IS THERE A CHOLINERGIC AND AN ADRENERGIC PHASE OF THE OCULOCARDIAC REFLEX DURING STRABISMUS SURGERY

We investigated the counterregulatory effect of the oculocardiac refle x (OCR) in 25 infants and children during strabismus surgery under thr ee experimental conditions. In group 1, a series of measurements were recorded when the OCR was elicited by traction. The beat-to-beat heart rate reduction ranged from -26 to -64 beats/min (median: -46 beats/mi n). Constant traction increased heart rate in all patients from +23 to +50 beats/min (median: +30.5; P<0.001). After a sudden release of the stimulation, heart rate rose further from +6 to +40 beats/min (median : +15; P<0.001). In group 2, atropine (0.01 mg/kg) was administered 3- 4 min prior to the same manipulations as in group 1. Constant traction changed heart rate from -1 to +20 beats/min (median: +4.5; P<0.01). I n group 3, a retrobulbar blockade suppressed the OCR and the counterre gulation completely. These findings indicate that there is an active c ounterregulatory process which maintains heart rate during traction at the extraocular muscles after the bradycardic reflex has been initiat ed. The bradycardia and the counterregulation may be referred to as ch olinergic and adrenergic phrases of the OCR. Atropine eliminates the c holinergic phase. Our study indicates that may be receptors and affere nt fibres for both phases, which can be blocked by local anaesthetics.