Smith R M, Gray B A
J Appl Physiol Respir Environ Exerc Physiol. 1982 Dec;53(6):1608-13. doi: 10.1152/jappl.1982.53.6.1608.
The purpose of this study was to evaluate transthoracic impedance (Z) as an index of total lung liquid content at constant lung gas volume (LGV). To this end we produced rapid changes in pulmonary blood volume (PBV) in anesthetized, paralyzed, closed-chest dogs with the airway occluded at functional residual capacity. Changes in PBV produced by inflation of balloons on catheters positioned in the left atrium (LA) or inferior vena cava (IVC) were estimated from the changes in chest wall recoil pressure, using the chest wall as a plethysmograph after calibration with changes in LGV. Whereas Z increased linearly with decreases in PBV (1-6 ml/kg) produced by the IVC balloon (% delta Z/delta PBV = -0.43 ml/kg, r = -0.81), Z did not change significantly with increases in PBV (1-6 ml/kg) produced by the LA balloon. These observations indicate that changes in PBV are not the primary determinant of changes in Z and raise the possibility that other hemodynamic events are more important. Whereas aortic pressure decreased with both IVC and LA balloon inflations, right atrial pressure (Pra) increased with mitral valve obstruction and decreased with IVC obstruction. Changes in chest wall blood volume in response to changes in Pra could explain the changes in thoracic impedance. Thus, even at constant LGV, events in the systemic circulation appear to invalidate Z as an indicator of lung liquid content.
本研究的目的是评估经胸阻抗（Z）作为在恒定肺气体容积（LGV）时肺总液体含量指标的情况。为此，我们在功能残气量时气道阻塞的麻醉、麻痹、闭胸犬中快速改变肺血容量（PBV）。通过将置于左心房（LA）或下腔静脉（IVC）的导管上的球囊充气产生的PBV变化，在校准LGV变化后使用胸壁作为体积描记器，根据胸壁反冲压力的变化来估算。IVC球囊产生的PBV减少（1 - 6 ml/kg）时，Z随PBV减少呈线性增加（%ΔZ/ΔPBV = -0.43 ml/kg，r = -0.81），而LA球囊产生的PBV增加（1 - 6 ml/kg）时，Z无显著变化。这些观察结果表明，PBV的变化不是Z变化的主要决定因素，并增加了其他血流动力学事件更为重要的可能性。IVC和LA球囊充气时主动脉压均降低，而右心房压（Pra）在二尖瓣梗阻时升高，在IVC梗阻时降低。Pra变化引起的胸壁血容量变化可以解释胸阻抗的变化。因此，即使在LGV恒定的情况下，体循环中的事件似乎也使Z作为肺液体含量指标无效。
