Vascular Autonomic Signal-Guided Photobiomodulation: Mechanisms and Clinical Applications in Autonomic Dysregulation

Journal of Complementary Therapies in Health ISSN 2975-9323 |eISSN 2975-9552 Journal of Complementary Therapies in Health 2026:4(1). doi:10.5281/zenodo.17910112 institutoptc.com/journal-complementary-therapies Clinical cases Vascular Autonomic Signal-Guided Photobiomodulation: Mechanisms and Clinical Applications in Autonomic Dysregulation. Oren Upekkha Ziv Ram1,2* and Eyal Levi Lidor1. 1 OLA Laser Acupuncture, Mafra, Portugal; 2 OLA Laser Acupuncture Academy, Portugal. * Correspondence: [email protected] Abstract Background: Dysregulation of the autonomic nervous system contributes to chronic conditions including insomnia, anxiety, chronic pain, and vertigo. Auricular stimulation can modulate autonomic, limbic, and sensorimotor pathways via cranial and cervical nerve afferents, influencing neurotransmitter release and anti-inflammatory signalling. The Vascular Autonomic Signal (VAS) provides real-time, feedback-driven identification of physiologically active auricular points through transient changes in radial pulse amplitude. Methods: This review synthesises the origins, physiology, and clinical applications of the VAS, integrating evidence from historical observations, experimental models, and imaging studies. The synergistic application of photobiomodulation (PBM) to VAS-responsive points is examined, highlighting mechanisms including mitochondrial activation, nitric oxide signalling, microcirculatory modulation, and stem-cell mobilisation. Results: Clinical illustrations demonstrate that VAS-guided PBM can stabilise autonomic tone, enhance sleep, reduce neuropathic pain, and improve functional outcomes. Personalised dosing guided by VAS attenuates overstimulation while promoting parasympathetic dominance and regenerative processes. Conclusions: VAS-guided PBM represents a precise, non-invasive, and adaptive approach for modulating autonomic function and supporting regenerative mechanisms. Structured training and potential automated detection systems are essential to enhance reproducibility. Although preliminary evidence is promising, larger controlled trials are required to define optimal parameters, effect sizes, and condition-specific protocols. This integrative modality offers a real-time, patient-specific tool for autonomic modulation within evidence-informed practice. Keywords: Vascular Autonomic Signal; Auricular Medicine; Photobiomodulation; Autonomic Dysregulation; Neuroimmune Modulation; Personalised Therapy. 1. Background Dysregulation of the autonomic nervous system is implicated in a wide range of chronic conditions, including insomnia, anxiety, chronic pain and vertigo 1-4. Vertigo and dizziness alone affect approximately 20–30% of adults at some point in life, and in many cases are associated with autonomic imbalance 5. Auricular medicine seeks to influence autonomic, limbic and sensorimotor pathways through stimulation of specific points on the external ear 6,7. Anatomically, the auricle is innervated by branches of the vagus (auricular branch of the vagus nerve), trigeminal (auriculotemporal nerve), facial nerve, and the greater and lesser auricular nerves 8-10. Stimulation of these fibres projects to brainstem Citation: Ram O. U. Z., Lidor E. L. Vascular Autonomic Signal-Guided Photobiomodulation: Mechanisms and Clinical Applications in Autonomic Dysregulation. Journal of Complementary Therapies in Health. 2026;4(1) 10.5281/zenodo.17910112 Academic Editor: Jorge Rodrigues Received: 8 November 2025 Reviewed: 20 December 2025 Revised: 9 December 2025 Accepted: 11 December 2025 Published: 12 December 2025 Publisher’s Note: IPTC stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Copyright: ©2026 by the authors. Submitted for open access publication under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). Journal of Complementary Therapies in Health 2026: 4(1). 2 of 12 Ram O. U. Z., Lidor E. L. Vascular Autonomic Signal-Guided Photobiomodulation: Mechanisms and Clinical Applications in Autonomic Dysregulation. doi:10.5281/zenodo.17910112 nuclei involved in autonomic regulation, and has been shown to modulate neurotransmitter release, including glutamate, γ-aminobutyric acid (GABA), acetylcholine and noradrenaline, as well as anti-inflammatory signalling pathways 11-14. These neurophysiological mechanisms provide a plausible basis for auricular therapeutic effects. Conventional auricular charts map numerous predefined points, yet inter-individual variability means that fixed prescriptions may not always identify the most responsive sites. The VAS provides a dynamic alternative 15. When a physiologically active auricular point is touched or exposed to a micro-stimulus, the examiner palpating the radial artery perceives a brief, transient change in pulse amplitude or tension, typically within one to three heartbeats 16. This real-time feedback allows clinicians to locate reactive points and to titrate stimulation intensity according to the patient’s autonomic responsiveness 17,18. PBM introduces an additional dimension to VAS guided practice. PBM involves delivering low-intensity red or near-infrared light to biological tissues. Photons in this range are absorbed primarily by mitochondrial chromophores such as cytochrome-c-oxidase, enhancing electron transport, increasing adenosine triphosphate (ATP) synthesis and promoting the release of nitric oxide (NO) 19-21. These photochemical effects trigger secondary signalling cascades, including controlled reactive oxygen species formation and modulation of gene expression and neuroimmune function 19,22. When PBM is applied to autonomic nerve-rich regions, measurable shifts in heart-rate variability have been reported, including increased parasympathetic indices (RSA, RMSSD) and reduced sympathetic stress markers, reflecting a shift toward parasympathetic dominance 23,24. Furthermore, PBM has been shown to mobilise endogenous stem cells, including neural and hematopoietic progenitors, in both preclinical and clinical studies 25-27. When PBM is delivered to auricular points identified through VAS palpation, the intervention can be tailored to the patient’s current autonomic state 15,28. This combined approach supports gentle rebalancing of sympathetic and parasympathetic tone and may facilitate regenerative processes without the need for needles 19,29,30. The purpose of this article is therefore to review the origins, physiology and clinical application of the VAS, to summarise emerging research that objectively characterises the reflex, and to illustrate how PBM can be personalised using VAS feedback to optimise therapeutic outcomes. 1.2. René Leriche’s Early Observation The earliest documented description of a stimulus-induced pulse change originates from the French vascular surgeon René Leriche, who in 1941 observed an unusual phenomenon while examining a patient following surgery for an arteriovenous aneurysm 31. When the skin overlying the femoral artery was touched, the arterial pulse exhibited a transient amplification; when the skin contact ceased, the pulse returned to baseline. Leriche interpreted this as evidence that cutaneous sensory input could influence vascular tone through reflexive autonomic pathways 28,31,32. At the time, the clinical relevance of the observation remained largely theoretical, and the phenomenon did not enter therapeutic practice. 1.3. Paul Nogier and the Réflexe Auriculo-Cardiaque Two decades later, the French physician Paul Nogier rediscovered and formalised this reflex within the emerging field of auriculotherapy 16. While palpating the radial pulse during examination, Nogier noted that touching specific points on a patient’s ear produced a brief, reproducible change in pulse amplitude. He termed this response the Réflexe Auriculo-Cardiaque (RAC) and demonstrated that the reflex could be used to locate physiologically active auricular points in real time 16. Nogier further observed that the change occurred within one to three heartbeat cycles, implicating rapid autonomic modulation rather than mechanical or hemodynamic changes. Journal of Complementary Therapies in Health 2026: 4(1). 3 of 12 Ram O. U. Z., Lidor E. L. Vascular Autonomic Signal-Guided Photobiomodulation: Mechanisms and Clinical Applications in Autonomic Dysregulation. doi:10.5281/zenodo.17910112 2. Evolution of VAS Terminology Over the decades following Nogier’s discovery, clinicians and researchers sought terminology that more accurately reflected the underlying physiology of the reflex. Early descriptions referred to the phenomenon simply as a pulse reaction or retained Nogier’s original French term RAC 16. However, this terminology implied a primarily cardiac origin and suggested that the ear–heart connection was unique. Subsequent investigations showed that similar reflexive pulse changes could be elicited by cutaneous micro-stimulation at other body sites, indicating that the response reflected a broader autonomic regulation of vascular tone rather than a direct cardiac reflex 33. As physiological studies in the 1970s and 1980s clarified the roles of arterioles, metarterioles and arteriovenous shunts in shaping pulse-wave propagation, several European researchers, including members of the German Academy of Acupuncture, introduced the term Vascular Autonomic Signal (VAS) 33,34. This designation emphasised that the reflex represents autonomic modulation of vascular resistance, detectable as a transient change in pulse amplitude, and that it can be recorded objectively using methods such as Doppler ultrasound and plethysmography, rather than being merely a subjective sensation in the examiner’s fingers. Today, the terms RAC and VAS are sometimes used interchangeably, but subtle distinctions persist. In French-speaking practice, RAC typically denotes the clinical palpation technique used to detect the reflex 28,32. In Germanand English-language literature, VAS is preferred to describe the physiological neurovascular event itself 28,32. Some practitioners deliberately reserve VAS for the objectively measurable component and RAC for the manual technique used to elicit it. This evolving terminology reflects the field’s progression from anecdotal clinical observation toward a mechanistic, research-driven interpretation of the reflex. 2.2. Physiological Basis Pulse Wave Dynamics When the left ventricle contracts, it generates two overlapping mechanical phenomena within the arterial system. The first is a rapidly propagating pressure or pulse (shock) wave that travels along the arterial wall at approximately 5–10 m/s 35-37. This wavefront reflects at points of branching and changes in vessel calibre, producing forward and retrograde components that combine constructively and destructively to shape the resulting waveform 36,37. The second phenomenon is the slower bulk ow of blood, which moves the fluid column itself at only a few centimetres per second. In central arteries these two phenomena are relatively distinct; however, in the peripheral vasculature, their interaction generates the palpable arterial pulse perceived at the wrist 37,38. At the radial artery, the pulse felt under the examining finger represents a composite of the primary forward wave generated by ventricular ejection and multiple reflected waves arising from the arteriolar and capillary beds. The contour and perceived tension of the pulse are in influenced by arterial elasticity, blood volume and the functional state of metarterioles and arteriovenous (AV) shunts, which determine how blood is distributed between capillaries and the superficial venous plexus. Shifts in microvascular tone can considerably alter the ratio of forward to reflected waves, even when cardiac output remains stable 39,40. Auricular and cutaneous stimulation interface with this system through the peripheral nervous system. The auricle receives sensory innervation from branches of the vagus, trigeminal and facial nerves, as well as from the greater and lesser auricular nerves 8. When a physiologically active auricular point is touched or illuminated, afferent signals project to the nucleus tractus solitarius (NTS) and related brainstem autonomic centres 41. These centres adjust efferent sympathetic and parasympathetic output to the microvasculature. A brief surge in sympathetic tone can constrict metarterioles and AV shunts, increasing reflected wave amplitude and producing a palpable “hump.” Conversely, a shift Journal of Complementary Therapies in Health 2026: 4(1). 4 of 12 Ram O. U. Z., Lidor E. L. Vascular Autonomic Signal-Guided Photobiomodulation: Mechanisms and Clinical Applications in Autonomic Dysregulation. doi:10.5281/zenodo.17910112 toward parasympathetic influence or vasodilatory signalling can soften the pulse, producing a transient “dip” 8,41. A defining feature of the Vascular Autonomic Signal is that the response is rapid and self-limiting. Because the reflex is mediated by short-loop autonomic feedback circuits, the pulse change typically lasts only one to three cardiac cycles before returning to baseline 36. This distinguishes the VAS from slower vasomotor responses driven by metabolic, hormonal or emotional influences. The speed, subtlety and reversibility of the VAS make it well suited as a real-time clinical feedback mechanism, allowing practitioners to determine immediately whether a stimulus is engaging the autonomic system without significantly altering systemic haemodynamics. 2.3. Neurovascular and biochemical pathways The VAS reflects not only mechanical modulation of arterial pulse dynamics but also complex neurovascular and biochemical signalling. Auricular stimulation activates afferent fibres from several cranial nerves, including the auricular branch of the vagus nerve, the auriculotemporal branch of the trigeminal nerve, and contributions from the facial, greater auricular and lesser occipital nerves 7,41-43. These afferent signals project to the nucleus NTS and associated brainstem autonomic centres, where they are integrated and relayed to sympathetic and parasympathetic efferent pathways 44,45. Stimulation of the vagal afferents is known to influence the release of several neurotransmitters and neuropeptides, including glutamate, aspartate, GABA, acetylcholine and noradrenaline, particularly within limbic and cortical regulatory circuits 46-48. Activation of the cholinergic anti-inflammatory pathway further modulates immune function by reducing the release of pro-inflammatory cytokines and influencing nitric-oxide synthesis 49-51. These neurochemical effects translate into measurable autonomic outcomes: increased vagal tone enhances heart-rate variability and promotes relaxation, while sympathetic activation decreases variability and increases cardiovascular tension 52-54. In the context of the VAS, a brief sympathetic surge can constrict metarterioles and arteriovenous shunts, generating the palpable “hump” response. A shift toward parasympathetic dominance can cause transient vasodilation, resulting in a “dip” in pulse tension. The reflex is rapid and self-limiting, consistent with short-loop autonomic feedback circuits 18,28,33,55. PBM interacts with these pathways in a complementary manner. Absorption of red or near-infrared photons by mitochondrial cytochrome c oxidase leads to the dissociation of NO from the enzyme, restoring electron transport and ultimately increasing ATP production and mitochondrial membrane potential 21,56,57. PBM also up-regulates nitric-oxide synthase, promoting NO-mediated vasodilation and improved microcirculation 58-60. Reactive oxygen species produced at low physiological levels act as second messengers, triggering transcriptional pathways that up-regulate anti-inflammatory and antioxidant responses 61-63. Stem and progenitor cells have been shown to be particularly sensitive to PBM-induced signalling, which can enhance their mobilisation, differentiation and tissue repair functions in both animal and human studies 64-66. By combining auricular stimulation with PBM, clinicians influence both afferent neural regulation and mitochondrial bioenergetics. This dual action helps rebalance sympathetic–parasympathetic tone, improve microvascular perfusion and promote cellular repair. These physiological mechanisms help explain why subtle stimulation applied to the ear can evoke a reproducible, transient change in radial pulse tension detected during VAS palpation. 2.4. Palpation Technique Reliable detection of the VAS requires both tactile sensitivity and a standardised, reproducible method 67. Journal of Complementary Therapies in Health 2026: 4(1). 5 of 12 Ram O. U. Z., Lidor E. L. Vascular Autonomic Signal-Guided Photobiomodulation: Mechanisms and Clinical Applications in Autonomic Dysregulation. doi:10.5281/zenodo.17910112 Finger selection and placement The VAS is typically palpated at the right radial artery using the left thumb, allowing the examiner’s right hand to perform auricular stimulation. The thumb should be relaxed and slightly flexed (approximately 110–120°), with the oval, sensitive portion of the thumb tip placed gently over the arterial wall. Excessive pressure must be avoided, as it can either dampen or fully occlude the pulse, masking the transient modulation associated with the VAS 67-69. Practitioners with thickened or calloused skin may need to lightly abrade the thumb pad to enhance tactile acuity. For those who initially struggle to perceive subtle pulse changes, the three-finger technique, lightly placing the index, middle and ringfingers over the artery, can enlarge the contact area and make the brief pulse deviation easier to detect 70. 2.5. Body positioning and environment The patient should be placed supine or seated with the forearm supported. The examiner stabilises the patient’s arm to reduce muscular tension and maintains a relaxed posture to prevent wrist and shoulder strain. A quiet, low-stimulus environment is essential, as external noise, temperature shifts or conversation can alter autonomic tone and confound the pulse response 70. If attention or tactile clarity decreases, the practitioner should pause briefly and resume, rather than continuing with degraded sensitivity. 2.6. Micro-stimulation and observation Auricular stimulation may be delivered via a gentle probe pressure, touch, auricular seed placement, or a brief PBM exposure. Stimulation is applied for one to two cardiac cycles only. If the auricular point is physiologically active, a transient modulation in pulse amplitude or tension is perceived within one to three beats. Stimulation must be reduced or stopped immediately once the VAS attenuates, to avoid overstimulation. When PBM is incorporated, wavelength, pulsing frequency, and exposure duration may be adjusted while monitoring the VAS to individualise dosing. 2.7. Sources of error and skill development Common barriers to reliable VAS detection include (Table 1): Table 1. Source of error and effect on examination. Source of Error Effect on Examination Excessive thumb pressure Pulse dampening or total occlusion (blocking the signal). Calloused or desensitised skin Reduced tactile perception; inability to feel subtle changes. Incorrect finger angle or broad contact surface Loss of waveform differentiation (blurring the "hump" vs. "dip"). Patient movement or muscle tension Irregular pulse contour (noise) complicating signal detection. Examiner fatigue or distraction Decreased sensitivity and higher risk of misinterpretation. Structured training significantly improves detection accuracy. Mentored practice is considered essential during skill acquisition 71,72. Journal of Complementary Therapies in Health 2026: 4(1). 6 of 12 Ram O. U. Z., Lidor E. L. Vascular Autonomic Signal-Guided Photobiomodulation: Mechanisms and Clinical Applications in Autonomic Dysregulation. doi:10.5281/zenodo.17910112 Some training programs utilise analogue vascular models (fluid-filled elastic tubes) to demonstrate how changes in vascular impedance alter pulse waveforms. Electronic auricular point locators and high-resolution pulse imaging can serve as useful adjuncts, providing objective confirmation while tactile sensitivity develops. Even experienced clinicians benefit from periodic recalibration to maintain precision 73. 3. Integration with Photobiomodulation When PBM is applied to auricular points identified through VAS palpation, the two modalities become synergistic 15,74. VAS determines which points are actively engaged in autonomic regulation at that moment and PBM provides a gentle, non-invasive stimulus that modulates cellular and vascular responsiveness at those same sites. This produces a precision-guided, patient-specific intervention, rather than a generalised or fixed-protocol stimulation approach. 3.1. Mechanistic Synergy with Autonomic Regulation PBM has measurable effects on autonomic nervous system balance. In a controlled study, laser stimulation of the lumbar and sacral regions resulted in increased parasympathetic tone, reflected by higher RSA and RMSSD, and reduced sympathetic stress index indicating a shift toward parasympathetic dominance 75. Because the VAS itself is a real-time reflection of autonomic tone, monitoring VAS during PBM allows the practitioner to titrate dose until the autonomic system begins to rebalance. Once the VAS attenuates, stimulation is stopped, preventing sympathetic overstimulation and ensuring dosing remains within the patient’s adaptive capacity 76. Furthermore, NO-mediated vasodilation induced by PBM may enhance the VAS amplitude by altering pulse-wave propagation, improving perceptual clarity for the practitioner. 3.2. PBM and Endogenous Stem-Cell Mobilisation An emerging area of interest is PBM’s influence on stem-cell activation and recruitment. In animal models, near-infrared PBM has been shown to expand neural stem-cell pools and promote dendritic arborisation and neuronal repair 77-79. Moreover, in a human pilot study, PBM applied to the tibial bone marrow increased circulating CD34+ stem cells from approximately 7.8% to 29.5%, while macrophage populations increased from 7.8% to 52.1% within 2–4 days 80. These findings suggest that PBM delivered to VAS-responsive auricular points may support both autonomic regulation and regenerative capacity, offering potential bene t for chronic pain, neuroinflammation and neurodegenerative conditions. 4. Clinical Illustrations 4.1. Case Study 1: Chronic Insomnia and Autonomic Hyperarousal A 70-year-old woman presented with a 20-year history of insomnia, characterised by difficulty initiating sleep, frequent nocturnal awakenings and daytime fatigue. Conventional pharmacological therapies had provided only short-term relief without improving sleep quality. During assessment, VAS palpation of the radial pulse identified reactive auricular points at Shen Men, Limbic System, Thalamus, and micro-areas corresponding to Heart and San Jiao, indicating autonomic hyperarousal with limbic involvement. PBM at 810 nm was applied in pulsed mode to each reactive point. Stimulation at each site was discontinued once the VAS attenuated, preventing overstimulation. Over six sessions delivered across four weeks (one to two weekly treatments), the patient reported: Journal of Complementary Therapies in Health 2026: 4(1). 7 of 12 Ram O. U. Z., Lidor E. L. Vascular Autonomic Signal-Guided Photobiomodulation: Mechanisms and Clinical Applications in Autonomic Dysregulation. doi:10.5281/zenodo.17910112 • Faster sleep onset; • Fewer night-time awakenings; • Improved morning refreshment and daytime function. Follow-up treatments every four weeks maintained clinical improvement without pharmacological support. This case demonstrates how VAS-guided PBM can stabilise autonomic tone and improve sleep regulation in chronic insomnia. 4.2. Case Study 2: Neuropathic Pain and Autonomic Dysregulation A 55-year-old man presented with five years of neuropathic low back pain secondary to lumbar disc herniation. Symptoms included burning dysaesthesia, hypersensitivity and sleep disturbance. Prior interventions— including analgesics, physiotherapy and nerve blocks—provided only temporary relief. VAS-guided auricular mapping identified strong responses at Lumbar Spin Sciatic Nerve, and Sympathetic Chain auricular zones. PBM at 810 nm was applied to the identified auricular points and to the paraspinal muscles, stopping each application when the VAS response diminished. After eight sessions over four weeks, the patient reported: • Marked reduction in pain intensity; • Improved mobility and daily function; • Normalised sleep quality. These improvements were sustained at a three-month follow-up. This case suggests that VAS-guided PBM may be clinically valuable for chronic neuropathic pain, likely by modulating both peripheral inflammation and central autonomic dysregulation. 5. Final remarks VAS represents a practical and reproducible interface between peripheral microstimulation and autonomic vascular regulation. By condensing complex haemodynamic and neurochemical processes into a transient pulse response, VAS palpation enables realtime, feedback-driven assessment at a single, anatomically defined site. Objective evidence from analogue vessel models, Doppler ultrasound, plethysmography, and highresolution optical imaging confirms that the VAS reflects genuine autonomic modulation rather than a subjective tactile impression. Integration with PBM enhances the therapeutic potential of VAS-guided interventions. PBM modulates mitochondrial activity, nitric oxide signalling, microcirculation, and neuroimmune balance, allowing tailored, feedback-responsive dosing that aligns with personalised medicine principles. Clinical observations suggest potential benefit in conditions characterised by autonomic dysregulation, including chronic pain, insomnia, vertigo, anxiety, and neuropathic dysfunction. Effective application of VAS-guided PBM requires structured training, tactile sensitivity, and consistent technique. Although preliminary evidence is encouraging, larger controlled trials are needed to establish effect sizes, optimal PBM parameters, and condition-specific protocols. Continued mechanistic research linking autonomic physiology, vascular dynamics, and neuroimmune modulation will strengthen the scientific basis of this approach. Ultimately, VASguided PBM offers a precise, adaptive, and evidence-informed modality, providing clinicians with a real-time tool to modulate autonomic tone while supporting the body’s intrinsic self-regulatory capacity. Journal of Complementary Therapies in Health 2026: 4(1). 8 of 12 Ram O. U. Z., Lidor E. L. Vascular Autonomic Signal-Guided Photobiomodulation: Mechanisms and Clinical Applications in Autonomic Dysregulation. doi:10.5281/zenodo.17910112 Author statement: Conceptualisation: O.U.Z.R.; Methodology: O.U.Z.R., and E.L.L.; Investigation: O.U.Z.R.; Visualisation: E.L.L.; Writing – Original Draft: O.U.Z.R.; Writing – Review and Editing: O.U.Z.R., and E.L.L. All authors have read and agreed to the published version of the manuscript. Acknowledgements: We extend our sincere thanks to the practitioners and patients who contributed their clinical observations, insights and feedback throughout this work. Their participation and curiosity continue to shape the evolution of VAS-guided practice. We also acknowledge the organisers and faculty of the Mastering the VAS training programme for permission to reference core educational frameworks and for fostering a collaborative, research-minded learning community dedicated to advancing auricular and autonomic medicine. Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Conflict of Interest: Oren Ram is an authorised distributor of RG Laser devices in Portugal and Spain and provides professional training in laser therapy. Eyal Levi Lidor declares no conflicts of interest. Institutional Review Board Statement: Not applicable. Informed Consent Statement: The patients have given written consent for the use of their data in this study. Data Availability Statement: The original contributions presented in this study are included in the article. 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