Muscle transformation in cardiomyoplasty: the effect of conditioning and mobilisation on perfusion, oxygenation and fatigue resistance in the latissimus dorsi muscle.
BACKGROUND
In the clinical application of transformed skeletal muscle to cardiac assistance there is evidence that the latissimus dorsi muscle (LDM) wrap can undergo atrophy, which would prevent it from providing a sustained functional improvement. Possible causes are ischaemia and degeneration related to the conditioning process. We studied the nutritional and structural changes occurring under different stimulation regimes with the aim of improving the conditioning protocol.


METHODS
Microelectrodes were used to measure regional perfusion and oxygenation in the rabbit LDM during mobilisation and subsequent repeated contraction. Group A muscles (n = 10) were conditioned for 6 weeks at 10 Hz, Group B muscles (n = 10) for 2 weeks at 2.5 Hz. Each muscle was then mobilised and tested in a hydraulic apparatus which recorded the pressure generated in a closed circuit.


RESULTS
Muscles of Group A and Group B demonstrated transformation of fibre type, with a predominance of type I (62 +/- 4%) fibres in Group A and type IIa (68 +/- 9%) fibres in Group B. There was no evidence of muscle degeneration. After 10 min of fatigue testing the pressure produced was 53 +/- 5% of initial values in Group A and 51 +/- 8% in Group B, compared to 8 +/- 1% in the control group (P < 0.001). Maximum rate of relaxation was faster in Group B than in Group A (46 +/- 3% vs. 36 +/- 3% of control muscle, P < 0.05). Mobilisation resulted in a decrease in the distal perfusion of the control muscles (P < 0.05) and PO2 decreased by 8.7 +/- 1.7 mmHg during a fatigue test, which resulted in rapid loss of contractile function to 46 +/- 1% of the initial value within 1 min. In both Groups A and B the perfusion of all regions of the muscles both before and after mobilisation was greater than that of controls. During the same fatigue test, the PO2 of the distal regions was maintained and the contractile function fell more slowly to between 70 and 80% of initial values within 1 min.


CONCLUSIONS
We showed that ischaemia in the distal region of the control LDM could result from mobilisation and repeated contraction. Muscle transformation improved perfusion and prevented a fall in tissue PO2 during a sustained series of contractions. Muscles that were conditioned at 2.5 Hz shared the improved perfusion of the fully transformed muscle, but had faster relaxation characteristics. Short periods of in situ conditioning prior to mobilisation may help to avoid ischaemic changes in distal parts of the LDM while achieving fatigue resistance in the grafted muscle at an earlier postoperative stage.
Barron
D J
DJ
Department of Cardiac Surgery, Royal Brompton Hospital and NHLI, London, UK. d.barron@rbh.nthames.nhs.uk
Etherington
P J
PJ
Winlove
C P
CP
Jarvis
J C
JC
Salmons
S
S
Pepper
J R
JR
D000818:Animals; D018421:Cardiomyoplasty; D004558:Electric Stimulation; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction; D018763:Muscle Fatigue; D018485:Muscle Fibers, Skeletal / Q000166:cytology; D018995:Myosin Heavy Chains / Q000378:metabolism; D009929:Organ Size; D010100:Oxygen / Q000097:blood*; D011817:Rabbits; D019739:Skeletal Muscle Ventricle / Q000098:blood supply / Q000473:pathology / Q000502:physiology*; D013385:Succinate Dehydrogenase / Q000378:metabolism; D019172:Transplantation Conditioning
D013385:Succinate Dehydrogenase; D018995:Myosin Heavy Chains; D010100:Oxygen