning weaning in patients with COPD: measurement of diaphragmatic activity with step-by-step decreasing pressure support level.

PURPOSE: The study objective was to determine an "optimal" individual pressure support (PS) level for beginning weaning with PS ventilation in patients with chronic obstructive pulmonary disease (COPD). MATERIALS AND METHODS: Eleven COPD patients intubated and ventilated for acute respiratory failure and judged ready for weaning were studied. The technique consisted of lowering the PS level from a point that was characteristic for each patient and measurable under controlled mechanical ventilation, after setting the ventilator as recommended for COPD patients judged ready for weaning, that is, peak inflation pressure (PIP). This determination was based mainly on exploring the diaphragm with an electromyographic technique by defining the optimal PS level as the lowest PS level associated with no EMG evidence of diaphragmatic stress. Diaphragmatic electromyographic activity (diEMG) was recorded by a bipolar esophageal electrode (Disa-Denmark), and the high-frequency electrical component/low-frequency ratio (H/L) was calculated. The reference H/L was determined during a few spontaneous ventilatory cycles. Muscle stress was defined as a greater than 20% reduction in H/L compared with the reference value. RESULTS: Optimal PS levels ranged from 4 to 24 cm H2O with a mean of 14+/-6 cm H2O. Two patients with optimal PS level at 4 cm H2O did not require weaning and were quickly extubated. For the nine other patients, optimal PS levels were found to be 70% of PIP; in none was it necessary during weaning to use PS levels higher than individual optimal PS levels. CONCLUSIONS: Optimal PS level established with diEMG monitoring seems to be a useful index for beginning weaning in the PS ventilation mode in COPD patients. The hypothesis of beginning weaning with a PS level equal to 70% of PIP needs to be tested.

Effects of water temperature on pulmonary volumes in immersed human subjects.

Pulmonary volumes and capacities have been measured at three water temperatures (Tw = 25, 34, 40 degrees C) in standing subjects immersed up to the shoulders. The comparison of data obtained in air with those obtained in thermoneutral immersion (Tw = 34 degrees C) confirms the results previously published in several studies. The comparison of data obtained in immersion at different Tw shows: 1. A significant decrease in vital capacity (VC) with bath temperature (VC 40 degrees C greater than VC 34 degrees C greater than VC 25 degrees C). The same decrease is observed in the inspiratory reserve volume (IRV) while the expiratory reserve volume (ERV), the residual volume (RV) and the functional residual capacity (FRC) do not vary. 2. A significant decrease in maximum breathing capacity (MBC) with bath temperature (MBC 40 degrees C greater than MBC 25 degrees C). 3. A significant increase in tidal volume (VT) in cold or hot water compared to thermoneutral water (VT40 degrees C greater than VT34 degrees C; VT34 degrees C less than VT25 degrees C) during quiet breathing. Breathing frequency does not change, thus ventilation (V) follows the same evolution as VT. The relative abdominal (ABD) contribution to VT, estimated by a double belt inductance plethysmograph, is reduced at Tw = 25 degrees C but unchanged at Tw = 40 degrees C compared to thermoneutral bath. Beside variations in the metabolic state, the variations of the pulmonary volumes as a function of Tw are estimated to be mainly due to alterations in respiratory muscles functioning.

Pulmonary capillary blood volume during immersion in water at different temperatures.

Pulmonary capillary blood volume (Qc) was determined for 7 subjects in the standing posture and immersed up to the sternal manubrium at three water temperatures: 34 degrees C +/- 0.5 degrees C, thermally neutral bath; 25 degrees C +/- 0.5 degrees C, cold bath; and 40 degrees C +/- 0.5 degrees C, hot bath. The Qc was calculated from the lung transfer factor DLco measured while breathing two gas mixtures (21.1% O2 and 90.0% O2) during breath holding. Control experiments in a dry air environment show that Qc values for standing posture decrease compared to the sitting values, owing to a redistribution of the intrathoracic blood volume to lower body parts as a result of gravity. Immersion at 34 degrees C in an upright position produces a significant increase in Qc (P less than 0.01). This is a result of the hydrostatic counterpressure: blood shifts from the periphery to the intrathoracic regions. Immersion at 25 degrees C increases Qc compared to the values obtained at 34 degrees C, but the difference is not significant. The contribution of vasoconstriction to blood volume shift in cold water is probably less important than that of hydrostatic counterpressure. During immersion at 40 degrees C, the rise in Qc is very significant (P less than 0.05). This may be explained by an increase in cardiac output and central blood volume when skin temperature is raised at 40 degrees C.

[Alveolar pressure during forced vital capacity. Method and application (author's transl)]. / Pression alvéolaire pendant la capacité vitale forcée. Méthode et application.

A method allowing the measurement of mean alveolar pressure (Palv) during forced vital capacity is described. The basis of the method is the calculation of the difference between mouth and chest flows, which are measured with a Fleisch pneumotachograph (PTG) and a volumetric plethysmograph respectively. Metrologic conditions of the calculation are discussed. During the forced expiration, the estimation of Palv is realized in good metrological conditions. During inspiration, the thermal condition of the PTG varies and the measured flow is not accurate; thus, the calculated Palv is only an estimation. Some examples of Palv vs mouth flow loops are shown. The simultaneous recordings of this loop and the usual V/V loop allow us to know if a low mouth flow is due to a high pulmonary impedance with high Palv or to a low Palv. For a given impedance, Palv measurement seems to be a good test of the respiratory muscle function.

Postprandial thermogenesis and hormonal release in lean and obese subjects.

One group of 10 obese people (1.72 times normal weight) was compared to a control group of 9 normal-weight subjects. Oxygen consumption (VO2), immuno reactive growth hormone (IRGH), and rectal temperature (Tre) were measured every 15 min on an average, during the 5 h following a protein meal composed of 6 egg-whites and 50 g of casein totaling 1 340 kJ. The results show that postprandial thermogenesis (PPT) is the same in both groups: maximum increase in VO2 averages 15% in the obese and 16% in the control groups respectively. Energy expenditure integrated over the 5 h was 129 kJ for the obese and 114 kJ for the control subjects, i.e. 9.6% and 8.5% of the energy meal content. The rise in Tre was identical for both groups (0.4 degrees C over 3 h). For IRGH, the preprandial reference figures were much lower in the obese: 52 pmole.dm-3, as compared to 145 pmole.dm-3. In all control subjects, the protein meal resulted in a IRGH peak of, on average, 455 pmole.dm-3 about 2 h after. This was not observed in 4 of the obese subjects, while in the remaining 6, the mean peak value was 165 pmole.dm-3, occurring after 1 h. The other hormonal or chemical compound simultaneously analysed (glucagon, cortisol, PRL, T3, glucose, lactate, NEFA) do not show any significant variations but insulin blood level for which a postprandial increase was measured in both groups. It is concluded that after a protein test meal: PPT in overweight people is no different from that in people of normal weight.(ABSTRACT TRUNCATED AT 250 WORDS)

Respiratory muscle function in trained and untrained adolescents during short-term high intensity exercise.

The breathing pattern and respiratory muscle function were investigated in ten trained and ten untrained adolescents (aged 15-16 years) while undergoing an incremental intensity exercise test on a cycle ergometer up to 80% maximal oxygen consumption (VO2max), maintained to exhaustion. Before and after exercise, maximal inspiratory (PImax) and expiratory (PEmax) pressures were measured at residual volume and total lung capacity, respectively. During exercise, the breathing pattern [tidal volume (VT), respiratory frequency (fR), ventilation] and the relative contribution of ribcage and abdomen to VT were assessed using inductance plethysmography. Electromyographic activities of transversus abdominis (EMGtr) and diaphragm (EMGdi) muscles were recorded and analysed during exercise. There was a difference in the change in the pattern of breathing between the trained and the untrained group; fR increased significantly (P < 0.05) at 40% VO2max for the untrained group. Before exercise there was no difference in the maximal respiratory pressures. Up to 60% and 80% VO2max, transversus abdominis and diaphragm muscle activity increased significantly in the trained adolescents. However in this group, no evidence of respiratory muscle fatigue appeared: PImax, PEmax and the frequency spectrum of EMGtr and EMGdi were not altered by exercise up to exhaustion. In the untrained group, who had high ventilatory responses, expiratory muscle function was unchanged at the end of the exercise, but signs of inspiratory muscle fatigue appeared in that PImax was significantly decreased after exercise.

Expiratory muscles and exercise limitation in patients with chronic obstructive pulmonary disease.

The aim of this study was to estimate, in patients with chronic obstructive pulmonary disease (COPD), the maximal strength of the expiratory muscles, its correlation with exercise performance and the effects of a specific physiotherapy. In 38 COPD men, aged 54 +/- 7 years, pulmonary function data, maximal alveolar pressure (Palv, max) developed during forced vital capacity, were measured using a whole-body plethysmograph and the maximal tolerated power (MTP), i.e. the highest power maintained for at least 3 min, was determined by a progressive test on a treadmill. Airway obstruction was severe (FEV1/FVC: 54 +/- 10%), Palv, max was lower than normal (74 +/- 36 vs. 130 +/- 48 hPa in 20 healthy men of the same age; p less than 0.01) and increased with airway resistance values (Raw); mean MTP was low: 115 +/- 30 W and individual values were inversely related to Raw values. Then, two subgroups of 14 patients were chosen at random. One subgroup received an abdominal muscle physiotherapy during 3 weeks. The other subgroup only received usual medical treatment. No modification in any parameter was found in the second subgroup. Specific physiotherapy of abdominal muscles improves significantly both Palv, max (118 +/- 45 hPa) and MTP (171 +/- 38 W; p less than 0.01), without any variation in other respiratory function parameters. We conclude that abdominal muscle weakness is common in COPD patients and can participate in the limitation in exercise performance. Specific physiotherapy increases abdominal muscle strength and seems to improve exercise tolerance by a still unexplained mechanism.

Early respiratory system mechanics and the prediction of chronic lung disease in ventilated preterm neonates requiring surfactant treatment.

The objective of this study was to evaluate the predictive value of the respiratory system compliance (Crs) and resistance (Rrs) measured before surfactant therapy to identify infants at risk for chronic lung disease (CLD). Measurements of Crs and Rrs were obtained on 44 ventilated neonates with respiratory distress syndrome (RDS) before and after surfactant therapy using the passive expiratory flow-volume method. It was found that in addition to a lower gestational age (GA) and a lower birth weight (BW), infants with CLD (n = 10) exhibited a lower Pa/AO(2) [Pa/AO(2) = PaO(2)/(PiO(2) - PaCO(2))] and higher Rrs before surfactant compared to the infants without CLD (n = 28). Improvement in gas exchange 18 h after surfactant was reduced in the CLD group. Finally, we concluded that a low GA (< 28 weeks), a low BW (< 942 g), a low Pa/AO(2) before and 18 h after surfactant or a high Rrs before surfactant (>0.21 cm H(2)O/ml/s) were associated with an increased risk of CLD.

Respiratory mechanics before and after late artificial surfactant rescue.

OBJECTIVE: To assess the effect of late administration of synthetic surfactant (Exosurf) on the ventilatory function of premature infants with hyaline membrane disease (HMD). METHODOLOGY: Prospective non-randomized study in the Neonatal Intensive Care Unit (NICU) of a major referral hospital. The patients included two groups of premature infants with a birthweight between 750 and 2000 g who developed HMD. In group 1 with moderate to severe HMD, 2 x 5 mL/kg doses of Exosurf were given 12 h apart (first dose given at a mean age of 18.7 +/- 3.4 h [mean +/- s.e.m.]). In group 2 with milder HMD, no surfactant was given. RESULTS: Significant reductions (P < 0.05) in the fraction of inspired oxygen (FIO2) occurred 6 h after surfactant administration (24 h of life) and by 48 h (64 h of life) in group 2. These improvements in gas exchange preceded improvements in passive respiratory compliance which occurred 24 h after surfactant (42 h of life) and by 72 h (88 h of life) in group 2 (P < 0.01). In both groups pulmonary resistance increased and was significant (P < 0.05) by 48 h (66 h of life) in group 1. CONCLUSIONS: Synthetic surfactant given as late as a mean age 18.7 +/- 3.4 h still improves gas exchange but these early improvements cannot be completely explained by modifications of respiratory compliance.