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Biomedical subjects

R T Kung

Publications and source records attributed to R T Kung.

18 recordsLinked to original sources
PubMed1996

Temperature-controlled laser photocoagulation of soft tissue: in vivo evaluation using a tissue welding model.

BACKGROUND AND OBJECTIVES: Laser surgical procedures involving photocoagulation of soft tissue have relied on subjective visual endpoints. The thermal damage to the denatured tissue in these procedures is highly dependent on the tissue temperatures achieved during laser irradiation. Therefore, a system capable of real time temperature monitoring and closed loop feedback was used to provide temperature controlled photocoagulation (TCPC). STUDY DESIGN/MATERIALS AND METHODS: The TCPC system consisted of a 1.32 microns Nd:YAG laser, an infrared thermometer, and a microprocessor for data acquisition and feedback control. A porcine skin model was used. Tissue welds were completed to evaluate the photocoagulation effects at different predetermined temperatures. A quantitative measurement of tissue photocoagulation was obtained by tensile strength measurements of the laser repairs. Histology of the irradiated tissue was used to determine the extent of thermal injury associated with different photocoagulation temperatures. RESULTS: The TCPC system was capable of maintaining a relatively constant temperatures (+/- 4 degrees C) during laser irradiation. The tensile strengths of acute repairs increased with temperature over the range studied (65-95 degrees C). Tensile measurements made after several days of healing showed that higher temperature (95 degrees C) welds had lower strengths than repairs completed at lower (65 degrees C or 75 degrees C) temperatures and were significantly lower at 3 days. Acute histology showed that the amount thermal damage was strongly dependent on the tissue temperature and increased both in tissue depth and lateral to the repair with temperature. The histologic results suggest that the increase in the acute repair tensile strength as the weld temperature increased was due to an increase in the depth of tissue photocoagulation. The increase in the lateral tissue injury measured histologically for higher temperature welds likely resulted in the decreased chronic tensile strengths, as a healing response to excessive thermal damage. CONCLUSION: Tissue temperatures can be controlled during laser photocoagulation of skin. The degree of acute and chronic tissue damage is highly dependent on the temperature during welding. By controlling the tissue temperature during laser procedures, the surgical outcome can be more reliably predicted and reproduced, as compared to the conventional open loop methods. In addition, the use of a TCPC system should significantly reduce the learning curve for photothermal surgical procedures.

Animals↗
PubMed1996

Laser assisted vascular welding with real time temperature control.

BACKGROUND AND OBJECTIVE: Previous studies in laser assisted vascular welding have been limited by the lack of a reliable end point for tissue fusion. As a means of improving the reproductibility of laser assisted repairs, a system incorporating real time temperature monitoring and closed loop feedback was used. STUDY DESIGN/MATERIALS AND METHODS: The system consisted of a direct view infrared thermometer for monitoring the laser heated spot, a 1.9 microns diode laser, and a microprocessor for data acquisition and feedback control of the laser power to maintain a constant tissue temperature. Rat aortas were welded under constant surface temperature conditions. RESULTS: In vivo temperature stability of +/- 2 degrees C was achieved over a temperature range of 70-90 degrees C pertinent to welding small vessels. When welds were completed using the feedback system to maintain the tissue temperature at 80 degrees C, the acute success rate was 100% and the burst pressure was 290 +/- 70 mmHg. CONCLUSION: These studies demonstrate that the use of real time monitoring and feedback control results in improved consistency for vascular tissue welding.

Anastomosis, Surgical↗
PubMed1996

A magnetically suspended and hydrostatically stabilized centrifugal blood pump.

A magnetically suspended centrifugal blood pump intended for application as a long-term implantable ventricular assist device has been built and tested. The rotor is freely suspended in the blood by magnetic and hydrostatic restoring forces. This design obviates the need for bearings and shaft seals, and eliminates the problems of reliability and thrombogenicity associated with them. The positional stability and hydrodynamic performance of the pump has been characterized in vitro at flows of up to 10 L/min at physiologic pressures. Radial position control is realized by an analog electronic feedback control system. The pressure distribution in the fluid surrounding the rotor provides dynamic control in the axial direction with no active feedback. Rotor excursion is less than 50 microns (mu) when the housing receives an impulse peaking at an acceleration of 40 g or upon sudden blockage of the flow. In vitro blood measurements indicate an acceptable level of hemolysis compared with that of a standard centrifugal pump.

Animals↗
PubMed1993

Absorption characteristics at 1.9 microns: effect on vascular welding.

A 1.9 microns laser was used to investigate the acute weld strengths for anastomoses of rat and rabbit aortas and femoral arteries. The wall thicknesses for these vessels approximately matched the optical absorption depth of 125 microns for 1.9 microns radiation in vascular tissues. A low power (150 mW) 1.9 microns laser was used. Laser power was delivered through silica fiber optics for manual control. The fiber tip was held approximately 1 mm from the target resulting in a laser spot size of 0.7 mm at the tissue. The linear delivery rate was approximately 0.3 mm/sec. Acute burst pressures of the welds showed a linear correlation with the reciprocal of the vessel radius. These results suggest that the product of the weld strength times the optical absorption depth is constant over the range of vessel sizes studied. A weld strength for a weld thickness equal to the optical absorption depth was determined to be 4 x 10(6) dynes/cm2, which is comparable to the strength of sutured anastomoses. These acute studies suggest that a laser wavelength with absorption depth in tissue matched to the vessel wall thickness should yield optimum welds. Therefore, a laser operating near 1.9 microns is suitable for small vessel welding.

Anastomosis, Surgical↗
PubMed1992

Arterial laser welding with a 1.9 micrometer Raman-shifted laser.

A new 1.9 micron Raman-shifted neodymium:yttrium aluminum garnet (Nd:YAG) laser was used for small vessel welding. Bursting pressures and stresses of sutured and laser-welded arteriotomies created in the rat femoral artery and aorta were measured. Sutured arteriotomies had a significantly higher burst stress than laser-welded arteriotomies. Although there were no significant differences in burst stress at the various laser powers tested, an optimal power was identified. The laser was also used to weld transected rat aortas. The average power delivered was 200 mW for 30 seconds per anastomosis. The average time for completing an anastomosis was 6 minutes compared with 18 minutes when sutures were used. In relation to proximal aortic diameter, there was a 7.9% decrease at the anastomosis immediately (n = 4), and a 6.6% and 4.9% increase occurred at 24 hours (n = 4) and 10 weeks (n = 5), respectively. Acute anastomotic compliance, and compliance at 24 hours and 10 weeks were decreased by 47.2%, 39.5%, and 47.8%, respectively, and were similar to sutured anastomoses. Histology showed little thermal denaturation of the aorta within 0.6 mm of the anastomosis, approximately 1 mm of medial cell death, and nearly normal elastic fiber alignment. One focal false aneurysm was noted at 10 weeks. Although the sutured and laser-welded anastomoses share similar compliance changes, the laser-welded anastomoses are more isodiametric. This preliminary experience with the 1.9 micron laser shows the distinct advantages of a handheld fiber, no requirement for cooling irrigation, speed, and no difference in compliance from sutured anastomoses.

Analysis of Variance↗
PubMed1990

Temperature as a periodontal diagnostic.

Elevated temperature, normally a characteristic of inflammation, is a potential indicator of periodontal disease. Conversely, local periodontal site temperatures within normal variation could suggest relative periodontal health. To evaluate this potential, a temperature probe was designed with rapid response (less than 1 s), high accuracy and reproducibility (+/- 0.1 degree C), good transducer thermal isolation and physical dimensions approximating those of a conventional periodontal probe. To compensate for subject-to-subject variations in core temperature, site temperatures were measured and expressed as differences relative to the sublingual temperature. A cross sectional study was conducted using this instrument in which pocket temperatures of 14 subjects with advanced adult periodontitis were measured and compared with the sulcus temperatures of 11 healthy subjects. Overall, the mean site temperature of the diseased subjects was 0.65 degree C higher than that of the healthy subjects. A natural posterior-to-anterior temperature gradient was observed with the posterior sites being hotter than the anterior sites. Tooth-by-tooth analysis showed that diseased teeth have higher temperatures than anatomically equivalent healthy teeth (p less than 0.01). Threshold temperatures for differentiating diseased and healthy teeth were determined to optimize sensitivity and specificity. The results suggest that site temperature is a diagnostic of inflammatory activity associated with periodontal disease. The specifically designed instrument detected significant disease-related departures from normality.

Body Temperature↗
PubMedDate not supplied

A unique left-right flow imbalance compensation scheme for an implantable total artificial heart.

A new method has been developed for accommodating the difference between pulmonary and arterial flows in a totally implantable, hydraulically actuated total artificial heart (TAH). The left and right sides are alternately pumped, with concurrent filling of one pump and ejection from the other. A small hydraulic fluid chamber is used to compensate for the higher left sided flow. This chamber is incorporated into the left inflow of the TAH, with the flexing bladder in contact with atrial blood, and the hydraulic fluid communicates with the right sided hydraulic chamber. The volume of hydraulic fluid that enters and exits the latter chamber constitutes a corresponding reduction in the right sided blood chamber stroke volume. Placement of this compensation chamber in the left side inflow provides a negative feedback of the right sided flow, based on the left atrial pressure (LAP). Higher LAP (indicating too much right sided flow) leads to higher fluid flow to and from the compensation chamber and a lower right sided blood flow and vice versa. The hydraulic flow resistance can be preadjusted to yield a 15% flow difference at an LAP of 15 mmHg.

Animals↗
PubMedDate not supplied

Chronic in vivo evaluation of an electrohydraulic total artificial heart.

Development of the Abiomed total artificial heart (TAH) designed for human use is progressing. Implant durations of longer than 60 days have been achieved in calves. The device consists of blood pumps, valves, and a hydraulic atrial flow balancing chamber fabricated from polyetherurethane. The energy converter, a centrifugal hydraulic pump with a rotary fluid switching valve, is positioned between the blood pumps. In two consecutive chronic in vivo studies (47 days and longer than 60 days), cardiac output was maintained in excess of 8 l/min. The atrial flow balancing chamber maintained a mean right-to-left pressure gradient of 7.5 and -1.4 mmHg in each respective study. There were no pulmonary complications. Platelet counts, fibrinogen concentrations, and hematocrit values returned to baseline levels within 20 days, whereas bilirubin, serum glutamic-oxaloacetic transaminase, blood urea nitrogen, and creatinine levels returned to normal within 1 week of implant. After the first post-operative day, plasma free hemoglobin levels of less than 10 mg/dl indicated no device-related hemolysis throughout the duration of the studies. At explant (47 day study), pathologic analysis showed no renal infarcts, no tissue necrosis, and no thermal damage. The device was fully encapsulated by 2-4 mm thick fibrous connective tissue. A newly designed textured-to-smooth surface inflow showed no signs of pannus ingrowth or thrombotic complications. These studies demonstrate that this TAH is suitable for long-term implantation.

Animals↗
PubMedDate not supplied

Progress in the development of the ABIOMED total artificial heart.

The ABIOMED implantable total artificial hearts in the final phase of engineering development. The system has a compact electrohydraulically driven energy converter sandwiched between two blood pumps, an internal electronics pack, an internal battery, a transcutaneous energy transmission coil for power transmission, and external wearable electronics pack and battery. The current effort is to complete development of the system during 1996 in preparation for formal pre clinical testing of the device. In vivo studies with the current thoracic unit (ABH II) have achieved 108 days of survival verifying the thermal, physiologic, and hematologic compatibility of the system. The abdominal implantable electronics pack showed no thermal dissipation problem. System improvements include scaling down the size of the thoracic unit, and efficiency enhancement in the power and hybrid electronics. The new system (ABH III) retains the flow capacity of greater than 10 L/min. Size reduction results in an atrial to sternal dimension that would fit 98% and 75% of men and women, respectively.

Animals↗
PubMedDate not supplied

Development of an efficient electrohydraulic total artificial heart.

The efficient use of space and energy is achieved in a new implantable total artificial heart (TAH). To fit the orthotopic thoracic space, toroidal blood pumps encircle an energy converter, consisting of a centrifugal hydraulic fluid pump and a rotary reversing valve. The new centrifugal pump produces cardiac outputs of 6 L/min, with an average hydraulic efficiency of 47%. Toroidal blood pumps encircling the pump deliver a 60 cc stroke with an 85% ejection fraction and have a predictable blood flow pattern with no stagnant regions. Components have been characterized in vitro, and blood contacting elements have been tested in vivo.

Blood Flow Velocity↗
PubMedDate not supplied

Device reliability.

Explore the source record for details and available documents.

Artificial Organs↗
PubMedDate not supplied

An atrial hydraulic shunt in a total artificial heart. A balance mechanism for the bronchial shunt.

An implantable TAH must be able to maintain physiologic atrial pressures over a range of left side shunt flows, which in humans can range up to 5% of the total cardiac output (CO). The authors describe the characteristics of an atrial hydraulic shunt in an electrohydraulic TAH. A small (10 cc stroke) chamber placed in line between the left atrial cuff and the inflow valve is shunted to the right hydraulic chamber. High left atrial pressure increases the volume displaced by this chamber; this concurrently reduces the right chamber stroke volume and flow relative to the left side. For left atrial pressures (LAP) between 0 and 15 mmHg, CO increased from approximately 3 to > 9 L/min (Starling-like behavior). This was attainable with bronchial flow settings between 0.2 to 0.7 L/min, satisfying physiologic needs. Left atrial pressure and RAP (right atrial pressure) tracked each other. The mean difference, LAP-RAP, remained within 5 mmHg at low filling pressures and approached 0 mmHg difference at high filling pressures. The results showed that the atrial hydraulic shunt method can adequately compensate for and manage physiologic left-right flow differences.

Animals↗
PubMedDate not supplied

A compact and noise free electrohydraulic total artificial heart.

The ABIOMED total artificial heart (TAH) is designed for long-term tether-free use in patients with end-stage heart disease. Blood pumping is achieved through hydraulic fluid motion across flexing diaphragms. The hydraulic power is derived from a miniature centrifugal pump (50% efficiency). Flow directional change needed for alternate left and right filling and ejection is achieved with a rotary valve. With no mechanical contact with the flexing membrane, the wedge angle between the two pumps sandwiching the energy convertor can be easily optimized for anatomic fit. The blood pumps (80 ml strokes) are fitted with trileaflet polyetherurethane valves (24 mm). The TAH is implanted using twist-lock stepless quick connectors to the inflow cuffs and outflow grafts. Left-right flow balance is achieved with an atrial hydraulic shunt placed between the left cuff and inflow valve. Animal studies show that the TAH fits very well in Long Horn calves weighing 90 to 100 kg and can provide cardiac output in excess of 10 L/min. A cadaver (85 kg) study showed the TAH fits within the pericardial region.

Adult↗
PubMedDate not supplied

Life testing of implantable batteries for a total artificial heart.

Although lithium cells may promise to be ideal as a rechargeable internal battery for a TAH, NiCd cells remain the most easily accessible off the shelf energy source. Twelve 1.2 A.hr prismatic NiCd (Sanyo, San Diego, CA) cells in series are being tested under the load condition of our TAH. The load consisted of a 1.5 A DC current with 1 A pulses of 40 msec duration at 3.33 Hz (100 bpm), a condition that can generate up to 8 L/min of cardiac output at physiologic pressures. Cells were tested at 37 degrees C. Cell voltages and temperatures were monitored. Testing was accelerated to five charge/discharge cycles per day. Discharge was terminated when any one cell dropped below 1.1 V. Charging (C/4) was continued until the battery voltage indicated a change in slope. Cell temperatures remained below 42 degrees C throughout the charge/discharge cycle. The battery pack settled to a nearly constant capacity of over 25 min after 10 cycles and has accumulated more than 1,000 cycles. Voltage differences among cells were small (SD < 25 mV), indicating consistency among cells. NiCd cells can serve as a reliable interim for TAH internal battery application.

Cadmium↗
PubMedDate not supplied

A tubular pediatric ventricular assist device. Design considerations and system characteristics.

A clinical need exists for the short-term use of pediatric ventricular assist device in children and small infants who are critically ill with heart failure unresponsive to pharmacologic support or, in the case of irreversible heart failure, as a bridge to a transplant device. The design considerations and device characteristics of a tubular pump are presented. The device consists of an integrally formed inflow valve, pump chamber, and outflow valve in a tubular construction. This design approach was selected due to its simplicity of fabrication, which can result in a reliable and low cost device. The inflow valve and pump are actuated pneumatically through a single drive line. The outflow valve can be either actively actuated or operated passively. A 5 ml stroke volume device was built and characterized in vitro and in vivo. This pump can generate 0.5 L/min at 100 beats per minute. Larger stroke volume devices can be and have been fabricated using the same principle.

Algorithms↗