How did the concept of acid base balance emerge?
Variable notions of acid and alkali have been part of medicine since antiquity. The concept of acidity and alkalinity were well known from their sensory perception, either gustatory from their taste or visual from the color changes they produced in certain dyes. Their taste is what provided their initial nomenclature. Acids tasted sour, hence the origin of the term “acid” from the Latin acere (sour), and its prototype the taste of acetic acid in vinegar, still known in Italian as aceto. Alkali, referring to that of the ash of charred wood or plants, whose principal constituent is potassium carbonate, is derived from the Arabic, al-qali, the word for roasting. Its taste is harder to describe, but, as the opposite of acid, it lacks tartness but leaves a distinctive sleek, somewhat soapy aftertaste in the mouth.
The changes in color they produce were first explored by the Catalan scholar Arnaldus de Villa Nova (1240–1311) using litmus, a dye extract from lichen, to test acidity. They were expanded and systematized by Robert Boyle (1622–1691), who described plant extracts that changed color in the presence of acids and bases. One such was an extract of violets that is blue but turns green in solutions that are basic and red when acid.
Early chemical studies in the 17th century by Johann Glauber (1607–1673) working in Amsterdam identified salts that resulted from the union of various acids and bases and attributed disease to disturbances in their balance in the body. A German chemist, Justin Liebig (1803–1873), ascribed acidity to the presence of hydrogen ions. With methodologic advances in chemical measurement, it was then recognized that blood is alkaline and the urine is acidic. One of the earliest studies on urinary acid and base constituents was published in 1812 by the Swedish chemist, John Jacob Brezilius (1770–1843), considered one of the founding fathers of chemistry. Interest in acid-base balance grew thereafter but remained descriptive in the main. The theory of electrolyte dissociation in aqueous solutions and the presence of hydrogen ions in acids and hydroxyl ions in bases proposed by the Swedish physicist Svante Arrhenius (1859–1927) in 1887 were instrumental in the subsequent development of concepts of acid-base solutions and buffers. For his contributions, Arrhenius was awarded the 1903 Nobel Prize for Chemistry “in recognition of the extraordinary services he has rendered to the advancement of chemistry by electrolytic theory of dissociation.” His concept was expanded by the Danish chemist Johannes N, Brønsted (1879–1947) and the Englishman Thomas M. Lowry (1874–1936), working independently, into the present Brønsted-Lowry theory characterizing acids by their affinity as proton donors and of alkali as proton acceptors.
Subsequent refinements in the instrumentation to measure the concentration of hydrogen and hydroxyl ions provided much of the advances in acid-base balance that followed. Research was stimulated by epidemics of cholera and subsequently diabetic ketoacidosis by such early pioneers in kidney physiology as Bernhard Naunyn (1839–1925), Lawrence Henderson (1878–1942), and Donald Van Slyke (1883–1971).
In 1911 Henderson introduced an equation for evaluating the buffering properties of weak acids and bases from their dissociation constant. The logarithmic transformation of Henderson’s equation by Karl Hasselbach (1874–1962) in 1917 yielded what is known now as the Henderson-Hasselbach equation. The fundamental importance of this mathematic equation in the subsequent elucidation of acid-base disorders notwithstanding, its complexity remains the principal cause of the difficulty encountered by most in understanding acid-base disorders. The use of hydrogen ion concentration expressed in nanomoles would resolve much of the difficulty associated with the continued, but unnecessary, use of the negative logarithmic expression of pH, which is just understood by a select few but is confusing to everyone else.
Structured studies in acid-base homeostasis and the role of the kidney in maintaining acid-base balance were undertaken during the period between the two world wars. The role of the kidney in the process was elucidated in the 1940s to a great extent by the studies of Robert F. Pitts (1908–1977) and his associates at Cornell University.
