Venegas J G, Harris R S, Simon B A
Department of Anesthesia and Critical Care, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
J Appl Physiol (1985). 1998 Jan;84(1):389-95. doi: 10.1152/jappl.1998.84.1.389.
Quantification of pulmonary pressure-volume (P-V) curves is often limited to calculation of specific compliance at a given pressure or the recoil pressure (P) at a given volume (V). These parameters can be substantially different depending on the arbitrary pressure or volume used in the comparison and may lead to erroneous conclusions. We evaluated a sigmoidal equation of the form, V = a + b[1 - e-(P-c)/d]-1, for its ability to characterize lung and respiratory system P-V curves obtained under a variety of conditions including normal and hypocapnic pneumoconstricted dog lungs (n = 9), oleic acid-induced acute respiratory distress syndrome (n = 2), and mechanically ventilated patients with acute respiratory distress syndrome (n = 10). In this equation, a corresponds to the V of a lower asymptote, b to the V difference between upper and lower asymptotes, c to the P at the true inflection point of the curve, and d to a width parameter proportional to the P range within which most of the V change occurs. The equation fitted equally well inflation and deflation limbs of P-V curves with a mean goodness-of-fit coefficient (R2) of 0.997 +/- 0.02 (SD). When the data from all analyzed P-V curves were normalized by the best-fit parameters and plotted as (V-a)/b vs. (P-c)/d, they collapsed into a single and tight relationship (R2 = 0.997). These results demonstrate that this sigmoidal equation can fit with excellent precision inflation and deflation P-V curves of normal lungs and of lungs with alveolar derecruitment and/or a region of gas trapping while yielding robust and physiologically useful parameters.
肺压力-容积（P-V）曲线的量化通常局限于计算给定压力下的比顺应性或给定容积（V）时的回缩压力（P）。这些参数可能因比较中使用的任意压力或容积而有很大差异，并可能导致错误结论。我们评估了形式为V = a + b[1 - e-(P-c)/d]-1的S形方程，以确定其表征在多种条件下获得的肺和呼吸系统P-V曲线的能力，这些条件包括正常和低碳酸血症性肺血管收缩的犬肺（n = 9）、油酸诱导的急性呼吸窘迫综合征（n = 2）以及机械通气的急性呼吸窘迫综合征患者（n = 10）。在该方程中，a对应于下渐近线的V，b对应于上、下渐近线之间的V差值，c对应于曲线真正拐点处的P，d对应于与大部分V变化发生的P范围成比例的宽度参数。该方程对P-V曲线的充气和放气支拟合效果同样良好，平均拟合优度系数（R2）为0.997±0.02（标准差）。当所有分析的P-V曲线的数据通过最佳拟合参数进行归一化，并绘制为(V-a)/b对(P-c)/d时，它们汇聚成一个单一且紧密的关系（R2 = 0.997）。这些结果表明，该S形方程能够以极高的精度拟合正常肺以及存在肺泡萎陷和/或气体潴留区域的肺的充气和放气P-V曲线，同时产生可靠且具有生理意义的参数。
