A scoping review mapped 100 experimental studies on device-based blood pressure control, finding research overwhelmingly targets high blood pressure while neglecting dangerous low-pressure conditions.
Peter L. Greechan, Ryan G. L. Koh and Paul B. Yoo screened 3,503 publications from Web of Science, Scopus and PubMed dated January 1, 2000, through October 23, 2024, bioengineer.org reported. The team published their findings in Bioelectronic Medicine.
100 Studies Show Skewed Focus
According to the review indexed by the National Center for Biotechnology Information, 65% of included studies used animal participants, while 36 involved humans. Invasive technologies appeared in 74% of reports, and 89% used non-randomized designs.
| Study Characteristic | Percentage |
|---|---|
| Animal participants | 65% |
| Invasive methods | 74% |
| Non-randomized designs | 89% |
| Acute experiments | 84% |
| Depressor responses only | 49% |
| Pressor responses only | 35% |
| Both responses documented | 13% |
Hypertension Drives Device Development
The review notes high blood pressure causes 13.5% of annual deaths globally and affects roughly 60% of people over 65 in developed countries. Ten to 20% of patients have resistant hypertension despite taking three or more medications.
Renal Denervation Trials
Catheter-based renal denervation remains the only FDA-approved device for resistant hypertension. Medtronic’s Symplicity Spyral produced a 17.4 mmHg office systolic reduction at two years in the SPYRAL HTN-ON MED trial, compared to 9.0 mmHg in sham controls.
The SPYRAL HTN-OFF MED trial showed a 6.6 mmHg reduction at three months without medications. ReCor’s ultrasound Paradise system achieved a 5.4 mmHg reduction at six months in RADIANCE II.
Other Depressor Devices
Carotid baroreflex stimulation with the Barostim neo system achieved a 14.5 mmHg systolic drop in the Neo Non-Randomized Hypertension Study. The BackBeat Moderato device achieved an 8.1 mmHg net reduction in ambulatory systolic pressure at six months in the MODERATO II pilot study.
Hypotension Research Lags
Orthostatic hypotension is a recognized problem in patient populations, according to the review. Yet only four of 48 studies noting pressor responses investigated neurostimulation specifically for orthostatic hypotension, with one addressing vasovagal syncope.
Functional electrical stimulation of lower limbs also raised mean blood pressure during orthostatic stress, Yoshida and colleagues demonstrated.
Invasive Versus Non-Invasive
Invasive devices appeared in 74% of studies because direct neural contact offers superior spatial selectivity. Non-invasive methods appeared in 26 studies but suffer from poorer anatomical precision, as seen in inconsistent transcutaneous auricular vagus nerve stimulation results.
Focused ultrasound targeted the solitary tract nucleus to lower blood pressure, Cao and colleagues showed. Transcranial alternating current stimulation over the dorsolateral prefrontal cortex altered sympathetic outflow to achieve transient drops.
Closed-Loop Systems Next
Future progress depends on automated closed-loop systems that trigger stimulation when pressure falls. Researchers proposed integrating photoplethysmography sensors for feedback. Bidirectional devices capable of both raising and lowering pressure represent another priority for primary autonomic failure patients.
Questions Readers Ask
Catheter-based renal denervation is the sole FDA-approved device modality. Medtronic's Symplicity Spyral radiofrequency system and ReCor's Paradise ultrasound system both reduced blood pressure in randomized sham-controlled trials.
The review found that 49% of studies documented only depressor responses, while just 35% reported pressor responses.
The Barostim neo system produced a sustained 14.5 mmHg systolic blood pressure drop in the Neo Non-Randomized Hypertension Study. The device holds FDA approval for heart failure and has shown efficacy in resistant hypertension patients who failed renal denervation.
Worth a look