Letter to editor
Basic Applied Myology 19 (4): 187, 2009
- 187 - Letter to Editor Linear muscle power for cardiac support
Dear Sir,
Dennis Trumble is to be congratulated on the progress he has made towards an efficient linear muscle energy converter, and for setting out the advantages and disadvantages of various approaches needed to translate this hydraulic work into useful cardiac assistance [5]. It is certainly helpful that the linear configuration does not require sacrifice of the perforating (so-called
‘collateral’) vessels, although this problem can be overcome by preconditioning [3]. However, Trumble underestimates the capacity for pumping blood that is offered by the skeletal muscle ventricle (SMV), for the following reason.
When the muscle is wrapped to form the artificial ventricle it compresses the lumen in two ways:
(a) by the shortening of its fibres, which reduces the circumference of the wrap, and (b) by the inward movement of the volume of the wrap. The latter arises because the outer fibre layers, being more lightly loaded, contract more rapidly than the inner fibre layers, so that the muscle bulges inwards during each contraction.
The importance of this effect is well illustrated in another application: the use of rectus abdominis muscle to create an artificial sphincter. Shortening of a sarcomeric muscle is normally limited to about 25%, and a double wrap of muscle of 3.6 mm thickness, around a lumen of 14 mm, would not, on this basis, be expected to cause occlusion. As a result of inward bulging, however, occlusion is total, and capable of resisting a pressure of 60 cm of water for prolonged periods ([2], and manuscript in preparation).
This phenomenon no doubt contributes to the pumping performance we have observed when an SMV is connected in circulation in pigs. Working in counterpulsation, SMVs proved capable of generating as much as 50% of the work of the native left ventricle in single contractions, and provided an assist at least equivalent to that of an intra-aortic balloon pump [1]. In dogs, SMVs were still providing effective diastolic augmentation when they were electively terminated after pumping in counterpulsation for up to 4 years [4].
There is therefore every reason to believe that this approach to long-term cardiac assistance is feasible and effective.
Stanley Salmons, Jonathan C. Jarvis Muscle Research Group
Department of Human Anatomy and Cell Biology University of Liverpool, UK
Address Correspondence to:
Emeritus Professor Stanley Salmons, Department of Human Anatomy and Cell Biology, University of Liverpool, The Sherrington Building, Ashton Street, Liverpool L69 3GE, UK E-mail: s.salmons@liverpool.ac.ukE-mail:
References
[1] Ramnarine IR, Capoccia M, Ashley Z, Sutherland H, Russold M, Summerfield N, Salmons S, Jarvis JC: Counterpulsation from the skeletal muscle ventricle and the intraaortic balloon pump in the normal and failing circulations. Circulation 2006; 114 (Suppl): I-10-15.
[2] Russold MF, Ramnarine I, Ashley Z, Sutherland H, Salmons S, Jarvis JC, Stomal sphincter configured from the rectus abdominis muscle in pigs. First results., Wood D, Taylor P, Eds., 9th Annual Conference of the International FES Society, Bournemouth, UK (Salisbury Health Care Trust, 2004).
[3] Salmons S, Jarvis JC: Cardiomyoplasty reviewed: lessons from the past, prospects for the future. Basic Appl Myol 2009; 19: 5-16.
[4] Thomas GA, Hammond RL, Greer K, Lu H, Jarvis JC, Shortland AP, Pullan DM, Salmons S, Stephenson LW: Functional assessment of skeletal muscle ventricles after pumping for up to four years in circulation. Ann Thorac Surg 2000; 70: 1281-1289.
[5] Trumble D: Linear muscle power for cardiac support: current progress and future direction.
Basic Appl Myol 2009; 19: 35-40.
