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At least 775 records · Page 43Linked to original sources
PubMed1990

Theoretical and experimental analysis of right ventricular bypass and univentricular circulatory support.

In this paper we examine the dynamic coupling between cardiac pump events and vascular arterial-venous factors that regulate the rate of blood flow around the circulation. A series of experiments were designed to test the feasibility of maintaining vascular and pulmonary function in the absence of the right heart and to characterize the physiologic and hemodynamic consequence of such an exclusion. Theoretical analysis of the cardiovascular system (excluding neuro-humoral factors) using both lumped time invariant and distributed compartmental mathematical equivalent representations, demonstrated that a change in cardiac output (Q) has an inverse-linear effect on venous and direct-linear effect on arterial pressure. A single blood-pump, in a form of a mechanical substitute or the biologic left-heart, alone can support the circulation. Cardiac output reserve is limited (50 percent of normal) because of the rapidly diminishing pulmonary venous-pressure as outflow is increased, irrespective of the pump's specific characteristics. Experiments in animals combined with mock-circulatory studies and computer modeling confirm that near normal flow can be sustained by increasing the stressed blood volume or reducing selectively the systemic venous compliance (i.e., inflatable pressure suit, venous constriction, intra-abdominal compression maneuvers, etc.). The right heart is not essential for normal pulmonary circulation but serves to maintain low systemic venous pressure and relatively high left-heart flow reserve. Purely mechanical properties of the vascular system determine the control and stability of the circulation.

Animals↗
PubMed1988

Use of mechanical devices for distal hemoperfusion during balloon catheter coronary angioplasty.

Previous attempts to protect the dependent myocardium during balloon catheter coronary angioplasty in animals and humans have had generally unsatisfactory results. This paper summarizes the authors' experience in investigating commercially available mechanical pumps for distal coronary hemoperfusion during balloon angioplasty. Both roller and piston pumps can attain adequate distal perfusion without significant side effects in the majority of patients. Our goal was to suppress angina for at least 5 min to prolong balloon inflation in awake patients. Minor T-wave changes without concomitant angina pectoris can be expected when the distal coronary bed is perfused with hypothermic blood. Side branch occlusion by the inflated balloon prevents effective protection of the corresponding part of the dependent myocardium during distal hemoperfusion, which may result in persistent angina and ST-T changes uncorrected by increasing the hemoperfusion rate. Distal coronary diffuse spasm, rare and transient, was the only immediate complication of this procedure. It is suggested that intense local wall stimulation could occur with a higher flow rate (jet effect). Improved balloon catheter pressure/flow characteristics and on-line continuous mechanical pumps should soon make distal coronary hemoperfusion through balloon catheters an accepted clinical technique.

Adult↗
PubMed1989

Development of compliance chamber diaphragms with reduced permeability.

The implantable ventricular assist systems currently undergoing clinical readiness testing shuttle the displaced gas between the non-blood side of the pumping diaphragm and an elastic chamber generally called a "compliance chamber" or variable volume device. The movement of the stored gas allows the pump to fill and empty without compression or expansion of the gas behind the pump diaphragm. The material used for the construction of compliance chambers should be fatigue resistant to withstand the 63 million flexes per year of the blood pump. The material should also be biocompatible and highly impervious to gases. Significant diffusion of gases from the compliance system necessitates external make-up gases to somehow be added to the internal system. Material selection is complicated by the fact that most fatigue-resistant elastomers also have high gas permeability. In order to solve this problem, bilayer compliance chambers have been developed using biocompatible and fatigue-resistant polyolefin rubber comolded with relatively impervious butyl rubber.

Assisted Circulation↗
PubMed1989

Bridging to cardiac transplantation.

Unilateral or bilateral prosthetic ventricles and artificial hearts have been used in bridging to transplantation for 4 years. Candidates for bridging to transplantation comprise patients who otherwise would be elective cardiac transplantation candidates who deteriorate rapidly before a donor heart can be found, or persons with sudden cardiac decompensation (eg, massive myocardial infarction with cardiogenic shock). In selecting patients for bridging to cardiac transplantation it is crucial that people are chosen who are good candidates for heart transplantation despite their rapidly deteriorating condition. This article compares the results of the devices available for use in this application, which include: the centrifugal pump; the Jarvik-7 orthotopic prosthetic ventricle; and the Thoratec, Novacor, and Thermedics heterotopic prosthetic ventricles.

Adolescent↗
PubMed1988

Pulmonary complications of a roller pump right ventricular assist device.

The pulmonary effects of a right ventricular assist device (RVAD) were evaluated in a model of ischemic right ventricular (RV) failure. The right coronary artery (RCA) was ligated for 240 min in 12 mongrel dogs. Group 1 (n = 5) was supported medically (iv fluids, epinephrine); Group 2 (n = 7) had an RVAD instituted 30 mins after RCA ligation, but no inotropic support was given. The RVAD was a standard roller pump providing right atrial to pulmonary artery flow which unloaded the RV. The ratio of area of infarction (AI) to area at risk (AR) of the RV was determined by vital dye staining. Total lung water (TLW) was determined by gravimetric analysis and expressed as milliliters per kilogram body weight. Throughout the experiment animals in Group 1 had significantly higher RV systolic pressures. Pulmonary vascular resistance was increased significantly in Group 2 at 4 hr (318% of baseline vs 33%). Mean pulmonary artery pressure increased significantly in Group 2 from 9.4 +/- 0.9 mm Hg at baseline to 21.0 +/- 5.0 mm Hg at 4 hr. Group 2 animals had a decreased AI/AR ratio (19 +/- 3 vs 57 +/- 9) and increased TLW (20 +/- 3 vs 9 +/- 1). Lung biopsies in Group 2 revealed perivascular, peribronchial, and intraalveolar hemorrhages that were not present in Group 1. In conclusion, a roller pump RVAD limits RV infarction but produces pulmonary hypertension, increases pulmonary vascular resistance, and creates pulmonary edema and hemorrhage in the process.

Animals↗
PubMed1988

Bridging to cardiac transplantation with pulsatile ventricular assist devices.

As cardiac transplantation becomes more commonplace in the treatment of end-stage heart failure and as suitable donors become less available, an increasing number of patients will require mechanical circulatory assistance to bridge to transplantation. Since 1982, refractory hemodynamic instability requiring placement of pulsatile ventricular assist devices (VADs) has developed in 11 candidates for transplantation aged 24 to 54 years (mean, 39.6 years). A pneumatic Pierce-Donachy pump was used in 9 patients and an electrical Novacor pump in 2. The cause of the cardiomyopathy was ischemic in 6, postpartum in 2, idiopathic in 2, and doxorubicin hydrochloride toxicity in 1. Seven patients required left ventricular support (LVAD); 4 required biventricular mechanical support (BVAD). Duration of support ranged from 8 hours to 91 days with flows ranging from 4.1 to 8.5 L/min (mean, 5.5 L/min). Although hemodynamic stability was achieved in all 11 patients, contraindications to transplantation developed in 5 patients during VAD support (renal failure in 4, sepsis in 3, disseminated intravascular coagulopathy in 1). The remaining 6 patients (4 with an LVAD, 2 with a BVAD) remained good candidates for transplantation despite major complications in 5 (mediastinal bleeding in 3, driveline infection in 3, development of preformed antibodies in 2, small embolic stroke caused by device malfunction in 1). The 3 patients who were supported the longest (24, 75, and 91 days) were ambulatory while awaiting a donor heart. All 6 patients underwent successful transplantation after 8 hours to 91 days (mean, 24 days) of support. Other than one sternal wound infection, there were no major complications after transplantation.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Kidney Injury↗
PubMed1997

Technique of right heart protection and deairing during heartmate vented electric LVAD implantation.

Continued experience with the TCI Heartmate Ventricular Assist System has led to improvements in our ability to avoid and manage right heart dysfunction during weaning from cardiopulmonary bypass. The advent of the electric device has intensified the need for these techniques because of its elevated minimal heart rate (50 beats/min) at start-up and the demands this places on the native right heart. We have developed and here describe a technique we have used successfully in our last 8 patients to assist in deairing and filling of the ventricular assist device, to partially support the right heart during the initial wean from cardiopulmonary bypass, and to avoid occasional overdistention of the right heart during early high left ventricular assist device flow.

Air↗
PubMed2000

Future directions of cardiac assistance.

During the past decade, mechanical circulatory support has gained increased acceptance as a treatment for patients with severe heart failure who are unresponsive to conventional treatment. Steady progress has been made with respect to technology, patient selection, and postoperative management. Currently, a wide array of circulatory assist pumps offers various levels of assistance and degrees of postoperative mobility. These devices not only save lives (lowering the mortality of heart transplant candidates by 55%) but, in some long-term bridge-to-transplant cases, permit hospital discharge and cardiac rehabilitation. More than 4000 patients have been supported by long-term assist pumps worldwide. In addition to being used for bridging to transplantation or bridging to the use of some other bridging device, long-term circulatory assist devices are being evaluated as bridges to recovery or alternatives to transplantation in selected patients with severe heart failure. Moreover, several total artificial hearts have shown considerable potential in calves and will soon undergo clinical trials aimed at permanent heart replacement. Eventually, as cardiac support or replacement devices become smaller, more durable, and less obtrusive, they may become as conventional and commonplace as pacemakers are today.

Animals↗