A computerized method for the measurement of alveolar ventilation (VA) and the mean alveolar partial pressures of CO2 and O2 is described and tested in healthy, awake fullterm (FT) newborns and preterm (PT) infants (postnatal age 40 days). This study emphasizes the technical pitfalls generally encountered when dealing with very small infants. A sensitive pneumotachograph with a small dead space volume and a low-flow sampling system for the gas analyzer are minimum requirements. Under these technical conditions, the major problem is the scanning time of the mass spectrometer (50 Hz), which fixes the time constant, as well as the digitization sampling rate of the gas signals. This rate was not sufficient when the respiratory rate was above 90 min-1. As critical visual evaluation of each breath is required, fully automatic access to mean alveolar data is not possible. The mean dead-space volume in both FT and PT infants was 2 ml.kg-1, with a VD/VT ratio of 0.3. The mean alveolar point was 2/3 VT, as found in adults. When expressed as ml.min-1.kg-1, VA appeared to be higher than in other studies, but related to the metabolic requirements. (VCO2 = 7.8 +/- 0.2 ml.min-1.kg-1 and VO2 = 8.0 +/- 0.2 ml.min-1.kg-1), in accordance with the state of vigilance of the neonates. Indeed, the PACO2 values, which depend on the ratio VCO2/VA, are in agreement with the values of PaCO2 generally considered normal in healthy newborns over 1 week of age.(ABSTRACT TRUNCATED AT 250 WORDS)
Summary23,25,35) that in adult asthmatic patients, atropine-like substances predominantly dilate larger upstream airways and that /3r-symThe bronchodilator~ response of three Pz-agonists (fenoterol, pathomimetics predominantly dilate smaller upstream airways. salbutamol, and terbutaline), administered by a metered aerosolThe relative contribution made by large and small airways to inhaler, was assessed in 19 asthmatic children after histamine-flow limitation is of major interest to several research groups. hi^ induced bronchoconstriction. At 1-min intervals, the changes in determination is important from the therapeutical point of view, total pulmonary flow resistance (RI) and dynamic lung compliance ,in,, it is preferable to use a bronchodilating substance that (C dyn) were measured. ~f t e r rank-ordering according to the base specifically affects the area of broncho-obstruction in the particline value of C dyn (62 to 200% predicted), the patients were ular patient. divided into two groups according to lung compliance: (1) patientsThere have been numerous studies on the effect of Ps-agonists with greater compliance (C dyn, 129 to 200% predicted) and (2) in &Idren. Little is known about their specific action on the small patients with lesser compliance (C dyn, 69 to 116% predicted). The and/or large especially the site of their action, since most effect of the three bronchodilators on the mean decrease of R1 and of the published studies conducted lung function tests in the form on the increase of C dyn was studied and analyzed for each drug of breathing manoeuvres-( F~~, = forced expiratory separately. In all patients, salbutamol was the most efficient volume set, FVC = forced vital capacity, PF = peak flow, FEF bronchodilator of small airways (P < 0.02). The most striking = forced expiratory flow at different percent of the vital capacity).feature of this fin-mimetic was observed in patients whose lungs These tests fail to detect changes in small airway caliber. Moreover were initially overinflated (functional residual capacity over 120% they are effort and cooperat~on-~epen~ent, ~redicted) but not obstructed before the histamine challenge (P The present study was, therefore, designed to ascertain whether < 0.005). In these subjects C dyn and R1 are normalized after the immediate bronchodilatory response of three Pr-sympathoinhalation of salbutamol. mimetic aerosols (fenoterol, salbutamol, and terbutaline) is similar After fenoterol and terbutaline inhalation, obstruction of the in asthmatic children after histamine respiratory challenge and large airways was not fully alleviated. In addition, these two drugs whether the preferential sites of action of these three drugs can be seemed not to affect the ventilatory asynchronism (C dyn altera-detected within the bronchial tree, tions) in patients whose lungs had been overinflated before drug inhalation (C dyn again around 150% predicted).
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