Robert T. V. Kung

Temperature‐controlled laser photocoagulation of soft tissue: In vivo evaluation using a tissue welding model

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).

Laser assisted vascular welding with real time temperature control

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.

Heart booster : A pericardial support device

BACKGROUND Congestive heart failure is a pervasive disease afflicting millions of people. For many, their quality of life can be significantly improved by a pericardial device that can enhance cardiac output without the added risk of thromboembolism associated with direct blood contact. METHODS A cardiac assist device with tubular elements is wrapped around the heart. Fluid is pumped into and out of the wrap causing contraction and dilation of its circumference. This contracting and relaxing action generates cardiac assistance without the need to contact blood. In vitro characterization and in vivo studies in calves were conducted to demonstrate the characteristics of the device. RESULTS In vitro characterization with the device wrapped around one-half of a ventricle to simulate left ventricular support demonstrated outputs of 6.5 L/min at physiological afterloads. In vivo studies in calves demonstrated both cardiac output and afterload enhancements when the device is activated. CONCLUSIONS This study provides a first demonstration of a device that provides cardiac support by a contraction and relaxation scheme with the device wrapped around the epicardium of the heart. The main feature of this actuation method is the potential for building a small device for implantation without blood contact.

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.

Differential scanning calorimetry of albumin solders: Interspecies differences and fatty acid binding effects on protein denaturation

Understanding albumin solder denaturation is important for laser tissue soldering. Human (HSA), bovine (BSA), porcine (PSA), and canine (CSA) albumin both fatty acid containing (FAC) and fatty acid free (FAF) were evaluated by using differential scanning calorimetry (DSC).

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.

Self-regulation of an electrohydraulic total artificial heart

The system control of an electrohydraulic total artificial heart (TAH) has been demonstrated. The TAH is a left-right alternately pumped system. Flow imbalance management is accomplished with a small hydraulic chamber in contact with left atrial blood. A two-level control hierarchy is used: (1) the rates of ventricular filling are governed by atrial pressures, and are adjusted on a beat-by- beat basis for the two sides; (2) the beat rate is changed to maintain full stroke at the operating filling rates. High filling pressures result in higher filling and ejection rates and a higher system beat rate, and vice versa. The control responds to atrial pressures and accommodates outflow pressure changes. The flow and beat rate increased from 31/min at 60 beats per min (BPM) to 7.21/min at 120 bpm as left atrial pressure (LAP) was varied from -4 mmHg to +20 mmHg. In vivo fluid loading studies showed beat rate variation of 70 to 96 bpm as LAP was varied from 2 to 8 mmHg with corresponding changes in flow rates.

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.

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.

Pediatric Mechanical Support with an External Cardiac Compression Device

We report a case of symptomatic axillary vein compression by the pectoralis minor muscle mimicking upper extremity thoracic outlet syndrome (TOS). The cause of obstruction was determined by clinical findings and dynamic venography. The patient underwent division of the pectoralis minor muscle with resolution of venographic findings and symptoms. Pectoralis minor compression of the axillary vein is a rare but described entity that needs careful review to reach the correct diagnosis and establish proper treatment.We report a case of symptomatic axillary vein compression by the pectoralis minor muscle mimicking upper extremity thoracic outlet syndrome (TOS). The cause of obstruction was determined by clinical findings and dynamic venography. The patient underwent division of the pectoralis minor muscle with resolution of venographic findings and symptoms. Pectoralis minor compression of the axillary vein is a rare but described entity that needs careful review to reach the correct diagnosis and establish proper treatment.The PediBooster external cardiac compression device is a minimally invasive, non-blood contacting Biventricular Assist Device (BiVAD) intended for pediatric use. It is being developed as a palliative therapy for acute Postcardiotomy Shock (PCS). The PediBooster extracardiac wrap is pneumatically actuated to circumferentially compress the heart, providing co-pulsation support. Attachment is via a novel hydrogel coating. Early versions of the wrap were tested in vivo using a single ventricle congenital heart disease model with postcardiotomy shock, which proved unstable and demonstrated high peri-operative mortality. The final wrap design was tested in 4 acute studies with piglets (5.1 ± 0.3 kg), where the combination of ASD and PA banding induced acute right ventricular dysfunction. Data collected included routine hemodynamic values, TEE, video of the exposed heart, and cardiac histology. The model proved stable for support durations ranging from 2 to 16 hours. The wrap restricted the heart in 3 of the 4 animals, as evidenced by increased diastolic LVP during support compared to the baseline failure condition. TEE and video data showed good attachment and function of the wrap, particularly during the final 16 hr study. This model of congenital heart disease shows promise for chronic (24-72 hr) studies. Ventricular filling during support may be improved by adjusting wrap dimensions to eliminate end diastolic restriction.