Abstract
Respiratory mechanics and thoraco-abdominal morphometry were evaluated in anesthetized, paralyzed, mechanically ventilated rats before and after controlled intraperitoneal injection of warm (37°C) saline. Respiratory system resistances and static elastance were determined in 9 animals using the end inflation occlusion method. Chest wall configuration at both functional residual capacity (FRC) and end inspiration (FRC + Vt) was evaluated in: (a) 6 rats by measurements of lateral and anteroposterior diameters, and circumferences at four levels: 3rd intercostal space, xiphoid, subcostal plane and crista iliaca; and (b) 8 rats by measurements of thoracic cephalo-caudal diameter. In addition, FRC changes were measured in 6 rats. Resistances were not altered but static elastance increased progressively. Morphometric changes were similar at both FRC and FRC + Vt: cephalo-caudal diameter diminished whereas all other diameters augmented; FRC decreased. In conclusion, intraperitoneal infusion of saline in rats augments elastance, and this is related to a cephalad deviation of the diaphragm plus an increase of the circumferences and diameters of the lower thorax.
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