[The impact of obesity on respiratory function]. / Impact fonctionnel respiratoire de l'obésité.

The respiratory impact of obesity can be both symptomatic (resting and exertional breathlessness) and functional (pulmonary function at rest and on exercise). The prevalence of breathlessness is increased in adult obese individuals, ∼50% at rest and ∼75% on exertion (mMRC score>0). Pulmonary function abnormalities in obese adults include reduced functional residual capacity (FRC) and expiratory residual volume (ERV), and less frequently reduced total lung capacity (a restrictive defect, with TLC below the 5th percentile of predicted is present in around 15% in severe obese adults), with normal residual volume (RV). Airflows are barely affected by obesity, but bronchial hyperresponsiveness (BHR) is very prevalent, which may be due to the loss of bronchoprotective effect of deep inspiration in obesity (mechanical pathophysiology of BHR). In children, the modifications of lung volumes seen are quite different: TLC is normal while FRC and RV are reduced, explaining the increase in FVC. FEV1/FVC is therefore reduced by obesity, without true airflow obstruction (dysanaptic growth). Resting oxygen consumption (V'O2) is increased due to obesity and normally increases with exercise. Maximum V'O2 is normal or weakly reduced in obese patients; on the other hand, the increase in respiratory load increases the oxygen cost of ventilation, which tends to be rapid, both at rest and during exertion. Finally, it should be noted that there is only limited statistical correlation between exercise dyspnoea and respiratory function abnormalities in obesity.

[Interpretation and use of routine pulmonary function tests: Spirometry, static lung volumes, lung diffusion, arterial blood gas, methacholine challenge test and 6-minute walk test]. / Interprétation et utilisation des explorations fonctionnelles respiratoires de routine de l'adulte : spirométrie, volumes non mobilisables, diffusion, hématose, test de provocation bronchique à la métacholine et test de marche.

Resting pulmonary function tests (PFT) include the assessment of ventilatory capacity: spirometry (forced expiratory flows and mobilisable volumes) and static volume assessment, notably using body plethysmography. Spirometry allows the potential definition of obstructive defect, while static volume assessment allows the potential definition of restrictive defect (decrease in total lung capacity) and thoracic hyperinflation (increase in static volumes). It must be kept in mind that this evaluation is incomplete and that an assessment of ventilatory demand is often warranted, especially when facing dyspnoea: evaluation of arterial blood gas (searching for respiratory insufficiency) and measurement of the transfer coefficient of the lung, allowing with the measurement of alveolar volume to calculate the diffusing capacity of the lung for CO (DLCO: assessment of alveolar-capillary wall and capillary blood volume). All these pulmonary function tests have been the subject of an Americano-European Task force (standardisation of lung function testing) published in 2005, and translated in French in 2007. Interpretative strategies for lung function tests have been recommended, which define abnormal lung function tests using the 5th and 95th percentiles of predicted values (lower and upper limits of normal values). Thus, these recommendations need to be implemented in all pulmonary function test units. A methacholine challenge test will only be performed in the presence of an intermediate pre-test probability for asthma (diagnostic uncertainty), which is an infrequent setting. The most convenient exertional test is the 6-minute walk test that allows the assessment of walking performance, the search for arterial desaturation and the quantification of dyspnoea complaint.

Implementing boundary conditions in simulations of arterial flows.

Computational hemodynamic models of the cardiovascular system are often limited to finite segments of the system and therefore need well-controlled inlet and outlet boundary conditions. Classical boundary conditions are measured total pressure or flow rate imposed at the inlet and impedances of RLR, RLC, or LR filters at the outlet. We present a new approach based on an unidirectional propagative approach (UPA) to model the inlet/outlet boundary conditions on the axisymmetric Navier-Stokes equations. This condition is equivalent to a nonreflecting boundary condition in a fluid-structure interaction model of an axisymmetric artery. First we compare the UPA to the best impedance filter (RLC). Second, we apply this approach to a physiological situation, i.e., the presence of a stented segment into a coronary artery. In that case a reflection index is defined which quantifies the amount of pressure waves reflected upon the singularity.

[Physiological characteristics associated with previous control in asthmatic children]. / Caractéristiques fonctionnelles associées au contrôle antérieur chez l'enfant asthmatique.

OBJECTIVE: To analyze MEF(50%) (central airways), RV/TLC (distal airways), reversibility of FEV(1) (bronchial tone, REV(FEV1)) and FE(NO) (inflammation) in relation to clinical events in asthmatic children on the assumption that mild symptoms and severe exacerbations in the previous 3 months could be associated with distinct functional characteristics. PATIENTS AND METHODS: A retrospective, single center, out-patient hospital study including all asthmatic children who had complete lung function testing (without and with bronchodilation) during a period of clinical stability, without treatment on the day of the test. RESULTS: Two hundred and forty-five children (11.4±2.4 years) were included: 114 (46%) were asymptomatic, 87 (36%) had minor symptoms and 44 (18%) had had a severe exacerbation in the past 3 months. FEV(1), FEV(1)/FVC and MEF(50%) were not different in these three groups. REV(FEV1) was higher in the symptomatic than in the asymptomatic group (P=0.019), RV/TLC was greater in the exacerbation group than in the asymptomatic group (P=0.019), and FE(NO) was higher in the symptomatic group than in the asymptomatic and exacerbation groups (P=0.006). CONCLUSIONS: In asthmatic children, minor symptoms and severe exacerbation in the previous 3 months are associated with distinct functional characteristics that are not detected by single baseline spirometry without treatment on the day of testing.