Selective stimulation of latissimus dorsi muscle for cardiac assist

The contractile power of the latissimus dorsi muscle (LDM) is used in skeletal muscle cardiac assist (SMCA) to augment the blood pumping ability of a failing heart. The LDM has three anatomically distinct, independently innervate segments-the transverse, oblique, and lateral. There are potential advantages to selectively stimulating these LDM regions. We hypothesized that (1) the three nerve branches could be stimulated selectively to activate individual muscle regions with little or no functional overlap, (2) the three muscle regions would generate similar force, and (3) nerves stimulated in combinations would generate forces corresponding to the sum of forces generated by the individual regions. In acute studies of canine LDM (n=5), regional electromyogram (EMG) and isometric force were recorded while branches of the thoracodorsal nerve were stimulated (via nerve-cuff electrodes) individually and in combinations. Analysis of regional EMG and force confirmed selective activation. Stimulation of lateral, oblique, and transverse branches of thoracodorsal nerve activated 53+/-5%, 20+/-9%, and 36+/-9% of the muscle, respectively; with corresponding developed forces of 48+/-6%, 21+/-8%, and 31+/-8% of total muscle force (R=0.98, p<0.05). Selective activation of LDM is possible with little or no functional overlap; however, the muscle regions were nonuniform. Selective stimulation may ultimately facilitate the use of performance enhancing stimulus protocols for SMCA.