Influence of lung inflation on the cross-sectional area of central airways in normals and in patients with lung disease.

The influence of lung inflation on the cross-sectional area of the trachea and main bronchi was investigated in 2 normal subjects, 2 patients with emphysema, and 1 patient with pulmonary fibrosis. Fiberoptic cinebronchoscopy was used to measure the cross-sectional area of the airways using calibrated small Teflon discs placed on the airway wall as reference. As an estimate of airway compliance at intermediate lung volumes, radial distensibility was defined as the change in cross-sectional area per change in airway pressure minus esophageal pressure divided by the cross-sectional area at functional residual capacity. Both in normal subjects and in patients with emphysema, the radial distensibility was larger in the trachea than in the main bronchi without differences between the right and left main bronchus. The area-pressure curves revealed alinearity and hysteresis in both groups with an increased distensibility in pulmonary emphysema. In a patient with pulmonary fibrosis, the distensibility was decreased by a factor of ten and the area-pressure curve was linear. These observations suggest altered static mechanics of extraparenchymal, intrathoracic airways in patients with pulmonary emphysema and fibrosis.

Continuous measurement of respiratory resistance in asthmatic children.

In 13 children (7-13 years old) with bronchial asthma in remission, respiratory system resistance was continuously measured by the forced oscillation method at 10 Hz, using on-line digital computer analysis. Corrections were made for mouth impedance which was determined from a prior Valsalva maneuver. Functional residual capacity was also periodically determined by the body plethysmographic technique in order to allow calculation of specific respiratory system conductance (SGRS). The total observation period of 45 min consisted of quiet breathing interrupted by vital capacity maneuvers. In a single-blind design, eight children were given 0.15 mg isoproterenol sulfate from a proprietary spray delivered in the beginning of an inspiratory vital capacity maneuver while five received a placebo (freon propellent alone). A significant increase in SGrs (+53%) was observed 75 sec after isoproterenol sulfate administration. SGrs peaked after 2 min (+ 61%) and remained elevated significantly for 10 min. No significant changes occurred in the placebo group. The immediate decrease in SGrs which was observed following control vital capacity maneuvers, was prevented by isoproterenol sulfate but not by the freon propellent. Our findings suggest that although peak bronchodilation does not occur before 2 min following isoproterenol sulfate inhalation, an effect, namely prevention of bronchoconstriction induced by a deep breath, is already detectable within seconds.

Tracheal mucous transport in experimental canine asthma.

Tracheal mucous velocity (TMV) was measured in experimental canine asthma. All 10 sensitive dogs exposed to an aerosol of Ascaris suum extract showed a decrease in TMV to about one-third of base-line values within 45 min whereas only half of them (reactors) responded with bronchospasm as measured by a significant reduction in specific respiratory system conductance (SGrs). Mean TMV remained decreased at the end of the 2-h observation period when mean SGrs had returned to base-line values in the reactors. Neither TMV nor SGrs changed in nonsensitive animals who inhaled ragweed antigen. Aerosols of acetylcholine and histamine increased TMV thereby excluding these mediators as responsible for the impairment of mucous transport in asthma. Nebulization of A. suum antigen together with a selective antagonist of slow reacting substance of anaphylaxis (srs-a) produced a marked increase of TMV in all dogs regardless of whether or not bronchospasm was elicited. This suggests that the observed decrease in TMV may be related to the release of SRS-A during the immunologic reaction.

Effects of lung inflation on pulmonary arterial blood volume in intact dogs.

The isolated effects of alterations of lung inflation and transmural pulmonary arterial pressure (pressure difference between intravascular and pleural pressure) on pulmonary arterial blood volume (Vpa) were investigated in anesthetized intact dogs. Using transvenous phrenic nerve stimulation, changes in transmural pulmonary arterial pressure (Ptm) at a fixed transpulmonary pressure (Ptp) were produced by the Mueller maneuver, and increases in Ptp at relatively constant Ptm by a quasi-Valsalva maneuver. Also, both Ptm and Ptp were allowed to change during open airway lung inflation. Vpa was determined during these three maneuvers by multiplying pulmonary blood flow by pulmonary arterial mean transit time obtained by an ether plethysmographic method. During open airway lung inflation, mean (plus or minus SD) Ptp increased by 7.2 (plus or minus 3.7) cmH2O and Ptm by 4.3 (plus or minus 3.4) cmH2O for a mean increase in Vpa by 26.2 (plus or minus 10.7) ml. A pulmonary arterial compliance term (Delta Vpa/Delta Ptm) calculated from the Mueller maneuver was 3.9 ml/cmH2O and an interdependence term (Delta Vpa/Delta Ptp) calculated from the quasi-Valsalva maneuver was 2.5 ml/cmH2O for a 19% increase in lung volume, and 1.2 ml/cmH2O for an increase in lung volume from 19% to 35%. These findings indicate that in normal anesthetized dogs near FRC for a given change in Ptp and Ptm the latter results in a greater increase of Vpa.

Relationship between frequency dependence of lung compliance and distribution of ventilation.

The previously demonstrated empirical association between frequency dependence of lung compliance and distribution of ventilation, the latter determined by the N(2) washout technique, was confirmed by establishing a mathematical link between the two tests. By assuming a two-compartment system with known compliances and making corrections for Pendelluft and common dead space mixing effects, the ratio of dynamic to static compliance (C(dyn)/C(st)) for any respiratory frequency can be calculated from the compartmental analysis of the N(2) washout at a single respiratory frequency. By using these equations, a good correlation was found between calculated and measured C(dyn)/C(st) in dogs with artificially induced bronchial obstruction and in young smokers or young nonsmokers after carbachol inhalation. A two-compartment N(2) washout was demonstrated in 10 young healthy smokers at one or two respiratory frequencies whereas all 10 normal controls showed a single exponential curve. These findings indicate that the non-invasive N(2) washout test is capable of predicting C(dyn)/C(st) and at the same time gives a direct measure of gas distribution. Further, it appears to be a highly sensitive method for the detection of "small airway disease."