Comparison of atlanto-axial artery hemodynamics during cervical spine manipulation with doppler ultrasound in rhesus macaques

Background: The vulnerability of atlanto-axial vertebral artery (C1-C2 VA) to cervical spine manipulation (CSM), resulting in compromised blood flow and possible cerebrovascular accident, is well recognized. It needs to build animal model for further investigate the blood flow changes in the vertebral arteries during cervical spine manipulation (CSM). Methods: Peak systolic velocity (PSV), end diastolic velocity (EDV), resistance index (RI) and lumen diameter of bilateral VAs were measured using duplex Doppler ultrasound in 6 healthy rhesus monkeys with the cervical spine in eight cervical positions used in CSM. Results: The mean PSV and EDV of both VAs were decreased significantly in contralateral rotation, extension-ipsilateral and -contralateral rotation, and extension-ipsilateral and -contralateral rotation with traction (P < 0.05). A significant increase (P < 0.05) in RIs with left rotation and extension-left rotation-traction was demonstrated in right VA. Doppler waveforms revealed that blood flow followed a dampened systolic waveform during contralateral rotation and extension-contralateral rotation, and a near occlusion in combined extension-contralateral rotation with traction. Conclusion: The VA of rhesus monkey is subjected to forces that are sufficient to reduce blood flow velocity in positions involving in contralateral rotation, extension-ipsilateral and -contralateral rotations as well as combined extension-rotation with manual traction. The study of hemodynamics of the vertebral artery in rhesus monkey, which apply to biologic and mechanical research, is need to further conduct.