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Biomedical subjects

H Guénard

Publications and source records attributed to H Guénard.

34 records · Page 2Linked to original sources
PubMedDate not supplied

A sampling method for mean alveolar gas in normal subjects and patients with respiratory disease.

The paper describes an alveolar gas sampling method based on the criterion of equality of mean alveolar (RA) and expired (RE) respiratory quotients. Expired gas is sampled at an expired volume equal to VT/2 + VD by means of a mechanical sampler controlled by an analog computer. Eleven normal subjects and 50 patients with cardiopulmonary disease have been tested. When the difference between mean alveolar and expired respiratory quotients did not exceed 0.05, the result was considered to be satisfactory. Such results have been obtained in 40 patients and all of the normal subjects. For the remaining 10 patients, either experimental error and/or particular non-homogeneities in ventilation seemed to be the cause of the unsatisfactory results. Arterial to alveolar PCO2 differences have been calculated. The mean difference in normal subjects was never negative (1.86 +/- 1.58 torr).

Analysis of Variance↗
PubMedDate not supplied

[Double-blind study on the action of almitrine in patients with polycythemia of high altitude].

Chronic polycythaemia in people living at high altitude is associated with hypoxaemia due to a marked reduction in hypoxic and hypercapnic drives. The effect of almitrine, a chemoreceptor stimulant, was evaluated in 40 patients, with haematocrit values over 57%, living in La Pa2 (3,600-4,000 m). Two studies were carried out. The aim of the first was to assess the ventilatory response, and the increase in PaO2 due to almitrine in a double blind, placebo controlled protocol including 40 patients (mean haematocrit 66.8%). Almitrine was given orally at a dose of 3 mg X kg-1. Variance analysis showed that three hours later there was a significant increase in PaO2 (+0.46 kPa), pH and respiratory frequency, with a significant reduction in PaCO2 (-0.4 kPa). The increase in ventilation (+17%) was not significant. The aim of the second study was to assess the effect of almitrine on the polycythaemia. It was given orally at a dose of 1.5 mg X kg-1 X day-1 to twelve patients over a four week period. Blood gases, ventilation (VE), oxygen consumption (VO2), carbon dioxide, production (VCO2) and haematocrit were measured every week. There was a slight but significant reduction in haematocrit (-3.5%). PaO2 and all the other measured parameters (VE, PaCO2, pH, VO2 VCO2) remained constant. The reduction in haematocrit was not therefore due to an increase in diurnal PaO2 but is perhaps due to the improvement in pulmonary ventilation during sleep.

Adult↗
PubMedDate not supplied

Effect of 26% oxygen breathing on ventilation and perfusion distribution in patients with cold.

Fourteen patients suffering from severe but stable chronic airway obstruction were studied while breathing room air and mildly hyperoxic mixture (26%). The data were collected at the end of each 30 min randomized breathing period. The multiple inert gas elimination technique was used to detect alterations in ventilation-perfusion (VA/Q) mismatching. Ventilatory, arterial and mixed venous blood gases, and hemodynamic measurements were made simultaneously. To show a possible effect of O2 on hypoxic pulmonary vasoconstriction (HPV), the fractional part of cardiac output perfusing low VA/Q areas was separated using as upper limit of VA/Q the compartments with PAO2 70, 60 and 50 mmHg while breathing oxygen, compared to the percentage of blood flow in the same areas limited by the same VA/Q unit in air breathing conditions. Only a few changes due to O2 are statistically significant: 1) a rise in PaO2 (+20.2 +/- 8.3 mmHg) and PvO2 (+4.2 +/- 2.18 mmHg) without any change in ventilation, respiratory frequency, pH, PaCO2, haemodynamics and overall criterion of distribution; 2) a moderate increase in inert gas dead space; 3) an increase in the percentage of blood flow under the limit when chosen at 50 mmHg (+3 +/- 2.8%). This change could be related to an inhibition of HPV response while breathing O2 in compartments previously placed above the limit in air. Consequently, their VA/Q decrease and their perfusions are summed with those under the limit in O2. These data suggest that mild hyperoxia has a slight but real deleterious effect on pulmonary gas exchange.

Aged↗
PubMedDate not supplied

[A rotative control plate for separation of inspired and expired gases (author's transl)].

Some drawbacks of the valve chamber are well known: high flow gas resistance, sensitivity to position and to condensation of water vapour, vibrations of the valve especially at high flow rate. To avoid these defects a rotative control valve separating inhaled and exhaled gases is described. A rotative plate shuts off one of two large ports and separates expired and inspired gases. The rotation of the plate is controlled by a sensor signal, which may be delivered by a pneumotachograph and switches on and off the electrical supply of the motor. The major characteristics of this valve are: its small dead space (11 cm3), a negligible error in the volumes which are to be displaced through either of the two ports, a total insensitivity to water condensation, a very low flow resistance and an insensitivity to position and displacement. This device may be adapted to infants and neonates.

Humans↗
PubMedDate not supplied

[Inert gas study of heliox gas exchange in patients with COPD].

Ventilation and perfusion distributions were measured in the patients with COPD breathing room air and normoxic helium-oxygen mixture (heliox) successively, using the multiple inert gas method. The D (A-a) O2 were calculated from ideal alveolar gas (Ai) and with West's gas mean model (A). Measured PaO2 and predicted PaO2 were compared during room air and heliox breathing. There were no change in overall distributions and in D (Ai-a) while D (A-a) O2 increase significantly during heliox breathing and the predicted PaO2 were significantly higher than the measured PaO2. Heliox breathing does not seem to change parallel heterogeneity in COPD. These results suggest an impairment of series heterogeneity and O2 diffusion during heliox breathing.

Helium↗
PubMedDate not supplied

[Hypoxemia and the hematocrit in pathologic polycythemia due to altitude].

81 patients living at La Paz (3,600-4,000 m altitude) and suffering from chronic polycythaemia, with an haematocrit greater than 57% were studied. They were selected on clinical and spirometric criteria to exclude from the study patients with associated pulmonary diseases. 45% of them were overweight (group O). The group of patients having a normal weight was divided into two equal groups: "young" patients (less than 35 years, J) and "old" patients (greater than 35 years, V). The important findings of this study were: 1) the existence of hypoxaemia in all groups: compared to the control group, the mean differences are -2 kPa for O and V groups and -1.3 kPa for J group; 2) the presence of slight hypercapnia (+0.3 kPa in J and V groups; +0.5 kPa in O group), excluding diurnal hypoventilation as the major source of hypoxaemia; 3) a significant linear correlation between the increase in PaCO2 and haematocrit in O and (J + V) groups; 4) a significant linear correlation between hypoxaemia and the increase in haematocrit, particularly in group J, but also in O and (J + V) groups; hypoxaemia is also well correlated with age in (J + V) group: PaO2 (kPa) = 11.42 -0.025 Age (yr) -0.061 Hct (%) The classical assumption of a chronic hypoventilation syndrome producing a progressive increase in haematocrit is discussed. Haematocrit is suspected as a causative factor of hypoxaemia, itself a well known factor producing polycythaemia. This mechanism could be the source of a vicious circle.

Adolescent↗
PubMedDate not supplied

BTPS calibration of heated Fleisch pneumotachometer.

The Fleisch pneumotachometer (PTM) gives the instantaneous respiratory gas flow, and when integrated provides the volume of gas displaced. Its output signal is proportional to the product of the flow and the viscosity of the gas. The calibration factor is thus different for inspiration and expiration. Since the exact value of the viscosity is unknown, accurate figures for flow cannot be obtained. This study examines the use of a precisely sinusoidal pump with adjustable speed and capacity, displacing air in a thermostatically controlled chamber containing water at 37 degrees C stirred by a propellor. Thus air at ambient temperature flows through the PTM on inspiration, and on expiration the gas exactly simulates in temperature and humidity that normally expired by a human subject. This makes the output signal asymmetrical, with the expired volume VTE being greater than the inspired value, the ratio VTE/VTI = 1.035. Other sources of error, notably temperature and pressure changes in the chamber and differences in the proportions of O2 and CO2 in the expired gas, have been considered from both a theoretical and experimental standpoint. Their combined effects produce a less than 0.5% error. Using this pump, the Fleisch PTM can be calibrated empirically without making any assumptions about the temperature and viscosity of the expired gas mixture.

Calibration↗
PubMedDate not supplied

[Pulmonary edema in pulmonary embolism].

We report a case of severe pulmonary embolism in a 37 years old man admitted to the intensive care unit for severe acute respiratory failure. The presenting signs and symptoms were typical for severe pulmonary oedema. Chest radiograph shortly after admission showed local alveolar shadows. In the absence of sepsis, haemodynamic evidence of left ventricular failure on catheterization of the right heart and because of the history of the recent illness, a tentative diagnosis of pulmonary embolism was made. The diagnosis was confirmed by selective pulmonary angiography. The latter demonstrated that pulmonary oedema had been localized only in areas with patent pulmonary arteries and, in addition, confirmed that left ventricular function was normal. Such a pattern of local pulmonary oedema is uncommon in patients and is reminiscent of that observed in animal experiments with severe pulmonary arterial obstruction and overperfusion of unblocked territories. Possible mechanisms of overperfusion oedema are discussed and the hypothesis that humoral factors may increase the permeability of pulmonary microvasculature in cases of severe pulmonary embolism is put forward.

Adult↗
PubMedDate not supplied

[Effects of oral almitrine on the distribution of VA/Q ratio in chronic obstructive lung diseases (author's transl)].

A double blind study of effects of a low dose of almitrine has been performed in patients with severe chronic obstructive lung diseases. Besides hemodynamic and ventilation data, ventilation-perfusion ratio distribution was measured by the inert gas method in order to try to explain the improvement in blood gases caused by this drug. At the dose of 1.5 mg/kg almitrine produces : 1) an increase in ventilation and PaO2, 2) no change in pulmonary vascular resistances compared to a rise on placebo, 3) a drop of 4% in the percentage of cardiac output perfusing low VA/Q lung units with a concomitant increase in lung units with VA/Q ratio between 0.1 and 10, and 4) no significant change in the distribution of ventilation. The change in the distribution of blood flow is one of the causes of the rise in PaO2, but its mechanism is at yet not clear. The present results suggest arterial vasoconstriction in units with very low VA/Q accompanied by diversion of blood flow towards lung units with higher VA/Q ratio.

Aged↗
PubMedDate not supplied

[Alveolar pressure during forced vital capacity. Method and application (author's transl)].

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.

Humans↗
PubMedDate not supplied

[Adaptation of body plethysmography to the study of respiratory mechanics during muscular exercise (author's transl)].

A pressure-corrected integrated flow plethysmograph allowing the study of mechanical characteristics of the ventilatory system during muscular exercise is described. In order to limit the increase in temperature inside the body box during exercise, a forced convective flow passes through the box. Thermal exchanges induced by this flow have been studied. They are sufficient to allow muscular exercise during 15 minutes at a constant power of 100 W. It has been verified that this type of box allows measurement of the usual parameters of ventilatory mechanics: pulmonary volumes, compliance, resistance using the panting method. The measurement of resistance during spontaneous breathing inside the box is not possible.

Airway Resistance↗