The Biochemistry of Benign Paroxysmal Positional Vertigo: A Theoretical Consideration

ABSTRACT

We present a theoretical discussion on the biochemistry of Benign Paroxysmal Positional Vertigo (BPPV) based on the knowledge that the otoconia are calcium carbonate crystals and that their migration into the posterior semicircular canal is responsible for BPPV. Our principal focus has been on the factors that could affect the solubility of the calcium carbonate crystals in endolymphatic fluid and hence their dissolution. We suggest two factors that could affect the dissolution of the otoconia: the concentrations of carbon dioxide and calcium ions in the endolymphatic fluid. Calcium carbonate is insoluble in water or in an aqueous medium at pH 7.4, but it can be solubilized by its conversion to calcium bicarbonate in the presence of an excess of carbon dioxide in the form of carbonic acid. The role of carbon dioxide in body metabolism is discussed, including its function in calcium transport and in the primary buffer system controlling blood pH. The second obvious factor influencing dissolution of the otoconia in the endolymphatic fluid is the concentration of calcium ions in the fluid. The role of calcium in body metabolism is discussed briefly including four factors that affect its concentration in the peripheral circulation. First, the parathyroid glands control the level of calcium ions in the peripheral circulation and respond to low levels by causing release of calcium from the bone structure into the circulation. Other factors are diets high in calcium and vitamin D and soluble calcium supplements such as calcium citrate combined with vitamin D. Finally, the effects of diuretics that cause loss of fluid with consequential loss of calcium from the peripheral circulation are mentioned. In view of these considerations, one can speculate that the dissolution of the otoconia debris in the posterior semicircular canal would be favored by a high concentration of carbon dioxide or carbonic acid and a low concentration of calcium ion in the endolymphatic fluid of the posterior semicircular canal. Hypothetically, one also can speculate that if these conditions could be made to prevail, then the occurrence or reoccurrence of benign paroxysmal positional vertigo or BPPV could be prevented.

KEYWORDS

Benign Paroxysmal Positional Vertigo (BPPV) - otoconia - calcium carbonate - calcium bicarbonate - endolymphatic fluid - parathyroid glands

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