Complex sentence: To induce the sign a patient's arm is compressed with a blood pressure cuff at 300 mmHg for three minutes; if within the three minute period the patient's hand undergoes painful carpal spasm then hypocalcaemia should be suspected.
Split into simpler sentences: To induce the sign, a patient's arm is compressed with a blood pressure cuff at 300 mmHg for three minutes. During that time, if the patient's hand undergoes painful carpal spasm then hypocalcaemia should be suspected.