Influence of acute isocapnic hypoxia on bronchial calibre and "expiratory reserve" volume in dogs

A computed tomographic scan assessment of endotracheal suctioning-induced bronchoconstriction in ventilated sheep

This study was directed at assessing changes in bronchial cross-sectional surface areas (BCSA) and in respiratory resistance induced by endotracheal suctioning in nine anesthetized sheep. Cardiorespiratory parameters (Swan-Ganz catheter), respiratory resistance (inspiratory occlusion technique), BCSA, and lung aeration (computed tomography) were studied at baseline, during endotracheal suctioning, and after 20 consecutive hyperinflations. Measurements performed initially at an inspired oxygen fraction (FI(O(2))) of 0.3 were repeated at an FI(O(2)) of 1.0. At an FI(O(2)) of 0.3, endotracheal suctioning resulted in atelectasis, a reduction in BCSA of 29 +/- 23% (mean +/- SD), a decrease in arterial oxygen saturation from 95 +/- 3% to 87 +/- 12% (p = 0.02), an increase in venous admixture from 19 +/- 10% to 31 +/- 19% (p = 0. 006), and an increase in lung tissue resistance (DR(rs)) (p = 0. 0003). At an FI(O(2)) of 1.0, despite an extension of atelectasis and an increase in pulmonary shunt from 19 +/- 5% to 36 +/- 2% (p < 0.0001), arterial O(2) desaturation was prevented and BCSA decreased by only 7 +/- 32%. A recruitment maneuver after endotracheal suctioning entirely reversed the suctioning-induced increase in DR(rs) and atelectasis. In three lidocaine-pretreated sheep, the endotracheal suctioning-induced reduction of BCSA was entirely prevented. These data suggest that the endotracheal suctioning-induced decrease in BCSA is related to atelectasis and bronchoconstriction. Both effects can be reversed by hyperoxygenation maneuver before suctioning in combination with recruitment maneuver after suctioning.

Hypoxia modulates mediator responses and neurotransmission in guinea-pig trachea in vitro

To discover whether hypoxia affects mediator responses and neurotransmission in tracheal smooth muscle, we studied in vitro tracheal segments from guinea-pigs under isometric conditions. Hypoxia itself did not alter the basal tone. The maximum response to acetylcholine and histamine under hypoxia was less than that under oxygenated conditions. The logarithm of 50% effective concentration (log EC50) of the response to acetylcholine under hypoxia was not altered, but the log EC50 of the response to histamine decreased significantly. In contrast to the response to exogenous acetylcholine, the maximum contractile response to electrical field stimulation (EFS) under hypoxia was not different from that under oxygenated conditions, but the logarithm of 50% effective frequency of contractions caused by EFS under hypoxia decreased significantly. On the other hand, non-adrenergic-non-cholinergic relaxation caused by EFS was unaffected by hypoxia. These observations suggest that hypoxia can modulate the responses of tracheal smooth muscle to acetylcholine, histamine and nerve stimulation.