Search PubMed⌕ Search

Biomedical subjects

H Guenard

Publications and source records attributed to H Guenard.

At least 19 recordsLinked to original sources
PubMed1999

Reduction of exercise-induced asthma in children by short, repeated warm ups.

AIM: To study the effect of a warm up schedule on exercise-induced asthma in asthmatic children to enable them to engage in asthmogenic activities. METHOD: In the first study, peak flows during and after three short, repeated warm up schedules (SRWU 1, 2, and 3), identical in form but differing in intensity, were compared in 16 asthmatic children. In the second study the efficiency of the best of these SRWU schedules was tested on 30 young asthmatic children. Children performed on different days a 7 minute run alone (EX1) or the same run after an SRWU (EX2). RESULTS: The second study showed that for most children (24/30) the fall in peak flow after EX2 was less than that after EX1. The percentage fall in peak flow after EX2 was significantly correlated with the percentage change in peak flow induced by SRWU2 (r = 0.68). The children were divided into three subgroups according to the change in peak flow after SRWU2: (G1: increase in peak flow; G2: < 15% fall in peak flow; G3: > 15% fall in peak flow). Only the children in the G3 subgroup did not show any gain in peak flow after EX2 compared with EX1. CONCLUSION: The alteration in peak flow at the end of the SRWU period was a good predictor of the occurrence of bronchoconstriction after EX2. An SRWU reduced the decrease in peak flow for most of the children (24/30) in this series, thus reducing subsequent post-exercise deep bronchoconstriction.

Adolescent↗
PubMed1998

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.

Aged↗
PubMed1998

[Respiration and aging].

Pulmonary aging is a term used to designate age-related alterations in pulmonary function. In includes both respiratory functions (ventilatory mechanics, gas exchange) and non-respiratory functions (immunity) of the lung. The age-related decline in respiratory function is not linear. Generally after 70 years, PaO2 no longer declines and, in elderly men, the FEV1/FVC ratio remains stable. Because of the wide variability of reference values, caution should be taken in interpreting changes in ventilatory mechanics (e.g. spirometry) in elderly people.

Aged↗
PubMed1995

Effect of nitric oxide on in vitro responsiveness of bovine bronchus and pulmonary vessels.

Experiments were conducted in bovine isolated bronchi and pulmonary vessels to test whether nitric oxide (NO) could reduce carbachol and hypoxia or KCl (120 mM) induced contraction. Segments of bronchus or pulmonary vessels were slipped around a water-filled balloon connected to a pressure transducer, and mounted in 3 ml thermostated chamber filled with Krebs-Henseleit solution equilibrated with different gas mixtures. NO-CO2-N2 mixtures containing 10, 50 or 100 ppm NO were prepared. The effect of methylene blue on intrinsic tone and the bias effect of residual red blood cells were assessed. The results demonstrate that NO has no obvious effect on the intrinsic tone, the force generated by carbachol stimulation, or the spontaneous relaxation after removal of carbachol, in bronchi, with the exception of 100 ppm which increased the relaxing rate in small bronchi. By contrast, 50 and 100 ppm NO caused 53 and 61% decrease in the hypoxia-induced pulmonary arterial contraction, respectively. One hundred ppm NO caused 40, 38, 50 and 66% decrease in the KCl-induced contraction in pulmonary artery (PA), small pulmonary artery (SPA), small pulmonary vein (SPV) and pulmonary vein (PV), respectively. Sodium nitroprusside (10(-5) M) and isoproterenol (10(-5) M) reduced the carbachol-induced increase in bronchial pressure by 80% and nearly 100%, respectively. The residual concentration of haemoglobin in the chamber cannot explain the lack of effect of NO on the bronchi.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Variations in flows and pressures during jet ventilation in the infant: a model study.

Ventilatory flow rates with either He-O2 (heliox) or N2-O2 (nitrox) mixtures during high frequency jet ventilation (HFJV) were calculated using a mathematical model, and were measured in a physical monoalveolar model of the infant lung. A constant flow was delivered to the model (Vd) drawing with it an entrained flow (Ve). When the inspiratory time (Tl) was long, a back flow (Vr) was generated that increased progressively as the alveolar pressure increased. In order to reduce Vr, the reflux time (Tr), i.e., the time needed for the injected gas to reflux, was measured (Trm) and calculated (Trc) with the model. The Tr depends on both chest-lung compliance and resistance to reflux as well as on the Ve/Vd ratio. For a given setting of the ventilator, values of Trm and Trc were significantly lower with heliox than nitrox (P < 0.01), and the correlation between Trm and Trc were fair with both gases. Tidal volume (VT) was calculated when the Tl was interrupted at Tr. The values of VT were significantly higher with helix than nitrox (P < 0.05). It is concluded that the evaluation of Tr during HFJV may provide useful information for setting the ventilator.

Airway Resistance↗
PubMed1994

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.

Airway Resistance↗
PubMed1994

Is proximal airway pressure a good reflection of peripheral airspace pressure in infants and children models under HFJV?

This experimental study was carried out to determine if an alveolar positive end-expiratory pressure (PEEP) could occur during high frequency jet ventilation (HFJV) in infants, and if tracheal pressure is a good estimation of alveolar pressure. We used physical models simulating a 1.5 kg premature (P), a 3 kg newborn (N) and a 6 kg child (C) with normal compliance and normal resistance. Moreover, in the N model, we used two different resistances and lung compliance heterogeneity was studied in the P model. Pressure was measured simultaneously in the tube simulating trachea (Paw) and in the bottle simulating the lung (Palv). HFJV was performed either via an endotracheal tube (ETT) or via a long catheter as in laryngoscopy. The ratio of injection time upon cycle duration (Ti/Ttot) was 20% or 30%, jet frequency was altered from 150 to 300 min-1 and the driving pressure was set as in clinical practice (0.5 and 0.6 bar). PEEP occurred mainly in N (1.1 to 3.2 cm H2O) and C models (0 to 3.5 cm H2O). It was inversely related to expiratory time (Te). The end-expiratory pressure drop between Palv and Paw (delta EEP) was higher in N and increased from 0.5 to 2 cm H2O with the shortening of Te and with airway resistances, i.e. the presence of ETT. In the heterogeneous model, PEEP and delta EEP were greater in the higher compliance alveolus. This study shows that the end-expiratory Palv is underestimated by end-expiratory Paw.(ABSTRACT TRUNCATED AT 250 WORDS)

Air Pressure↗
PubMed1994

In vitro accuracy of three blood O2 saturation optic catheter systems.

OBJECTIVE: The measure of the precision and accuracy of three optic SvO2 systems in vitro (SAT-2 Baxter, oximetrix 3 Abbott, HEMOPRO-2 Spectramed in a wide range of saturations (24-85%) and hematocrit (20-40%). DESIGN: In vitro comparison of the results given by a Co-Oximeter and the SvO2 systems. MEASUREMENTS AND RESULTS: 144 blood samples were tonometered with a variety of gas mixtures. Measurements of SvO2 were compared to those obtained by means of a Co-Oximeter, the difference (dSO2) between paired values were calculated. Precision was evaluated from confidence intervals (2SD) and accuracy was tested using dSO2 figures. As there was no difference in either precision or accuracy among catheters for a given system, data obtained from a given system were pooled. Mean precision was 14.2%, 8.6%, 9% for the Spectramed, Baxter and Abbott systems, respectively. CONCLUSION: The rather low reliability of the optic method should be borne in mind in patients with low SvO2 and/or low hematocrit.

Analysis of Variance↗
PubMed1993

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.

Adolescent↗
PubMed1993

Helium-oxygen mixture in respiratory distress syndrome: a double-blind study.

In a randomized, controlled trial, the lungs of infants with respiratory distress syndrome were ventilated with either a helium-oxygen mixture or a nitrogen-oxygen mixture. In the helium-oxygen group, infants required a lower inspired oxygen concentration and a shorter duration of ventilation. There were also fewer deaths and fewer cases of bronchopulmonary dysplasia in the helium-oxygen group.

Airway Resistance↗
PubMed1993

Membrane diffusion of the lungs in patients with chronic renal failure.

Patients with chronic renal failure (CRF) and haemodialysis treatment usually have a reduced CO transfer factor. The aim of this study was to evaluate the effects of alveolar wall fibrosis and of anaemia on gas diffusion in the lungs. The NO and CO transfer factors of the lung (TLNO and TLCO) were measured, simultaneously, in 15 patients haemodialysed three times a week for 1-10 yrs. Assuming that NO is highly reactive with blood, Tlno is thus directly proportional to the membrane diffusion factor (DmCO). The lung capillary blood volume (Vc) was derived from the set of the two transfer equations. Transfer factors were measured between haemodialysis sessions. All patients but one were anaemic, with haemoglobin concentrations ranging 61-151 g.l-1. All had decreased Vc, and a decreased DmCO was observed in 14 patients. However, after correction for the anaemia, Vc values were normal with the exception of three patients. The percentage decrease in DmCO with respect to normal was correlated with the time elapsed since the first haemodialysis. These results support the idea of a progressive development of haemodialysis-induced chronic lung disease, that may be related to a mechanism of complement activation by a bio-incompatible membrane (Cuprophane). Accordingly, patients with compromised cardiopulmonary functions should be dialysed with a bio-compatible membrane.

Anemia↗
PubMed1992

Lung density and lung mass in emphysema.

Mean lung density (dm) and radiologic (VLx) lung volume can be calculated using CT scan data. As many emphysematous patients are overdistended, the analysis of dm alone could be meaningless. However, lung mass (m) can be calculated as the product of dm and VLx. Twenty-four patients suspected of mild or severe emphysema as judged by roentgenographic and physiologic examinations as well as 16 healthy subjects were included in the protocol. They all underwent both a CT scan of the whole lung and functional tests from which the following were derived: airway resistance, forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC), total lung capacity (TLC), CO transfer capacity, quasi-static compliance at functional residual capacity (FRC), and blood gases. All CT scans were performed at the FRC of each patient. The dm was lower in emphysema patients than in healthy subjects, as m was greater in patients than in healthy subjects; 1,303 +/- 398 g and 997 +/- 133 g, respectively. Although dm values were significantly correlated to FEV1, FEV1/FVC, and TLC, m values were not correlated to any of these functional indices. Unexpectedly, these results show that most patients (22/24) with emphysema have a normal or increased lung mass. Normal or above normal m values might be due to oversecretion in some patients. Nevertheless, the synthesis of new tissue due to chronic inflammation is the most likely explanation that could account for this finding.

Adult↗
PubMed1991

High frequency jet ventilation and upper tracheal stenosis: a model study.

A chest-lung model, consisting of a human laryngo-tracheo-bronchial tree cast (4 or 5 bronchial generations) tightly enclosed in a 100 l rigid box was used to assess the potential efficiency of high frequency jet ventilation in patients with upper tracheal stenosis. The elasticity of the air in the box stimulated normal adult chest-lung compliance. Diaphragms (0.5 or 1.5 cm thick) were inserted into the upper trachea to simulate stenoses of 0.7, 1, 1.5 and 1.75 cm inner diameter. A rigid injector-catheter (5 mm outside diameter) was directed in the axis of the trachea with its tip 2.5 cm beneath the stenosis. The end inspiratory alveolar pressure (PA), the end expiratory pressure (PEEP) and the tidal volume (VT) were measured at a rate of 100/min and 30% inspiratory to total periods ratio. Entrained flow, Vem, measured at the start of air insufflation, was compared to that calculated (Vec) from a simple model. For a given setting of the ventilator, PEEP, PA--PEEP and VT were approximately linearly related to the difference in diameters of stenosis and injector. While PEEP decreased, both PA--PEEP and VT increased with increasing diameter of stenosis. When the diameter of the stenosis was higher than 1.5 cm no changes in PA--PEEP and VT were observed, owing to the narrowest section of the larynx. Vec was always higher than Vem. The thickness of the stenosis did not affect the results, and the diameter of the stenosis appeared to be the main factor affecting the ventilatory parameters under our experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

High-Frequency Jet Ventilation↗
PubMed1990

Determination of lung capillary blood volume and membrane diffusing capacity in patients with COLD using the NO-CO method.

Lung capillary blood volume (Qc) and the membrane diffusing capacity (Dm) can both be determined from the combined measurement of nitric oxide (NO) and carbon monoxide (CO) transfers using the single-breath method. In ten healthy subjects, no differences was observed between the values of transfer factor of the lungs for carbon monoxide (TLCO) recovered after a 3 s or 9 s breath-holding time (tBH). The NO-CO method could thus be used with a short tBH and a low fraction of inspired nitric oxide (FINO) (8 ppm). However, in ten patients with chronic obstructive lung disease (COLD), the values of both transfer factor of the lungs for nitric oxide (TLNO) and TLCO were underestimated by around 20% at a short tBH (3 s). In COLD patients, the NO-CO method therefore requires a longer tBH and a higher inspired fraction of NO (30 ppm) than in healthy subjects. Similar values of Dm and Qc were obtained using the NO-CO method and the two-step conventional method, at two levels of the oxygenation. The former method gave less scatter. Furthermore, TLNO is independent of the fraction of inspired oxygen (FIO2) and directly proportional to carbon monoxide membrane diffusing capacity (DmCO).

Adult↗
PubMed1989

Variations in flow and intraalveolar pressure during jet ventilation: theoretical and experimental analysis.

Alteration in flow and pressure in a chest-lung model during jet ventilation was studied from a theoretical and experimental standpoint. The model consisted of a stiff box, with an inserted cast of the bronchial tree, simulating either normal or low compliance of the human chest-lung. Airway resistances in the model could be altered. A constant driving flow (Vd) was applied through the opening of the trachea at various rates. The driving flow drew in a constant flow (entrained flow = Ve) and increased the box pressure (PA), which in turn induced an increasing back flow (Vr). Vd, Ve-Vr and PA were measured. Theoretical analysis of time variation in box pressure showed a monoexponential pattern which was confirmed experimentally. Tr, the time at which back flow and entrained flow become equal could be predicted taking the physical characteristics of the experimental set-up and the values of Vd and Ve into account. Tr values depended mainly on the compliance of the experimental set-up. Increasing the resistances was found to reduce Ve. In practice, the efficiency of jet ventilation for gas exchange at a frequency below 4 Hz is known to be mainly related to the volume of gas flowing in the trachea towards the alveoli. This efficiency generally depends on the values of Tr and the inspiratory period (TI). A value of TI less than or equal to Tr will thus improve the jet ventilation efficiency.

Adult↗