S.C.M. Luijendijk

Tonic activity in inspiratory muscles during continuous negative airway pressure

We studied tonic inspiratory activity (TIA) induced by continuous negative airway pressure (CNAP) in anaesthetized, spontaneously breathing cats. TIA in the diaphragm and parasternal intercostal muscles (ICM) was quantified in response to tracheal pressure (PTR) = -0.3 to -1.2 kPa. To differentiate between reflexes from rapidly adapting receptors (RARs), slowly adapting receptors (SARs) and C-fiber endings different temperatures of the vagus nerves (TVG) were used between 4 and 37 degrees C. At PTR = -1.2 kPa mean TIA values were 41% and 62% of peak inspiratory EMG activity of control breaths for the diaphragm and ICM, respectively. After vagotomy and for TVG < 6 degrees C CNAP did not induce TIA anymore. Changes in inspiratory and expiratory time during vagal cooling down to 4 degrees C confirmed the selective block of conductance in vagal afferents of the three types of lung receptors. We conclude that CNAP-induced TIA results from stimulation of RARs. Our data strongly indicate that stimulation of SARs suppresses TIA, whereas C-fiber endings are not involved in TIA at all. The results suggest that part of the hyperinflation in bronchial asthma may be caused by TIA in response to mechanical stimulation of RARs.

The excretion of highly soluble gases by the lung in man

AbstractThe excretion (E) of inert gases by the lung depends on, among other things, their blood-gas partition coefficients (λ). According to conventional gas exchange models, E should increase with increasing λ However, recent models that take into account the tidal character of breathing and the buffering capacity of lung tissue predict that E will show a minimum in the range of large λ values (λ>10). Further, this local minimum should shift to larger λ values in exercise conditions as compared to rest conditions. The aim of this study is to verify this predicted behaviour of E. The experiments were carried out with seven healthy subjects at rest and at three work loads (50 W, 100 W and 150 W) on a bicycle ergometer. The behaviour of E was determined from the results of a simultaneous washin of four tracer gases: ethyl acetate (λ≈75), acetone (λ≈330), ethanol (λ≈2000) and acetic acid (λ≈20000). The washin lasted 4 min, and E was calculated from E = 1−pĒ/pI, where pI and PĒ are the partial pressures of the tracer gas in inspired and mixed expired gas determined from the recordings obtained during the last minute of washin. pI and PĒ were measured with a mass spectrometer. Comparison of the E values of the four gases shows that at rest a minimum value for E is found for acetone. In exercise conditions, however, the smallest E value is found for the more soluble ethanol or acetic acid. Further, under exercise conditions the E values for ethyl acetate and acetone are larger than their respective values at rest. In general, the experimental findings are consistent with the predicted behaviour of E. This means that gas exchange in the airways between gaseous and dissolved tracer gas in the airway lumen and in the airway tissue, respectively, cannot be ignored for highly soluble tracer gases. In addition, the observed differences between the E values of the four highly soluble tracer gases imply that the dead space ventilation (

Collateral ventilation and the sloping alveolar plateaus of He and SF6: A model study

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Sloping alveolar plateaus of He and SF6 measured in excised cat lungs ventilated at constant volume by pressure changes

) depends on λ, i.e. the value of

Intrapulmonary gas mixing and pulmonary gas exchange in artificially ventilated dogs

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Intrapulmonary gas mixing and the sloping alveolar plateau in COPD patients with macroscopic emphysema

is not unique. Therefore, the result for