Associations of Intracortical Facilitation and Inhibition of the Soleus with Popliteal Venous Flow

Abstract

The soleus muscle is functionally important to maintain venous return and consequently cardiac output by compressing underlying veins in order to increase blood flow back to the heart. Previous literature has reported that soleus dysfunction may contribute reduced venous retune. Soleus dysfunction have been attributed to altered intracortical excitability within the central nervous system. However, there is little investigation that has examined associations of intracortical facilitation and inhibition of the soleus with venous flow in the popliteal vein. Determining these associations may help to establish neurophysiological mechanisms that cause altered venous return. PURPOSE: Determine if intracortical facilitation and inhibition of the soleus are associated with popliteal venous flow. METHODS: Ten participants (8M, 2F; 20.3±0.9yrs; 165.0±7.6cm; 61.0±5.4kg) were enrolled in this current study. Paired-pulse transcranial magnetic stimulation was used to assess intracortical facilitation (ICF) and short-interval intracortical inhibition (SICI) in the soleus muscle. Blood flow velocities in the popliteal vein were measured using Dropper ultrasound in a standing position and immediately after five repetitions of maximum voluntary isometric contraction (MVIC) strength of the plantar flexors. Peak velocity and time-averaged maximum velocity (TAMAX) were assessed. Pearson Product Moment Correlations were used to examine associations of ICF and SICI in the soleus with measures of blood flow velocity in the popliteal vein. Significance was set a priori at p<0.05. RESULTS: TAMAX immediately after MVIC was moderately correlated with ICF (r=0.63, p=0.03) and SICI (r=0.59, p=0.04). CONCLUSION: These findings indicate the potential for associations of intracortical facilitation and inhibition of the soleus with blood flow velocities in the popliteal vein. Further study with a large sample size is needed to examine these associations in specific pathological condition in order to determine the effects of clinical dysfunctions on venous return.