The Influence of Muscle Blood-flow on the Circulation in Bones 105 



carried out under physiologically normal conditions providing that careful dissection 

 was performed. Studies on different tissues in the same limb were also shown to be 

 possible and the dependence of blood-flow in one tissue on the blood-flow in another 

 could be investigated. The present studies have been designed to examine the relation 

 between the circulation in bone and in the overlying muscle. 



Materials and methods 



Experiments were conducted on 15 adult cats anaesthetized with chloralose 

 (80 mg. per kg.). Tracheotomy was performed. Heparin was given to prevent 

 coagulation around the probes and cannulae. In 5 experiments the animal was fixed 

 in a frame to prevent movement of the hind limb in spite of muscle contraction. The 

 right tibia was transfixed at the upper and lower ends by a Kirschner wire held 

 rigidly in a frame and the pelvis was similarly fixed; the femur and its overlying 

 muscles which were to be examined remained undisturbed. 



Pressure was measured by Statham pressure transducers; arterial blood pressure 

 from a carotid artery and femoral intramedullary pressure from a cannula in the 

 upper third of the right femur. Saline was used as a conducting medium. 



Bloodflow was recorded in ten experiments using the heated thermocouple technique 

 (Shaw, 1963) and in five using the temperature compensated flow velocity probe 

 (Shaw, 1964); one probe was placed in the medulla of the upper third of the right 

 femur and another in the adjacent quadriceps muscle. In the studies using the heated 

 thermocouple the output was fed into Pye D.C. amplifiers and recorded by a Siemens- 

 Ediswan Pen recorder. The output from the temperature compensated flow velocity 

 probe was fed into an A.C. Amplifier (Cybernetics Laboratories) and the records tran- 

 scribed by a U.V. Recorder (S.E. Laboratories). In some animals estimation of the 

 hind-limb venous return was made with an electronic drop-counter sampling from 

 the femoral vein In the femoral triangle and simultaneous records of muscle blood- 

 flow were made with the temperature compensated flow velocity probe. The output 

 from the drop-counter was fed directly Into the U.V. recorder. Similarity In flow 

 changes recorded by the drop-counter and probe were considered to validate the 

 latter method as a means of estimating rate of change of muscle blood-flow. 



The right femoral nerve was exposed in the femoral triangle and Isolated and 

 divided in a paraffin pool. Platinum electrodes were used for nerve stimulation and 

 square wave stimuli through an R.F. probe were used. Stimulus parameters were 

 varied from 2 — 8 volts; 250 //sec. to 1 m.sec. duration and 10 per min. to 100 per sec. 

 frequency. The size of this stimulus Is sufficient to stimulate all components of the 

 nerve. 



Decamethonium iodide was given to examine the eflect of peripheral nerve 

 stimulation on bone blood-flow when the surrounding muscles are paralysed. 



Results 



Stimulation of the proximal cut end of the femoral nerve caused a rise in arterial 

 blood-pressure which was reflected In the rise In femoral Intramedullary pressure 

 and bone and muscle blood-flow. 



Stimulation of the peripheral cut end of the femoral nerve was also carried out: 



(1) Continuous stimulation caused an Initial fall In muscle blood-flow, but during 



sustained muscle contraction the blood flow increased above the resting level until 



