ABSTRACT
Carbon dioxide transfer is increased when the gas phase of a hollow fiber membrane lung is operated at hypobaric pressures. Oxygen transfer is augmented by hyperbaric pressures. However, uncoated hollow fibers transmit gas bubbles into the blood when operated at a pressure greater than 800 mmHg and may have increased plasma leakage when operated at hypobaric pressures. Ultrathin polymer coatings may avoid this problem while reducing thrombogenicity. The authors coated microporous polypropylene hollow fibers with 380 microns outer diameter and 50 microns walls using 1, 2, 3, and 4% solutions of polysulfone in tetrahydrofuran by dipping or continuous pull through. These fibers were mounted in small membrane lung prototypes having surface areas of 70 and 187 cm2. In gas-to-gas testing, the longer the exposure time to the solution and the greater the polymer concentration, the less the permeation rate. The 3% solutions blocked bulk gas flow. The coating was 1 micron thick by mass balance calculations. During water-to-gas tests, hypobaric gas pressures of 40 mmHg absolute were tolerated, but CO2 transfer was reduced to 40% of the bare fibers. Hyperbaric gas pressures of 2,100 mmHg absolute tripled O2 transfer without bubble formation.
Subject(s)
Artificial Organs , Lung , Oxygenators, Membrane , Carbon Dioxide , Cardiopulmonary Bypass/instrumentation , Equipment Design , Evaluation Studies as Topic , Humans , In Vitro Techniques , Microscopy, Electron , Oxygen , Polymers , Pressure , Pulmonary Gas Exchange , Sulfones , Surface PropertiesABSTRACT
It may be possible to design an intravascular membrane lung with gas transfer properties augmented by the natural flow oscillations in the venous and pulmonary circulation caused by the beating heart and ventilatory movements. The authors used a simple dye visualization technique, the Pierce-Donachy assist pump, and mass spectrometry to investigate these effects on membrane lungs made with tethered, blind-ended, microporous, polypropylene fibers using in vitro tests in water saturated with O2, CO2, and He. Prototypes were constructed on a 7.5 Fr pulmonary artery catheter. The fibers had an outer diameter (OD) of 380 microns and a wall thickness of 50 microns and were mounted on 4.8 mm OD sleeves. Control measurements were taken over a range of steady water flows from 0.4 l/min to 3 l/min. While pumping the same water flow rates with a roller pump, the Pierce-Donachy pump generated pulsatile flow at a rate of 45 beats/min and a systolic duration of 300 msec. This produced a phasic flow with an instantaneous average flow velocity varying from 0 to as high as 46 cm/sec. O2 and CO2 transfer increased by as much as 91% and 59%, respectively. The largest effects were seen at the lower water flow rates.
