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Biomedical subjects

R E Clark

Publications and source records attributed to R E Clark.

At least 271 records · Page 15Linked to original sources
PubMed1980

Thymectomy for myasthenia gravis in the young adult. Long-term results.

An 8 year experience with a prospective treatment program for patients with myasthenia gravis is reviewed with particular focus on the results in patients less than 35 years of age. Twenty myasthenic young adults with an average age of 24 years and a duration of symptoms of 22 months, excluding two with the juvenile form, had thymectomy followed by short-term anticholinesterase and long-term prednisone therapy. All of the 18 patients with a short duration of symptoms are in markedly improved condition and 61% of them are in remission after a mean postoperative period of 32 months. The longest follow-up period is 7.3 years. Two patients have mild improvement. There was no correlation between thymic disease and clinical result. Complete en bloc extirpation of all thymic and adjacent tissue through a median sternotomy is advocated. The patients were treated postoperatively with prednisone, 100 mg/day, a regimen which gradually is changed to every other day medication and finally a gradual reduction of dosage. There have been no operative or late deaths and no serious complications of therapy. The effects have been long lasting, with not a single instance of significant recurrence of symptoms of myasthenia gravis 6 months after thymectomy.

Adolescent↗
PubMed1979

Nifedipine: a myocardial protective agent.

The effectiveness of the calcium antagonist nifedipine in preserving postischemic myocardial function and structural integrity was experimentally demonstrated in isolated rabbit hearts, in conscious dogs subjected to myocardial infarction, in open chest anesthetized dogs with normothermic regional ischemia induced for 1 to 2 hours and in dogs undergoing hypothermic global ischemia for 2 hours followed by 2 hours of reperfusion. Nifedipine had a beneficial effect on postischemic myocardial stiffness and mitochondrial calcium accumulation, which were correlated. Administration of nifedipine at the onset of myocardial infarction increased blood flow to ischemic zones of myocardial infarction and resulted in less loss of creatine kinase. It reduced by two- to three-fold the volume of the ischemia-reperfusion injury induced by left anterior descending coronary arterial occlusion and release and preserved indexes of hemodynamic function. Nifedipine was found effective in protecting myocardial performance and structure after 2 hours of global ischemia during hypothermic cardiopulmonary bypass. It is suggested that this agent may be useful as an adjunct to cold cardioplegia in man for enhanced myocardial protection during cardiac surgery.

Animals↗
PubMed1979

Tissue damage from electrosurgical power output variations in hamster tongues.

An investigation was designed to determine the differences in the amount of tissue damage produced by variations in the amount of cutting power delivered to the hamster tongue with electrosurgery. By dividing the power of an electrosurgical instrument into 5 W intervals, from the lowest setting which would produce a cut up to the 50 W setting, histometric comparisons were made in the hamster tongue. Histologic analysis showed the following: 1. The 30 W power interval produced less tissue damage than any other power interval. 2. The 25 and 35 W intervals produced significantly greater damage than the intervals from 40 thorugh 50 W. 3. Histologically the experimental defect showed an area of coagulation necrosis approximately 50 mu wide along the margin of the incision. Tissue damage decreased laterally and inferiorly from the surface of the defect except at the 30 W setting, where the damage in the epithelium and the damage in the connective tissue were essentially equal. 4. There is some validity to the sparking-dragging test for setting the power interval of an electrosurgical instrument. 5. Higher power values which produce excessive sparking should be avoided by the clinician during electrosurgery due to the imprecise nature of the clinical incision.

Animals↗
PubMed1979

An improved isolated heart preparation for external assessment of myocardial metabolism.

To facilitate characterization of myocardial metabolism with the use of positron-emitting tracers, we developed an isolated heart preparation designed to simulate physiological levels of flow and substrate extraction. Isovolumically beating hearts were perfused retrograde at 60 mmHg with modified non-recirculating Krebs-Henseleit (KH) solution with or without washed sheep red blood cells at a hematocrit of 25 or 40 (KH-RBC25, KH-RBC40). Left ventricular (LV) systolic pressure averaged 63 mmHg with KH alone, 78 with KH-RBC25, and 98 with KH-RBC40. LV dP/dt, pressure-time index, and oxygen consumption increased in an analogous fashion. Fatty acid extraction increased from 1.5% with KH to 11.8% in hearts perfused with KH-RBC40, although net uptake was not increased markedly because of the associated differences in flow (4.6 ml.g-1.min-1 with KH and 1.5 with KH-RBC40). Hearts perfused with erythrocyte-rich media exhibited functional and metabolic stability and less edema. The preparation avoids intrinsic limitations encountered with buffer-perfused hearts and should prove useful for characterization of cardiac metabolism with radiolabeled tracers relevant to positron emission transaxial tomography.

Animals↗
PubMed1979

Comparison of bubble and membrane oxygenators in short and long perfusions.

Eighty patients had cardiopulmonary bypass (CPB), half having short (109 +/- 11 minutes) perfusions and half having long (188 +/- 14 min) perfusions. Twenty patients in each group were perfused with bubble oxygenators (Bentley, Harvey, or Galen) and 20 with membrane oxygenators (Modulung or Teflo). Hemodilution to a hematocrit value of 22.5% +/- 1.4% and hypothermia to 28 degrees +/- 2 degrees C were used in all patients. Complete hemograms, sequential multiple analyzer 18 tests, coagulation profiles, blood gases and pH, three immunoglobulins, and two complement fraction proteins were sampled as follows: three times before perfusion, one to ten times during perfusion, 1 hour immediately after perfusion, and 4, 24, and 48 hours postoperatively. Data in concentration terms were compared statistically and reported as mean and standard error for each subset. Additionally, rates of gain or loss were calculated in terms of quantity per liter of blood pumped per minute. During perfusion for both duration sets, use of a membrane oxygenator resulted in greater pump flows (4.55 +/- 0.15 L/min versus 3.75 +/- 0.11 L/min), lower total peripheral resistances (1,125 +/- 63 dynes.sec.cm-5 versus 1,652 +/- 115 dynes.sec.cm-5), and greater urinary outputs (9.4 +/- 1.1 ml/min versus 2.2 +/- 0.6 ml/min) than in the bubble oxygenator subsets. Comparisons of measured and calculated data in the immediate postperfusion interval showed no differences between bubble and membrane oxygenator subsets for short perfusions. In long perfusions, the membrane subset had lower plasma hemoglobin and white cell concentrations and generation rates, smaller (3 to 8 1/2 times) losses of IgG, IgM, C3 and shed blood necessitating less transfusion, and greater C4 losses. The membrane oxygenator systems used were more complex and costly and offered no advantages for short perfusion in adults. In anticipated long perfusions or where bleeding may be a problem, a membrane oxygenator appears more efficacious than bubble systems. For perfusions of less than 2 hours, membrane oxygenators had no biochemical or hematologic advantage over the bubble devices used in this study.

Blood Cell Count↗
PubMed1979

In vitro durability of Hancock Model 242 porcine heart valve.

Two Hancock Model 242 prostheses, tissue anulus diameter 21 mm., were tested in a closed, low-volume, accelerated fatigue tester. The fluid media was sterils fresh-frozen plasma. The normal human aortic root was simulated. The cyclic rate was 20 Hz at 37 degrees C. The prostheses developed severe fatigue at 77 million cycles. Fraying of the free edges was found after 2 million cycles. Small tears near the commissures and then holes between collagen bundles at the base of the leaflets appeared at 7 million cycles. At 71 million cycles the leaflets began to tear and complete prolapse, with gross valvular insufficiency occurring at 77 million cycles. The accelerated wear of Hancock procine prosthesis is frequency dependent and independent of media and the flow geometry of the testing device.

Animals↗
PubMed1978

Histologic evaluation of electrosurgery with varying frequency and waveform.

This investigation was designed to determine the differences in tissue alteration produced by electrosurgical machines with different carrier frequencies and waveforms. Histologic analysis showed that: 1. The machine with full-wave rectification and the lowest frequency of operation (machine I, 1.7 MHz) produced significantly greater tissue alteration in the superficial tissue layers than the full-wave rectification machines with higher frequencies of operation. 2. The continuous-output waveform produced significantly less tissue alteration in the superficial tissue layers than the modulated type at the same frequency of operation. 3. Histologically, the experimental defect showed a band of coagulation necrosis approximately 50 mu wide along the margin of the incision. Tissue destruction decreased laterally and inferiorly from the surface of the defect. 4. The experimental defect was similar in shape to the physical form of the cutting electrode.

Animals↗
PubMed1978

Durability of prosthetic heart valves.

Accelerated fatigue testing of clinical heart valves has been performed at cyclic rates of 33 to 35 cycles per second at 37 degrees C using water for non-biological valves and glutaraldehyde solutions for tissue valves. Flows were in the physiological range, and the pressure difference across each valve during closure was 100 +/- 25 mm Hg. The results showed that major fatigue occurred for the Starr-Edwards 2320 at 150 million cycles, the Hufnagel trileaflet at 124 million cycles, the Björk-Shiley Delrin disc at 140, the Björk-Shiley Pyrolite disc at 973, the Beall 103 at 60, the Hancock porcine at 62, the Carpentier-Edwards porcine at 34, and the Ionescu-Shiley porcine pericardial prosthesis at 65 million cycles. The Lillehei-Kaster was removed after 762 million cycles without discernible wear. Three facts emerged from the testing data: (1) the component worn in vitro wears in vivo; (2) the sites of in vitro fatigue on the component are identical to clinical specimens; and (3) those valves that have high durability in vitro have given similar performance in patients. The in vitro and clinical data for tissue valves do not correlate. The possible reasons for the discrepancy are discussed, and a note of caution is made regarding realistic expectations of clinical durability of tissue valves.

Bioprosthesis↗
PubMed1978

Percutaneous transthoracic aspiration needle biopsy.

An experience based on 1,211 patients has shown aspiration needle biopsy to be a valuable technique for diagnosing bronchogenic carcinoma and other localized intrathoracic lesions that are beyond the reach of the fiberoptic bronchoscope. In 896 patients with malignant intrathoracic neoplasm, the aspirate demonstrated malignant cells in 96%. A false cytological diagnosis of carcinoma occured in 2 patients, for a true positive rate of 99%. However, the true negative rate was only 87%. In 77% of 31 immunosuppressed patients, the causative agent of a focal infectious process was diagnosed. Pneumothorax was the only notable complication, occuring in 24% of patients, with 14% requiring chest tube drainage. The procedure is relatively simple and rapid, generally causes little patient discomfort, and can be performed in virtually any hospital.

Adolescent↗
PubMed1978

Multiple valve replacement: changing status.

Review of our experience with multiple valve replacement over a 6-year-period revealed a recent marked reduction in operative risk. Operative mortality for 62 patients operated on before 1974 was 34%; for 44 patients operated on since 1974, mortality was only 11%. In both groups, mortality was clearly related to the preoperative cardiac functional status. Several recent technical advances including myocardial protection by topical hypothermia, shortened perfusion time, and the intraaortic balloon pump may all have contributed to the reduced operative risk.

Aortic Valve↗
PubMed1978

The retrorectal space.

Ninety-nine adults with an enlarged retrorectal space on barium enema examination have been evaluated. Measurements were based on previously described methods using the lateral view of the barium filled rectum. In 38.4% of the cases there was no lesion (normal variations). The rest were classified as inflammatory conditions, tumours, and miscellaneous lesions. It is concluded that an increased width of the presacral space per se does not necessarily connote a lesion. Pathological widening of the space is usually associated with changes of the contour of the rectum, abnormalities of the sacrum, or other alterations of the presacral soft tissues.

Barium Sulfate↗
PubMed1978

Diminished radiopacity of contrast material: a urographic sign of ureteral calculus.

Eleven patients with unilateral ureteral calculus had excretory urography which showed the radiopacity of excreted contrast material to be diminished on the side of the calculus. This finding was of diagnostic importance in nine patients who demonstrated little or no dilatation of the urinary tract proximal to the calculus. Other forms of unilateral renal disease, such as acute pyelonephritis, can produce the same urographic finding.

Contrast Media↗