The purpose of this study was to assess the applicability of the conditioned latissimus dorsi muscle as an energy source for circulatory assist devices. The authors developed a pneumatic chamber as a muscle actuator. The pneumatic chamber placed between latissimus dorsi muscle and chest wall was compressed by the burst stimulated muscle and, thereby, converted muscle contractile power into pneumatic pressure. The authors report the performance of the implanted pneumatic chamber at a chronic phase, and the capability of the conditioned muscle in situ as an energy source for circulatory assist devices. Six adult mongrel dogs were used. At the first operation, a pacemaker for muscle conditioning and the pneumatic chamber were implanted. After 12 weeks of muscle conditioning, the performance of the pneumatic chamber with conditioned muscle was evaluated. The pressure generating capability of a chamber buried in fibrous adhesions was reduced to approximately 65% of that of a chamber without adhesions. The stroke volume and stroke work of the assist device driven by the developed pneumatic pressure were measured. The maximum stroke work of the circulatory assist was greater than the stroke work of the right ventricle, but less than that of the left ventricle. In respect to stroke volume, the pneumatic chamber could drive the circulatory assist device against not only a pulmonary range of afterload, but also a systemic range of afterload, when high pre load was available. These results indicate that the compressive skeletal muscle pump with conditioned latissimus dorsi muscle generates acceptable hemodynamic work for right ventricular bypass or aortic counterpulsation. In the long-term, the interface between tissue and actuator is the major obstacle to developing a muscle powered assist device.
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