Registry: ClinicalTrials.gov; Identifier: NCT02220803; Title: A Short Term Open, Randomized Cross-over Trial Exploring the Effect of Carbonic Anhydrase Inhibition by Acetazolamide on Sleep Apnea Associated Hypertension and Vascular Dysfunction; URL: https://clinicaltrials.gov/ct2/show/NCT02220803 and Registry: EU Clinical Trials Register; EudraCT Number: 2013-004866-33; Title: A short term open, randomized cross over trial exploring the effect of carbonic anhydrase inhibition by acetazolamide on sleep apnea associated hypertension; URL: https://www.clinicaltrialsregister.eu/ctr-search/search?query=2013-004866-33.

Carbonic anhydrase inhibition reduces apnoeic events in sleep disordered breathing. Zonisamide inhibits carbonic anhydrase, and induces weight loss in obese patients. This study explored the relative influence of these two properties, which may both alleviate obstructive sleep apnoea (OSA). Continuous positive airway pressure (CPAP) was used as a standard care comparator.47 patients with moderate-to-severe OSA and a body mass index of 27-35 kg?m -2 were randomised to receive either zonisamide, placebo or CPAP for 4 weeks. The open extension phase (20 weeks) compared CPAP and zonisamide. Polysomnography, biochemistry and symptoms were evaluated.At 4 weeks, zonisamide reduced apnoea/hypopnoea index (AHI) by a mean¡SD 33¡39% and oxygen desaturation index by 28¡31% (p50.02 and 0.014, respectively; placebo adjusted). The mean compliance adjusted reduction of AHI after zonisamide and CPAP was 13 and 61%, respectively, (p50.001) at 24 weeks. Body weight was marginally changed at 4 weeks, but reduced after zonisamide and increased after CPAP at 24 weeks (-2.7¡3.0 kg versus 2.3¡2.0 kg, p,0.001). Zonisamide decreased bicarbonate at 4 and 24 weeks. Side-effects were more common after zonisamide.Zonisamide reduced OSA independent of body weight potentially by mechanisms related to carbonic anhydrase inhibition. The effect was less pronounced than that obtained by CPAP. @ERSpublicationsThe carbonic anhydrase inhibitor zonisamide reduces sleep apnoea, but the effect is inferior to CPAP treatment

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Carbonic anhydrase (CA) activity increased with apnea-hypopnea index and related nocturnal hypoxemia measures in patients with obstructive sleep apnea (OSA). Altered CA activity may constitute a component that modulates respiratory control and hemodynamic regulation in patients with OSA.

Whole blood carbonic anhydrase activity (CAa) is increased in patients with obstructive sleep apnea (OSA). Our study investigated the influence of positive airway pressure (PAP) or CA inhibitor acetazolamide (ACT) therapy on CAa, OSA and blood pressure. Thirty‐three OSA patients (21 hypertensive, body mass index (BMI) 37 ± 7 kg/m2 and apnea–hypopnea index (AHI) of 47 ± 31 events/hr) were followed‐up after PAP treatment (compliance, 4.7 ± 1.5 hr/day; duration, median 6 [IQR 6,6] months) (Cohort A). A second OSA Cohort (B) contained nine hypertensive patients (BMI, 29 ± 4 kg/m2; AHI, 39 ± 20 events/hr) with 2‐week treatment of ACT, PAP or ACT + PAP in an open crossover study. CAa was assessed at baseline and at the end of each treatment period. In Cohort A, baseline CAa was higher in hypertensive, compared with normotensive, patients (1,033 ± 204 versus 861 ± 201 units, p = .028). PAP treatment reduced systolic/diastolic blood pressure but not CAa (−9 ± 11/−5 ± 7 mmHg and −20 ± 289 units, p < .001, <.001 and .70). In Cohort B, blood pressure was reduced in both ACT‐treated groups (−10 ± 10/−5 ± 7 mmHg, p = .043 and .019; and −5 ± 5/−13 ± 13 mmHg, p < .001 and .009). AHI was reduced in both groups: ACT only, −17 ± 9 events/hr p = .001; and ACT + PAP, −39 ± 19 events/hr, p < .001. PAP did not change CAa (p = .98) but activity tended to decrease after ACT with or without PAP (p = .081 and .056). CAa is elevated in hypertensive OSA patients. Long‐term PAP reduced blood pressure without affecting CAa. ACT reduced blood pressure and CAa. Increased CAa may constitute a physiological characteristic in OSA, contributing to comorbid hypertension.

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BackgroundObstructive 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.MethodsA 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.ResultsArterial 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).ConclusionsThere 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12931-017-0607-9) contains supplementary material, which is available to authorized users.

Short sleep time assessed by polysomnography was associated with hypertension in this community-dwelling population. Short sleep and presence of sleep apnea appear to independently link to hypertension.