Effect of heliox breathing on flow limitation in chronic heart failure patients.

Patients with chronic heart failure (CHF) exhibit orthopnoea and tidal expiratory flow limitation in the supine position. It is not known whether the flow-limiting segment occurs in the peripheral or central part of the tracheobronchial tree. The location of the flow-limiting segment can be inferred from the effects of heliox (80% helium/20% oxygen) administration. If maximal expiratory flow increases with this low-density mixture, the choke point should be located in the central airways, where the wave-speed mechanism dominates. If the choke point were located in the peripheral airways, where maximal flow is limited by a viscous mechanism, heliox should have no effect on flow limitation and dynamic hyperinflation. Tidal expiratory flow limitation, dynamic hyperinflation and breathing pattern were assessed in 14 stable CHF patients during air and heliox breathing at rest in the sitting and supine position. No patient was flow-limited in the sitting position. In the supine posture, eight patients exhibited tidal expiratory flow limitation on air. Heliox had no effect on flow limitation and dynamic hyperinflation and only minor effects on the breathing pattern. The lack of density dependence of maximal expiratory flow implies that, in CHF patients, the choke point is located in the peripheral airways.

Bronchodilation test in COPD: effect of inspiratory manoeuvre preceding forced expiration.

The effects of an inspiratory manoeuvre preceding forced expiration on functional tests performed under routine conditions before and after inhalation of a bronchodilator drug (salbutamol) were assessed on 150 consecutive chronic obstructive pulmonary disease outpatients. The patients performed forced vital capacity manoeuvres either immediately after a rapid inspiration (manoeuvre no. 1) or after a slow inspiration with a 4-6 s pause (manoeuvre no. 2). Under baseline conditions, forced expiratory volume in one second (FEV1) values were 8% (% control) larger with manoeuvre no. 1 than no. 2. FEV1 values increased with salbutamol administration by approximately 8% and were, on average, still 7% larger with manoeuvre no. 1 than no. 2. The incidence of reversibility, assessed according to American Thoracic Society criteria, was 76% when manoeuvre no. 2 was selected to represent baseline conditions and manoeuvre no. 1 was chosen to represent the effects of bronchodilator administration, whereas the lowest incidence (2%) was found when manoeuvre no. 1 was selected to represent baseline conditions and manoeuvre no. 2 was chosen to represent the effects of bronchodilator administration. These results indicate that the time dependence of the forced vital capacity manoeuvre has an important impact on the assessment of routine lung function in a clinical setting and supports the notion that the time course of the inspiration preceding the forced vital capacity manoeuvre should be standardised.

Factors influencing the shape of the inspiratory flow.

An index (IS), quantitating the departure of the inspiratory flow profile (IFP) from the rectangular one, i.e. the optimal profile (IS=0), was computed from pneumotachograms recorded in 26 normal, anesthetized subjects breathing spontaneously through the endotracheal tube (ETT) or face mask (FM) with or without added resistances (R) and in 27 awake subjects breathing through the mouth and FM in the supine and seated posture at rest and during exercise (40 W) on a cycloergometer, through the nose and FM, and through the mouthpiece (MP). During anesthesia, IS decreased with R both while breathing through the ETT (DeltaIS=-0.037+/-0.006 (SE); P<0.001) and FM (DeltaIS=-0.054+/-0.008; P<0.001). This indicates that (a) the change of IFP towards the optimal shape is reflex in nature and related to the dynamic inspiratory load, and (b) tracheobronchial mechanoreceptors and inspiratory muscles are involved in this response. The reflex is also operative in awake subjects, since IS decreased whenever the inspiratory dynamic load was increased, as on turning from seated to supine posture (DeltaIS=-0.024+/-0.003; P<0.001), shifting from mouth to nose breathing (DeltaIS=-0.034+/-0.003; P<0.05), from rest to mild exercise (DeltaIS=-0.066+/-0.005; P<0.001). The different IS value between FM and MP breathing (DeltaIS=0.036+/-0.004; P<0.001) indicates, however, that other factors, likely behavioral, also affect the IFP.

Gas exchange rates and chlorophyll content of epi- and endolithic lichens from the Trieste Karst (NE Italy).

The photosynthetic activity of calcicolous endo- and epilithic lichens from the Trieste Karst area (NE Italy) was investigated. The data consist of: (a) gas exchange rates of Acrocordia conoidea, Petractis clausa, Rinodina immersa (endolithic), and Aspicilia calcarea (epilithic), recorded at different combinations of temperature, water content and radiation flux values, (b) chlorophyll content values of nine species, and (c)δ13 C values measured in 24 lichen species with different growth-forms. The results show that: (1) the maximum photosynthetic rates of endolithic lichens are rather small, ranging between 0·2 and 1·5µmol CO2 m-2 h-1 at optimal conditions; (2) the relation between thallus water content and photosynthesis differs from that of foliose and fruticose lichens; the optimum water content of endolithic lichens is particularly small, when expressed in g H2 O cm-2 ; (3) the algae of endolithic lichens, which belong to different systematic groups, are light-saturated at a small radiation flux; (4) chlorophyll contents of endolithic lichens are rather large, being similar to those of some parmelioid lichens. The ecological implications of the endolithic growth-form are briefly discussed. Endolithic lichens should be regarded as slow-growing, stress-tolerant organisms, which are rather similar in their physiology to epilithic crustose lichens; they have a high resistance to CO2 diffusion, saturation being reached only at a very large CO2 concentration.