Sergio A. Hayashida

Avaliação do desempenho hemodinâmico do dispositivo de assistência ventricular InCor como substituto do coração esquerdo

BACKGROUND: The mechanical circulatory assistance is a therapeutic option in cases of cardiogenic shock refractory to the pharmacological treatment, and is frequently used as a bridge for heart transplantation. OBJECTIVE: To evaluate the action of the Ventricular Assist Device (VAD) developed by the Bioengineering Division of the Instituto do Coracao, implanted as a substitute of the left heart. PATIENTS AND METHODS: Ten Girolando calves with medium weight of 73 kg were studied. The VAD-InCor implant was accomplished with the drainage cannula positioned in the left atrium (LA) or in the apex of the left ventricle and the replacement cannula implanted in the descending thoracic aorta. The pressures of the right and left heart, cardiac output and the flow of VAD were determined before and after the pharmacological induction of myocardial failure, at different levels of vacuum of the drainage system. RESULTS: Values of the flow of VAD with the drainage in LA were of 2.2 ± 0.5 l/min without vacuum, of 3.7 ± 0.4 with vacuum of 10 mmHg, of 4.3 ± 0.4 with vacuum of 20 mmHg and of 4.8 ± 0.6 with vacuum of 30 mmHg. The values of the pressure of LA were: 11.7 ± 6; 9.8 ± 5.3; 8.5 ± 4.4 and 5.6 ± 3.3 mmHg under the same conditions, respectively. With the ventricular cannula, the VAD flow was 4.2 ± 0.6 without vacuum and of 4.4 ± 0.7 with vacuum of 10 mmHg, with of LA pressure of 11.1 ± 2 and 10.3 ± 3.5 mmHg in the two conditions. Those results were observed in similar hemodynamic conditions, with the VAD flow responsible for a greater percentile of the total cardiac output according to the level of vacuum. That percentile was of 86 ± 13% with the atrial cannula and vacuum of 30 mmHg and of 97 ± 3% with the ventricular drainage and vacuum of 10 mmHg. CONCLUSIONS: The VAD-InCor demonstrated its effectiveness as a substitute of the left heart. The performance of this device was proportional to the level of vacuum of the drainage system and was better with the ventricular cannula.

In vitro and in vivo evaluation of lyophilized bioprosthetic valve.

Freeze-drying of biological tissues allows for dry storage and gamma ray sterilization, which may improve their use as a medical prosthesis. The objective of this study was to evaluate the rehydration characteristics and hydrodynamic performance of prosthetic valves before and after lyophilization. Two size 23 bovine pericardium aortic valve prostheses from different manufacturers were evaluated in a Shelhigh (Union, NJ, USA) pulse duplicator (80 ppm, 5 L/min) before and after lyophilization. Flow and transvalvular pressure gradient were registered in vitro and in vivo, and images of opening and closing of the prosthesis were obtained in the pulse duplicator in a digital camera. Rehydration was evaluated by comparison of dry valve weight with valve weight after 15 min, and 1, 24, 48, and 72 h in saline solution, inside the pulse duplicator. In vivo performance was assessed by surgical implantation in Santa Inês young male sheep in the pulmonary position after 30 min rehydration with 0.9% saline. Transvalvular pressure gradient and flow measurements were obtained immediately after implantation and 3 months after surgery when valves were explanted. Captured images showed a change in the profile opening and closing of valve prosthesis after lyophilization. The gradient measured (in vitro) in two valves was 17.08 ± 0.57 and 18.76 ± 0.70 mm Hg before lyophilization, and 34.24 ± 0.59 and 30.40 ± 0.97 mm Hg after lyophilization. Rehydration of both lyophilized valves was approximately 82%. Drying changed the profile of the opening and closing of valve prostheses, and increased on average by 83% the gradient in vitro tests. The result of the in vivo tests suggests maintaining pressure levels of the animal with the lyophilized prostheses within acceptable levels.

Alternative parameters for evaluating the performance of skeletal muscle in cardiac assistance.

This article describes a system designed to study the force, intramuscular pressure (IP), thickening (TH), and electromyographic (EMG) activity of the latissimus dorsi muscle in response to electrical stimulation. Experiments were carried out on fresh unconditioned muscles freed from the left flank insertion and fixed to contract isometrically. Statistical analysis of the data obtained demonstrated that IP and EMG activity were linearly related to force. The thickening of the muscle was found to be sensitive only to large variations in force, in a linear fashion.