Peter A Stewart
Encyclopedia
Peter A. Stewart was a Canadian
physiologist
who introduced an alternate approach to understanding acid base physiology.
He outlined his model in a paper in 1978, 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. Stewart introduced the term "strong ion difference" or [SID] to 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 [H+] to these three independent variables. The quartic equation was solved numerically by computer and has never been validated by titration or phsyiological 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 disorders related to changes in plasma albumin
concentration).
, 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 [SID], ATOT and PCO₂ as independent variables, and [H+] 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 [H+] in terms of [SID], ATOT and PCO₂, but people take it as support for the characterisation of variables as dependent and independent.
, Manitoba
in 1921. He graduated with honours from the University of Manitoba
in 1943. Post-graduate qualifications were obtained from the University of Minnesota
: 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
. In 1965, he joined Brown University
as Professor of Medical Science.
He retired to Orcas Island
in the Strait of Juan de Fuca near Seattle in 1983, and died in 1993.
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
physiologist
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...
who introduced an alternate approach to understanding acid base physiology.
He outlined his model in a paper in 1978, 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. Stewart introduced the term "strong ion difference" or [SID] to 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 [H+] to these three independent variables. The quartic equation was solved numerically by computer and has never been validated by titration or phsyiological 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 disorders related to changes in plasma albumin
Human serum albumin
Human serum albumin is the most abundant protein in human blood plasma. It is produced in the liver. Albumin constitutes about half of the blood serum protein...
concentration).
Criticism
Ole Siggaard-AndersenOle Siggaard-Andersen
Ole Siggaard-Andersen is a Danish clinical chemist who elucidated much acid base physiology. He jointly invented the concepts of base excess and standard base excess....
, 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 [SID], ATOT and PCO₂ as independent variables, and [H+] 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 [H+] in terms of [SID], ATOT and PCO₂, but people take it as support for the characterisation of variables as dependent and independent.
Biographical information
Peter was born in WinnipegWinnipeg
Winnipeg is the capital and largest city of Manitoba, Canada, and is the primary municipality of the Winnipeg Capital Region, with more than half of Manitoba's population. It is located near the longitudinal centre of North America, at the confluence of the Red and Assiniboine Rivers .The name...
, Manitoba
Manitoba
Manitoba is a Canadian prairie province with an area of . The province has over 110,000 lakes and has a largely continental climate because of its flat topography. Agriculture, mostly concentrated in the fertile southern and western parts of the province, is vital to the province's economy; other...
in 1921. He graduated with honours from the University of Manitoba
University of Manitoba
The University of Manitoba , in Winnipeg, Manitoba, Canada, is the largest university in the province of Manitoba. It is Manitoba's most comprehensive and only research-intensive post-secondary educational institution. It was founded in 1877, making it Western Canada’s first university. It placed...
in 1943. Post-graduate qualifications were obtained from the University of Minnesota
University of Minnesota
The University of Minnesota, Twin Cities is a public research university located in Minneapolis and St. Paul, Minnesota, United States. It is the oldest and largest part of the University of Minnesota system and has the fourth-largest main campus student body in the United States, with 52,557...
: 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
Emory University is a private research university in metropolitan Atlanta, located in the Druid Hills section of unincorporated DeKalb County, Georgia, United States. The university was founded as Emory College in 1836 in Oxford, Georgia by a small group of Methodists and was named in honor of...
. In 1965, he joined Brown University
Brown University
Brown University is a private, Ivy League university located in Providence, Rhode Island, United States. Founded in 1764 prior to American independence from the British Empire as the College in the English Colony of Rhode Island and Providence Plantations early in the reign of King George III ,...
as Professor of Medical Science.
He retired to Orcas Island
Orcas Island
Orcas Island is the largest of the San Juan Islands, which are located in the northwestern corner of Washington state in San Juan County, Washington.-History:...
in the Strait of Juan de Fuca near Seattle in 1983, and died in 1993.