Biomedical subjects

H Guénard

Publications and source records attributed to H Guénard.

At least 19 recordsLinked to original sources

PubMed2006

[Physiological factors influencing pulmonary capillary volume and membrane diffusion].

BACKGROUND: The lung is subject to many physiological changes during life. The aim of this study was to identify factors that influence gas transfer, which depends on membrane diffusion (Dm) and pulmonary capillary blood volume (Vc). METHODS: Dm and Vc measurements were performed at rest in 135 healthy patients divided into three groups according to age and after an exercise in 22 non-trained children. Measurements were made using a simultaneous transfer of 2 gases; nitric oxide (NO) and carbon monoxide (CO). RESULTS: Dm was correlated with height in the adult group and with weight in the elderly group. Vc was not correlated with weight in the three studied groups, but correlated with height in the adult group. Dm and Vc declined with age (p<0.05), For Dm this started at the age of forty whereas a fall in Vc was apparent at sixty. Pulmonary and vascular ageing could explain these results. Sex had no effect on Dm and Vc. Exercise led to a significant rise in Dm and Vc (p<0.05) which was attributed to pulmonary capillary distension and recruitment. CONCLUSION: Knowledge of these physiological changes permits a better understanding of pathological changes.

Adolescent↗

PubMed2005

Expiratory flow limitation and obstruction in the elderly.

Elderly people commonly suffer from dyspnoea, which may stem from expiratory flow limitation (EFL). The relationship between EFL, as assessed by the negative expiratory pressure method and spirometric indices, was investigated in an elderly French population. Subjects, aged 66-88 yrs, filled in socio-demographic and standardised questionnaires, which dealt with: medical history, smoking status and respiratory symptoms. EFL measurements and forced expiratory manoeuvres were performed. Validated measurements were obtained in 750 out of 1,318 subjects: 47% were EFL+ (EFL >0), with a higher prevalence in females than in males. EFL and forced expiratory volume in one second (FEV1) were correlated with age. A total of 116, from the 750 subjects, with no medical history and no symptoms, served as a healthy group. The prevalence of EFL+ subjects increased with the grade of dyspnoea and was highest in respiratory and cardiac patients when compared with the healthy subjects. EFL did not correlate with FEV1/forced vital capacity (FVC), the usual index of obstruction. Some elderly subjects (15%) with dyspnoea but with no medical history, mainly females with small FVC and normal FEV1/FVC, had a greater EFL than the healthy subjects. In elderly people, expiratory flow limitation measurements, along with the usual forced expiratory volume in one second/ forced vital capacity ratio, may be of value for the interpretation of dyspnoea.

Age Factors↗

PubMed2004

[Physiological aspects of the decline of pulmonary function with age].

After peaking between the age of 20 and 30 years, pulmonary function declines gradually with age. This decline is related to changes in respiratory dynamics (lung mechanics, gas exchange) and also to non-respiratory factors (e.g. changes in the immune system). This age-related fall in pulmonary function is not linear, for example there is no further decline in mean PaO2 in men and women, nor in the FEV1/FVC ratio in men, afterthe age of 70 years. Caution is required when interpreting changes in pulmonary mechanics in the elderly due to greater variability of reference values in this age group.

Adaptation, Physiological↗

PubMed2002

[Physiological aspects of the decline of pulmonary function with age].

After peaking between the age of 20 and 30 years, pulmonary function declines gradually with age. This decline is related to changes in respiratory dynamics (lung mechanics, gas exchange) and also to non-respiratory factors (e.g. changes in the immune system). This age-related fall in pulmonary function is not linear, for example there is no further decline in mean PaO(2) in men and women, nor in the FEV1/FVC ratio in men, after the age of 70 years. Caution is required when interpreting changes in pulmonary mechanics in the elderly due to greater variability of reference values in this age group.

Adaptation, Physiological↗

PubMed2000

Determinants of the difference between expired and core temperatures: effect of a breath-hold.

After a 30-s breath-hold (BH), expired temperature (TE) does not reach core temperature. One explanation is that the gas in the airways is not in thermal equilibrium with the airway walls. This possibility was eliminated by comparing TE in six subjects breathing either helium-oxygen or air after a BH. Another possibility is that the airway walls and surrounding tissues have sufficient thermal inertia to slow down thermal equilibrium during BH. This was checked by measuring oral and upper esophageal temperatures after cooling or heating the airways. It took more than 2 min for these temperatures to recover their steady-state value. Six subjects were requested to perform a long apnea after hyperventilating for 1 min and then taking a single breath of 100% oxygen. TE was still lower than core temperature after a 1-min BH, and there was no difference after a 2-min BH. The difference between expired and core temperatures during BH thus appears to be due to the thermal inertia of the airways and their surrounding tissues.

Adult↗

PubMed2000

Distribution of lung density and mass in patients with emphysema as assessed by quantitative analysis of CT.

STUDY OBJECTIVE: To assess the effects of emphysema on the apex-to-base gradient of lung density (D) and lung mass (M) and to explore the relationship between M and lung function. METHODS: CT scans of whole lungs were performed in 12 healthy subjects and 29 patients who were breathing at functional residual capacity, after which lung function tests were performed. Whole D and M and regional D (RLD) and M (RLM) were calculated. The degree of emphysema was scored. RESULTS: The RLM for each height did not differ significantly between patients with disease and healthy subjects, while RLD was significantly lower in the patients with disease. A less marked nonlinear, increasing, craniocaudal gradient of D was observed in the group with disease, suggesting that the distension increases progressively from the apex to the base. RLD and RLM in the 40 to 90% lung height differed significantly among patients in the emphysema group with normal, high, and low M compared to the healthy subjects. M did not differ significantly between patients with centrilobular and panlobular emphysema, which was thought to stem from the marked variations in the results. Vital capacity was lower in the patients with low M. CONCLUSIONS: The lower RLD in the group with low M was due to both lung overinflation and to tissue loss, while in the groups with high or normal M, it was due only to lung overinflation.

Adult↗

PubMed1997

The inhibitory effect of fluoride on carbachol-induced bovine bronchial contraction.

The effect of sodium fluoride (NaF) on the responsiveness of airway smooth muscle was investigated in bovine bronchial segments. NaF (0.5-10 mM) induced a delayed concentration-dependent active pressure (AP) and reduced the lactate concentration in the solution. Pyruvate (10 mM) increased the NaF-induced contraction. There was a 50 +/- 7% decrease in carbachol (10 microM)-induced AP when bronchi were pretreated with NaF (5 mM) and a 37 +/- 9% decrease when NaF (5 mM) was added during the maintained carbachol-induced contraction. These inhibitory effects were enhanced by KCN and hypoxia. When bronchi were pre-incubated with 10 microM verapamil, a calcium channel inhibitor, the contractile effect of 5 mM NaF was reduced to 8 +/- 3% of the control. PKC activity in bronchial smooth muscle was significantly increased by NaF (5 mM). Staurosporine (30 nM) abolished the contractile effect of NaF. These results suggest that: (1) NaF either contracts or relaxes bronchial smooth muscle depending on the experimental conditions; (2) the relaxing effect is related to the inhibitory action of NaF on glycolysis; (3) the contractile effect of NaF is possibly mediated by modulation of a calcium channel via a PKC-dependent pathway; (4) carbachol-induced contraction is glycolysis pathway dependent in the absence of NaF but switches to oxidative dependent in its presence.

Animals↗

PubMed1996

Effects of nitric oxide inhalation on pulmonary serial vascular resistances in ARDS.

The pulmonary vasculature site of action of nitric oxide (NO) in patients with acute respiratory distress syndrome (ARDS) is still unknown. Seven patients were studied during the early stage of ARDS. The bedside pulmonary artery single-occlusion technique, which allows estimation of the pulmonary capillary pressure (Pcap) and segmental pulmonary vascular resistance, was used without NO or with increasing inhaled NO concentrations (15 and 25 parts per million [ppm]). Systemic circulatory parameters remained unaltered during 15 ppm NO inhalation, whereas 25 ppm NO inhalation slightly decreased mean systemic arterial pressure from 76.7 +/- 5.1 (mean +/- SEM) to 69 +/- 5.2 mm Hg (p < 0.01). Mean pulmonary arterial pressure (Ppam) and mean pulmonary capillary pressure (Pcapm) fell during 25 ppm NO inhalation from 27.4 +/- 3.5 to 21 +/- 2.2 mm Hg (p < 0.001) and from 14.8 +/- 1.5 to 10.7 +/- 1.4 mm Hg (p < 0.001) respectively, the total pulmonary resistance decreased by 28% (p < 0.01). The resistance of the capillary-venous compartment fell during 25 ppm NO inhalation from 100 +/- 16 to 47 +/- 16 dyn x s x m(2) x cm(-5) (p < 0.01), whereas the pulmonary arterial resistance was unchanged. In these patients NO inhalation during the early stage of ARDS reduces selectively Ppam and Pcapm by decreasing the pulmonary capillary-venous resistance. This latter effect may reduce the filtration through the capillary bed and hence alveolar edema during ARDS.

Administration, Inhalation↗

PubMed1996

Pulmonary gas exchange in elderly subjects.

Although important alterations in structure and function develop with age, the hypothesis that the lungs are capable of maintaining adequate gas exchange for the maximum human life span is generally accepted. This hypothesis was examined by measuring arterial oxygen and carbon dioxide tension (Pa,O2 and Pa,CO2) alveolo-arterial differences in oxygen and carbon dioxide tension (PA-a,O2 and Pa-A,CO2), steady state transfer capacity of the lung for carbon monoxide (TL,CO,ss) as well as the gas exchange ratio (R) in a series of 74 healthy subjects aged more than 68 yrs (69-104 yrs). In addition, Pa,O2 and Pa,CO2 were measured in a series of 55 young healthy subjects, who acted as controls. In the elderly subjects, except for TL,CO,ss, there was no significant correlation between any of the other variables and age. However, for a given Pa,CO2, Pa,O2 was always lower in the group of elderly subjects than in the group of young control subjects. TL,CO,ss, as well as TL,CO,ss/minute ventilation (V'k) ratio, was correlated with age, according to the following regression equations: TL,CO,ss (mL.min-1.kPa-1) = 126-0.90 x age (yrs), and TL,CO,ss/V'k (kPa-1 x 10(3)) = 13.5-0.085 x age, respectively. These results show that arterial oxygen tension did not decrease with age in this series of elderly subjects. However, the decrease in steady-state transfer capacity of the lungs for carbon monoxide with age indicates that oxygen transport could be diffusion-limited in elderly subjects, at least when oxygen consumption is increased.

Adult↗

PubMed1995

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.

Age Factors↗

PubMed1994

Bronchial smooth muscle energetics: effect of iodoacetate and hypoxia.

The active pressure (AP) and the oxygen consumption (VO2) of segments of bovine bronchi were measured during a 10 microM carbachol stimulation. VO2 did not increase during the carbachol-induced contraction whereas there was a twofold increase in the lactate production. Addition of the glycolytic blocker, iodoacetate (83 microM), decreased the AP to 68.9 +/- 6.4% of control value (n = 10, P < 0.05) whereas VO2 remained constant. The lactate concentration in the physiological solution decreased significantly (P < 0.05). When the solution was supplemented with pyruvate (10 mM), the effect of iodoacetate was antagonized. Under hypoxic condition, i.e. when the solution was bubbled with 5% CO2 in N2, VO2 decreased sharply to 7.7 +/- 3.1% of control (n = 8, P < 0.05) whereas AP did not change. The combined effect of iodoacetate and hypoxia led to a fall in both AP (12.4 +/- 3.0% of control, n = 7, P < 0.05) and VO2 (21.2 +/- 5.1%, P < 0.05). These results suggest that the energy required by bronchial smooth muscle to generate contraction could be supplied by either the aerobic or the anaerobic pathway.

Animals↗

PubMed1992

Responsiveness to histamine in human sensitized airway smooth muscle.

Passive sensitization of human isolated airway smooth muscle increases contractile responses to histamine. We looked to see whether this increase was due to an alteration in the relative role of histamine H1 and H2 receptors. Human bronchial spiral strips obtained at thoracotomy were passively sensitized by incubation in serum from atopic asthmatic patients to Dermatophagoïdes pteronyssinus and control strips were incubated in serum from healthy non-allergic non-atopic subjects. We also studied spiral strips dissected from two spontaneously sensitized human lung specimens. Cumulative concentration-response curves (CCRC) to Ca2+ (10(-5) -3 x 10(-2) M) were constructed either in the presence of 10(-5) M histamine alone or in that of the combination histamine and the H2 antagonist cimetidine (10(-5) M). Unlike in the absence of histamine, Ca2+ CCRC in the presence of histamine alone were significantly shifted to the left in the passively sensitized tissues (mean EC50: 5.7 x 10(-4) M) compared to control ones (mean EC50: 9.3 x 10(-4) M, n = 6, P < 0.05). Addition of cimetidine to histamine did not alter the Ca2+ CCRC either in the control or in passively or spontaneously sensitized airway smooth muscle. These results suggest that (i) passive sensitization increases contractile response to Ca2+ of human bronchial smooth muscle in the presence of histamine; (ii) this increase is not due to a difference in the H1- vs H2-mediated response; and (iii) H2-mediated effects do not play a significant role in spontaneously sensitized human lung as both in the non-sensitized and passively sensitized lung.

Aged↗

PubMed1991

Pulmonary diffusion limitation after prolonged strenuous exercise.

To determine the effect of strenuous prolonged exercise on alveolo-capillary membrane diffusing capacity, 11 marathon runners aged 37 +/- 7 years (mean +/- SD) were studied before and during early recovery (28 +/- 14 min) from a marathon race. Lung capillary blood volume (Vc) and the alveolo-capillary diffusing capacity (Dm) were determined in a one-step maneuver by simultaneous measurements of CO and NO lung transfer (DLCO and DLNO, respectively) using the single breath, breath-holding method. After the race, both DLCO and DLNO were significantly decreased in all subjects (-10.9 +/- 4.8%, P less than 10(-4) and -29.0 +/- 11.1%, P less than 10(-4), respectively). The mean value of the derived DmCO decreased by -29.3 +/- 11.1%, whereas Vc had not entirely returned to control resting value. Although these results do not indicate the detailed mechanism involved, interstitial lung fluid was suspected to accumulate, particularly in alveoli, during the race. We concluded that the high overall work load and the extended duration of the exercise both contributed to a transient change in the structure of the alveolo-capillary membrane thereby affecting the diffusing capacity of the alveolo-capillary membrane.

Adult↗

PubMed1987

Effect of breathing dry warm air on respiratory water loss at rest and during exercise.

The changes in respiratory water loss with time, expressed as the mass of water vapour lost per liter BTPS of ventilation (MH2O), and expired temperature (TE), used to calculate the relative humidity (ERH), were investigated in ten normal subjects while breathing warm dry air by mouth (PIH2O = 0 kPa; TI = 30 degrees C): at rest for a period of 35 min; during 15 min light muscular exercise (50 W); at increasing work load from 50 to 100 W between the 5th and 10th min of the exercise. The data collected were compared to those obtained in room air conditions (PIH2O = 0.68-1.3 kPa) and under conditions with slightly heated inspired air (TI = 28-30 degrees C). At rest, when breathing dry warm air MH2O and ERH fell during the first 15 min, while they recovered their initial values during the last 20 min. In contrast no differences in MH2O or ERH were observed when breathing ambient warm air. At constant and moderate work load for 15 min, the respiratory water loss fell significantly (compared to the 5th min) at the 10th and the 15th min when breathing warm dry air. The added hyperpnea which was obtained by increasing work load from 50 to 100 W between the 5th and 10th min of exercise did not further reduce MH2O and ERH. The transient fall in MH2O and ERH, which lasted at least 15 min either at rest or during muscular exercise, suggested that the mechanism underlying humidification of expired gas is overwhelmed by thermal stress. Since the upper airways mucosa is unable to saturate expired gas, this also suggested that the mucosa is dehydrated and probably hyperosmotic. The progressive recovery in MH2O and ERH after 15 min of warm dry air breathing at rest, suggest operation of a slow adaptive mechanism.

Female↗

PubMed1986