Oxygen Read online

  2 Nitre (potassium nitrate, KNO3), gives every appearance of condensing from the air as a white crust on well-manured soils (containing nitrogen). It has some remarkable properties.

  Besides being a fine fertilizer, it was used for preserving meat and as a folk remedy. When added to drinks, nitre cools them down as effectively as ice, yet when taken as a medicine produces a strong warming effect. The acid of nitre ( aqua regia, or ‘queen of waters’) could dissolve gold, an attribute that appealed to alchemists. Nitre is also the chief component of gunpowder, which was invented by Chinese alchemists in the ninth century.

  4 • INTRODUCTION

  evidently believed he had discovered the Elixir of Life, “without which no mortal can live, and without which nothing grows or is generated in the world.” His ideas went beyond theory. Sendivogius almost certainly produced oxygen by heating nitre, and may well have explained his methods to the Dutch inventor and fellow alchemist Cornelius Drebbel, a lost hero of Renaissance science.

  Drebbel gave a brilliant demonstration of the practical utility of oxygen in 1621. After constructing a solar-powered perpetual-motion machine and a variety of refrigerators and automata for King James I of England, Drebbel built the world’s first submarine. King James, accompanied by thousands of his subjects, stood on the banks of the River Thames to watch its maiden voyage from Westminster to Greenwich, a distance of ten miles. Manned by twelve oarsmen, the wooden submarine apparently stayed under water for three hours. Much of the interest centred on how Drebbel had managed to refresh the air for the rowers during this time. According to eye-witness accounts, discussed some years later (in 1660) by the great chemist Robert Boyle, Drebbel had used a bottle of ‘liquor’ (others referred to it as a gas) to refresh the ‘vital’ parts of the air:

  Drebbel conceived that it is not the whole body of the air, but a certain quintessence, or spirituous part of it, that makes it fit for respiration, which being spent, the remaining grosser body, or carcass (if I may so call it) of the air, is unable to cherish the vital flame residing in the heart…. For when, from time to time, he [Drebbel] perceived the finer and purer part of the air was consumed… he would, by unstopping a vessel full of this liquor, speedily restore to the troubled air such a proportion of vital parts, as would make it again, for a good while, fit for respiration.

  Presumably, Drebbel had succeeded in bottling oxygen gas, following the instructions of his mentor Sendivogius, by heating nitre. Sendivogius, Drebbel and Boyle clearly thought of the air as a mixture of gases, one of which was the vital gas oxygen. They recognized that in confined spaces the air was depleted of oxygen by breathing or burning. Boyle certainly saw respiration and combustion in similar terms — the vital flame residing in the heart — even if he did not appreciate how exactly analogous the two reactions really were. Boyle’s contemporary and Fellow of the Royal Society, John Mayow, went even further: he showed that aerial nitre (oxygen), when breathed into the lungs, gave arterial blood its red

  Elixir of Life — and Death • 5

  colour. Aerial nitre, he said, was a normal constituent of the air, from where it “becomes food for fires and also passes into the blood of animals by respiration…. It is not to be supposed that the air itself, but only its more active and subtle part, is the igneo-aerial food.” In other words, despite his archaic vocabulary, Mayow had a strikingly modern concept of oxygen as early as 1674.

  Against this background, Priestley’s attachment to the phlogiston theory (the idea that burning releases an invisible substance) a century later looks almost comical, although he was by no means alone. Guided by false phlogiston, the study of airs had been groping at shadows for the best part of a century. To account for experimental results, phlogiston was assigned a positive weight, no weight at all, or a negative weight, depending on the requirements. Even those who credit Priestley with the discovery of oxygen accept that his adherence to this theory blinded him to the true meaning of his discovery.3 In another sense, though, Priestley was uncannily prescient. He foresaw not only the medical applications of oxygen (which he persisted in calling dephlogisticated air) but also its potential danger. In his Experiments and Observations on Different Kinds of Air, published in 1775, Priestley mused on his own experiences of breathing pure oxygen:

  The feeling of it to my lungs was not sensibly different from that of common air; but I fancied that my breast felt peculiarly light and easy for some time afterwards. Who can tell but that, in time, this pure air may become a fashionable article in luxury…. From the greater strength and vivacity of the flame of a candle, in this pure air, it may be conjectured, that it might be peculiarly salutary to the lungs in certain morbid cases, when the common air would not be sufficient to carry off the putrid effluvium fast enough.

  But, perhaps, we may also infer from these experiments, that though pure dephlogisticated air [oxygen] might be very useful as a medicine, it might not be so proper for us in the usual healthy state of the body; for, as a candle burns out much faster in dephlogisticated than in common air, so we might, as may be said, live out too fast [Priestley’s italics] and the animal powers be too soon exhausted in this pure kind of air. A moralist, at least, may say, that the air which nature has provided for us is as good as we deserve.

  3 To be fair to Priestley, he was perfectly aware of the problems with the phlogiston theory.

  He compared phlogiston with light and heat, which could not be weighed either (then as now).

  6 • INTRODUCTION

  Anyone inhaling pure oxygen in an ‘oxygen bar’ today might smile at Priestley’s quaint analogy and moral sentiments, but few researchers would disagree with the substance of these remarks. Strikingly, Priestley’s words contain the first suggestion (to my knowledge) that oxygen might accelerate ageing. This caution was lost on his contemporaries, who went on to embrace the medical potential of oxygen before the end of that century. Despite suspicions, its toxicity was not documented for a further hundred years.

  The first person to use pure oxygen therapeutically, on a large scale at least, was Thomas Beddoes. Beddoes founded the Pneumatic Institute for inhalational gas therapy in Bristol in 1798, in which he employed the brilliant young chemist Humphry Davy. The pair aimed to treat diseases hitherto found incurable. Unfortunately, they were overly ambitious in their choice of patients, and their treatments offered little clinical benefit.

  Worse, impurities in the gas frequently caused inflammation of the lungs.

  (Ironically, the inflammation may not have been caused only by impurities; pure oxygen also inflames the lungs.) Faced with these problems, as well as unreliable supplies of oxygen, the institute closed its doors in 1802. Davy later described his work there as “the dreams of misemployed genius, which the light of experiment and observation has never conducted to truth”.

  This pattern of hopes and failures persisted throughout much of the nineteenth century. Problems with impurities, and diverse methods of delivery to the patient, meant that a clinical consensus never emerged.

  Sometimes oxygen was inhaled directly from a mask or bag. In other cases, the gas was bubbled through a bucket of water placed near the bed, and the air of the room fanned towards the patient. Failure must have been assured. With such disparate procedures, and little in the way of systematic comparisons, it is hardly surprising that outcomes were dis-crepant. Advocates of oxygen therapy claimed miraculous cures (which may have been true in conditions such as pneumonia) but the voices of mainstream medicine were for the most part unimpressed, arguing that any perceived benefits were transitory, palliative or imaginary. The gap was forced even wider by the usual quacks and charlatans, who peddled a secret preparation known as ‘compound oxygen’ to a gullible public.

  Some claims made in the 1880s were remarkably similar to those made today by proponents of ‘active oxygen’ therapies. They were dismissed then, as today, by ethical practitioners of oxygen therapies.

  Elixir of Life — and Death • 7

  Medical inte
rest in oxygen therapies picked up after a number of anecdotal reports suggested that higher oxygen pressures really did affect health. For example, patients with pneumonia living at high altitude in cities like Mexico City, where the oxygen pressure is low, were found to have a better chance of recovery if rushed down to the plains, where oxygen pressure is higher. Similarly, patients with cardiovascular disease generally fared better at sea level than at high altitude. Impressed by these reports, the American physician Orval Cunningham reasoned that still higher barometric pressures might amplify the effect. Following a number of apparent successes, a grateful client helped finance construction of the largest-ever hyperbaric chamber in Cleveland, Ohio, in 1928 — a million-dollar hollow steel ball, 20 metres [65 feet] in diameter and five stories tall, pressurized to about twice the atmospheric pressure at sea level.

  Cunningham fitted out his giant steel ball as a hotel, with a smoking lounge, restaurant, rich carpeting and private rooms. Unfortunately, he used compressed air, not oxygen, so the total oxygen pressure was no higher than could have been achieved with a mask, at a fraction of the cost. Worse, rather than treating people with conditions such as pneumonia and cardiovascular disease, who might have benefited, he over-stepped the mark by treating patients with diabetes, pernicious anaemia and cancer, on the fallacious grounds that all these conditions were caused by anaerobic (oxygen-hating) bacteria. Both his objectives and his results failed to impress the American Medical Association, who condemned the scheme as “tinctured much more strongly with economics than with scientific medicine”. The steel ball lasted but a few years before being dismantled and sold for scrap in 1942, contributing to the American war effort.

  Cunningham should have known better. Despite the equivocal history of oxygen therapy, the field had finally been put on a scientific footing by the distinguished Scottish physiologist John Scott Haldane (father of the biologist J. B. S. Haldane) in the early years of the twentieth century. Haldane was an expert in diving medicine and had spent the First World War using oxygen to treat injuries caused by chlorine gas. He summed up his experiences in the groundbreaking book, Respiration, published in 1922, in which he argued that some patients with respiratory, circulatory and infectious conditions could be cured by continuous oxygen inhalation. Given properly, he said, oxygen therapy was not just palliative, but could break the vicious cycle of degeneration, giving the body an opportunity to recover its own healthy equilibrium.

  8 • INTRODUCTION

  Haldane’s tenets underpin modern oxygen therapies, yet even today we do not have a clear appreciation of how beneficial these therapies can be. A large clinical trial, reported in the prestigious New England Journal of Medicine in January 2000, showed that inhalation of 80 per cent oxygen for two hours halved the risk of wound infection after colorectal surgery, compared with routine practice (30 per cent oxygen for two hours). The finding that a simple treatment can make a big difference is encouraging; but the fact that a treatment available in essentially the same form for 200

  years can still make medical headlines at the start of the twenty-first century is salutary. If nothing else, it illustrates just how far the progress of science can be impeded by a professional knee-jerk response to the inflated claims of quacks and charlatans.

  Another reason for caution was spelled out by Haldane early in the twentieth century — the possibility of oxygen toxicity. Haldane himself had written that:

  The probable risks of prolonged administration of pure oxygen must be borne in mind and if necessary balanced against the risks of allowing the oxygen-want to continue. No fixed rule can be given. The proper course to pursue must be determined by the physician after careful observation of the patient, and in the light of experience and knowledge.

  It is understandable that physicians prefer to err on the side of caution; but what are these risks? Haldane’s careful wording makes them sound a little theoretical, but oxygen, especially under pressure, can cause shock-ingly physical reactions, as Haldane knew well from his own research in diving medicine.

  The toxicity of oxygen is slow-acting, or hidden from view, in normal circumstances. Many people receive oxygen therapy in hospital, or spend days, sometimes weeks, in oxygen tents, or inhale oxygen in bars with no ill effects. Astronauts often breathe pure oxygen for weeks on end, though in space the capsule is pressurized to only one third of atmospheric pressure, which makes it equivalent to breathing 33 per cent oxygen.

  The difference that pressure makes to the oxygen concentration in the atmosphere explains why three astronauts died when Apollo 1 caught fire in 1967, as they were completing tests on the ground. In space, the inside of the capsule is always pressurized to a higher pressure than the surrounding vacuum, which means that spacecraft are built to withstand

  Elixir of Life — and Death • 9

  a greater pressure inside than outside. To maintain this pressure differential, Apollo 1 was pressurized to above atmospheric pressure while on the ground. Unfortunately, the spacecraft was still being ventilated with pure oxygen. This meant that instead of an atmosphere equivalent to 33 per cent oxygen, the astronauts were actually breathing the equivalent of 130 per cent oxygen. In this oxygen-rich atmosphere, a spark from the electrical wiring led to an uncontrollable fire, which reached a temperature of 2500°C within minutes.

  But oxygen is more than just a fire risk: it is toxic to breathe.

  This toxicity depends on the concentration and duration of exposure.

  Most people can breathe pure oxygen for a day or two, but we cannot breathe it for longer without risk. If the concentration of oxygen is increased even more by compressing the gas, then the toxic effects become dramatic.

  The realization that oxygen is toxic came from the experiences of the earliest scuba divers, towards the end of the nineteenth century. (The word scuba was a later coinage, and stands for self-contained underwater breathing apparatus.) Scuba divers were vulnerable because they carried their breathing apparatus with them, and usually breathed pure oxygen.

  The oxygen in the apparatus could be compressed by water pressure.

  Breathing pure oxygen at depths below about 8 metres [26 feet] causes seizures similar to an epileptic grand-mal — a disaster if the diver loses consciousness underwater.

  Oxygen convulsions were first described systematically by the French physiologist Paul Bert, professor of physiology at the Sorbonne in Paris. In his celebrated 1878 monograph on barometric pressure, Bert discussed the effect of oxygen on animals subjected to different pressures in a hyperbaric chamber. Very high oxygen concentrations caused convulsions and death in a matter of minutes. The following decade, in 1899, the Scottish pathologist James Lorrain Smith showed that lower levels of oxygen could have an equally deadly, but delayed, effect. Animals exposed to 75 per cent oxygen or more (at normal air pressure) had such serious inflammation of the lungs after a few days that they died. For this reason, oxygen dosages in hospitals are always strictly controlled. Convulsions and lung injury became familiar worries to scuba divers, however. Both Paul Bert and James Lorrain Smith are still commemorated in diving terminology. Unfortunately for Smith, his unusual name, along with his habit of styling himself J. Lorrain Smith, frequently turns the tribute into the ‘Lorraine Smith’ effect.

  10 • INTRODUCTION

  While many divers were careful not to dive too deep while breathing pure oxygen, the Navy could not always afford to be so cautious. In the British Royal Navy Submarine Escape Handbook, published in 1942, seamen were instructed to watch out for the symptoms of oxygen poisoning: “tingling of the fingers and toes, and twitching of the muscles (especially around the mouth); convulsions followed by unconsciousness and death if a remedy is not taken.” Naval divers during the war invented a mythical monster, Oxygen Pete, who lurked at the bottom of the sea waiting to molest unwary divers. Oxygen toxicity ‘hits’ during this time were referred to as “getting a Pete”.

  A more rigorous understanding of oxygen toxicity, human limits and g
as mixtures was clearly needed, and J. B. S. Haldane was commissioned by the Royal Navy to follow in the footsteps of his father. Always an advocate of being one’s own rabbit, Haldane subjected himself and his colleagues to various oxygen concentrations under different pressures, noting how long it took before convulsions set in.4 Exposure to pure oxygen at seven atmospheres pressure led to convulsions within five minutes. He later wrote that:

  The convulsions are very violent, and in my own case the injury caused to my back is still painful after a year. They last for about two minutes and are followed by flaccidity. I wake in a state of extreme terror, in which I may make futile attempts to escape from the steel chamber.

  Nonetheless, his efforts were successful. The Royal Navy secretly developed various nitrogen/oxygen (nitrox) mixtures, which lowered the risk of both oxygen toxicity and nitrogen narcosis (the ‘bends’). These nitrox mixtures were used by British commandos defending Gibraltar in the Second World War, and were kept such a close secret that even the US

  Navy did not find out until the 1950s. Using nitrox mixtures the British divers could operate at greater depths. A major element of British strategy was to lure the combatants into deep waters until they were overwhelmed by convulsions. Mugged by oxygen: perfidious Albion indeed!

  4 In a celebrated essay on self-experimentation, “On being one’s own rabbit”, published in 1928, Haldane wrote that “to do the sort of things to a dog that one does to the average medical student requires a license signed in triplicate by two archbishops.” He also thought it peculiar that so few chemists wondered what it actually felt like to become more acid or alkaline, or dilute.

  Elixir of Life — and Death • 11

  Breathing oxygen at high concentration is obviously toxic. Above about two atmospheres of pressure, pure oxygen causes convulsions and sometimes death. Oxygen accounts for about a fifth of atmospheric pressure, so pure oxygen at two atmospheres pressure is ten times our normal exposure. At lower concentrations, oxygen is unlikely to cause convulsions, but breathing pure oxygen at normal atmospheric pressure (five times our normal exposure) for a few days can still cause life-threatening lung damage. Such serious inflammation of the lungs prevents us from breathing properly. Ironically, we then cannot pass oxygen into the blood stream, so we actually die from oxygen starvation to the rest of the body.