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A S Khalafalla

Publications and source records attributed to A S Khalafalla.

7 recordsLinked to original sources
PubMed1988

Skeletal muscle grafts applied to the heart. A word of caution.

Latissimus dorsi pedicle grafts (LDPGs) were wrapped around the heart in eight dogs. In four dogs, the LDPGs were stimulated chronically; the remaining four dogs served as unstimulated controls. Right-sided cardiac filling pressures were normal in all dogs when measured 4 months after graft application. Mean tension generated by the viable LDPGs was 153 +/- 49.9 g. LDPGs contracting in synchrony with the heart did not increase cardiac output. In one dog, the aortic pressure changed from 140/100 to 155/85 mm Hg during synchronous contraction of the LDPG. Three dogs were placed on cardiopulmonary bypass, and their hearts were placed in fibrillation. The LDPGs were then stimulated at a burst frequency of 85 Hz and contracted vigorously. Under these conditions, the left ventricular pressure increased by an average of 15 mm Hg with each LDPG contraction; however, the mean aortic pressure was virtually unchanged. Left ventricular and aortic pressures of 125/20 and 125/65 mm Hg, respectively, could be obtained with manual compression of the fibrillating heart. This study indicates that although LDPGs can be made to contract chronically and in synchrony with the heart, they do not necessarily augment left ventricular performance.

Animals↗
PubMed1987

Implantable extra-aortic balloon assist powered by transformed fatigue-resistant skeletal muscle.

The hypothesis tested in this study was whether a skeletal muscle could be transformed to be fatigue resistant, to be used to power an implantable extra-aortic balloon assist device, and therefore to provide dynamically significant cardiac assistance. Eight dogs underwent implantation of an Itrel pacemaker to stimulate the thoracodorsal nerve over 8 to 18 weeks and transform the latissimus dorsi muscle. Biopsies of these muscles confirmed near complete (up to 98%) transformation into fatigue-resistance type I muscle fibers, identified by the adenosinetriphosphatase histochemical stains. Biochemical assays showed conversion of myosin isoforms to that of myocardial V3 phenotype, decreased activity of anaerobic glycolytic marker, and increased activity of aerobic enzyme marker, which indicated greater resemblance of such muscle to the myocardial fibers. In four dogs, the optimal stimulation parameters of such muscles in response to a burst stimulator, which synchronizes and summates the muscle contraction, were studied and compared with the contralateral, nontransformed muscle. Fatigue tests confirmed the marked fatigue resistance of the transformed muscle. In four dogs, a 100 ml balloon was placed beneath the transformed latissimus dorsi muscle and connected to the thoracic aorta with a Dacron graft. By means of the optimal burst-stimulating parameters identified above, the latissimus dorsi muscle was stimulated to contract during diastole, compressing the balloon to achieve diastolic augmentation while allowing the balloon to fill during systole. A 39% increase (p less than 0.001) in the "subendocardial viability index" (diastolic pressure-time index/tension-time index) was obtained as calculated from the left ventricular and ascending aortic pressure tracings. We conclude that the skeletal muscle can be transformed to resemble myocardium, which can generate sufficient force to provide hemodynamically significant and clinically relevant counterpulsation.

Animals↗
PubMed1985

Left ventricular assistance in dogs using a skeletal muscle powered device for diastolic augmentation.

A pulse train stimulator was developed for skeletal muscle stimulation synchronous to the myocardium. Left ventricle contraction was augmented by a stimulated rectus abdominis muscle pedicle grafted into the left ventricular wall. A miniaturized and programmable stimulator was built. The stimulation parameters for this device were optimized and the configuration of a skeletal muscle powered assist device for cardiac assistance was investigated in acute canine experiments. A hydraulic balloon preparation was used to characterize stimulation parameters and to compare rectus abdominis, latissimus dorsi and pectoralis major muscles as power sources. Assist devices evaluated included a left ventricle apico-aortic conduit with a central pumping chamber and an extra-aortic balloon pump. The pumping chambers were either wrapped by the rectus abdominis and latissimus dorsi pedicles, or placed deep into the pectoralis major. The optimal stimulation parameters were pulse trains of 200 msec duration containing pulses 240 mu wide at a frequency of 35 pulses/second. There was no fatigue over a ten hour period despite stimulation at a rate of 120 contractions/minute. Muscle dissection and selection were determinants of fatigability. However, counter-pulsation was possible regardless of the muscle selected. The most efficient device was an extra-aortic balloon pump. There was a consistent increase in subendocardial viability index (DPTI/TTI). The advantages in using a skeletal muscle power source for diastolic rather than systolic assistance were established.

Abdominal Muscles↗