The effect of induced muscle tension and fatigue on the oculocardiac reflex.

INTRODUCTION

We investigated surgeon-modified factors in the oculocardiac reflex (OCR) including repeating tension after return to baseline pulse (fatigue) or modifying the tension place on the extraocular muscle (EOM).

METHODS

A control group of 842 adult and pediatric strabismus cases underwent controlled, 200 gram, 10-second square wave tension on at least two EOM. The effect of TENSION was studied in 90 random cases by placing a tension of 50 grams on one of the later muscles and a tension of 400 grams on another subsequent muscle. The effect of FATIGUE was studied in 30 cases when the initial tension elicited a profound bradycardia. The heart rate was allowed to return to within 96% of pre-tension levels, and the same muscle had a second identical tension.

RESULTS

For the 842 control cases, aged 12 +/- 16 (s.d.) years, initial 200 gram OCR was -16.9 +/- 19% and the second muscle 15 +/- 7 minutes later was significantly less percent change -14.6+/- 17%, paired t=3.9, p= .0001. TENSION: OCR was a similar reduction of 16-18% for 200 gram and 400 gram tension but had a modest reduction of 10% for 50 gram EOM tension. FATIGUE: For cases with profound initial OCR, waiting 3 minutes produced only a 17% reduction in OCR severity.

CONCLUSION

A surgeon can reduce oculocardiac reflex by exerting very gentle 50 gram tension on the EOM or waiting for return to baseline heart rate before fatiguing the reflex. These reductions are of less clinical value than pharmacologic intervention.