Biomedical subjects
J L Plewes
Publications and source records attributed to J L Plewes.
Cardiovascular responses to hemodilution and controlled hypotension in the dog.
Cardiovascular responses to acute hemodilution and controlled hypotension were studied in mongrel dogs anesthetized with halothane and paralyzed with pancuronium. Regional blood flows were determined by microsphere injections. Hemodilution to an hematocrit of 23% was produced by removal of whole blood and simultaneous infusion of Ringer's lactate solution. Subsequently, hypotension to a mean arterial pressure of 55 mmHg was produced for 90 min by intravenous infusion of trimethaphan. The hypotension resulted entirely from a 55% decrease in total peripheral resistance. Thirty minutes after initiation of controlled hypotension, there were significant increases in blood flow to the brain, liver, skeletal muscles, and diaphragm. However, at 30 min, calculated oxygen delivery had decreased to brain (-16%), renal cortex (-51%), heart (-45%), and retina (-44%). By 90 min, retinal, adrenal, and renal cortical blood flows were decreased significantly relative to control, and cerebral blood flows had returned to control levels. Absence of changes in acid-base status during the period of hemodilution and hypotension may indicate that whole body oxygen delivery was maintained at adequate levels. However, major decreases in calculated oxygen delivery after 90 min to critical tissue beds such as renal cortex (-67%) and retina (-78%) indicate that extension of the procedure past 30 min may involve risks that are not warranted by the benefits.
Bilateral simultaneous spontaneous rupture of the quadriceps tendons. Five case reports and a review of the literature.
Five cases are presented of bilateral simultaneous rupture of the quadriceps tendon and the English literature of six isolated case reports is reviewed. All the patients were men, and most were over 50 years old. The injury often happens in elderly people and there is diagnostic confusion with other causes of inability to use the legs, notably with mild strokes. In three of our five cases there was a delay in diagnosis. The cardinal features are diffuse swelling around the knee, a visible or palpable suprapatellar defect and the inability to lift the straight leg despite a functioning quadriceps and normal activity in all other muscle groups in the leg. In all our patients operative repair was undertaken, followed by six weeks immobilisation in plaster and subsequent physiotherapy. Even late repair was associated with successful rehabilitation of the patient and a return to useful function.
Role of computer graphics in simulations for teaching physiology.
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Peripheral circulatory responses to acute hyperoxia.
Acute hyperoxia (1 atm) in anesthetized dogs produced a 14% decrease in cardiac output relative to that observed with FIo2 = 0.21 and was associated with 7% decreases in heart rate and stroke volume. Changes in the distribution of peripheral blood flow during hyperoxia, as measured with radioactive labeled microspheres, included decreases in renal cortical flow (-20%), retinal blood flow (-27%), and blood flow to the caudate nucleus, mesencephalon, hippocampus, and cerebellum. Absolute blood flow to intestinal viscera, to respiratory and skeletal muscle, and to fat were unchanged. Simulation of these changes in cardiac output and distribution of blood flow using a digital computer model show a minimal change in the pattern of nitrogen gas elimination, with nitrogen partial pressures in the "slowest" body compartment within 1% of control by 60 min.
Transpleural diffusion of carbon dioxide.
Carbonic anhydrase in lung tissue might play a role in speeding the movement of CO2 between blood and alveolus. To test this hypothesis, we measured the transpleural diffusion rate of CO2 and compared it to that of oxygen, argon, and nitrogen, before and after inhibition of carbonic anhydrase activity with acetazolamide. Experiments were performed in exsanguinated dog lungs, which allowed study of CO2 dynamics in the absence of carbonic anhydrase activity from erythrocytes. The relative rate of movement of CO2 and the other gases into and out of the lung, agreed with that predicted solely on the basis of molecular weight and solubility. We conclude that there is no evidence for facilitated diffusion of CO2 across the pleural tissue.
Lung carbonate dehydratase (carbonic anhydrase), CO2 stores and CO2 transport.
A study of CO2 storage in excised, exsanguinated lungs revealed that CO2 stores include a compartment which reaches equilibration very rapidly (less than 3s) and a slower compartment which equilibrates with a half-time of approximately 15 s. Inhibition of carbonate dehydratase (carbonic anhydrase, EC 4.2.1.1) does not change the slope of the total CO2 dissociation curve of the lung but does increase the slow compartment at the expense of the fast. CO2 diffusion across the pleura is approximately 20 times faster than that of O2, a relationship that is not affected by inhibition of carbonate dehydratase. The role of tissue CO2 stores in limiting respiratory fluctuations of PCO2 or pH in arterial blood is only minor and may be of significance only in rapid, deep inspiration. CO2 uptake or release by the stores is out of phase with blood CO2 exchange. As a consequence, the time course of CO2 exchange at the mouth during expiration cannot be used to predict alveolar or capillary CO2 exchange.
Amount and rates of CO2 storage in lung tissue.
The slope of the lung tissue CO2 dissociation curve and the rate of storage of CO2 in the lung tissue were studied at 22 degrees C and at 37 degrees C in 21 isolated, bloodless dog lungs with a total of 465 separate observations. Results at the two temperatures were similar. The slope of the tissue dissociation curve of lung tissue at a PCO2 of 40 torr was approximately 0.3 ml CO2 X 100 g wet tissue-1 X torr-1. Normally, this storage was 90% complete in about 5 seconds. After carbonic anhydrase inhibition by acetazolamide, the total storage capacity was unchanged, but the rate at which storage occurred decreased significantly, so that it took about 25 seconds for 90% of the storage to be completed.
Varying the temperature around the scrotum of a conscious dog between 15 degrees C and 31 degrees C does not affect respiration or metabolism.
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Familial frontonasal dermoid cysts. Report of four cases.
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Sciatica caused by sacral-nerve-root cysts.
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Sciatica caused by sacral-nerve-root cysts.
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