Independent associations between arterial bicarbonate, apnea severity and hypertension in a sleep apnea cohort

Abstract

Introduction: Obstructive sleep apnea (OSA) is characterized by intermittent hypoxia and hypercapnia. CO 2 production, transport and elimination are influenced by the enzyme carbonic anhydrase (CA). We hypothesize that elevations in CA are associated with sleep apnea severity and increased blood pressure in OSA patients. Aims: We investigated the association between arterial standard bicarbonate (StHCO 3 - ) concentration as a proxy for CA activity, OSA severity and hypertension. Methods: A retrospective cohort study investigating OSA patients at an academic hospital (n=830, age 51±10 yrs, body mass index [BMI] 30±5 kg/m 2 , apnea hypopnea index [AHI] 32±24 n/h). An overnight polygraphy recording was performed. Office systolic/diastolic blood pressure (SBP/DBP), lung function test, and arterial blood gas analysis including StHCO 3 - were assessed during daytime. Results: StHCO 3 - was associated with AHI (Spearman correlation, r=0.16, p - was independently associated with AHI after adjustment for sex, age, BMI, smoking, alcohol, hypertension, pO2 and pCO2 (StHCO3 - Q1 vs. Q4, β=10.6, p - was associated with a diagnosis of hypertension or DBP but not SBP adjusting for sex, age, BMI, smoking, alcohol, pO2, pCO2 and apnea severity (p=0.007, 0.048 and 0.45, respectively). Conclusions: Artial StHCO 3 - was independently associated with OSA severity, hypertension status and office DBP. Elevated StHCO 3 - may reflect the high CA activity which has been linked to the nocturnal hypoxia as well as the prevalent occurence of hypertension in OSA.