In the early 1980s, there was increasing concern that the dramatic improvement in the survival of immature infants had been accompanied by an increase in incidence of pulmonary complications, some seriously crippling and eventually fatal. Both barotrauma and oxygen toxicity had been considered in the pathogenesis of these disorders; circulatory disorders as a result of failure of closure of the ductus arteriosus or fluid overload had also been proposed as contributory factors. Reports of successful application of the principles of high frequency ventilation (HFV) in the treatment of infants with RDS and particularly those with severe interstitial emphysema raised hopes that this technique might prevent barotrauma to the lungs and stimulated physicians and engineers to develop new equipment useful in ventilating small infants.