Gregory R. Mason

Fluid reabsorption and glucose consumption in edematous rat lungs.

Solute and water uptake were studied in isolated perfused rat lungs with airspaces filled with the perfusion fluid. The albumin in this solution was labelled with Evans blue (T-1824), and uptake of fluid from the airspaces was documented by an increase in T-1824 concentration in airway fluid of 6.5 ± 1.6% (n = 5, SEM) at 1 hour and 12.2 ± 0.9% (n = 10) at 2 hours. The only detectable osmotic force that could have contributed to a loss of fluid from the alveolar fluid was a decrease in airspace glucose concentrations, which fell much more rapidly (from 150 mg/dl to 58.7 ± 7.1 mg/dl, n = 10, after 2 hours) than plasma glucose (from 150 mg/dl to 128.9 ± 3.7 mg/dl). Addition of 5 ± 10−5 M terbutaline to the perfusate and airspace solutions nearly doubled fluid reabsorption at 1 hour, an effect that was inhibited by propranolol and did not appear to be related to glucose consumption. Exposure to terbutaline for 2 hours increased epithelial permeability to 3H-mannitol and 22Na+. These observations suggest that active sodium transport and epithelial metabolism or transport of glucose in airway fluid may each play a role in the reabsorption of edema fluid.

Pulmonary Imaging in Pregnancy: Maternal Risk and Fetal Dosimetry

A Tc-99m macroaggregated albumin (MAA) perfusion lung scan and a Tc-99m DTPA aerosol ventilation scan were performed for suspicion of pulmonary embolism (PE) in a patient who was ten weeks pregnant. There was considerable reluctance on the part of the obstetricians to permit this study. Standard MIRD dose estimates to the fetus were performed, which showed a maximum fetal exposure of about 50 mrem. It was concluded that the risk to mother and fetus from undiagnosed and untreated PE is much greater than the negligible risk to the fetus from the radiation exposure; fear of fetal radiation damage should not be a deterent to performing these scans.

99mTc-DTPA aerosol deposition and clearance in COPD, interstitial disease, and smokers.

The application of 99mTc-DTPA radioaerosols to a variety of clinical disorders is described. With the development of simple equipment that can deliver very small droplets, this approach has become increasingly popular for measurements of the distribution of ventilation in patients with obstructive lung disease and suspected pulmonary embolism. In addition. by determining the rate at which the radionuclide is cleared from the lung, information has been obtained concerning the permeability of the pulmonary epithelium to extracellular indicators. Accelerated clearance rates have been found in patients with a variety of chronic interstitial lung diseases indicating that epithelial permeability is increased. Accelerated clearance rates have also been found with acute inflammation of the lung such as the adult respiratory distress syndrome and pneumocystis pneumonia. Furthermore, rapidly reversible increases in 99mTc-DTPA clearance occur in smokers and may be related to the inflammatory changes that contribute to the development of emphysema.

Diffusion of labeled water and lipophilic solutes in the lung

A perfused, in situ rabbit lung preparation was used to study the diffusion of tritiated water and labeled lipophilic solutes from the airways into the pulmonary vasculature. Following instillation into the airways, initial concentrations of labeled ethanol and butanol in the left atrial outflow usually exceeded those of 3H2O when the lungs were perfused at 37 degrees. In contrast, initial concentrations of [14C]acetone equaled 3H2O concentrations, and those of [14C]antipyrine were below 3H2O concentrations. Increasing the rate of perfusion increased concentrations of the labeled butanol and acetone but decreased that of antipyrine relative to 3H2O. This suggests that the tissues separating the gaseous and vascular compartments of the lung are more permeable to 3H2O than to antipyrine but less permeable to 3H2O than to the alcohols and acetone. Cooling slowed permeation of ethanol and antipyrine relative to 3H2O but seemed to slow diffusion of butanol less than that of 3H2O. These differences cannot be related to movement in the aqueous phase and suggest that cooling slows solute diffusion through lipid membranes. This phenomenon appears to be related to the activation energy of each molecule between the aqueous and lipid phases rather than a phase change in the membrane. 3H2O seems to diffuse through aqueous regions of the air-perfusate barrier.

Application of nuclear medicine techniques to the study of ARDS.

Radionuclide techniques used for the diagnosis and study of ARDS include the routine clinical procedures of perfusion lung scanning, gallium and white-cell imaging, as well as PET, indicator dilution methods for measuring extravascular lung water, and means of measuring protein accumulation, protein flux, and solute transfer. The techniques that reflect the rate of protein leak from the microvasculature and sensitive measures of rapidly reversible alveolar injury appear most promising. While clinical usefulness remains to be documented, these methods may ultimately assist with the diagnosis of ARDS and with the evaluation of prognosis and therapy.