Increased arterial standard bicarbonate is associated with hypertension in patients with obstructive sleep apnea – data from the European Sleep Apnea DatAbase (ESADA)

<b>Introduction:</b> Obstructive sleep apnea (OSA) is associated with altered acid-based balance, increased carbonic anhydrase activity and arterial standard bicarbonate (HCO₃). The current study aimed to address the association between HCO₃ and arterial hypertension in OSA patients. We hypothesized that HCO₃, as a surrogate marker of carbonic anhydrase activity, was elevated in hypertensive OSA patients compared with their normotensive counterparts. <b>Methods:</b> Subjects with a polysomnography study and arterial blood gas analysis in the European Sleep Apnea Database were selected (n=3535, 72% male, 38% hypertensives, age 52±12 years, body mass index 33.1±6.9 kg/m² and Apnea-Hypopnea Index 38±28 events/h). Patients with respiratory failure (PaO₂≤8 kPa and/or PaCO₂≥6.5 kPa) were excluded. Concomitant medication was determined according to ATC codes. Arterial hypertension was defined as a physician diagnosed condition with ongoing antihypertensive medication. <b>Results:</b> Mean HCO₃ was significantly higher in hypertensive compared with normotensive patients (24.3±2.7 vs. 23.9±2.4 mmol/l, p&lt;0.001). In a generalized linear model, HCO₃ was independently associated with arterial hypertension diagnosis after controlling for sex, age, body mass index, waist-to-hip ratio, smoking, intake of diuretic medication, comorbidities, PaCO₂ and apnea-hypopnea index (β [95%CI] 0.06 [0.01 - 0.11], p=0.022). <b>Conclusions:</b> A higher HCO₃ is associated with a prevalent arterial hypertension in OSA patients. Hypertension in OSA may mechanistically be linked to more severe OSA in combination with increased carbonic anhydrase activity.