Stimuli factor of muscular receptors, extraocular muscles and oculocardiac reflex (OCR)
Authors: Duvallet Alain , Duvallet Emilie , Beaudry Michele , Lhuissier François 
Published: May 2024

Introduction: The oculocardiac reflex (OCR) was first described in 1908 as a reduction in heart rate secondary to direct pressure on the eyeball. OCR has been described during ophthalmologic procedures. This is also a standard test for peripherical autonomic and vagal system with the diving reflex and overtraining. The aim studied the specificities of stimuli of stretch receptors wich can be the traction at the extraocular muscles. Materials: 7 rabbits were included on the study. The anesthesia was done by an Intraperitoneal administration of ethyl carbamate. During all the study the rabbit is immobilized with a gripping frame for the head. Heart rate and RR were measured with EKG was recorded online. Methods: Bilateral pressure is applied using a mechanical pressure compression device, ranging from 100 to 800 mmHg, either instantaneously or in 15 or 30 seconds. For each pression we studied the variations of the RRspace (RRmax and RRt function of time) compared with the RRcontrol. If no variation, RRmax/RRcontrol and RRt/RRcontrol =1 Results: Response to abrupt compression RRmax varied linearly and significantly with pression. Response to progressive compression did not show any significant variation either during rise of pressure or when pressure was reached. Time-based response was studied from 56RR intervals. With abrut compression, the increase was effective from the first or second RR intervals. Depending on the pressure, it increased up to the 20th, presented a peak and decreased even with maintained pressure. The RR interval reverted to the control (RR/tRR = 1) around the 40th interval. With progressive stimulation, the maximum elongation value is lower, with an identical decay. Discussion: Our work showed the characteristics of stimulating factor: we used pressure on eyeballs, as in a sports medicine test (cardiac parasympathetic analysis) and in emergencies for the reduction of arrhythmias. This principal factor is tension in function of time, with an elongation of the periorbital muscles and the neuromuscular spindle. This is a proprioceptive sensory mecano-receptor sensitive to elongation. It is made up of primary neuromuscular fibers known as nuclear sac fibers and secondary neuromuscular fibers known as nuclear chain fibers. The former are 'phasic' (i.e. reacting to a variation in tension) and the latter 'tonic' (i.e. reacting directly to tension). Our work showed that the neuromuscular fibers of the nuclear sac type are stimulated by variations in tension as a function of time. Platen (1961) in ocular surgery introduced the notion of traction on the oculomotor muscles. In ‘OpenAnesthesia 2023’ Dennath Chatterjee did a synthesis work in the traction and anesthesia factors. In sports medicine, the dive reflex has been shown to be responsable of arythmia and paroxysmal supraventricular tachycardia. To trigger this reflex, several tests have beeen proposed. A recommandation during clinical examination is the OCR or Carotid glomus massage, with record of EKG and cardiac frequency. Conclusion: The OCR is defined by a reduction in heart rate from direct pressure on the eyeball. Afferent and efferent pathways are known and studied. But the stimulating factor must be studied. We have demontred that is the elongation of neuro-muscular fibers according to the time that excites the phasic fibers. This notion must be integrated both in eye surgery and in tests to highlight the cardiac parasympathetic balance, especially in sports physiology. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.