Characterizing Autonomic Dysfunction in POTS
Neurologists and engineers from Taiwan attempt to gain insight into the mechanism of autonomic dysfunction in POTS.
New Research
Yeh, S.-J. et al. The relationship between cardiovagal baroreflex and cerebral autoregulation in postural orthostatic tachycardia disorder using advanced cross-correlation function. Sci Rep 14, 25158 (2024).
https://www.nature.com/articles/s41598-024-77065-7
- Published on 24th October 2024
- Case-control
- 18 patients, 10 controls
- Evidence for Pathology
- Researchers from Taiwan and USA
- Funded by the National Science and Technology Council of Taiwan
Headlines
- Baroreflex and Cerebral Autoregulation are two components of the autonomic nervous system that can be characterized using non-invasive methods.
- POTS patients show a "phase-lag" in Baroreflex function when tilted, which the authors report as contrary to expectations and their measurements of controls.
- POTS patients show weaker Cerebral Autoregulation when tilted than controls as calculated using the study's numerical methods.
This study is an intriguing but hard-to-interpret attempt to shed light on the specifics of autonomic dysfunction using a novel numerical technique. Hopefully further work in this area will clarify the nature of this dysfunction from the perspective of expected physiology and the pathology present in POTS.
Review
In this rare glimpse beyond the anglosphere researchers from Taiwan measured differences in autonomic function in POTS compared to controls. In particular, they measured two components of the autonomic nervous system:
- Arterial cardiovagal baroreflex, or simply Baroreflex (BR), the regulating mechanism that links heart rate HR and arterial blood pressure, plus
- Cerebral Autoregulation (CA), the relationship between blood pressure and blood flow through the brain.
Participants' beat-to-beat arterial blood pressure and heart rate data was acquired using a Finapress finger cuff during supine and tilted postures. Afterwards they used a mathematical technique called cross-correlation on the data to quantify the "phase relationship"–difference in timing–between the signals to interrogate the participants Baroreflex (BR) function. Before doing this they had to filter out all the high frequency oscillations due to the heart beating and other movements; interestingly, the BR is "a major player in the production of BP and HR oscillations with periods from seconds to minutes", which is slower than one might think given the heart can beat up to 3 or 4 times per second. "Seconds to minutes" is exactly the kind of timescale where things go visibly wrong in POTS patients though.
Sadly, the great promise of this method was not fully realized in this study. The results are opaque, and avoid quantifying the phase difference between heart rate and blood pressure signals in POTS or control groups, and the distributions within the groups. The article does state that there is a "phase-lag characteristic of the baroreflex in POTS", which the authors report as contrary to expectations, but the result is hard to interpret.
In addition, the researchers measured cerebral blood flow using transcranial doppler ultrasound, with the participants wearing a 5-MHz transducer over their temporal bones (major plates of the skull lying around and slightly behind each ear). The phase relationship between mean arterial blood pressure measured using the finger cuff, and the mean cerebral blood flow velocity was analysed to get a measure of Cerebral Autoregulation (CA). They showed that "CA in the POTS group trended to mild dysfunction and slightly differed from the healthy group [when tilted]."
Sadly this work's focus on the details of numerical technique, and not the results as relevant to patients, results in some very weak evidence from the perspective of POTS pathology. The idea and stated results may represent an intriguing insight however, and one that gives food for thought. The real question remains: why is there dysfunctional blood pressure control in POTS?
Thank you to all of the patients, families, doctors, healthcare professionals, scientists, engineers and everyone else working to understand and improve the lives of people with POTS. Please join and subscribe.
