Effects of Maturation on Changes in Lung Mechanics During Continuous Intravenous Infusion of Histamine in Piglets. 1796

Abstract

Background. Increases in lung resistance (RL) due to i.v. histamine bolus are reported to become more pronounced with postnatal maturation (Dreshaj et al; J. Appl. Physiol. 81(4): 1785-1791, 1996). Objective. To determine if postnatal development affects the changes in RL and lung elastance (EL =1/compliance) during constant infusion of histamine. Methods. We continuously measured airway opening pressure (Pao), flow and esophageal pressure (Pes) during 30-minute intravenous infusions of histamine in seven tracheostomized, anesthetized, paralyzed and mechanically ventilated (constant tidal volume) piglets [3 newborn (4-6 days, 2.5-3.0 Kg) and 4 weaned (8 weeks, 12.3-18 Kg)]. Measurements were repeated at two concentrations (0.5 and 5.0 μg/Kg/min). RL and EL were determined by multiple linear regression; i.e., Pao(t)-Pes(t)=RL·flow(t) + EL·volume(t). Results. For both groups, RL and EL increased with histamine in a dose dependent fashion. The increases in EL were comparable regardless of dose. Changes in RL were similar at the lower histamine dose (figure). At the higher dose, the increases in RL were similar during early infusion ( 10 min) in older piglets. Conclusion. Differences in the response to histamine, in older versus newborn piglets, were only evident as a sharper rise in RL during the latter part of the higher dose infusion. Such age dependence of RL is consistent with histamine bolus data. We speculate that this phenomenon may be related to increased central airway involvement in the response as opposed to a predominantly peripheral effect because: 1) the sharp rise in RL did not coincide with a similar increase in EL, and 2) rise in RL only occurs late, when accumulation of histamine may have led to bolus-like conditions. Supported in part by an equipment grant from Novametrix Medical Systems Inc.