[Establishment of a mathematical model of static pressure-volume curve in acute respiratory distress syndrome].

Objective: To explore the use of second derivate in seeking the inflection points of pressure-volume (P-V) curves and compare it with the step-by-step regression method.
Methods: Under general anesthesia, tracheotomy was done in 6 adult sheep, warm physiological saline was used to lavage the respiratory, followed by alveolar lavaged via tract through bronchofiberscope to reproduce acute respiratory distress syndrome (ARDS). The low flow technique was used to trace the P-V curves before and after the saline lavage, and features of the curves were analyzed with the software of Findgraph.
Results: The above two methods fit the P-V data well with good accuracy both in inflation and deflation limbs in normal and ARDS animals. From the graph of second derivate, the characteristic points of the P-V curves could be exactly obtained, and the low inflection points obtained by this method were well correlated with lower inflection point (LIP) +2 cm H(2)O (1 cm H(2)O=0.098 kPa) obtained by step-by-step regression method.
Conclusion: The graph of second derivate gained from P-V curves is useful to describe the inflection points, so that it can be helpful in instructing in setting the required parameters of the ventilator in the treatment of ARDS.