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Biomedical subjects

H Guenard

Publications and source records attributed to H Guenard.

At least 19 recordsLinked to original sources
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↗
PubMed1988

Pulmonary gas exchange in Andean natives with excessive polycythemia--effect of hemodilution.

Pulmonary gas exchange in Andean natives (n = 8) with excessive high-altitude (3,600-4,200 m) polycythemia (hematocrit 65.1 +/- 6.6%) and hypoxemia (arterial PO2 45.6 +/- 5.6 Torr) in the absence of pulmonary or cardiovascular disease was investigated both before and after isovolemic hemodilution by use of the inert gas elimination technique. The investigations were carried out in La Paz, Bolivia (3,650 m, 500 mmHg barometric pressure). Before hemodilution, a low ventilation-perfusion (VA/Q) mode (VA/Q less than 0.1) without true shunt accounted for 11.6 +/- 5.5% of the total blood flow and was mainly responsible for the hypoxemia. The hypoventilation with a low mixed venous PO2 value may have contributed to the observed hypoxemia in the absence of an impairment in alveolar capillary diffusion. After hemodilution, cardiac output and ventilation increased from 5.5 +/- 1.2 to 6.9 +/- 1.2 l/min and from 8.5 +/- 1.4 to 9.6 +/- 1.3 l/min, respectively, although arterial and venous PO2 remained constant. VA/Q mismatching fell slightly but significantly. The hypoxemia observed in subjects suffering from high-altitude excessive polycythemia was attributed to an increased in blood flow perfusing poorly ventilated areas, but without true intra- or extrapulmonary shunt. Hypoventilation as well as a low mixed venous PO2 value may also have contributed to the observed hypoxemia.

Adult↗
PubMed1988

Effect of dry warm air on respiratory water loss in children with exercise-induced asthma.

The variation in respiratory water loss (RWL) over time, expressed as the mass of water vapor lost per liter (body temperature and pressure, saturated) of ventilation (MH2O), was investigated in two groups: (1) children with exercise-induced asthma; and (2) healthy children. Children were matched for age and sex and went without medication for at least 12 hours before each experiment. The children breathed dry warm air (TI = 28.4 degrees C +/- 0.3 degree C) for 15 minutes while bicycling at constant and moderate work load (50 W). The MH2O was measured by collecting and weighing the expired water vapor (1) at rest breathing in warm conditions of inspired gas (control values), (2) every five minutes during exercise while breathing dry warm air, and (3) four minutes after the end of exercise. Pulmonary function tests were performed before and six minutes after exercise. The results were abnormal only in children with exercise-induced asthma. During exercise, RWL significantly fell (compared to control value) at the tenth and 15th minute in both groups. Whereas normal subjects recovered their initial values for MH2O four minutes after stopping exercise, asthmatic children still had a reduction in respiratory water loss. During exercise, MH2O decreased a little more in healthy than in asthmatic children. The decrease in MH2O in both groups suggests that the means to fully humidify expired gas are overwhelmed by thermal stress. The lack of increase in MH2O in asthmatic children on stopping exercise suggests that the airway mucosa is unable to produce enough water vapor and is thus dehydrated and probably hyperosmotic.

Asthma↗
PubMed1987

Prevention of exercise-induced asthma by oxitropium bromide.

A vagal mechanism appears to be involved in the development of exercise-induced asthma (EIA), although previous studies have failed to demonstrate a protective effect of anticholinergic drugs against post-exercise bronchoconstriction. To reassess this hypothesis the effect of a new anticholinergic drug, Oxitropium Bromide (OTB) has been studied in ten subjects with documented EIA. There was no change after inhalation of a placebo. Administration of OTB led to bronchodilatation and totally blocked post-exercise bronchoconstriction in 7 patients, and it did so partly in 2. The response to the drug appeared to depend on pretest respiratory function. Thus, the anticholinergic drug OTB may protect against EIA in most patients, confirming the role of a vagal cholinergic mechanism in EIA.

Adolescent↗
PubMed1987

Determination of lung capillary blood volume and membrane diffusing capacity in man by the measurements of NO and CO transfer.

NO and CO lung transfer values (TL) were measured separately in 14 healthy subjects (7 men, 7 women), using the single breath technique. Five repetitive maneuvers were performed by each subject for TLNO and TLCO determinations. The inspired mixture contained either 8 ppm NO or 0.25% CO, with 2% He, 21% O2 in N2. In order to measure an appreciable fraction of NO in the alveolar gas it was necessary to shorten the breath holding time to 3 sec. TLNO was about five times greater than TLCO. This result suggests that the specific conductance of blood (theta) for NO is very high and that the second term of the second member of the equation 1/TLNO = 1/DmNO + 1/(theta NO.Qc) is therefore negligible. DmCO and Qc values can thus be computed from TLNO and TLCO measurements. The results obtained with this method are very close to those reported in the literature; for men DmCO = 79.0 +/- 14.3 ml.min-1.Torr-1, Qc = 78.0 +/- 13.2 ml and for women DmCO = 59.0 +/- 10.1 ml.min-1.Torr-1, Qc = 59.5 +/- 11.6 ml.

Adult↗
PubMed1987

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.

Humans↗
PubMed1987

[Pulmonary ventilation/perfusion ratio].

The ratios of ventilatory (V) and perfusion (Q) flow rates in the lung are to a large extent responsible for the efficiency of gas exchange. In a simplified monocompartmental model of the lung, the arterial partial pressure of a given gas (Pa) is a function of several factors: the solubility of this gas in blood, its venous and inspired partial pressures and the V/Q ratio. In a multicompartemental model, the mean arterial partial pressure of the gas is a function of the individual values of Pa in each compartment as well as the distribution of V/Q ratios in the lung and the relationship between the concentration and the partial pressure of the gas. The heterogeneity of the distribution of V/Q results from those of both V and Q. Two factors are mainly responsible for this heterogeneity: the gravity and the morphometric characteristics of bronchi and vessels. V/Q ratios are partially controlled at least in low V/Q compartments since hypoxia in these compartments leads to pulmonary arteriolar vasoconstriction. However lungs V/Q ratios range from 0.1 to 10 with a mode around 1. Age, muscular exercise, posture, accelerations, anesthesia, O2 breathing, pulmonary pathology are factors which may alter the distribution of V/Q ratios.

Animals↗
PubMed1986

Improvement in ventilation-perfusion relationships by almitrine in patients with chronic obstructive pulmonary disease during mechanical ventilation.

Although the respiratory stimulant effects of almitrine bismesylate (AB) via an action on the peripheral chemoreceptors have been demonstrated, the mechanism of its intrapulmonary action has not yet been elucidated. In order to abolish the stimulation of ventilation, observed in studies on spontaneously breathing patients, an investigation of patients suffering from severe COPD under constant mechanical ventilation, with FIO2 = 0.21, during the weaning period was carried out. Eighteen patients were randomly divided into 2 groups (9 receiving 1.5 mg/kg AB and 9 receiving placebo). The ventilatory and hemodynamic variables, blood and alveolar gases, and the VA/Q ratio distributions using the multiple inert gas technique were collected before treatment with drug or placebo, as well as 90 and 180 min afterwards. The PaO2 was found to be raised 90 min after AB administration (+57 +/- 3.9 mm Hg, p less than 0.01) and remained above the baseline value at 180 min (+5.4 +/- 4.6 mm Hg, p less than 0.01). Compared with those in the placebo group, these increases were significant (p less than 0.01). A slight decrease in PaCO2 but similar in the 2 groups was observed despite constant ventilation. The hemodynamic data were the same for the 2 groups. The changes in overall criteria of the distributions (mean VA/Q and SD) were small. The main finding was a decrease in the percentage of the perfusion flowing through the true shunt and the underventilated areas after AB treatment. In the control group, the blood flow percentage in the true shunt and low VA/Q units was either stable or increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Almitrine↗
PubMed1986

Platelet kinetics in stable atopic asthmatic patients.

The kinetics of platelets labeled with indium-111 were investigated in 13 healthy subjects as well as in 9 patients in the asymptomatic interattack stage of asthma. The survival times of platelets in healthy subjects was 8.9 +/- 1 days; in asthmatic subjects it was 4.7 +/- 1.3 days (p less than 0.001). The survival curve is of a biexponential form in asthmatics, thus suggesting the presence of 2 populations: one with a short life span (23 +/- 7 h), representing a third of the total population (33 +/- 9%), and the other with a normal life span. No single preferred site of platelet sequestration was found. These results suggest the presence of functional or anatomic lesions of platelets in asthmatic patients, which can be explained only hypothetically at the present time.

Adult↗
PubMed1985

Series dead space for inert gases in healthy subjects.

In ten normal subjects, series dead space was determined for six intravenously infused inert gases (SF6, ethane, cyclopropane, fluothane, ether, acetone) from their expired and alveolar concentrations. The method for sampling alveolar gas was based on the criterion of identity of mean alveolar and expired gas exchange ratios. Inert gases were analysed chromatographically. Acetone, the most soluble gas, yielded the lowest dead space, the difference to the other gases being about 4.5%. This is probably due to the non-infinite value of the series dead space ventilation-perfusion ratio (VA/Q) which was estimated at about 2,000. The diffusivity, inversely related to the molecular weight, also played a role, the heaviest gas (fluothane) having a greater dead space than the lightest (ethane). The underestimation of the dead space from acetone is expected to be greater in subjects with low tidal volume and high bronchial blood flow, i. e. in some patients with respiratory disease.

Humans↗
PubMed1985

Determinants of hypoxemia during the acute phase of pulmonary embolism in humans.

The determinants of hypoxemia were studied in 10 patients with acute pulmonary embolism demonstrated by pulmonary angiography. Two patients were mechanically ventilated, and in the 8 who breathed room air spontaneously, the mean arterial PO2 was 61.5 mmHg. Measurements of the distributions of ventilation (VA) and perfusion (Q) against VA/Q ratios by the multiple inert gas infusion technique demonstrated an increase in VA/Q inequality. The major part of pulmonary blood flow was distributed in a mode near to, or slightly above, a VA/Q ratio of 1. The cumulative fraction of blood in true shunt and low VA/Q mode (VA/Q less than 0.01) was 9.1%. For a small part of the AaDO2 (13%), an oxygen diffusional component was found. The remaining hypoxemia was due to the fall in the mixed venous PO2 (PVO2), irrespective of its cause: low cardiac output, low hemoglobin concentration, high oxygen consumption, low P50. The fall in PVO2 led to a fall in end-capillary blood PO2 in both shunt or ventilated and perfused units. We conclude that the major determinant of hypoxemia in these patients suffering from acute pulmonary embolism is the fall in PVO2. This is enhanced by a moderate increase in the fraction of blood flowing through low VA/Q units. Diffusion impairment plays only a minor role.

Acute Disease↗
PubMed1985

Gas exchange alterations in patients with chronic obstructive lung disease.

In a series of 23 patients with COPD, Wagner et al showed three distinct patterns of VA/Q distributions and a correlation between Burrows' clinical classification and the observed distribution patterns. Using the inert gas method, we studied 51 patients suffering from severe but stable COPD (FEV1 = 0.84 +/- 0.38 L; PaO2 = 58.5 +/- 10.5 mm Hg; PaCo2 = 48 +/- 6 mmHg; Ppa = 22 +/- 8 mmHg) breathing room air in a steady state. The H pattern (high mode of VA in high VA/Q) was found in 24 cases. There was an L pattern (Q mode in low VA/Q units) in nine cases and an HL (high-low) pattern in 16 cases (two patients were assigned another group). The analysis of the distribution data confirmed that VA/Q heterogeneity was the main factor underlying gas exchange disturbances in COPD. The PaO2 of the H subjects was higher than that of both HL (p less than 0.02) and L subjects. The true shunt value in the L group was significantly lower than in the H and HL groups. However, the relationship between clinical or functional aspects and distribution was not direct. The fraction of patients of H, HL, or (H + HL) types was nearly identical in the three clinical groups. The H pattern was found to be predominant in cases of COPD.

Aged↗
PubMed1985

[The inert gas method in respiratory physiopathology].

The main results obtained, in healthy or unhealthy man, with the inert gas method are gathered together. The major factor at the source of hypoxemia is the uneven distribution of VA/Q ratios. The fall in the partial pressure of oxygen in mixed venous blood amplifies this effect. Only hypoxemia, during muscular exercise, in patients with interstitial lung diseases could be explained, in part, by a decrease in membrane diffusion and a reduction in the transit time of blood in pulmonary capillaries. The differences between the methods used to analyse pulmonary gas exchange are discussed.

Adult↗