ABSTRACT
OBJECTIVE: Adjustable differential pressure (DP) valves in combination with fixed anti-siphon devices are currently a popular combination in counteracting the effects of cerebrospinal fluid overdrainage following implantation of a ventriculoperitoneal shunt system. The study examined the flow performance of three DP valves in successive combination with an anti-siphon device in an in vitro shunt laboratory with and without vertical motion. METHODS: We analyzed three DP valves (Codman Hakim Medos programmable valve [HM], Codman CertasPlus [CP], and Miethke proGAV [PG], in combination with either Codman SiphonGuard [SG] or Miethke ShuntAssistant [SA]), resulting in the evaluation of six different valve combinations. Defined DP conditions between 4 and 40 cm H2O within a simulated shunt system were generated and the specific flow characteristics were measured. In addition, combinations with SA, which is a gravity-dependent valve, were measured in defined spatial positions (90°, 60°). All device combinations were tested during vertical motion with movement frequencies of 2, 3, and 4 Hz. RESULTS: All valve combinations effectively counteracted the siphon effect in relation to the chosen DP. Angulation-related flow changes were similar in the three combinations of DP valve and SA in the 60° and 90° position. In CP-SA and PG-SA, repeated vertical movement at 2, 3, and 4 Hz led to significant increase in flow, whereas in HM-SA, constant increase was seen at 4 Hz only (flow change at 4Hz, DP 40 cm H2O: PG (opening pressure 4 cm H2O) 90°: 0.95 ml/min, 60°: 0.71 ml/min; HM (opening pressure 4 cm H2O) 90°: 0.66 ml/min, 60°: 0.41 ml/min; CP (PL 2) 90°: 0.94 ml/min, 60°: 0.79 ml/min; p < 0.01); however, HM-SA showed relevant motion-induced flow already at low DPs (0.85 ml/min, DP 4 cm H2O). In combinations of DP valve with SG, increase of flow was far less pronounced and even led to significant reduction of flow in certain constellations. Maximum overall flow increase was 0.46 ± 0.04 ml/min with a HM (opening pressure 12 cm H2O) at 2 Hz and a DP of 10 cm H2O, whereas maximum flow decrease was 1.12 ± 0.08 with a PG (opening pressure 4 cm H2O) at 3 Hz and a DP of 10 cmH2O. CONCLUSION: In an experimental setup, all valve combinations effectively counteracted the siphon effect in the vertical position according to their added resistance. Motion-induced increased flow was consistently demonstrated in combinations of DP valve and SA. The combination of HM and SA especially showed relevant motion-induced flow already at low DPs. In combinations of DP and SG, the pattern of the motion induced flow was more inconsistent and motion even led to significant flow reduction, predominantly at DPs of 10 and 20 cmH2O.
Subject(s)
Hydrocephalus/surgery , Ventriculoperitoneal Shunt/instrumentation , Gravitation , Humans , Motion , Prostheses and Implants/adverse effects , Prostheses and Implants/standardsABSTRACT
For the estimation of the diagnostic value of plasma concentrations of total bile acids and ammonia in liver disease healthy controls (n = 23) as well as animals sick with different diseases were examined. The reference values for total bile acids and ammonia in the plasma of sheep range from 18-166 mumol/l and 15-64 mumol/l, respectively. While animals with chronic copper poisoning (n = 18), vitamin E/selenium deficiency (n = 15) and with diseases not affecting the liver (n = 8) did not show significant differences in concentrations of total bile acids and ammonia from those of the healthy controls, this could be proven for animals with severe hepatopathy or hepatoencephalopathy. Furthermore, some of the latter group showed increased ammonia concentrations in the liquor cerebrospinalis and multifocal vacuolation of the central nervous system. The determination of total bile acids and ammonia in the diagnosis of liver disease in sheep would also be useful. The hepatoencephalic syndrome should therefore be considered as possible differential diagnosis in animals showing neurological signs.
