FLOW DYNAMICS THROUGH SPINAL NEEDLES

We examined the flow pattern produced when liquid dye was actively inj ected into a fluid medium at various flows through five different comm only used spinal needles. At all flows, the Whitacre-type needles prod uced a directional stream exiting at an angle from the longitudinal ax is. At intermediate rates the stream developed tracks which disappeare d at faster rates. The Quincke needle always produced an undeviated st ream of dye and did not form tracks at any how rate. When a perspex pl ate (representing the spinal cord) was interposed in front of the need le, the dispersion of dye was always unidirectional from the Whitacre needle and bidirectional from the Quincke needle. The dye adhered to t he surface of the plate as a concentrated film at slow rates and at fa ster rates it dispersed turbulently for both types of needle.