Month: January 2015

Oxygen’s three major forms are dynamically interrelated: molecular oxygen (O₂), atomic oxygen (O), and ozone (O₃). Each form has a more or less dominant role in different layers of the atmosphere: O₂ in the troposphere (< 8 km over the Poles to > 16km over the Equator), O₃ in the stratosphere (< 50 km), and O in the exosphere (> 500 km) where most O₂ and O₃ are photo-dissociated by ultraviolet radiation. About 90% of Earth’s atmospheric mass, estimated at 5.2 x 10²¹ g, of which 1.18 x 10²¹ g is oxygen, is located < 15 km above its surface. Gravity, temperature, radiation, and planetary rotation influence oxygen distribution variously at different atmospheric levels.*

Oxygen’s chemical reactivity is determined by the unpaired electron’s spin pattern in O’s outer orbital. When two Os form O₂ the parallel spin pattern of each outer orbital electron is maintained even as the electrons are shared. This anomaly confers relative stability to ground state O₂. Because the Pauli exclusion principle holds that anti-parallel spin electrons must pair with parallel spin electrons, the two parallel spin electrons occupying O₂’s outer domain do not readily react with other moieties at the same time. Energy must be expended to overcome this electron restriction to produce spin reversal for O₂ to react. Thus, reduction of O₂ to H₂O progresses stepwise via energy-dependent serial electron transfers that create distinct reactive intermediaries with different half-lives, diffusion capabilities, biological significance, and toxicity.

It is this oxygen property related to outer orbital electron spin restriction that frames the “oxygen paradox,” defined here as obligate aerobic life-form dependency on a chemical reduction process that produces invariably harmful intermediaries hazardous to the very life forms that produce them. Implicit in the oxygen paradox is another paradox – free radical (FR) production amounts to self-generated “inner radiation,” protection from which is conferred by intrinsic antioxidant capacity.

 

*The technically minded reader may want to review or read:

Stepniewski W, Stepniewski Z, Bennicelli RP, Glinski J. Oxygenology in Outline. Institute of Agrophysics PAS, Lublin 2005

Early Clinical Oxygen Supplementation

Oxygen supplementation grew gradually in medicine. First Mayow then Boyle demonstrated absence of air made mammalian life impossible by 1666. Priestly in 1774 and Lavoisier in 1777 isolated and demonstrated oxygen as air’s vital component. Beddoes medicalized oxygen as a panacea in 1789 through his Pneumatic Institute in Bristol, which closed in 1800. Thereafter oxygen use fell out of favor. (Warnock E, Tovell RM. Oxygen therapy and resuscitation. Anesthesiology. 1940; 1:187-204)

The roots of oxygen supplementation in anesthesia are also instructive. Availability, purity, equipment, logistics, and indications for use factored into acceptance. Most early anesthetics using ether, chloroform, and nitrous oxide were delivered in room air (FiO2 0.21) with the patient breathing spontaneously. The first inhaled ether anesthetic was reported in 1846. (Bigelow HJ. Insensibility during surgical operations produced by inhalation. Boston Med Surg J. 1846; 35:309-17) Hooper reported using oxygen after ether anesthesia to aid recovery in April 1847. (Hooper W. Inhalation of oxygen for resuscitating etherized patients. The Pharmaceutical Journal. 1847; 6:508-9)

Supplemental oxygen was first used to treat nitrous oxide poisoning in the 1860s. (Andrews E. The Oxygen Mixture, a new anaesthetic combination. Chicago Medical Examiner. 1868; 9:656-61) A common anesthetic technique then relied on 100% nitrous oxide inhalation until signs of adequate anesthesia appeared—stretor, jacitation, and lividity. With the patient obtunded near asphyxiation the procedure was performed. Blood loss was minimal as death was near. At surgery’s end oxygen was given for rescue treatment. (Smith WDA, The introduction of nitrous oxide and oxygen anaesthesia. Brit J Anaesth. 1966; 38: 950-62)

Volatile agent-oxygen combinations surfaced in the late 19^th C. Who to credit is a matter of dispute. Kreutzmann cited Neudorfer in Vienna in his 1887 report. (Kreutzmann H. Anaesthesia by choloroform and oxygen combined: preliminary report. Pacif Med Surg J. 1887; 30:462-3) Suarez published his “Spanish method” in 1898. (Diz JC, Franco A. A Spanish pioneer in the use of oxygen in anaesthesia. International Congress Series. 2002; 1242:121-5) Routine oxygen supplementation during and after inhalation anesthesia grew in the mid-20^th C. Increased muscle relaxant use likely hastened oxygen’s acceptance as part of anesthesia.

Awareness about how too little and too much oxygen affects life also grew gradually. Claude Bernard’s early lectures on anesthetics and asphyxia were published in 1875. (Bernard C. Lectures on anesthetics and on asphyxia. Translated by BR Fink. Park Ridge, IL:Wood Library-Museum of Anesthesiology. 1989) Paul Bert, a Bernard protégé, reported central nervous system oxygen toxicity effects in animals and other toxic effects on plants and animals in 1878. William Osler’s first textbook edition published in 1892 made no reference to supplemental oxygen. Lorrain Smith induced fatal pneumonia in rabbits with two to four days of 80% oxygen exposure in 1899. (Barach AL. Widening scope of oxygen therapy in the treatment of disease. Anesth Analg. 1932; :71-7)

Oxygen supplementation got a boost with efficacious poison gas-induced pulmonary injury treatment with 40% to 50 % oxygen during WW I. Barcroft and Haldane demonstrated hypoxemia’s relationship to harmful effects between 1914 and 1922. Enthusiasm built afterward to where Cohen, quoted by Buettner, said in 1931: “Oxygen to be efficacious must be used freely, frequently, fearlessly, and almost constantly, nor must its use be postponed until the patient is moribund for it will not revive the dead.” (Buettner JJ. Oxygen therapy. Anesth Analg. 193; 10:39-44) A new “oxygen culture” was thus born out of war-time experience.

By 1932 Barach endorsed specific indications for oxygen supplementation: lobar and bronchopneumonia; postoperative atelectasis; atelectasis of the new-born; acute and chronic cardiac failure; chronic pulmonary fibrosis; and (in combination with carbon dioxide) carbon monoxide poisoning and morphine poisoning. For these conditions he advocated an oxygen therapy range of between 30% and 60%. (Barach AL. Widening scope of oxygen therapy in the treatment of disease. Anesth Analg. 1932; :71-7) By 1940-41 the indications and physiological considerations applicable to oxygen supplementation were defined for cardiac disease, resuscitation, and “asphyxia neonatorum.” (Warnock E, Tovell RM. Oxygen therapy and resuscitation. Anesthesiology. 1940; 1:187-204) (Behkne AR. Certain physiological principles underlying resuscitation and oxygen therapy. Anesthesiology. 1941; 2:245-60)

 

 

The creation and use of artificial oxygen atmospheres is of extremely recent origin by evolutionary standards. Indeed, the capacity of organisms to adapt to artificial oxygen atmospheres is constrained by the fact that extreme concentration exposures are artificial, usually acute and abrupt, mostly post-reproductive, and ultimately unsustainable for long periods of time. Much as wood cannot evolve protections against intense thermal injury (burning), eucaryotic cells have not evolved — and possibly cannot evolve unequivocally — to withstand even short term, serious oxidative injuries induced by extreme oxygen exposures.

While the word “oxygen” dates to the 18th C, knowledge about oxygen’s production and properties dates to the 8th C or earlier.* Credit for oxygen’s “discovery” should not be ascribed to any one person, place, or time but regarded as a metaphor based in fact for how we come to know what we know — and may still come to know in the future.

Chinese experimenters recognized as early as the 8th C that a substance released by heating potassium nitrate could react with carbon and sulfur but not gold. Italian scientist, artist, and inventor Leonardo da Vinci (1452-1519) postulated in the 15th C that air consisted of two parts: one consumed by burning and one not, corresponding to oxygen and nitrogen, respectively. Polish alchemist Michael Sendivogius Polonos (1566-1636) postulated in the early 1600s that an “areal food of life” circulated from earth to air via the same potassium nitrate — saltpeter — pathway that, when heated, released the “Elixir of Life.” His concept was put to a practical test in 1621 when a Dutchman, Cornelius Drebbel (1572-1633), created the first known artificial oxygen atmosphere, one capable of sustaining 12 men who remained submerged under water in a wooden submarine for three hours.

John Mayow (1641-1679, English), who studied respiration and physiology at Oxford in the 17th C, conducted a series of experiments that shed light on the properties and nature of oxygen. He probably deserves more credit than he typically receives for his work in this empirical domain. His experiments showed that select metals increased in weight when heated in the presence of his mysterious gas; that this marvelous and wondrous gas composed about 20% of the atmosphere; and that mice kept under a bell jar in the presence of a burning candle expired soon after the candle extinguished presumably because this gas was exhausted. These observations led him to conclude that spiritus nitro-aereus — oxygen by another name — was present in the atmosphere, transfered via the lungs to the blood by breathing, and consumed in respiration so as to sustain life itself.

Other curious and intrepid proto-chemists produced the “release of oxygen” by heating various metals: Ole Borch (1626-1690, Denmark) in 1678 (saltpeter), Steven Hales (1677-1761, England) in 1731 (saltpeter), Pierre Bayen (1725-1798, France) in 1774 (mercury oxide). However, there are three names most commonly cited in connection to the isolation, characterization, and naming of oxygen, fairly or not: Carl Wilhelm Scheele (1742-1786, Swedish), Joseph Priestly (1733-1804, English), and Antoine Lavoisier (1743-1794, French). Perhaps the improved communication flow and revolutionary spirit abounding in the 18th C explains why these three scientists typically receive credit for things predecessors also accomplished in some form.

Scheele isolated oxygen from various nitrates; Priestly isolated “deflogisticated air” from mercuric oxide using sunlight as a heat source and essentially replicated Mayow’s work with bell jars, mice, and candles — with the added feature of breathing the gas himself to see how it made him feel; while Lavoisier conducted derivative investigations but ultimately gave oxygen its name, after the Greek for “acid-former,” under the misconception that anything acting like an acid had to contain oxygen.

While all three deserve credit for experiments, reports in letters, and formal publications; Lavoisier is the one who campaigned most actively to gather fame to himself for the discovery of oxygen. Beheaded during the French Revolution, he nonetheless claimed: “This theory [the oxygen theory] is not as I have heard it described, that of the French chemists (e.g, Bayen), it is mine (elle est la mienne); it is a property which I claim from my contemporaries and from posterity.”**

It was not long after Priestly published “Experiments and Observations on Different Kinds of Air” (1775) that the therapeutic potential of oxygen to treat various respiratory conditions and unrelated diseases was recognized and exploited. The first commercial use of artificial oxygen atmospheres for medical purposes was initiated by Thomas Beddoes (1760-1808) at his Pneumatic Institute in Bristol, England in 1798. This short-lived enterprise shut down in 1802. Of great interest is the fact that Humphry Davy (1778-1829, England) of nitrous oxide fame; and James Watt (1736-1819) of steam engine fame were partners with Beddoes in his enterprise — one which, practically speaking, upended the tight relationship between evolution and atmospheric oxygen content; while changing forever the way medicine would view and handle oxygen therapy in patient care settings.

 

*Technically minded readers might enjoy reading or reviewing:

Lane N. Oxygen. The Module that made the World. Oxford, 2002

Stępniewski W, Stępniewska Z, Bennicelli RP, Gliński J. Oxygenology in Outline. Institute of Agrophysics PAS, Lublin, 2005

http://www.chemistryexplained.com/elements/L-P/Oxygen.html

**http://todayinsci.com/QuotationsCategories/O_Cat/Oxygen-Quotations.htm

What drove oxygen accumulation in the earth’s atmosphere? Scientists have theories with supportive data but ultimate answers are elusive and always engender additional intriguing questions.*

What is unquestioned is that ancient oxygen atmospheres developed slowly over the eons, fluctuated before they flourished, and see-sawed before they stabilized. How atmospheric dynamism pressured various and varied organisms to adapt, evolve, dominate, die off, and otherwise reshape the barren and burning terrain of our beautiful, infant planet is both a marvelous story and germane to how we should view oxygen today.

As will become evident through future posts, evolution has equipped humans — mere blips in planetary time — with a greater capacity to withstand low oxygen levels than high oxygen levels. That’s “because” early evolution proceeded from extremely low oxygen fractions to the current 21% level with only a brief period of time spent at higher levels (a few million years) estimated to have peaked around 30% to 35% of total atmospheric pressure. In a real sense, to paraphrase the poet T.S. Eliot, “in our beginning is our end.” Not only is biology our destiny; destiny is in our biology. How true when it comes to oxygen.

As mentioned in a previous Oxygenologist entry, our late Proterozoic and early Phanerozoic eons saw oxygen levels rise enough to support complex oxygen-sustained organisms. This means life forms capable of metabolizing hydrogen sulfide, methane, and other gasses preceded, co-existed with, and probably co-operatively interacted with oxygen-dependent organisms in oxygen-rich eons and eras. It also means critical oxygen levels had to be attained before the most complex animals (metazoans) could populate and dominate our chemically volatile earth.

Planetary biogeochemical cycles saw complex interactions among minerals, water, gasses and the full spectrum of radiation (infra-red to cosmic) before a floor and a ceiling level for planetary ancient oxygen atmospheres could develop. The floor was set when saturated complex iron, carbon, sulfur, and other mineral substance “burials” permitted enough oxygen to accumulate as a measurable atmosphere in oxidative/reductive equilibrium with the volatile and volcanic surface mantle; the ceiling was set when conflagrations of organic matter (paleofires) periodically drew down maximum atmospheric oxygen levels, above which all combustibles could consumed, but below which combustibles could be cyclically restored. Between the two extremes life-forms evolved that depend on oxygen protected by a burgeoning ozone layer capable of shielding surface organisms from the highest levels of cosmic radiation capable of inducing genetic mutations.

 

*Technically-minded readers might be interested in reading:

Berner RA. Atmospheric oxygen over the Phanerozoic time. Proc Natl Acad Sci USA. 1999; 96:10955-7

Goldblatt C, Lenton TM, Watson AJ. Bistability of atmospheric oxygen and the Great Oxidation. Nature. 2006; 443:683-6

Plavansky NJ, Reinhard CT, Wang X, Thomson D, McGoldrick P, Rainbird RH, Johnson T, Fischer WW, Lyons TW. Low mid-proterozoic atmospheric oxygen levels and the delayed rise of animals. Science. 2014; 346:635-8

 

 

Oxygen atmospheres on earth have varied dramatically over the eons and eras. Scientists refer to the eons as the Hadean (4.5 to 4.0 billion years ago), Archean (4.0 to 2.5 billion years ago), Proterozoic (2.5 to 0.5 billion years ago); and Phanerozoic (0.5 billion years ago to the present). The Hadean eon is undivided; the Archean eon is subdivided into Eo-, Paleo-, Meso- and Neo- eras; the Proterozoic into Paleo-, Meso-, and Neo- eras; the Phanerozoic into Paleozoic, Mesozoic, and Cenozoic eras — this last, our current era.

Each eon, era, and subdivision marks a milestone in the remarkable story — too complex to cover here — of oxygen’s planetary equilibration amid shifting complex physical systems to accumulate and “stabilize” at the 21% atmospheric level we most naturally breathe today.  The inseparable parallel story is how life forms developed and evolved to handle oxygen within the eons’ and eras’ volatile atmospheric conditions.*

As remarkable as the story of oxygen’s past is, its present and future point in a different direction. The isolation of oxygen at various times between the 15th and the 18th centuries moved us to where we are today: capable of creating oxygen atmospheres containing levels far in excess of 21%. Attainment of this feat preceded awareness of oxygen’s biophysical significance and development of a nomenclature suitable to its medicinal properties. In brief, we used oxygen medically before we understood its importance, risks, benefits, and limitations. Interestingly, the 20th century saw humanity asking how to control “the atom” — radiation — in multiple settings. Perhaps the 21st century will see us determining how to rationally use and wisely control oxygen in medical settings.

* The technically minded reader might enjoy: Hsia CWC, Schmitz A, Lambertz M, Perry SF, Maina JN. Evolution of air breathing: oxygen homeostasis and the transition from water to land and sky. Compr Physiol. 2013; 3:849-915. doi:10.1002/cphy.c120003

Oxygen supports life. At sea level the atmosphere is close to 21% oxygen, a condition that has taken an estimated 500,000,000 years to develop. Humans and many other multicellular aerobic organisms have evolved over shorter time periods to function optimally at this modest oxygen level. They have also developed limited abilities to withstand and repair damage caused by excessive oxygen levels. Because oxygen levels vary under different environmental and physiological conditions (high altitude, intrauterine life) adaptation to lower levels also occurs. This adaptation, evidence suggests, is more robust and evolutionarily appropriate than adaptation to high levels of oxygen.

Medical oxygen use dates to the late 18th century. It has come into sustained use since the early to mid 20th century, primarily following extension of anesthesia-type artificial ventilation methods to early intensive care settings. In the medical setting oxygen is used as a drug, primarily to reverse low blood and tissue oxygen levels as measured by oxygen saturation monitors and blood gas samples. A problem arises, however, when oxygen is used empirically or in settings where a documented need for supplemental oxygen does not exist. Though technically oxygen supplementation is prescription-governed, non-physicians often implement oxygen or make oxygen level adjustments without specific instruction. This results in inappropriate medical oxygen use. It is known that excessive or inappropriate oxygen supplementation can be harmful; what is unknown is to what specific extent or degree and by what timetable harm can become manifest in any person’s health. This blog will explore these, and related topics in the near future.