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Biomedical subjects

S R Igo

Publications and source records attributed to S R Igo.

45 records · Page 3Linked to original sources
PubMed1975

Effects of an abdominal left ventricular assist device on myocardial oxygen supply/demand ratios in normally perfused and ischemic bovine myocardium.

The effects of an abdominal left ventricular assist device (ALVAD) on subendocardial oxygen supply/demand ratios as reflected by diastolic pressure-time index/tension-time index (DPTI/TTI) were investigated in calves. Control DPTI/TTI ratios were 1.09 plus or minus 0.12 (mean plus or minus SD). With ALVAD actuation the ratios increased to 5.73 plus or minus 3.2. Following circumflex coronary artery occlusion, control ratios decreased to 0.04 plus or minus 0.05 in the ischemic area and 0.97 plus or minus 0.20 in the nonischemic areas. With ALVAD actuation in the presence of circumflex occlusion, the depressed ratios were increased to 1.37 plus or minus 0.39 in the ischemic zone and 9.71 plus or minus 2.5 in the nonoccluded segments. Subendocardial oxygen supply/demand ratios were significantly improved by ALVAD assistance following induced subendocardial ischemia.

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PubMed1975

An abdominal left ventricular assist device: preclinical studies.

An abdominally positioned left ventricular assist device (ALVAD) has been evaluated in our most recent series of 25 calves weighing 99 plus or minus 12 kg. The ALVAD is a pneumatically actuated bladder pump, positioned subdiaphragmatically and connected between the left ventricular apex and the infrarenal abdominal aorta. The mean survival time in the calves was 41 days and the longest 65 days. The major effects of the pump are reduction of all indices of left ventricular work and increases in systemic perfusion. In the awake, unanesthetized calf, left ventricular pressure, dP/dt, and stroke work were decreased while peak aortic pressure, stroke volume, and cardiac output increased. These effects were corroborated at cardiac catheterization two to four weeks postoperatively; left ventriculograms also showed increases in ejection fraction. These data demonstrate the ALVAD's effectiveness in assuming left ventricular function and support over extended periods. The device has been developed for short-term postoperative clinical use in patients with reversible left ventricular failure.

Abdomen↗
PubMed1975

Evaluation of cardiac function and venous return curves in awake, unanesthetized cialves with an implanted total artificial heart.

1) The implanted TAH offers a method of evaluating the effects of varying physiologic demands cardiac output and venous return. 2) Cardiac output and venous return measurements offer a method of evaluating system design of the device and driving and control-logic improvements in awake, unanesthetized animals. 3) The obtained cardiac function and venous return curves suggest that the present TAH is less responsive to increases in right atrial pressure than the natural heart, but is still completely controlled by venous return. Therefore, it is extremely important to make every effort to eliminate any factor causing excessive venous return.

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PubMedDate not supplied

Anatomic considerations for abdominally placed permanent left ventricular assist devices.

To determine anatomic parameters for a permanent, electrically actuated left ventricular assist device (LVAD), the effects of abdominal placement of pneumatic LVADs used as temporary support for patients awaiting heart transplantation was studied. Understanding the anatomic constraints imposed by the abdominal viscera in LVAD placement is crucial, because improper placement can result in compression or obstruction of adjacent structures. Anatomic compatibility was assessed in four men (age 22-48 years) who were supported by the LVAD for over 1 month (range 35-132 days). The pump was intraperitoneally placed in the left upper quadrant. Radiographic techniques were employed, including CT scanning (with patients supine) and contrast imaging (patients in anatomical position), and the pump and conduits appeared to be properly positioned, with minimal compression of the body of the stomach, and no obstruction of adjacent organs. Three patients returned to a solid food diet and exercised daily by stationary cycling and walking. No signs of migration or erosion of the pump were present at the time of LVAD removal and cardiac transplantation. Successful clinical experience with short-term use of the LVAD suggests that the electrically actuated device can be well tolerated in patients requiring permanent left ventricular assistance.

Abdomen↗
PubMedDate not supplied

Comparative in vitro evaluations of vascular graft compliance during dynamic loading.

A prosthetic vascular graft should be nonthrombogenic, compliant with anastomosed vessels and resist excessive dilatation or aneurysm formation. Mechanical performance of a negatively charged, glutaraldehyde-tanned bovine heterograft was evaluated, in vitro, during dynamic loading conditions. The grafts were 16 cm in length with internal diameters of 6 mm (n = 10), 8 mm (n = 12), and 10 mm (n = 8). The prostheses were pneumatically cycled, using intragraft balloons, at a pulse pressure of 120/70 mmHg and a rate of 80 beats/min in 37 degrees C saline for 2.6 million cycles (22.6 days). At selected intervals, the diastolic and pulse volumes of the grafts were measured and compliance calculated. These studies demonstrated that this vascular prosthesis had a high initial compliance, independent of graft diameter. During dynamic loading, diastolic volume increased whereas pulse volume and compliance decreased 12%, 43%, and 49%, respectively (P less than 0.001). Greater than 75% of the changes occurred within 5 days after the onset of testing. Despite these changes, isocompliance was demonstrated for the BioPolyMeric grafts following 22 days of cycling, yielding values similar to those reported for human saphenous vein.

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