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Biomedical subjects

M E DeBakey

Publications and source records attributed to M E DeBakey.

At least 55 records · Page 3Linked to original sources
PubMed1993

Long-term fate of the aortic root and aortic valve after ascending aneurysm surgery.

OBJECTIVE: The authors determined in which patients tube graft replacement could be used. SUMMARY BACKGROUND DATA: Tube graft replacement of ascending aortic aneurysms requires no coronary anastomoses and preserves the native aortic valve, but aortic insufficiency or aortic root aneurysms may develop requiring reoperation. Use of Bentall or Cabrol composite valve graft procedures obviates these problems but requires prosthetic valve replacement and coronary reattachment, both of which are associated with complications. These two procedures have been applied increasingly but because of renewed interest in aortic valve preservation and reconstruction, the authors determined in which patients tube replacement could be used. METHODS: The authors analyzed the fate of 277 patients, mean age 49 +/- 14 years, operated on between 1953 and 1992 by techniques that preserved the aortic root. The most common pathology was atherosclerosis in 104 patients. Perioperative mortality since 1975 was 14%. RESULTS: Fifteen patients required reoperation on the ascending aorta or aortic root; ascending aneurysm reoperation (6 patients); aortic valve replacement (8 patients), and a combined procedure (1 patient). Of these 15 patients, 8 had Marfan's syndrome, 10 had dissections, and 5 had medial degeneration/necrosis. CONCLUSIONS: Simple tube graft replacement of the ascending aorta was a durable technique in patients without Marfan's syndrome or medial degeneration/necrosis and allowed preservation of the native aortic valve in many patients.

Adolescent↗
PubMed1993

In vitro performance of the Baylor/NASA axial flow pump.

A cooperative effort between Baylor College of Medicine and NASA/Johnson Space Center is under way to develop an implantable axial flow left ventricular assist device (LVAD). The pump is intended as an assist device for either pulmonary or systemic circulatory support for more than 3 months' duration. Currently, in vitro studies are under way to reduce the hemolysis generated by the axial flow pump. A system utilizing a testing matrix has been developed to analyze the effects of different pump parameters on hemolysis. The following parameters are being investigated: impeller blade tip geometry, impeller/flow tube clearance, impeller/stator clearance, number of impeller blades, number of stator blades, and length of the impeller. To date, an index of hemolysis of 0.038 g/100 L has been achieved. The test matrix is not complete, and further improvements are expected.

Animals↗
PubMed1992

Experimental and clinical evaluation of a noninvasive reflectance pulse oximeter sensor.

The objective of this study was to evaluate a new reflectance pulse oximeter sensor. The prototype sensor consists of 8 light-emitting diode (LED) chips (4 at 665 nm and 4 at 820 nm) and a photodiode chip mounted on a single substrate. The 4 LED chips for each wavelength are spaced at 90-degree intervals around the substrate and at an equal radial distance from the photodiode chip. An optical barrier between the photodiode and LED chips prevents a direct coupling effect between them. Near-infrared LEDs (940 nm) in the sensor warm the tissue. The microthermocouple mounted on the sensor surface measures the temperature of the skin-sensor interface and maintains it at a present level by servoregulating the current in the 940-nm LEDs. An animal study and a clinical study were performed. In the animal study, 5 mongrel dogs (weight, 10-20 kg) were anesthetized, mechanically ventilated, and cannulated. In each animal, arterial oxygen saturation (SaO2) was measured continuously by a standard transmission oximeter probe placed on the dog's earlobe and a reflectance oximeter sensor placed on the dog's tongue. In the first phase of the experiment, signals from the reflectance sensor were recorded while the dog was immersed in ice water until its body temperature decreased to 30 degrees C. In the second phase, the animal's body temperature was normal, and the oxygen content of the ventilator was varied to alter the SaO2. In the clinical study, 18 critically ill patients were monitored perioperatively with the prototype reflectance sensor. The first phase of the study investigated the relationship between local skin temperature and the accuracy of oximeter readings with the reflectance sensor. Each measurement was taken at a high saturation level as a function of local skin temperature. The second phase of the study compared measurements of oxygen saturation by a reflectance oximeter (SpO2[r]) with those made by a co-oximeter (SaO2[IL]) and a standard transmission oximeter (SpO2[t]). Linear regression analysis was used to determine the degree of correlation between (1) the pulse amplitude and skin temperature; (2) SpO2(r) and SaO2(IL); and (3) SpO2(t) and SaO2(IL). Student's t test was used to determine the significance of each correlation. The mean and standard deviation of the differences were also computed. In the animal study, pulse amplitude levels increased concomitantly with skin temperature (at 665 nm, r = 0.9424; at 820 nm, r = 0.9834; p < 0.001) and SpO2(r) correlated well with SaO2(IL) (r = 0.982; SEE = 2.54%; p < 0.001).(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1992

Spinal oxygenation, blood supply localization, cooling, and function with aortic clamping.

Similar to other methods of organ preservation, "spinoplegia" may protect the spinal cord from the effects of oxygen desaturation during aortic cross-clamping. In porcine experiments, spinal cord O2 saturation was studied during intraoperative localization of the blood supply to the spinal cord using hydrogen; division of arteries not supplying the spinal cord; aortic cross-clamping for 60 minutes; and 60 minutes after unclamping. In 5 animals, 120 mL of cold saline solution with lidocaine (100 mg/dL) was infused into the aorta during aortic cross-clamping. During sequential localization, O2 saturation dropped by 40.02% (standard deviation, 20.16%) for T-14 artery testing versus a decrease of 17.27% (standard deviation, 11.88%; p = 0.0075) for L-5 artery segment testing in the control animals and returned to baseline thereafter. During aortic cross-clamping maximal O2 desaturation was 5% of baseline (15.7%; p less than 0.0001), which improved slightly by 30 minutes after clamping (48% of baseline +/- 37.37%; p = 0.048 versus maximum) and then returned to baseline (97.1% of baseline +/- 41%) with unclamping; 5 minutes later, hyperoxygenation occurred with a progressive decline thereafter (68% of baseline +/- 29.3%; p = 0.025, 45 minutes after unclamping versus baseline). The decrease in spinal motor evoked potentials was significantly less (p less than 0.02) in the treated group. Intraoperative hydrogen testing in 8 patients was demonstrated to be safe. It accurately localized reattached arteries, and O2 saturation of the spinal cord fell by 56% (standard deviation, 29%; p = 0.0025) with aortic cross-clamping. We conclude that spinal cord ischemia occurs with aortic cross-clamping in both animals and humans.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Development of a totally implantable electromechanical total artificial heart: Baylor TAH.

A totally implantable, one-piece, electrome-chanical total artificial heart (TAH) intended for permanent human use has been developed. It consists of left and right pusher-plate pumps (63 cc design stroke volume) sandwiching a thin center piece with a compact electromechanical actuator. The pusher-plates are shaped conically to accommodate an actuator in the space between them. The actuator consists of an efficient and durable planetary roller screw and direct current brushless motor. The left master alternate pumping mode was implemented utilizing the left pump pusher-plate position signal. The blood-contacting surface was coated with a dry gelatin to yield long-term clot-free performance. Trileaflet tissue valves of 27 and 23 mm are used in the inflow and outflow ports. The diameter and thickness of the TAH are 97 and 82 mm. the overall volume is 510 cc, and the weight is 620 g. Anatomic fit was confirmed in 26 heart transplant recipients (body weight 78 kg and surface area 2 m2) without compressing adjacent organs. The pump performance study revealed that the TAH can yield outputs of 3-8 L/min against the 100 mm Hg afterload with 1-10 mm Hg filling pressure. The input power to the motor ranged from 7 to 12 W, with an efficiency of 18% to 14%. A one-week in vivo calf study demonstrated adequate performance of the TAH, particularly the regulation of atrial pressures. Good anatomic fit and good biocompatibility were also demonstrated.

Animals↗
PubMed1992

Development of totally implantable electromechanical artificial heart systems: Baylor ventricular assist system.

An implantable electromechanical ventricular assist system (VAS) intended for permanent use has been developed. It consists of a conically shaped pumping chamber, a polyolefin (Hexsyn) rubber diaphragm attached to a conically shaped pusher-plate, and a compact roller-screw actuator. Design stroke volume is 63 ml. The device weighs 620 g, and has a total volume of 348 ml. The pump can provide 8 L/min flow against 120 mm Hg afterload with a preload of 10 mm Hg. The inner surfaces are biolized by dry gelatin coating, with inflow and outflow ports accommodating tissue valves. Three subacute in vivo validation studies have been conducted in calves up to two weeks. The entire system functioned satisfactorily in both the fill/empty and the fixed-rate modes. There was no thromboembolic complication without anticoagulation. The pump showed reasonable anatomical fit inside the left thorax. This VAS is compact, efficient, quiet, and easy to control.

Animals↗
PubMed1992

A compact centrifugal pump for cardiopulmonary bypass.

A majority of the cardiopulmonary bypass (CPB) systems still utilize bulky roller pumps. A direct-drive small centrifugal pump intended for second-generation CPB pump has been developed. The pump has a 50 mm diameter impeller and provides a 6 L/min flow at 3,000 rpm against 300 mm Hg. A flexible drive shaft allows us to separate the pump head from the console resulting in easier manipulation. An in vitro study showed that the pump generated less hemolysis (index of hemolysis = 0.0011, comparable to the value for Bio-medicus BP-80). To improve blood flow around the shaft-seal region and to reduce thrombus formation around the shaft, six holes were drilled through the impeller. In biventricular bypass experiments using calves, our pump demonstrated excellent antithrombogenicity and durability for 48 h. And the compact and atraumatic centrifugal pump system showed excellent performance and easy manipulation under actual CPB conditions in animal.

Animals↗
PubMed1992

Versatile one-piece total artificial heart for bridge to transplantation or permanent heart replacement.

A versatile, one-piece total artificial heart (TAH) system that can be driven by either an electromechanical acutator (EM-TAH) or a pneumatic source (P-TAH) has been developed. The common units for both TAHs are the conically shaped left and right pusher-plate-type pumps (63 ml SV) that sandwich a thin centerpiece (18 mm) having a respective actuator. The EM actuator, mounted in the middle of the centerpiece, consists of a direct-current brushless motor and a roller screw while the pneumatic actuator consists of a low-pressure air source. The outer diameter of the pumping unit is 97 mm with its central thickness being 82 mm; overall volume is 510 cc. The TAH is operated in the left master alternative ejection mode with the left pump fill signal. High-flex-life Hexsyn rubber is used as the diaphragm, and the blood-contacting surface is coated with dry gelatin. The TAH can provide 3-8 L/min flow with a preload of 1-10 mm Hg against 100 mm Hg afterload. Anatomical fit of the pumping unit has been demonstrated in the pericardial space of 26 heart transplant recipients with average body weight of 78 kg. To date, 2 P-TAH and 4 EM-TAH (1 week) implantations were performed in 80-100 kg calves demonstrating excellent anatomical fit, controllability, and biocompatibility. This versatile TAH is suitable for a bridge to transplantation or permanent heart replacement.

Animals↗
PubMed1991

The National Library of Medicine. Evolution of a premier information center.

From a small collection of medical publications in the Surgeon General's Office in 1836, the National Library of Medicine has developed into the leading repository of medical information in the world. Despite strong opposition and impediments from certain quarters, involving considerable machinations and intrigue, the determination of interested medical leaders and sympathetic members of Congress triumphed in having this remarkable institution established on the campus of the National Institutes of Health, Bethesda, Md. As a participant in many of the negotiations preceding that decision, I have happily witnessed the transformation of the Library, long housed in cramped, makeshift quarters, to its present magnificent structures in the heart of our nation's foremost medical research center. Its prodigious collection of print, audiovisual, and electronic information; its imaginative research projects; its excellent outreach program; and its innovative services and products are indispensable to all practicing health professionals, scientists, and medical educators, as well as to journalists, government officials, and others. The ultimate beneficiary, of course, is the patient.

History, 19th Century↗
PubMed1991

Heterotopic heart transplantation and native heart ventricular arrhythmias.

Heterotopic heart transplantation has been said to be contraindicated in patients with serious native heart arrhythmias that produce hemodynamic instability. Placement of heterotopic allografts, however, can theoretically act as a biological biventricular assist device to provide hemodynamic support during these unstable rhythms. Further, this operation might beneficially alter the hemodynamic milieu of heart failure such that the arrhythmias are ameliorated. Described is our experience with 4 patients with heart failure receiving heterotopic cardiac allografts, documenting changes in native heart arrhythmia that occurred. These cases demonstrate that heterotopic grafts can adequately sustain hemodynamics during malignant native heart dysrhythmia. We believe native heart ventricular arrhythmias are not a contraindication to heterotopic heart transplantation.

Arrhythmias, Cardiac↗