Acta Neurol Belg. 2018 Nov 23. doi: 10.1007/s13760-018-1051-4. [Epub ahead of print]
Adrenergic hyperactivity: a missing link between multiple sclerosis and cardiovascular comorbidities?
The aim of the study is to investigate differences in non-standard adrenergic baroreflex sensitivity (BRS) indices in patients with different phenotypes of multiple sclerosis (pwMS) and healthy controls (HC). Retrospective analysis of types of systolic blood pressure (BP) curves during Valsalva maneuver (VM) [balanced (BAR), augmented (AAR) and suppressed (SAR) autonomic responses] and adrenergic baroreflex sensitivity (BRSa) measured with BRSa1, α-BRSa and β-BRSa in patients with clinically isolated syndrome (CIS), relapsing remitting multiple sclerosis (RRMS), progressive multiple sclerosis (PMS) and HC. We also investigated correlations between BRSa1, α-BRSa, β-BRSa and resting catecholamine levels. pwMS had higher α-BRSa compared to HC (p = 0.02). There was no difference in BRSa1, s and β-BRSa between patients with CIS, RRMS and PMS. There was no association between pwMS and HC, and the type of sBP curve [χ2 = 4.332, p = 0.114]. pwMS and BAR or AAR had higher supine systolic and diastolic BP compared to pwMS and SAR. There was a significant correlation between α-BRSa and upright systolic BP (rp =0.194, p = 0.017), α-BRSa and norepinephrine (rs =0.228, p = 0.021), and BRSa1 and epinephrine (rs = 0.226, p = 0.040). pwMS and HC exhibit different alpha-adrenergic response to Valsalva maneuver. These results may explain the connection between MS and increased cardiovascular risk.
How many reading this post, were infact aware that compared to the general population, having MS puts you at higher risk of heart disease and heart failure (or congestive cardiac failure)? Moreover, how many of you knew that the risk of having a heart attack or stroke increases in the first year of diagnosis?! (Christiansen CF, 2010)
What exactly is going on here? The autonomic nervous system (rarely talked about when the nervous system is discussed) may be involved, which is a concerning, since it controls much of our body’s physiology, including how fast our heart beats.
The autonomic nervous system is divided into two parts: sympathetic and the parasympathetic (see diagram above). In MS there might be a problem with the sympathetic pathways.
One way of studying this system is to assess the response of your blood pressure to a Valsalva manoeuvre (e.g. holding your breath). When working without any glitches, the sympathetic pathways should be able to respond with changes in BP as necessary. In healthy young adults three distinct patterns in systolic (i.e. the top portion of your blood pressure reading) blood pressure have recorded in response to a Valsalva manoeuvre: balanced (BAR), augmented (AAR) and supressed (SAR) autonomic responses (see Figure below).
In this study, on comparing those with MS and those without, it was apparent that there was adrenergic hyperactivity – the thing that results in arterial hypertension (or raised blood pressure). Although, all participants in the study for all intense and purposes had normal blood pressure during the study, suggesting that this may be a future risk? There were also differences in the BP curves lying flat depending on your baseline BP response (BAR, AAR or SAR). Those with BAR and AAR had higher BP lying flat than those with SAR, indicating autonomic dysfunction.
A condition called POTS (postural orthostatic tachycardia syndrome), which is a mild form of autonomic dysfunction, has also recently been found to be an indicator of a more active disease course in CIS (first presentation of MS), so again there appears to be a link in all of this (Habek M, 2017).
So, here we have a possible explanation for an association between cardiovascular risk and MS. It may therefore not mere coincidence that raised blood pressure is frequently reported as a co-morbidity with MS. Whether, it’s simply the disease that is the direct cause still needs to be elucidated.
Figure: Three types of systolic blood pressure curves during Valsalva maneuver: balanced autonomic response (BAR), suppressed autonomic response (SAR) and augmented autonomic response (AAR)