Journal of Thermal Biology 31 (2006) 181–185 Possible role of the internal vertebral venous plexus during exercise in humans Osamu Shido a,Ã , Megumi Maruyama a , Akihiko Wada b , Kazushige Oda b , Abdul Haque Md a , Hajime Kitagaki b a Department of Environmental Physiology, School of Medicine, Shimane University, 89-1 Enya-cho, Izumo 693-8501, Japan b Department of Radiology, School of Medicine, Shimane University, Izumo 693-8501, Japan Accepted 22 November 2005 Abstract The internal vertebral venous plexus (IVVP) is an extensive vascular network surrounding the spinal cord. However, little attention has been paid to its physiological role. During leg exercise, warm blood returns from the legs to the heart. If a portion of the blood is conveyed via the IVVP, it may warm the spinal cord and facilitate thermoregulatory responses. To assess this, we investigated how venous blood from the legs return to the body core. Direct contrast-enhanced magnetic resonance (MR) venography clearly demonstrated the anterior IVVP at the lumbar and thoracic regions in one subject after leg exercise, partially supporting our hypothesis. r 2005 Elsevier Ltd. All rights reserved. Keywords: Direct contrast-enhanced MR venography; Posture; Thermoregulation 1. Introduction The spinal canal venous plexus is an extensive, valveless vascular network which extends the entire length of the vertebral column (Batson, 1940, 1957; Greon et al. 1997). It parallels, joins and at the same time bypasses the long- itudinal veins of the thoracic and abdominal cavities, and then unites with the superior and inferior vena cava. The spinal column is a sturdy structure which protects its contents from the direct effect of intra-thoracic and intra- abdominal pressure changes, and also protects the epidural venous plexus. Thus, blood flow in the internal vertebral venous plexus (IVVP) is likely to be in either direction depending on the changes of the intra-thoracic and intra- abdominal pressures. From a clinical standpoint, there are several reports showing a significant role of the IVVP in returning venous blood from the lower body to the central venous system in humans (Batson, 1940; O ¨ ge et al., 2001) and animals (Coman and deLong, 1951; Harada et al., 1992). For instance, the migration of foreign matter in the femoral vein to the spinal canal via the venous route has been reported (O ¨ ge et al., 2001); and, according to Batson’s theory of spinal metastases, prostatic carcinoma preferen- tially metastasizes to the vertebral bone through the vertebral venous system (Coman and deLong, 1951; Harada et al., 1992). However, little attention has been paid to the physiological role of the IVVP, even though the venous system comprehensively surrounds the pivotal organ, the spinal cord. During lower leg exercise, blood flow to active muscles increases greatly. The blood passing through the muscles is warmed, and this blood with the highest temperature in the body returns to the body core. It is quite possible that a portion of the venous blood returning from the legs is conveyed through the IVVP, because of periodic changes in intra-abdominal pressure due to exercise. Indeed, it has been suggested that voluntary contraction of the abdominal muscle elevates intra-abdominal pressure to a level that can cause inflow of intra-abdominal venous blood into the IVVP (Suzuki et al., 1993). The venous blood returning from the legs then warms the tissue in the spinal canal, including the spinal cord, when the blood passes through the highly developed IVVP (Greon et al. 1997). The spinal cord has been ARTICLE IN PRESS www.elsevier.com/locate/jtherbio 0306-4565/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jtherbio.2005.11.009 Ã Corresponding author. Tel.: +81 853 20 2111; fax: +81 853 20 2110. E-mail address: o-shido@med.shimane-u.ac.jp (O. Shido).