E. Converse Peirce

The membrane lung

Summary o 1. Measurements of oxygen and carbon dioxide transmission through Teflon, polyethylene and cellophane film are given. Of these, Teflon is the most satisfactory membrane presently available for use in an artificial lung. 2. Since the transmission rate of oxygen through the membrane greatly exceeds its diffusion rate through the blood and there is no limitation imposed on the oxygen pressure in the gas phase, the maximum exchange of oxygen in a membrane lung is primarily a function of the fluid phase dimensions and consequently of lung design. 3. Since the diffusion of carbon dioxide through blood is very rapid, the dimensions of the fluid phase (lung design) have relatively little influence on the availability of carbon dioxide to the membrane. Carbon dioxide elimination in a Teflon lung is determined almost entirely, therefore, by the characteristics of the membrane and the safe pressure of carbon dioxide in the blood. 4. Using the maximum transmission of carbon dioxide by 0.0005 inch Teflon, adequate oxygenation is achieved with a relatively crude lung design, utilizing 20 to 25 per cent of the maximum membrane diffusibility for oxygen.

Techniques of Extended Perfusion Using a Membrane Lung

Abstract Nine lightly sedated, chronically instrumented, trained dogs underwent venoarterial bypass for 5 hours. Three animals bled from the ascending aorta from flow probe erosion and 1 required resuscitation from air embolization during cannulation. The normal animals exhibited a reduction in pulse, respiration, systolic pressure, cardiac contractility, and external cardiac work. The sick animals were readily supported, those with aortic rupture by recycling the shed blood. Eight lightly anesthetized dogs were perfused for 24 hours. Four had arteriovenous perfusion and tolerated modest respiratory insufficiency. Four had venovenous perfusion and tolerated several hours of severe respiratory insufficiency. The glomerular filtration rate was about normal, but there was weight gain, hemodilution, and marked extracellular volume retention unless a diuretic was given. Blood volume control required maintenance of packed cell volume. Progressive acidemia was not a problem, and alkalization was not required. Blood trauma was acceptably small. Platelet counts seldom fell below 50%; white cell counts fell initially but exceeded the control levels at 24 hours; and plasma hemoglobin reached a peak at 12 to 18 hours and then fell to a final level of about 44 mg. per 100 ml. There were no coagulation disturbances.

A comparison of pulsatile and nonpulsatile pumping for ex vivo renal perfusion

Abstract Dog kidneys were perfused in an ex vivo circuit using a 10-minute interval of autoperfusion (with a slightly damped natural pulse) as a control mode and similar periods of pulsatile and nonpulsatile pumping, randomly alternated, as experimental perfusion modes. In one group of 10 experiments, flow was regulated to the preceding control flow with an occlusive finger pump. In a second group of 10 experiments, pressure was regulated to the preceding control pressure by means of a pressure-controlled servo pump. Pulsation resulted in equal flow at significantly lower pressure in the “adjusted pressure” group. In addition, a degree of autoregulation persisted. Constant pressure appeared superior to constant flow as a means of regulating perfusion, since this provided automatic adjustment to the progressive rise in renal resistance that occurred. Edema did not develop during the five-hour periods of perfusion, indicating the basic soundness of both regulating methods. The most logical explanation for the superiority of pulsatile flow is to be found in the viscoelastic properties of the renal vessels which impart a capacitive flow effect that is augmented by pulsatility. The higher frequency, “natural,” pulse was superior to both experimental pump pulses indicating the desirability of further defining the characteristics of an optimal pulse under various conditions of storage including hypothermia.

STUDIES IN PERFUSION HYPOTHERMIA WITH SPECIAL REFERENCE TO "DEEP HYPOTHERMIA" AND CIRCULATORY ARREST.

Summary o 1. Perfusion hypothermia produces large temperature gradients within the body since organs are cooled roughly in proportion to their basal blood flows. The difference between the coldest and the warmest portion of the body after 30 minutes of perfusion exceeds 25° C. 2. The average body temperature, which provides a proper measure of total body cooling, may be calculated from the arteriovenous temperature difference and the extracorporeal flow rate. 3. True “deep” hypothermia is not obtainable by reasonable periods of perfusion alone. 4. An important rise of core temperatures occurs during circulatory arrest in hypothermia because of the relatively high average body temperature. 5. High average body temperatures lead to continuing production of lactic acid in muscle tissue, whereas low core temperatures impair lactic acid metabolism. Thus metabolic acidosis is progressive in prolonged perfusion hypothermia, and is accentuated by total circulatory arrest. Progressive acidosis may be minimized by uniform profound cooling by combining external with perfusion hypothermia. 6. Diluents appear to have little effect on total body heat exchange during perfusion cooling. 7. Perfusion warming has a differentially greater effect on core organs. Though these are readily brought to a normal range, much of the animal may remain cold.