Proceedings of the Physiological Society

Abstract

Water-metering device which simultaneously operates and measures the output of a blood pump. By I. DE BURGH DALY.Institute of Anrimal Physiology, Babraham, CambridgeA low-output blood pump of small blood capacity was required for the control and measurement of arterial volume inflow.Blood pump. The sectional elevation (inset A) shows the Perspex body of the pump into which are inserted three tapered (10) spigots carrying the inlet (a) and outlet (b) valves and the water chamber (c) separated from the blood chamber (d) by the rubber diaphragm (e). Large circular heads (f) with fluted edges facilitate insertion and withdrawal of the spigots. The valves are strips of thin rubber sheet fixed lightly over the inlet and outlet orifices (as shown) or are conventional flattened rubber tubing. The volume of the pump chamber, inlet and outlet channels is 2l5 ml. Pulsatile pressure changes in the water chamber are produced by connecting it alternately with a water-pressure head and with atmospheric pressure. This is done by rotary or electromagnetically operated valves.Rotary valve. The logitudinal (B) and cross (C) sections show a spindle (g) which under operating conditions rotates in the body (h). Communication between parts 1 and 2 and between 3 and 4 in the body takes place alternately by means of two 1200 slots cut in the spindle 180°out of phase. Port 1 is connected to a pressure head of water; ports 2 and 3 are both connected to the inlet (i) of the pump-water chamber, and port 4 to a volume-flow recorder operating at atmospheric pressure. Thus ports 2 and 3 can be regarded as a single port alternately communicating with port 1 and port 4. Rubberpressure tubing or polythene tubing is used for the connexions. When ports 1 and 2 communicate the water flowing into the water chamber (c) displaces an equivalent amount of blood through the blood-pump output valve (b). When ports 3 and 4 communicate the elastic recoil of the rubber diaphragm displaces the water through port 4 and at the same time draws in an equivalent amount of blood through the input valve (a). Thus the volume inflows and outflows of the rotary-valve assembly and the blood pump should be similar.The 'systolic' output of the blood pump mainly depends upon the compliance of the membrane and the difference between the pressures in the water Hg and the pump-output pressures varied from 0 to 126 mm Hg, whereas in Expts. IV and V the output pressures were approximately zero and the waterinflow pressures varied from 0 to 150 mm Hg. In Expt. III the water flow was intermittently controlled 51 times per minute by electromagnetically operated clamps on the rubber-tubing connexions. In one series of observations the water-inflow pressure was 100 mm Hg and the pump output pressures 20 to 100 mm Hg; in the other the corresponding values were 200 mm Hg and 25-175 mm Hg. The outputs of the rotary valve tend to exceed somewhat those of the blood pump especially at the lower outputs. This was in part due to incompetence of the valves at the lower pump outputs, and in...