Ventilator, lung, laboratory animal
Accession #: 2008048
Description: This is a piston driven lung ventilator where the tidal inhaled volume is adjusted by varying the excursion of a piston and exhalation to atmosphere is achieved by means of a linked valve box. It is a time-cycled quasi-sinusoidal flow generator of purely mechanical construction. A constant speed motor drives a speed reduction gearbox which, in turn, drives a rotating shaft via a multi-diameter pulley system. Frequency is adjusted by transferring the belt to pulleys of appropriate diameter. The shaft is ground so that when it passes through a valve manifold, gas is redirected to or from the animal via a breathing system. The drive shaft terminates in an eccentric drive flange connected to a crank that drives a piston. The piston, as it reciprocates, displaces gas to and from the valve assembly. During the inspiratory phase, air is delivered to the patient from the cylinder. During the expiratory phase, the animal exhales to atmosphere while the cylinder refills with fresh gas. The inspiratory flow waveform is a distorted half sine wave. Manufactured by Harvard Apparatus Ltd., Edenbridge, Kent, UK though identical versions were available from Palmer Ltd. These devices were often known as Harvard or Palmer pumps.
During the late 1960s, this type of pump (Palmer Ltd.) was used in the neonatal unit at the Glossop Terrace Maternity Hospital, Cardiff to ventilate neonates with RDS (respiratory distress syndrome) also known as Hyaline Membrane Disease. Without treatment, severely affected infants were doomed to die of respiratory failure. This is a condition wherein the ease with which the lungs can be inflated with air is regionally compromised by the absence of a biological surfactant. By using a pump, the problem can be partly oversome but the force necessary tends to cause rupture to parts of the lung that are relatively normal. The obstetric anaesthetist was called upon to supervise airway management and to ensure that the pump was regularly oiled with machine oil to prevent the valve module from overheating and seizing. There was no formal humidification system. Overall clinical management was undertaken by the Department of Paediatrics. Until this clinical application was developed, there was no long-term experience of the practical difficulties of ventilating infant lungs. Very few babies, thus treated, survived the experience and some of those who died were found to have lungs contaminated by traces of machine oil. The poor initial success rate was partly because of technical failings and partly because the technique was reserved for only those infants severely affected and at the point of death. Experience derived from those early years has transformed the effectiveness and applicability of assisting the breathing of newborn babies.