poliomyelitis in the developed world. because of this, and the development of modern ventilators, and widespread use of tracheal intubation and tracheotomy, the iron lung has mostly disappeared from modern medicine. in 1959, 1,200 people were using tank respirators in the united states, but by 2004 that number had decreased to just 39. by 2014, only 10 people were left with an iron lung. replacement positive pressure ventilation systems are now more common than negative pressure systems. positive pressure ventilators work by blowing air into the patient's lungs via intubation through the airway; they were used for the first time in blegdams hospital, copenhagen, denmark, during a polio outbreak in 1952. it proved a success and soon superseded the iron lung throughout europe. the iron lung now has a marginal place in modern respiratory therapy. most patients with paralysis of the breathing muscles use modern mechanical ventilators that push air into the airway with positive pressure. these are generally efficacious and have the advantage of not restricting patients' movements or caregivers' ability to examine the patients as significantly as an iron lung does. continued use despite the advantages of positive ventilation systems, negative pressure ventilation is a truer approximation of normal physiological breathing and results in a more normal distribution of air in the lungs. it may also be preferable in certain rare conditions, such as central hypoventilation syndrome, in which failure of the medullary respiratory centers at the base of the brain results in patients having no autonomic control of breathing. at least one reported polio patient, dianne odell, had a spinal deformity that caused the use of mechanical ventilators to be contraindicated. at least a few patients today still use the older machines, often in their homes, despite the occasional difficulty of finding replacement parts. joan headley of post-polio health international said that as of may 28, 2008, about 30 patients in the u.s. were still using an iron lung. that figure may be inaccurately low; houston alone had 19 iron lung patients living at home in 2008. martha mason of lattimore, north carolina died on may 4, 2009, after spending 60 of her 72 years in an iron lung. on october 30, 2009, june middleton of melbourne, australia, who had been entered in the guinness book of records as the person who spent the longest time in an iron lung, died aged 83, having spent more than 60 years in her iron lung. in 2013, the post-polio health international (phi) organizations estimated that only six to eight iron lung users were in the united states; as of 2017 its executive director knew of none. press reports then emerged, however, of at least three (perhaps the last three) users of such devices, sparking interest amongst those in the makerspace community such as naomi wu in the manufacture of the obsolete components, particularly the gaskets. one is retired lawyer paul alexander, 77, of dallas. in 2021, the national public radio programs radio diaries and all things considered gave a report on martha lillard, one of the last two americans depending on the daily use of an iron lung, which she had been using since 1953. in her audio interview, she reported that she was having problems obtaining replacement parts to keep her machine working properly. covid-19 pandemic in early 2020, reacting to the covid-19 pandemic, to address the urgent global shortage of modern ventilators (needed for patients with advanced, severe covid-19), some enterprises developed prototypes of new, readily-producible versions of the iron lung. these developments included: a compact, torso-sized "exovent" developed by a team in the united kingdom, which included the university of warwick, the royal national throat nose and ear hospital, the marshall aerospace and defence group, the imperial college healthcare nhs trust, along with teams of medical clinicians, academics, manufacturers, engineers and citizen scientists; a full-size iron lung developed in the united states by a team led by hess services, inc., of hays, kansas.