Intramuscular haemodynamics using near infra-red spectroscopy as a research strategy to understand chronic muscle pain pathophysiology

Recently, localized intramuscular haemodynamic disturbance has been recognized as one of the cardinal features of a chronically painful muscle. To test this hypothesis, we have carried out several studies that have assessed intramuscular haemodynamics to understand more about haemodynamic alteration under conditions of an experimentally induced vasoreactive challenges in healthy controls and in patients with chronic muscle pain using near infra-red (NIR) spectroscopy. In addition, we have validated the NIR based haemodynamic signals by comparing against a water signal intensity change taken from a transverse T₂-weighted magnetic resonance image (MRI) of the muscles. As a result, we discovered that muscle pain patients have a diminished ability to vasodilate in painful muscle. We also provided powerful evidences that NIR data (total haemoglobin level), transcutaneously taken from the muscles in humans could be an analogue of intramuscular haemodynamics.