(i) Cross-sectional case–control: test whether a blood-derived Ω proxy (from ionized calcium and blood-gas–derived pH/HCO3-/pCO2, temperature-corrected to 37 °C; arterial preferentially, venous acceptable with caveats) is independently associated with prevalent BPPV after adjustment for confounders (age, sex, BMI, renal function, vitamin D/PTH, diabetes/respiratory disease, diuretic/acetazolamide/PPI use, and hydration). Here, PTH is linked to respiratory system disorder.