Dr. Beggs presented on plethysmography at the 2013 ISNVD http://isnvd2013.euromedicpoland.com/us ... tracts.pdf
INTERPRETATION OF CERVICAL PLETHYSMOGRAPHY DATA WITH RESPECT TO THE
DIAGNOSIS OF CHRONIC CEREBROSPINAL VENOUS INSUFFICIENCY
Clive Beggs, PhD, Simon Shepherd, PhD, Erica Menegatti, PhD, Paolo Conforti, MD, Mirko Tessari, RVT and Paolo Zamboni, MD
1Medical Biophysics Laboratory, University of Bradford, Richmond Road, West Yorkshire, Bradford, UK
2Vascular Diseases Centre, University of Ferrara, Ferrara, Italy
There is considerable debate regarding the applicability of magnetic resonance imaging and echo color Doppler (ECD) scan techniques for assessing cerebral venous return . This has generated much scientific controversy regarding the diagnosis of chronic cerebrospinal venous insufficiency (CCSVI) [2, 3], which is characterized by restricted venous outflow from the brain. It is however possible to assess cerebral venous return in relation to the change in a subject’s position by means of a novel cervical plethysmography method, which utilizes a passive straingauge collar . While the new cervical plethysmography technique has great potential as a low cost diagnostic tool for CCSVI, much remains unknown about the haemodynamics associated with this procedure. The aim of this study was therefore to gain a deeper understanding of the observed haemodynamics associated with this new diagnostic tool.
Materials & Methods
In a single-center, cross-sectional, blinded case-control study, 40 healthy controls and 44 CCSVI patients underwent cervical plethysmography. All participants were previously scanned using ECD sonography and separated into two subsets, a control group and a CCSVI group. The plethysmography procedure involved placing a strain-gauge collar around the subjects’ necks and tipping them from the upright (90o) to supine position (0o) in a chair. Once stabilized, they were returned to the upright position, allowing blood to drain from the neck. Measured outcomes included venous volume (VV), filling time (FT), filling gradient (FG) required to achieve 90% of VV, residual volume (RV), emptying time (ET), and emptying gradient (EG) required to achieve 90% of emptying volume (EV), where EV=VV-RV. A novel mathematical model was developed to calculate the hydraulic resistance of the extracranial venous system for each subject in the study .
The rate at which venous blood discharged in the vertical position (EG) was significantly faster in the controls (2.73 mL/second 1.63) compared with the patients with CCSVI (1.73 mL/second 0.94; P = 0.001). In addition, respectively, in controls and in patients with CCSVI, the following parameters were highly significantly different: FT 5.81 1.99 seconds vs 4.45 2.16 seconds (P = 0.003); FG 0.92 0.45 mL/second vs 1.50 0.85 mL/second (P < 0.001); RV 0.54 1.31 mL vs 1.37 1.34 mL (P = 0.005); ET 1.84 0.54 seconds vs 2.66 0.95 seconds (P < 0.001). The mean hydraulic resistance of the extracranial venous system was 10.28 (SD 5.14) mmHg.s/mL in the healthy controls and 16.81 (SD 9.22) in the CCSVI patients (p<0.001).
Cerebral venous return haemodynamics of the patients with CCSVI were markedly different from those of the controls, with the hydraulic resistance of the CCSVI patients being on average 63.5% greater in the CCSVI patients. As such, this appears to corroborate Monti et al , who found reduced cerebral venous outflow in the upright position to be strongly associated (p<0.0001) with MS. Given that CCSVI has been shown by many researchers to be associated with MS [7-9], this suggests the presence of abnormal cerebral venous drainage hydrodynamics in many patients with MS . Furthermore, the results suggest that cervical plethysmography has great potential as an inexpensive screening device and as a postoperative monitoring tool.