Inline Shunt Flow Monitor for Hydrocephalus

• Published in: Analytical chemistry (Washington) 2017-08, Vol.89 (15), p.8170-8176
• Main Authors: Qin, Chuchu, Stamos, Brian, Dasgupta, Purnendu K
• Format: Article
• Language: English
• Subjects: Body fluids; Brain; Brain damage; Brain injury; Cerebrospinal fluid; Chemistry; Error detection; Flow velocity; Head; Hydrocephalus; Inflammation; Medical procedures; Skull; Temperature; Temperature effects; Thermistors
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/acs.analchem.7b02034

In hydrocephalus, cerebrospinal fluid (CSF) builds up in the cranial cavity causing swelling of the head and potentially brain damage. A shunt to drain the fluid into a body cavity is now universally used, but failure is all too common. Techniques for ascertaining shunt failure are time-consuming, expertise-dependent, and often inconclusive. We report here an inline system that reliably and quantitatively measures the CSF flow rate. The system uses a single thermistor to both heat the surrounding and to sense the temperature. In the heating mode, the thermistor is subjected to a 5 s voltage pulse. In the sensing mode, it is part of a Wheatstone’s bridge, the output being proportional to temperature. The signal, V i – V f, which is the net change ΔV in the bridge output immediately before and after the heat pulse, depends both on the flow rate and the surrounding temperature. In vitro, a single equation, flow rate = 3.75 × 10–6 × ΔV (−9.568+1.088 V i) provided good prediction for the flow rate, with 6.3% RMS relative error. The sensor behavior is reported for flow rates between 0–52.5 mL/h at 32–39 °C, adequately covering the range of interest.