Peter Arthur Robert Stewart (1921–1993) was a

Canadian Canadians (french: Canadiens) are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of ...

physiologist Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical a ...

who introduced an alternate approach to understanding acid–base physiology. He outlined his model in a paper in 1978, and explained it his 1981 book, ''How to Understand Acid–Base''. The book was unavailable for many years, then made available on-line and finally reprinted in 2009, with additional chapters on current applications in clinical medicine. The Stewart approach models the complex chemical equilibrium system known as

acid–base balance In chemistry, an acid dissociation constant (also known as acidity constant, or acid-ionization constant; denoted ) is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction :HA A ...

. Stewart introduced the term "strong ion difference" or IDto mean the concentration of strongly dissociating cations minus the concentration of strongly dissociating anions. He characterised this, the total weak acid concentration and the partial pressure of CO₂ as independent variables and formulated a quartic equation relating ⁺to these three independent variables. The quartic equation was solved numerically by computer and has never been validated by titration or physiological experiments. The model ignores intracellular and extravascular compartments. The impact of the Stewart analysis has been slow in coming but there has been a recent resurgence in interest, particularly as this approach provides explanations for several areas which are otherwise difficult to understand (''e.g.'', dilutional acidosis,

acid–base disorder Acid–base imbalance is an abnormality of the human body's normal balance of acids and bases that causes the plasma pH to deviate out of the normal range (7.35 to 7.45). In the fetus, the normal range differs based on which umbilical vessel is ...

s related to changes in plasma albumin concentration).

Criticism

Ole Siggaard-Andersen, author of the textbook, ''the Acid–Base Status of the Blood'', wrote, "the Stewart approach is absurd and anachronistic." This is because Stewart began by characterising ID A_TOT and P_CO₂ as independent variables, and ⁺as the dependent variable of interest. He wrote down the equations for equilibrium concentrations derived from the law of mass action, and eliminated all other "dependent" variables. This naturally yielded an equation that phrased ⁺in terms of ID A_TOT and P_CO₂, but people take it as support for the characterisation of variables as dependent and independent.

Biographical information

Peter was born in

Winnipeg Winnipeg () is the capital and largest city of the province of Manitoba in Canada. It is centred on the confluence of the Red and Assiniboine rivers, near the longitudinal centre of North America. , Winnipeg had a city population of 749,6 ...

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in 1921. He graduated with honours from the

University of Manitoba The University of Manitoba (U of M, UManitoba, or UM) is a Canadian public research university in the province of Manitoba.University of Minnesota The University of Minnesota, formally the University of Minnesota, Twin Cities, (UMN Twin Cities, the U of M, or Minnesota) is a public university, public Land-grant university, land-grant research university in the Minneapolis–Saint Paul, Tw ...

: Master of Science in physics and mathematics in 1949, and a PhD in biophysics in 1951. In 1954, he took up a position as Associate Professor of Physiology, Physics and Biometry at

Emory University Emory University is a private research university in Atlanta, Georgia. Founded in 1836 as "Emory College" by the Methodist Episcopal Church and named in honor of Methodist bishop John Emory, Emory is the second-oldest private institution of ...

. In 1965, he joined

Brown University Brown University is a private research university in Providence, Rhode Island. Brown is the seventh-oldest institution of higher education in the United States, founded in 1764 as the College in the English Colony of Rhode Island and Providenc ...

as Professor of Medical Science. He retired to

Orcas Island Orcas Island () is the largest of the San Juan Islands of the Pacific Northwest, which are in the northwestern corner of San Juan County, Washington. History and naming of the island The name "Orcas" is a shortened form of ''Horcasitas,'' fro ...

in the Strait of Juan de Fuca near

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in 1983, and died in 1993.

References

Stewart's original text at acidbase.orgIn memory of Peter Stewart
{{DEFAULTSORT:Stewart, Peter A. 1921 births 1993 deaths People from Winnipeg University of Manitoba alumni University of Minnesota College of Science and Engineering alumni Canadian physiologists Emory University faculty Brown University faculty