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Biomedical subjects

R F Davis

Publications and source records attributed to R F Davis.

At least 73 records · Page 4Linked to original sources
PubMed1982

Swanson implant arthroplasty of the wrist in rheumatoid arthritis.

Severe involvement of the wrist in rheumatoid arthritis poses great functional restrictions in eating, maintaining personal hygiene, and in performing general daily activities. Twenty-six Swanson radiocarpal implant arthroplasties were performed in 23 patients. Patients' average age was 57 years, with a preoperative diagnosis in all patients of rheumatoid arthritis. Follow-up averaged 33 months (range, 5-47 months). The principal indication for surgery was pain in 23 wrists and wrist deformity in three wrists. Particular attention was paid to postoperative functional status and to any changes in performance of routine activities of daily living pertinent to the wrist. Employing a pain rating scale of 1-4, preoperative scores averaged 3.71 on the operated side and postoperative scores, 1.75. Postoperative activities of daily living that benefited from the improved extension capability of the wrist showed significant improvement. No significant improvement resulted in those activities necessitating strength or fine motor control. Prosthesis fracture in one patient, and recurrence of ulnar deviation in two patients, were the major complications. Capsular reconstruction and tendon transfer to balance the wrist were integral components of the procedure.

Adult↗
PubMed1982

Bone blood flow in the femora of anesthetized and conscious dogs in a chronic preparation, using the radioactive tracer microsphere method.

The radioactive tracer microsphere method is applicable to the study of the hemodynamics of bone. As observed previously by others, areas of predominantly cancellous bone produce higher blood flow measurements than do areas of predominantly cortical bone. Bone containing fatty marrow has lower blood flow rates than does bone containing hematopoietic marrow. Blood flow to the femoral neck was the greatest measured (26.74 +/- 1.95 ml/min/100 gm), while the diaphyseal region was the area with the lowest flow (4.67 +/- 0.46 ml/min/100 gm). There was no significant difference between consecutive measurements using up to five differently labeled radioactive microspheres. This enabled observations of the effects of an experimental procedure on bone blood flow in the same animal. Additionally, there was no statistically significant differences between regional blood flows measured 40 days apart in the same animal. Bone blood flow measurements were slightly lower in anesthetized than in conscious dogs. The RTM method is the one most suitable for the estimation of bone blood flow under either acute or chronic conditions.

Anesthesia↗
PubMed1982

Acute oliguria after cardiopulmonary bypass: renal functional improvement with low-dose dopamine infusion.

Hemodynamic and renal function response to low-dose (100 and 200 micrograms/min) dopamine infusion was studied in 15 adult cardiac surgical patients who manifested combined oliguria and left ventricular dysfunction postoperatively. Patients were studied an average of 6.6 h after ICU admission, at normothermia and after 2 consecutive hourly urine output determinations of less than 0.5 ml/kg . h in the presence of a left atrial or pulmonary artery occlusion pressure over 12 mm Hg. Dopamine infusion at 100 micrograms/min produced improvement in creatinine, osmolar and free water clearances (70 +/- 10 to 115 +/- 13, 37 +/- 4 to 93 +/- 16 and --15 +/- 2 to --37 +/- 10 ml/min, respectively), and urinary sodium concentration (15 +/- 5 to 29 +/- 10 mEq/L). Urine flow improved overall from 22 +/- 2 to 54 +/- 9 ml/h; however, in 9 of 15 patients, flow was less than 0.5 ml/kg . h (33 +/- 5 to 50 +/- 6 ml/h). In each of these 9 patients, dopamine infusion at 20 micrograms/min further improved urine flow as well as measured renal function. Plasma renin activity measured in 9 of the 15 patients before and during the 100 micrograms/min dopamine infusion was decreased from 1.95 +/- 0.57 to 0.73 +/- 0.39 ng/ml . h. The hemodynamic effect of both dopamine doses was increased cardiac output coupled with decreased systemic (SVRI) and pulmonary vascular resistance index (PVRI). In these 15 patients, low-dose dopamine infusion produced significant improvement in renal function, with resolution of oliguria in every case, and with no deleterious hemodynamic effect.

Adult↗
PubMed1981

Brain tissue pressure measurement during sodium nitroprusside infusion.

The effect of acute 25% decrease in mean arterial pressure (MAP) produced by sodium nitroprusside (SNP) infusion on mean intracerebral and cerebral perfusion pressures was examined in 7 swine with intracranial hypertension. All animals were anesthetized (alpha-chloralose), paralyzed (pancuronium bromide), orotracheally intubated and mechanically ventilated to maintain normocapnia. An epidural balloon was incrementally inflated to produce the desired brain tissue pressure (BTP) which was measured by an intracerebral microtransducer implanted contralateral to the balloon. MAP was measured from the carotid artery; cerebral perfusion pressure (CPP) was calculated as: MAP - BTP. During mildly (14 +/- 1 (SE) mm Hg) or moderately (37 +/- 3 mm Hg) increased BTP, SNP infusion increased BTP (17 +/- 1 and 44 +/- 3 mm Hg, respectively) (p less than 0.05). During severely increased BTP (70 +/- 4 mm Hg), SNP decreased BTP (53 +/- 4 mm Hg, p less than 0.05). Despite this variable BTP, CCP consistently decreased during SNP infusion. BTP and supratentorial subarachnoid cerebrospinal fluid pressure correlated closely; however, the supratentorial subarachnoid pressure consistently underestimated BTP. These findings suggest that estimation of BTP obtained from subarachnoid screw-type devices may not accurately record the pressure within cerebral tissue and the SBNP should not be administered to patients with known or suspected intracranial hypertension unless an intracranial (either BTP or subarachnoid) pressure is being monitored.

Animals↗
PubMed1981

Electrical Properties of the Plasmalemma and Tonoplast in Valonia ventricosa.

Studies were made on the electric potentials of the plasmalemma (E(co)) and tonoplast (E(vc)) in small cells (1-3 mm diameter) of Valonia ventricosa. To measure E(co), microelectrodes with long tapers were inserted into the vacuole with the path of electrode entry off-center. The microelectrode then was pushed across the vacuole and into the cytoplasm on the opposite side of the cell. A reference electrode was placed in the artificial seawater bathing the cell. A similar method was used to measure E(vc) except that the reference electrode was placed in the vacuole.Both E(co) and E(vc) were influenced by light. In the light, E(co) was -70 millivolts and it changed to -60 millivolts in the dark (cytoplasm-negative to outside). For E(vc), the potentials were +86 millivolts in the light and +69 millivolts in the dark (vacuole-positive to cytoplasm). The vacuole potential (E(vo)) was demonstrated to be the algebraic sum of E(co) and E(vc). For example, in the light, the sum of the means (+/-se) for E(co) (= -70 +/- 1) and E(vc) (= +86 +/- 5) is +16 millivolts, which is comparable to the measured E(vo) of +17 +/- 2 millivolts. In the dark, the sum of E(co) (= -60 +/- 3) and E(vc) (+69 +/- 6) is +9 millivolts and the measured value of E(vo) is +9 +/- 4 millivolts.The external K(+) concentration had a controlling effect on both E(co) and the direct current resistance of the plasmalemma, which suggests that E(co) is largely a K(+) diffusion potential. The tonoplast electrical properties were affected only slightly by external K(+).The data presented are indicative of a K(+) electrogenic influx pump in the tonoplast. It is also considered possible that H(+) might be electrogenically pumped from the cytoplasm both into the vacuole and to the cell exterior.

Journal Article↗
PubMed1981

Prevention of cigarette smoking-induced platelet aggregate formation by aspirin.

The purpose of this study was to determine whether aspirin could prevent a decrease in the platelet aggregate ratio that we previously found after cigarette smoking. Twenty healthy nonsmokers, who had not taken aspirin in the preceding seven days, smoked two tobacco cigarettes without filters during a 20-minute period. The mean platelet aggregate ratios before and after smoking were 0.91 and 0.80, respectively. When the experiments were repeated 48 hours later and seven to 18 hours after the ingestion of one tablet of aspirin (0.32 g), there was no decrease in the platelet aggregate ratio after smoking. The mean post-smoking platelet aggregate ration after aspirin (0.93) was significantly higher than before aspirin. We conclude that aspirin prevented cigarette smoking-induced platelet aggregate formation.

Adolescent↗
PubMed1980

Autoradiographic method for measuring the ischemic myocardium at risk: effects of verapamil on infarct size aftr experimental coronary artery occlusion.

Investigation of the efficacy of pharmacologic agents affecting myocardial infarct size after coronary artery occlusion is complicated by the variability of collateral flow among experimental animals which results in variability of infarct size. To overcome this difficulty, we developed an autoradiographic method to delineate the ischemic area at risk of necrosis after coronary artery occlusion and we invetigated the potential protective effect of a calcium antagonist verapamil. The left anterior descending coronary arteries of 25 barbiturate-anesthetized dogs were occluded. Thirty minutes later, highly radioactive human albumin microspheres labeled with 99mTc were injected into the left atrium. One hour after coronary artery occlusion, dogs were randomized to control or treated groups; the latter received a 0.2 mg/kg loading dose and 0.6 mg/kg per hr maintenance dose of verapamil intravenously. Eight hours after coronary artery occlusion, the dogs were killed, the hearts were excised, and the left ventricle was sectioned parallel to the atrioventricular groove; infarct size was determined planimetrically after incubation in triphenyl tetrazolium chloride. The slices were then exposed to high-speed x-ray film with image-enhancing screens. The percentage of left ventricle that was ischemic, as determined by planimetry of autoradiographs, was similar in treated and control animals (36.6 +/- 2.0% compared to 37.3 +/- 2.8%, respectively). Of the ischemic area, 92.0 +/- 4.3% was infarcted in control animals and 70.5 +/- 5.1% was infarcted in treated animals (P < 0.01). Thus, this autoradiographic method using 99mTc-labeled human albumin microspheres is useful in delineating the area of ischemia after coronary artery occlusion and in evaluating the efficacy of pharmacologic agents designed to protect ischemic myocardium. Verapamil, administered 1 hr after coronary artery occlusion, is effective in limiting infarct size.

Albumins↗
PubMed1979

Cryogenic preservation of isolated rat Islets of Langerhans: effect of cooling and warming rates.

Isolated rat Islets of Langerhans have been frozen to and stored at -196 degrees. After thawing, these islets were capable of secreting near normal levels of insulin in response to graded glucose challenge. Maximal retention of functional viability as measured by the ability of the islets to secrete insulin in response to a glucose challenge was obtained after freezing islets at a cooling rate of approximately 75 degrees per minute in the presence of 1.0 mol/1 dimethyl sulfoxol followed by warming at rates of greater than 3.5 degrees/minute. The critical freezing parameters include the time and temperature of exposure to dimethyl sulfoxide, the rate of cooling, the temperature of the post-thaw dilution from the freezing medium and the presence of serum in the dilution medium.

Animals↗
PubMed1979

Effects of ouabain and low temperature on the sodium efflux pump in excised corn roots.

Ouabain (0.05 millimolar) and low temperature (4 C) both caused the tissue Na(+) content of excised 5-day-old corn roots to increase, indicating that there is an inhibition of the Na(+) efflux pump. Na(+) efflux was measured utilizing three different methods. Each method gave similar results in terms of rate and ouabain sensitivity. With one of these methods, the compartmental efflux method, it was demonstrated that rates for Na(+) efflux increase as the external Na(+) concentration is increased; e.g. the efflux rates are 0.529, 1.78, and 3.64 microequivalents per gram fresh weight per hour for external NaCl concentrations of 1, 10, and 30 millimolar, respectively. The data indicate that the Na(+) efflux pump is located in the plasmalemma of root cells.Na(+) efflux was stimulated for 30 to 60 minutes after the introduction of ouabain. This was followed in 60 to 90 minutes by an inhibition of Na(+) efflux. The Na(+) efflux rate returned to the original level on the removal of ouabain.The transport of Na(+) to the xylem vessels was stimulated by ouabain which most likely is a consequence of the ouabain-induced increase in cytoplasmic Na(+) content.Ouabain (0.05 millimolar) had little or no effect on K(+) and Cl(-) contents, and this implies the lack of an effect of ouabain on K(+) and Cl(-) fluxes. Ouabain at a concentration of 0.01 millimolar had no effect on Na(+) flux or on tissue ion content. With 0.5 millimolar ouabain the tissue contents of K(+), Na(+), and Cl(-) were greatly reduced.Evidence is presented indicating that ouabain has no effect on Na(+) efflux in pea roots.

Journal Article↗
PubMed1978

Membrane Potential in Phaeoceros laevis: Effects of Anoxia, External Ions, Light, and Inhibitors.

Gametophyte cells of Phaeoceros laevis (L.) Prosk. have vacuole electric potentials (PDs) of about -175 millivolts; the steady PD is not affected by light but small transient PDs result after changing from light to darkness or darkness to light. The PD is more negative than the Nernst potentials for any of the permeating ions. Changes in the concentration of any one of the external ions between 0.1 and 10 mm have only a very small effect on the PD. Increases in external pH cause the PD to depolarize by a few millivolts. Azide, 2,4-dinitrophenol, and NH(4)Cl each cause rapid and reversible depressions of the PD; the effects of these agents are similar in magnitude in the light and in the dark. Anoxia depolarizes the PD by about 30 millivolts in the light and by about 60 millivolts in the dark. Ouabain and 3-(3,4-dichlorophenyl)-1,1-dimethylurea have no effects on the PD. It is concluded that the membrane potential is controlled by an electrogenic efflux pump, possibly for H(+). It is also concluded that the source of energy for the pump is respiration and not photosynthesis.

Journal Article↗
PubMed1977

Hypocalcemia, hyperphosphatemia, and dehydration following a single hypertonic phosphate enema.

Previous reports of hypocalcemia and hyperphosphatemia following use of phosphate enemas have either been in patients with renal disease or followed prolonged abuse of these products. The two patients described here had marked elevation of serum phosphate and concomitant lowering of serum calcium secondary to absorption of phosphate from a single administered enema. Associated moderate dehydration resulted in poor renal excretion of the absorbed phosphate and prolongation of hypocalcemia. Hydration was effective in permitting clearance of phosphate and restoration of normocalcemia.

Child, Preschool↗
PubMed1976

Electrochemical gradients and k and cl fluxes in excised corn roots.

The compartmental analysis method was used to estimate the K(+) and Cl(-) fluxes for cells of excised roots of Zea mays L. cv. Golden Bantam. When the measured fluxes are compared to those calculated with the Ussing-Teorell flux-ratio equation, an active inward transport of Cl(-) across the plasmalemma is indicated; the plasmalemma K(+) fluxes are not far different from those predicted for passive diffusion, although an active inward transport cannot be precluded. Whether fluxes across the tonoplast are active or passive depends upon the vacuolar potential which is unknown. Assuming no electropotential gradient, the tracer flux ratios are fairly close to those predicted for passive movement. However, if the vacuole is positive by about 10 millivolts relative to the cytoplasm, the data suggest active inward transport for K(+) and outward transport for Cl(-).Fluxes to the xylem exudate were found to be more accurately estimated from the specific radioactivity of the cytoplasm (symplasm) than from the external solution specific radioactivity. The electrochemical gradients for K(+) and Cl(-) between the xylem vessels and the surrounding stelar parenchyma indicate active K(+) and passive Cl(-) movement into the vessels. The data are interpreted as being in accord with radial transport through the symplast into living vessels.

Journal Article↗