The present invention relates generally to the use of vitamin B12 alone or in combination with other photoprotective agents, including specifically other vitamins such as vitamin B9 and vitamin B3, or any chemical derivative of these vitamins and their salts, as a filter to protect cells against the damaging effects of ultraviolet light. Since cardiac ischemia is often a precursor to acute myocardial infarction or ventricular fibrillation, the technique thereby provides a method for predicting the possible onset of AMI or VF. The plunger assembly support structure includes a wall having a slot therein.