Fretschner R, Laubscher T P, Brunner J X
Klinik für Anaesthesiologie und Transfusionsmedizin, Universität Tübingen, Germany.
Intensive Care Med. 1996 Dec;22(12):1328-34. doi: 10.1007/BF01709546.
The aims of the present study were 1) to evaluate a method for identification of "slowly" distensible compartments of the respiratory system (rs), which are characterized by long mechanical time constants (RC) and 2) to identify "slowly" distensible rs-compartments in mechanically ventilated patients.
Prospective study on a physical lung model.
Intensive Care Unit, University Hospital, Tübingen.
19 patients with severe lung injury (acute respiratory distress syndrome, ARDS) and on 10 patients with mild lung injury.
Positive end-expiratory pressure (PEEP)-increasing and -decreasing steps of about 5 cmH2O were applied and the breath-by-breath differences of inspiratory and expiratory volumes (delta V) were measured. The sequence of delta Vs were analyzed in terms of volume change in the "fast" compartment (Vfast), the "slow" compartment (Vslow), total change in lung volume (delta VL) and mechanical time constant of the slow compartment (RCslow). Thirty-eight measurements in a lung model revealed a good correlation between the preset Vslow/delta VL and Vslow/delta VL measured: r2 = 0.91. The Vslow/delta VL measured amounted to 0.94 +/- 0.15 of Vslow/delta VL in the lung model. RCslow measured was 0.92 +/- 0.43 of the RCslow reference. Starting from a PEEP level of 11 cmH2O PEEP-increasing and PEEP-decreasing steps were applied to the mechanically ventilated patients. Three out of ten patients with mild lung injury (30%) and 7/19 patients with ARDS (36.8%) revealed "slowly" distensible rs-compartments in a PEEP-increasing step, whereas 15/19 ARDS patients and 1/10 patients with mild lung injury showed "slowly" distensible rs-compartments in a PEEP-decreasing step (78.9% vs 10%, P < 0.002, chi-square test).
The gas distribution properties of the respiratory system can be easily studied by a PEEP-step maneuver. The relative contribution of the "slow" units to the total increase of lung volume following a PEEP step could be adequately assessed. "Slowly" distensible rs-compartments could be detected in patients with severe and mild lung injury, however significantly more ARDS patients revealed "slow" rs-compartments in PEEP-decreasing steps. The influence of "slowly" distensible rs-compartments on pulmonary gas exchange is unknown and has yet to be studied.
本研究的目的是：1）评估一种识别呼吸系统“缓慢”可扩张腔室的方法，这些腔室的特征是机械时间常数（RC）较长；2）识别机械通气患者中“缓慢”可扩张的呼吸系统腔室。
对物理肺模型进行前瞻性研究。
图宾根大学医院重症监护病房。
19例重度肺损伤（急性呼吸窘迫综合征，ARDS）患者和10例轻度肺损伤患者。
应用呼气末正压（PEEP）增减约5 cmH₂O的步骤，并测量吸气和呼气量的逐次呼吸差异（δV）。根据“快速”腔室（Vfast）、“缓慢”腔室（Vslow）的容积变化、肺容积的总变化（δVL）和缓慢腔室的机械时间常数（RCslow）分析δV的序列。在肺模型中的38次测量显示，预设的Vslow/δVL与测量的Vslow/δVL之间具有良好的相关性：r² = 0.91。测量的Vslow/δVL相当于肺模型中Vslow/δVL的0.94±0.15。测量的RCslow为RCslow参考值的0.92±0.43。从11 cmH₂O的PEEP水平开始，对机械通气患者应用PEEP增加和PEEP降低步骤。10例轻度肺损伤患者中有3例（30%）和19例ARDS患者中有7例（36.8%）在PEEP增加步骤中显示出“缓慢”可扩张的呼吸系统腔室，而19例ARDS患者中有15例和10例轻度肺损伤患者中有1例在PEEP降低步骤中显示出“缓慢”可扩张的呼吸系统腔室（78.9%对10%，P < 0.002，卡方检验）。
通过PEEP步骤操作可以轻松研究呼吸系统的气体分布特性。可以充分评估“缓慢”单元对PEEP步骤后肺容积总增加的相对贡献。在重度和轻度肺损伤患者中均可检测到“缓慢”可扩张的呼吸系统腔室，然而，在PEEP降低步骤中，ARDS患者中显示“缓慢”呼吸系统腔室的比例明显更高。“缓慢”可扩张的呼吸系统腔室对肺气体交换的影响尚不清楚，有待进一步研究。
