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Flow Characteristics of the Spitz‐Holter Valve
Author(s) -
Forrest D. M.
Publication year - 1962
Publication title -
developmental medicine and child neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.658
H-Index - 143
eISSN - 1469-8749
pISSN - 0012-1622
DOI - 10.1111/j.1469-8749.1962.tb03167.x
Subject(s) - diaphragm (acoustics) , ball valve , ventricle , amplitude , pulsatile flow , globe valve , cardiology , mechanics , materials science , medicine , acoustics , physics , optics , structural engineering , vibration , engineering
E xperiments in vitro to measure flow using a static pressure head give inconstant results due to the inertia of the valve cusps. A system using a fluctuating pressure gives consistent results for each valve, but different valves differ widely. The low pressure valve (sub‐dural) gives higher flow rates at all pressures than the normal pressure valve, but the flow through all valves at a mean pressure of 100 mm. water is so low as to be useless, never being higher than 25 ml/day. Thus it is of no value to discuss the cut‐off pressure of valves. Flow rises steeply with increase of pressure; at a mean pressure of 200 mm. water a low pressure valve may pass between 300 and 500 ml./day while a normal pressure valve may pass up to 150 ml./day. The working environment of the valve is very variable, but a typical pressure tracing from the lateral ventricle of a hydrocephalic shows waves synchronous with the heart of amplitude of 12 mm. water. When the child is at rest but conscious, slower waves of 20 seconds' duration and amplitude of 40 mm. water appear. The resting pressure is no different whether the child is lying quietly or sucking a teat. Crying may cause a rise of 300 mm. water or more in peaks of 5–20 seconds. The venous chambers above the diaphragm show fluctuation between — 100 and + 50 mm. water while resting, while below the diaphragm pressures range from + 20 to +100 mm. water. Crying produces a rise in pressure synchronous with, but not so great as that in the lateral ventricle. The posture of the patient affects the pressure; raising the body to an angle of 30° increases the pressure gradient by 100 to 150 mm. water. Pumping the valve manually gives an output of about 7 ml./100 pumps.