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. 2017 Jun 28;18(1):130.
doi: 10.1186/s12931-017-0607-9.

Independent Associations Between Arterial Bicarbonate, Apnea Severity and Hypertension in Obstructive Sleep Apnea

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Free PMC article

Independent Associations Between Arterial Bicarbonate, Apnea Severity and Hypertension in Obstructive Sleep Apnea

Davoud Eskandari et al. Respir Res. .
Free PMC article

Abstract

Background: Obstructive sleep apnea is characterized by intermittent hypoxia and hypercapnia. CO2 production, transport and elimination are influenced by the carbonic anhydrase enzyme. We hypothesized that elevated standard bicarbonate, a proxy for increased carbonic anhydrase activity, is associated with apnea severity and higher blood pressure in patients with obstructive sleep apnea.

Methods: A retrospective analysis of a sleep apnea cohort (n = 830) studied by ambulatory polygraphy. Office systolic/diastolic blood pressure, lung function, and arterial blood gases were assessed during daytime.

Results: Arterial standard bicarbonate was increased with apnea severity (mild/moderate/severe 24.1 ± 1.8, 24.4 ± 1.7 and 24.9 ± 2.9 mmol/l, respectively, Kruskal-Wallis test p < 0.001). Standard bicarbonate was independently associated with apnea hypopnea index after adjustment for sex, age, body mass index, smoking, alcohol, hypertension, pO2 and pCO2 (standard bicarbonate quartile 1 vs. quartile 4, β = 10.6, p < 0.001). Log-transformed standard bicarbonate was associated with a diagnosis of hypertension or diastolic blood pressure but not systolic blood pressure adjusting for cofounders (p = 0.007, 0.048 and 0.45, respectively).

Conclusions: There was an independent association between sleep apnea severity and arterial standard bicarbonate. The link between high standard bicarbonate and daytime hypertension suggests that carbonic anhydrase activity may constitute a novel mechanism for blood pressure regulation in sleep apnea.

Keywords: Acid base; Blood pressure; Carbonic anhydrase; Hypercapnia; Obstructive sleep apnea.

Figures

Fig. 1
Fig. 1
Study flow chart
Fig. 2
Fig. 2
Arterial standard bicarbonate concentrations by sleep apnea severity class
Fig. 3
Fig. 3
Prevalence of hypertension by sleep apnea severity and arterial standard bicarbonate quartile

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