Discussion
HTN, OSA, apnea, hypoxemia, OSA deterioration, cardiovascular regulation disturbance, SDB
DISEASE, SECONDARY, HTN
Our study demonstrated that at 3-year follow-up after RDN there is a worsening of OSA, i.e. an increase in the severity indices (AHI, ODI, hypoxemia burden). However, these changes are not associated with the BP response.To our knowledge our study is the first to assess sleep parameters over 1 year after RDN. Our results do not support the previously suggested hypothesis of the beneficial effect of RDN on OSA. Since none of the previous studies has demonstrated a potential of RDN in OSA deterioration, we presume our patients experienced conventional progression of the disease.On the other hand, the controversial results can be explained by the high variability in cohort characteristics in different studies. Thus, Shantha and Pancholy [Several studies enrolled CPAP-users [Intriguingly, a study which involved patients without CPAP-therapy did not confirm beneficial effects of RDN on OSA characteristics. Daniels et al. [In our cohort, BP response at 3-year follow-up remained significant for both office systolic (The evidence from Symplicity HTN-1, HTN-2 и HTN-3 [Another factor potentially associated with the RDN efficacy (for both BP values and OSA indices) is the type of the RDN catheter system. In our cohort, unipolar catheter Simplicity Flex™ was used in 17 patients, balloon technology multi-electrode catheter Vessix™ – in 9, and spiral catheter Symplicity Spyral™ – in 2 patients. So the majority of patients were operated by the unipolar system which might be of lower efficacy efficiency [The studies which support the beneficial effect of RDN on OSA severity suggest that RDN resulting in a decrease in sympathetic drive leads to a reduced extracellular fluid volume associated with the lower rostral fluid shift during sleep in recumbent position [Although we have not found a clear positive impact of RDN on OSA, the lack of BP elevation associated with the “natural” OSA progression may reflect a positive effect of RDN in this cohort of patients. Indeed, OSA progresses over time and in the lack of appropriate correction by CPAP therapy, one might expect the progression of cardiovascular regulation disturbance as well, resulting in non-response to the RDN procedure. Our findings contradict this assumption revealing the preserved effect of RDN on BP suppression despite the progression of OSA.The strengths of our study include a comprehensive evaluation of the patients, and exclusion of secondary HTN, full in-lab PSG both at baseline and a follow-up scored by the same expert specialists, long-term follow-up of the cohort and the fact that none of the patients used CPAP-therapy either at baseline or during follow-up.Our study has certain limitations which should be considered when interpreting the results. These include a non-randomized trial design, rather small sample size and loss to follow-up, the lack of short-term PSG assessment. The latter could result in missing short-term changes. The lack of a comparison to an untreated group is an important limitation, as we cannot exclude that AHI would have increased even more over 30 months in an untreated comparison cohort. However, as indicated earlier the worldwide data demonstrate no significant changes in apnea index (leading to a different diagnosis [SDB vs. no SDB] or severity evaluation) over up to 5 years [