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Biomedical subjects

R Peslin

Publications and source records attributed to R Peslin.

At least 37 records · Page 2Linked to original sources
PubMed1997

Vasodilators, aortic elasticity, and ventricular end-systolic stress in nonanesthetized unrestrained rats.

We evaluated the effect of different vasodilators on ventricular end-systolic stress by investigating the impact of sodium nitroprusside, nifedipine, and hydralazine on blood pressure, aortic stiffness, and wave reflection during drug-induced hypotension (to 80 mm Hg mean blood pressure) in normotensive (central aortic mean blood pressure, 116 to 119 mm Hg; systolic pressure, 133 to 137 mm Hg), nonanesthetized, unrestrained rats. Aortic stiffness was evaluated from the slope of the linear regression relating pulse wave velocity (PWV) to central aortic mean or pulse pressure. The fall in central aortic systolic blood pressure was less than the fall in mean pressure, especially after hydralazine (122+/-4 mm Hg; sodium nitroprusside, 107+/-2; and nifedipine, 112+/-3 mm Hg; P<.05). The PWV/mean pressure slope was linear, positive, and similar in all three groups (hydralazine, 3.3+/-0.2; sodium nitroprusside, 3.8+/-0.3; and nifedipine, 3.9+/-0.3 cm x s[-1]x mm Hg[-1]; P>.05). The PWV/pulse pressure slope was linear, negative, and less steep in the case of hydralazine (-4.9+/-0.6; sodium nitroprusside, -15.5+/-3.7; and nifedipine, -13.5+/-2.9 cm x s[-1] x mm Hg[-1]; P<.05). The travel time and augmentation index of the reflected wave were similar in all groups. In conclusion, sodium nitroprusside and nifedipine had a more beneficial effect on end-systolic stress than did hydralazine. This does not appear to be related to any specific effect on wave reflection or the "static" relationship between PWV and aortic mean blood pressure; it may be related to the effects of these drugs on the "dynamic" relationship between PWV and pulse pressure.

Animals↗
PubMed1997

Inspiratory dynamic obstruction detected by forced oscillation during CPAP. A model study.

Assessment of upper airway mechanics in patients with obstructive sleep apnea/hypopnea (OSA) can be carried out qualitatively from indirect signals (flow pattern, snoring, strain gauges, inductance plethysmography) or quantitatively by means of invasive estimation of esophageal pressure. The forced oscillation technique (FOT) is a noninvasive method of potential interest for quantitatively assessing airway obstruction in the sleeping patient. The aim of this work was to ascertain in a model study whether FOT could provide an index of airway obstruction when applied at the conditions of total and partial occlusions similar to the ones found in patients with OSA. An airway analog closely mimicking upper airway collapsibility was constructed and mechanically characterized by the relationship between its flow, upstream and downstream pressures as well as by means of FOT. We simulated total collapse (apnea), different levels of partial collapse with flow limitation (hypopnea), and release of airway obstruction when the collapsible analog was used as an artificial upper airway in a spontaneously breathing subject submitted to continuous positive airway pressure (CPAP) up to 14 cm H2O.s/L. The results showed that the amplitude of airway impedance measured by FOT was a suitable index to detect obstruction in collapsible segments. We concluded from this realistic model study that FOT could be a valuable tool for quantitatively assessing airway obstruction in patients with OSA treated with CPAP. This noninvasive technique is potentially useful both in studying upper airway mechanics in detail and in automatically monitoring airway obstruction in routine studies.

Airway Obstruction↗
PubMed1996

Respiratory system reactance as an indicator of the intrathoracic airway response to methacholine in children.

The upper airways may contribute to increases in airway resistance in response to a bronchial challenge, and thus decrease the specificity of such challenge tests to diagnose airway hyperresponsiveness when forced oscillation techniques are used to evaluate changes in respiratory system resistance (Rrs). A concomitent decrease in respiratory system reactance (Xrs) may indicate a change in the intrathoracic airways and/or lung parenchyma, provided that extrathoracic airway wall motion is prevented. To test the value of Xrs in the evaluation of bronchial hyperresponsiveness, we studied the respiratory impedance response to methacholine in 38 children with a history of asthma (aged 6-14.5 years), and compared the results to changes in the forced expiratory volume in one second (FEV1). Rrs and Xrs were measured by the forced oscillation technique with pseudorandom (11 subjects) or sinusoidal (27 subjects) pressure variations applied around the child's head to minimize upper airway wall motion. Changes in Rrs and in Xrs at 12 Hz (Rrs12, Xrs 12) correlated significantly with changes in FEV1 (P < 0.005). A decrease in FEV1 > or = 20% was observed in 23 subjects. When these 23 subjects were compared with the 15 children who did not show significant changes in FEV1, the responding group had larger mean +/- SEM changes in Rrs (116.0 +/- 13.2% vs 60.4 +/- 11.4%, P < 0.006) and in Xrs (-2.1 +/- 0.4 hPa.s/L vs -0.9 +/- 0.3 hPa.s/L, P < 0.03) than the nonresponders. The receiver operating characteristics (ROC) curve analysis was used to assess the diagnostic value, i.e., specificity and sensitivity, of different levels of change in Rrs and Xrs, with reference to FEV1. The overall incidence of false results was similar for Rrs and Xrs. The optimum diagnostic value for Rrs was a 70% increase, which corresponded to a sensitivity of 87% and a specificity of 67%. For Xrs the optimum decision level was -1 hPa.s/L, corresponding to a sensitivity of 70% and a specificity of 80%. It is concluded that Xrs may improve the specificity of the forced oscillation technique in interpreting the airway response to methacholine. This may be of particular interest in young children unable to perform forced expirations.

Adolescent↗
PubMed1996

Assessment of respiratory pressure-volume nonlinearity in rabbits during mechanical ventilation.

The volume dependence of respiratory elastance makes it difficult to recognize actual changes in lung and chest wall elastic properties in artificially ventilated subjects. We have assessed in six anesthetized, tracheotomized, and paralyzed rabbits whether reliable information on the static pressure-volume (PV) curve could be obtained from recordings performed during step variations of the end-expiratory pressure without interrupting mechanical ventilation. Pressure and flow data recorded during 5- and 10-hPa positive-pressure steps were analyzed in the time domain with a nonlinear model featuring a sigmoid PV curve and with a model that, in addition, accounted for tissue viscoelastic properties. The latter fitted the data substantially better. Both models provided reasonably reproducible coefficients, but the PV curves obtained from the 5- and 10-hPa steps were systematically different. When the PV curves were used to predict respiratory effective elastance, the best predictor was the curve derived from the 10-hPa step with the viscoelastic model: unsigned differences averaged 8.6 +/- 11.1, 26.9 +/- 36.4, and 5.5 +/- 5.8% at end-expiratory pressures of 0, 5, and 10 hPa, respectively. This approach provides potentially useful, although not highly accurate, estimates of respiratory effective elastance-volume dependence.

Animals↗
PubMed1996

Correction of thermal artifacts in plethysmographic airway resistance measurements.

Specific airway resistance (sRaw) measured by body plethysmography without conditioning of the inspired air to BTPS exhibits a strong frequency dependence related to the fact that the warming and wetting of the gas in the airways is not instantaneous (R. Peslin, C. Duvivier, M. Vassiliou, and C. Gallina. J. Appl. Physiol. 79: 1958-1965, 1995). We have tested three methods in 21 healthy subjects to correct for that artifact by using a simple model, assuming a first-order thermal process characterized by a single time constant. The corrections required entering an assumed constant value for (methods 1 and 2) and/or for airway inertance (methods 1 and 3) and/or measuring the inspired gas temperature and water vapor saturation (methods 2 and 3). The frequency dependence of sRaw was measured from 0.5 to 3 Hz both with (sRawETPS) and without (sRawam) gas conditioning. With optimal values for and/or airway inertance, the mean difference between sRawam and sRawETPS was close to zero with all three methods, but the root mean square difference was significantly lower with method 2 (0.83 +/- 0.35 hPa.s compared with 1.21 +/- 0.54 and 1.20 +/- 0.49 hPa.s with methods 1 and 2, respectively). We conclude that the thermal artifact of sRaw measurements may be best corrected by using temperature measurements and an assumed time constant (0.152 s with our equipment).

Adult↗
PubMed1996

Effect of expiratory flow limitation on respiratory mechanical impedance: a model study.

Large phasic variations of respiratory mechanical impedance (Zrs) have been observed during induced expiratory flow limitation (EFL) (M. Vassiliou, R. Peslin, C. Saunier, and C. Duvivier. Eur. Respir. J. 9: 779-786, 1996). To clarify the meaning of Zrs during EFL, we have measured from 5 to 30 Hz the input impedance (Zin) of mechanical analogues of the respiratory system, including flow-limiting elements (FLE) made of easily collapsible rubber tubing. The pressures upstream (Pus) and downstream (Pds) from the FLE were controlled and systematically varied. Maximal flow (Vmax) increased linearly with Pus, was close to the value predicted from wave-speed theory, and was obtained for Pus-Pds of 4-6 hPa. The real part of Zin started increasing abruptly with flow (V) > 85% Vmax and either further increased or suddenly decreased in the vicinity of Vmax. The imaginary part of Zin decreased markedly and suddenly above 95% Vmax. Similar variations of Zin during EFL were seen with an analogue that mimicked the changes of airway transmural pressure during breathing. After pressure and V measurements upstream and downstream from the FLE were combined, the latter was analyzed in terms of a serial (Zs) and a shunt (Zp) compartment. Zs was consistent with a large resistance and inertance, and Zp with a mainly elastic element having an elastance close to that of the tube walls. We conclude that Zrs data during EFL mainly reflect the properties of the FLE.

Electric Impedance↗
PubMed1996

Separation of airway and tissue properties by transfer respiratory impedance and thoracic gas volume in reversible airway obstruction.

The aim of this study was to establish the ability to estimate separate airway and tissue properties from transfer respiratory impedance (Zrs,tr) data in the presence of airway obstruction. Zrs,tr, thoracic gas volume (TGV) and airway resistance (Raw,pleth) were measured in the presence of obstruction and after use of a bronchodilator (BD) in 13 normal or asymptomatic asthmatic adults and 28 children with symptomatic asthma. An analytical approach was used to solve the equations of a simplified variant of DuBois' model, including airway resistance (Raw*) and inertance (Iaw), tissue compliance (Ct) and resistance (Rt) and pulmonary gas compliance (Cg). The equations of the model could not be reliably solved in four children before BD. Mean Raw,pleth was not different from mean Raw* in adults before (mean +/- SEM) (3.4 +/- 0.5 vs 3.1 +/- 0.3 hPa.s.L-1) or after BD (1.4 +/- 0.2 vs 1.8 +/- 0.2 hPa.s.L-1), or in children after BD (2.9 +/- 0.3 vs 3.2 +/- 0.2 hPa.s.L-1, respectively). In children before BD, Raw* was significantly underestimated compared with Raw,pleth (3.8 +/- 0.4 vs 5.4 +/- 0.6 hPa.s.L-1). Overall, a significant positive correlation was found between the difference [Raw,pleth - Raw*] and Raw,pleth (r = 0.82). In adults, BD induced a decrease in Raw* and Rt, an increase in Ct, and no change in Iaw. In children after BD, there was no significant change in Raw* or Ct, whilst Rt decreased and Iaw increased. Taking Raw,pleth as the gold standard, it is concluded that coherent estimation of parameters of DuBois' model may be obtained from combined Zrs,tr and TGV measurements in normal subjects and moderately obstructed adults, but not in children with significant airway obstruction. This seems to be due to the systematic under-estimation of Raw*.

Adolescent↗
PubMed1996

Expiratory flow limitation during mechanical ventilation detected by the forced oscillation method.

We have previously observed large phasic variations of respiratory mechanical impedance in chronic obstructive pulmonary disease (COPD) patients mechanically-ventilated for acute respiratory failure, and postulated that they were due to expiratory flow limitation (EFL). The aim of this study was to test that assumption experimentally and to assess the value of impedance for automatic and noninvasive detection of EFL during mechanical ventilation. The study was performed: 1) in a mechanical analogue, including a flow-limiting element; and 2) in eight anaesthetized and paralysed rabbits, before and during histamine infusion. In both instances, EFL was obtained by lowering the expiratory pressure, using a computer-controlled ventilator; the absence of flow increase when expiratory pressure was further lowered was taken as evidence of EFL. Impedance was measured by applying 15 Hz oscillations at the airway opening. Its real (Re) and imaginary (Im) parts were measured separately during the inspiratory and the expiratory phases, and their differences were related to the mean inspiratory modulus. With the analogue, EFL was accompanied by large decreases both of Re and Im during the expiratory phase. In the rabbits, phasic variations of Re were variable in sign and were not significantly different with and without EFL. In contrast, EFL systematically and specifically decreased Im during the expiratory phase. A threshold of -50% provided a sensitivity of 96% and a specificity of 100% for detecting EFL. The observed phasic variations may be explained by airway wall shunt properties. The study suggests that a large decrease of the imaginary part of impedance during the expiratory phase is a sensitive and specific index of expiratory flow limitation during artificial ventilation.

Animals↗
PubMed1996

Frequency dependence of specific airway resistance in a commercialized plethysmograph.

Specific airway resistance (sRaw) measured by body plethysmography has been shown to decrease markedly with decreasing breathing frequency when the inspired air is not conditioned to body temperature, atmospheric pressure and saturation with water vapour (BTPS). The phenomenon has been attributed to noninstantaneous gas warming and wetting in the airways. The aim of this investigation was to assess whether the phenomenon was also present in a commercialized plethysmograph featuring an "electronic BTPS correction". Airway resistance (Raw) and sRaw were measured in 15 healthy subjects at six breathing frequencies ranging 0.25-3 Hz, using a constant volume plethysmograph in which a correction for non-BTPS gas conditions was applied by electronically flattening the box pressure-airway flow loop (Jaeger Masterscreen Body, version 4.0). The temperature and water vapour saturations in the box averaged 26.5 +/- 1.3 degrees C and 59 +/- 6%, respectively. Raw and sRaw exhibited a clear positive frequency dependence in all but one subject. From 0.25 to 3 Hz Raw increased from (mean+/-SD) 0.62 +/- 0.55 to 1.71 +/- 0.76 hPa x s x L-1 (p<0.001), and sRaw from 2.34 +/- 1.90 to 7.55 +/- 3.08 hPa x s (p<0.001). The data are consistent with a simple model, in which gas conditioning in the airways and external dead space occurred with a time constant of 0.39 s. We conclude that the electronic BTPS correction of the instrument was inadequate, probably because it is assumed that gas conditioning in the airways is instantaneous. We recommend that, with similar instruments, airway resistance be measured using as high a panting frequency as feasible.

Adult↗
PubMed1995

Potential for lung sound monitoring during bronchial provocation testing.

BACKGROUND: The use of lung sound monitoring during bronchial provocation testing has not been clearly demonstrated. The appearance of wheeze and changes in inspiratory breath sound intensity have been analysed and related to changes in spirometric parameters and to airways hyperresponsiveness. METHODS: Lung sounds were recorded in 38 patients undergoing a routine carbachol airway challenge (CAC) test. Spirometric testing was performed before and after the inhalation of each of five cumulative doses of 320 micrograms carbachol; a fall in forced expiratory volume in one second (FEV1) by 20% or more was considered as significant. Lung sound analysis was carried out using a computerised system. RESULTS: The CAC test was positive (CAC+) in 21 patients and negative (CAC-) in 17. At the final stage of the challenge, wheeze was identified in 10 positive patients (48%) and in one negative patient (6%); in non-wheezers the inspiratory breath sound intensity decreased significantly from baseline in 11 CAC+ patients (mean (SD) change -35 (24%)) but not in 16 CAC- patients (mean (SD) change 5 (24%)). In all non-wheezers a linear relationship was found between breath sound intensity and the squared inspiratory airflow (r = 0.53-0.92) which became looser after the inhalation of carbachol. CONCLUSION: When unertaking bronchial provocation testing the accurate identification of wheeze may prove useful in avoiding or shortening the test because of the presumed relationship between wheeze and airways hyperresponsiveness. Changes in breath sound intensity may also be useful, but further studies are required to define the threshold for significant changes in this index.

Adult↗
PubMed1995

T model partition of lung and respiratory system impedances.

The aim of this work was to demonstrate that the three compartments of the lung T network and the chest wall impedance (Zcw) can be identified from input and transfer impedances of the respiratory system if the pleural pressure is recorded during the measurements. The method was tested in six healthy volunteers in the range of 8-32 Hz. The impedances resulting from the decomposition confirm the adequacy of the monoalveolar structure commonly used in healthy subjects. Indeed, the T shunt impedance is well modeled by a purely compliant element, the mean compliance [0.038 +/- 0.081 (SD) l/kPa], which coincides within 9.5 +/- 6.3% of the alveolar gas compressibility derived from thoracic gas volume (0.036 +/- 0.011 l/kPa). The results obtained provide experimental evidence that the alveolar gas compression is predominantly isothermal and that lung tissue impedance is negligible throughout the whole frequency range. The shape of Zcw is consistent with a low compliance-low inertance pathway in parallel with a high compliance-high inertance pathway. We conclude that the proposed method is able to reliably identify the T network featuring the lung and Zcw.

Adult↗
PubMed1995

Lung and respiratory impedance at low frequency during mechanical ventilation in rabbits.

We have tested in eight rabbits the feasibility of measuring respiratory (Zrs) and lung (ZL) impedances in the low-frequency domain, including below the breathing frequency (fb), during conventional mechanical ventilation (CMV). The animals were tracheotomized and ventilated with a tidal volume (VT) of 20 ml at a fb of 1 Hz. The excitation signal was provided by a flow generator connected in parallel with the ventilator; it included six components ranging from 0.45 to 14.8 Hz, which met the neither-sum-nor-difference criterion of B. Suki and K. Lutchen (IEEE Trans. Biomed. Eng. 39: 1142-1151, 1992) to minimize the influence of nonlinearities. Zrs and ZL were also measured at the same mean lung volume and with the same excitation signal both during apnea and when the ventilator signal was replaced by a sine wave with the same VT and fb (SMV). The real parts (Re) of both Zrs and ZL, as well as the effective elastances, were significantly larger during apnea than during CMV and SMV over the whole frequency range. Re(Zrs) and Re(ZL) were similar during CMV and SMV above fb but they were lower during CMV at 0.45 Hz. The latter difference seems to be related to the presence of harmonics of fb and of additional frequency components due to pulse amplitude modulation. We conclude that, because of nonlinearities, it is feasible to measure Zrs and ZL during CMV only at and above fb.

Animals↗
PubMed1995

Analysis of low-frequency lung impedance in rabbits with nonlinear models.

Lung mechanics was studied in six paralyzed tracheotomized rabbits ventilated with a specially devised computer-controlled ventilator. The target flow waveform contained noninteger multiple frequencies ranging from 0.83 to 6-10 Hz and met a neither-sum-nor-difference criterion to minimize the effects of nonlinearity (B. Suki and K. Lutchen. IEEE Trans. Biomed. Eng. 39: 1142-1151, 1992). The actual flow, however, contained harmonics of the two lowest frequencies. Measurements were performed at mean airway pressure (Paw) levels of 8 and 12 hPa and during histamine-induced bronchoconstriction. Smooth impedance curves were observed in unchallenged rabbits at low mean Paw levels. In contrast, unrealistic impedance fluctuations, suggestive of cross talk from the unwanted frequency components in the flow input, were seen at high mean Paw levels and during acute bronchoconstriction. Model analysis was performed by using the actual flow signal as an input to various nonlinear models. The impedance fluctuations observed at high mean Paw levels were well simulated by a model featuring a volume-dependent elastance, and those observed after histamine were almost perfectly reproduced by a model where resistance increased with the reciprocal of lung volume. We conclude that impedance data biased by cross talk may provide useful information on the presence and nature of respiratory system nonlinearities.

Airway Resistance↗
PubMed1995

Thermal artifacts in plethysmographic airway resistance measurements.

Measurements of airway resistance (Raw) by body plethysmography during unconditioned air breathing are implicitly based on the assumption that the warming and humidification of air in the airways are instantaneous. Simulation with a simple model suggests that Raw may be frequency dependent and substantially underestimated at most breathing frequencies if the time constant of gas conditioning (theta) is between 0.01 and 0.3 s. We measured the frequency dependence of the real (Re) and imaginary parts of the relationship between the plethysmographic signal and airway flow from 0.5 to 3 Hz in six healthy subjects in several situations. During breathing of unconditioned air through a heated pneumotachograph, Re increased by 47 +/- 70% between 2 and 3 Hz; the data were consistent with a theta of 0.087 +/- 0.023 s. Additional dead spaces moderately increased theta: 0.105 +/- 0.031 and 0.120 +/- 0.027 s with 50-cm-long polyvinyl chloride and copper tubes, respectively. During breathing of saturated air conditioned at 34, 36, 38, and 40 degrees C, Re exhibited a much smaller positive frequency dependence, most of which was probably due to a flow dependence of Raw. We conclude that unless the inspired gas is conditioned, plethysmographic Raw is likely to be substantially underestimated, particularly when measured during spontaneous breathing.

Adult↗
PubMed1994

Two-frequency analysis of respiratory mechanics in artificially ventilated rabbits.

The frequency dependence of respiratory mechanical properties was studied in 10 paralyzed, artificially ventilated rabbits, by superimposing a single sinusoidal signal with a frequency of 10, 20 or 30 Hz upon the ventilator waveform. The tracheal pressure and flow signals were analyzed both with the usual first order model, which provided total respiratory elastance (Ers) and resistance (Rrs), and by Fourier analysis, which provided respiratory impedance (Zrs) at the breathing frequency (0.85 Hz) and at the superimposed oscillation frequency. The real part of Zrs (Re(Zrs)) decreased by 30% from 0.85 to 10 Hz (P < 0.001), but did not vary significantly from 10 to 30 Hz. This finding is satisfactorily explained by tissue viscoelasticity. Following a histamine aerosol, the frequency dependence of Re(Zrs) changed very little in three out of four rabbits, but increased substantially in the fourth. In that instance, assuming that lung hysteresivity was not markedly modified by histamine, the results suggest inhomogeneous airway obstruction and/or airway wall shunting.

Airway Resistance↗
PubMed1994

Tracheal wheezes during methacholine airway challenge (MAC) in workers exposed to occupational hazards.

Methacholine airway challenge (MAC) is a simple and useful means to assess bronchial hyperreactivity in workers exposed to various occupational hazards. Recently, wheeze detection by tracheal auscultation has been proposed as an indicator of bronchial responsiveness during bronchial provocation test in children. Our aim was to examine the relationship between the appearance of wheezes and the concurrent changes in forced expiratory volume in one second (FEV1) observed during MAC test in adults. Three cumulative doses of a methacholine solution (100 micrograms, 500 micrograms and 1500 micrograms) were inhaled by 45 workers with occupational exposure to flour dust. Spirometry was done using an electronic spirometer. Tracheal sounds were recorded with an electronic stethoscope placed over the anterior cervical triangle, 2 cm above the sternal notch. The amplified sounds were stored on magnetic tape, band-pass filtered (50-2000 Hz), and digitized at a sampling rate of 4096 Hz into a GenRad Vibration Control System. Wheezes were detected by fast Fourier transform (FFT) analysis and their presence compared to a 20% fall in FEV1. A positive MAC test by spirometry was found in 12 subjects whereas wheezes were identified in 14 subjects. Among the wheezing subjects, nine had a positive MAC test (range of fall in FEV1 = 20.6 to 42.3%) and five had a negative one (range of fall in FEV1 = 3.6 to 16.9%). Moreover, no wheezes were found in the remaining three subjects with a positive MAC test (range of fall in FEV1 = 20.7 to 27.4%). Taking a 20% fall in FEV1 as reference, wheezes were 75% sensitive and 84.8% specific to detect airflow obstruction. In conclusion, since it carries a significant although small false-negative rate, the acoustic technique based upon wheeze detection cannot, at the present time, fully replace spirometry during airway challenge testing in subjects with suspected asthma.

Adult↗
PubMed1994

Comparative effects of laryngeal mask and tracheal tube on total respiratory resistance in anaesthetised patients.

We compared the effects of the laryngeal mask and tracheal tube on total respiratory resistance in 10 anaesthetised, mechanically ventilated patients undergoing otological microsurgery. The subjects were randomly divided into two groups. In the first group, the tracheal tube (Rüsch) was inserted for the first series of measurements. This was then replaced by a laryngeal mask (Intavent) and a second series of measurements was made during the first hour of operation. In the second group, the same protocol was applied with inverse order in the use of the devices. From the measurement of respiratory flow and pressure at the airway opening, total respiratory resistance was calculated by multiple linear regression. The data were corrected to eliminate the previously determined nonlinear resistance of the two devices. Arterial blood pressure, electrocardiogram, oxygen saturation and end-tidal carbon dioxide concentration were continuously monitored. With the laryngeal mask and the tracheal tube, mean (SE) minute ventilation was 9.4(0.9)l.min-1 and 8.1(0.9)l.min-1, respectively for end-tidal carbon dioxide concentrations between 3.6 and 4.1%. Although the glottic resistance was included in the measurement performed with the laryngeal mask but not with the tracheal tube, mean (SE) total respiratory resistance was not significantly different with the two devices (0.61(0.32) and 0.69(0.35) kPa.l-1.s, respectively). Leakage was avoided with the laryngeal mask because the insufflation pressure never exceeded 1.7 kPa except in one patient suffering from severe chronic obstructive pulmonary disease who had a total respiratory resistance of 1.45 kPa.l-1.s. During the first hour of the operation all respiratory variables remained stable irrespective of the device used.

Adult↗