Intraoperative lung edema monitoring by microwave reflectometry

Interstitial hydraulic conductivity and interstitial fluid pressure for avascular or poorly vascularized tumors

A correct description of the hydraulic conductivity is essential for determining the actual tumor interstitial fluid pressure (TIFP) distribution. Traditionally, it has been assumed that the hydraulic conductivities both in a tumor and normal tissue are constant, and that a tumor has a much larger interstitial hydraulic conductivity than normal tissue. The abrupt transition of the hydraulic conductivity at the tumor surface leads to non-physical results (the hydraulic conductivity and the slope of the TIFP are not continuous at tumor surface). For the sake of simplicity and the need to represent reality, we focus our analysis on avascular or poorly vascularized tumors, which have a necrosis that is mostly in the center and vascularization that is mostly on the periphery. We suggest that there is an intermediary region between the tumor surface and normal tissue. Through this region, the interstitium (including the structure and composition of solid components and interstitial fluid) transitions from tumor to normal tissue. This process also causes the hydraulic conductivity to do the same. We introduce a continuous variation of the hydraulic conductivity, and show that the interstitial hydraulic conductivity in the intermediary region should be monotonically increasing up to the value of hydraulic conductivity in the normal tissue in order for the model to correspond to the actual TIFP distribution. The value of the hydraulic conductivity at the tumor surface should be the lowest in value.

Surfactant protein A (SP-A) and angiotensin converting enzyme (ACE) as early biomarkers for pulmonary edema formation in ventilated human lung lobes

OBJECTIVE

Ex vivo perfused and ventilated lung lobes frequently develop pulmonary edema. We were looking for a suitable and early detectable biomarker in the perfusion fluid indicating lung cell damage and loss of tissue integrity in ventilated human lung lobes. Therefore, we elucidated whether surfactant protein A (SP-A) and angiotensin-converting enzyme (ACE) were measurable in the perfusion fluid and whether they were suitable indicators for edema formation occurring within the experimental time frame of 1-2 h.

METHODS

Patients (n = 39) undergoing a lobectomy, bilobectomy or pneumonectomy due to primary bronchial cell carcinoma were included in the studies. Lung lobes were extracorporally ventilated and perfused for up to 2 h. Two different perfusion fluids were used, plain perfusion buffer and perfusion buffer containing packed erythrocytes or buffy coats. Perfusion fluid samples were analyzed for SP-A and ACE using immunoassays served as perfusion fluids.

RESULTS

SP-A and ACE concentrations were analyzed in fluid sample sets of 39 and 33 perfusion experiments, respectively. Degrees of edema formation were arbitrarily classified into three groups (≤ 29, 30-59, ≥ 60 % weight gain). The maximum increase of SP-A and ACE concentrations in the perfusate was significantly higher for more pronounced edemas in case of perfusions using a mixture of blood components and buffer. Interestingly, the time courses of ACE and SP-A were highly similar.

CONCLUSION

We suggest that SP-A and ACE are promising early biochemical markers for the development for pulmonary edema formation in the ex vivo lung lobe perfusion.