The Influence of Muscle Blood-flow on the Circulation in Bones 107 



Stimulation of the peripheral cut end of the femoral nerve after injection of 

 decamethonium caused a fall in muscle blood-flow without affecting the circulation 

 in bone. 



Discussion 



The simultaneous rise in arterial pressure, intramedullary pressure and blood flow 

 and in muscle blood-flow which occurred when the proximal cut end of the femoral 

 nerve was stimulated could be ascribed to a central effect on arterial pressure 

 similar to stimulating a dorsal nerve root. The surprising feature was the sudden 

 increase in intramedullary pressure and blood flow in bone like that shown by 

 Trueta and Valderrama (1965) in dogs. 



The fall and subsequent rise in muscle blood-flow during continuous stimulation 

 of the distal cut end of the femoral nerve suggests that during muscle contraction the 

 pressure on the muscle veins empties them. Sustained or rapidly repeated contraction 

 probably increases muscle blood-flow by arteriolar and capillary dilatation; an effect 

 of the products of local metabolism in spite of raised intramuscular tension. Muscle 

 relaxation further increased blood flow due to vasodilatation with vessels unrestricted 

 by external compression. The gradual fall in medullary pressure and blood flow in 

 bone which was observed may have been a passive effect owing to the diminished 

 resistance in the vascular bed of the overlying muscle. 



The present studies suggest the possibility of a passive role of intra-meduUary 

 blood-vessels during phases of varying blood flow in muscle; that muscle contraction 

 squeezes blood into bone via venous channels is the more attractive idea, because 

 blood flow and intramedullary pressure tend to follow a similar pattern; that muscle 

 occludes the veins during its contraction and therefore causes a barrier to outflow 

 from bone is hardly acceptable, because blood returning from the femur may escape 

 from veins above the level of the contracting muscle. It may be that under certain 

 conditions the circulation in the medulla may act by a venturi effect in respect of 

 vessels in the surrounding soft tissues. 



In some circumstances such as fracture of a long bone the haemodynamic system 

 of the medulla is destroyed and these effects would be abolished. Destruction of the 

 haemodynamic system may account for the oedema of the lower limb which is so 

 well-known after bony injury and prolonged immobilisation, and for the high 

 incidence of venous thrombosis after operations on the hip (Tubiana and Duparc, 

 1961). 



Vascular connections between muscle and bone may be important collateral 

 channels for the spread of tumour cells. They may also be of importance in providing 

 ischaemic muscle or bone with an alternative route for a blood supply (Zucman, 

 1960). 



In the present studies no direct effect of nerve stimulation on the circulation in 

 bones was found. However, there is little doubt that changes in muscle blood-flow 

 have a considerable influence on the circulation in bone through the osseomuscular 

 circulation which Heald (1951) originally described. 



Summary 



Stimulation of the proximal and peripheral cut ends of the femoral nerve in 

 anaesthetized cats had no direct effect on the circulation in bone. The changes in 



