We found a new clinic phenomenon that some hemifacial spasm patients were accompanied by sinus bradycardia. We noticed that in most of these patients, ventrolateral medulla oblongata was compressed by artery loop and decompression at ventrolateral medulla oblongata was effective for their sinus bradycardia. Most of these patients were right hemifacial spasm patients (14/18). We firstly clinically studied and described this phenomenon in Surgical Neurology and proposed the hypotheses that compression at ventrolateral medulla oblongata can lead to heart rate decrease and decompression at ventrolateral medulla oblongata can result in heart rate increase. We designed animal experiments to verify our hypotheses and to explore the likely mechanism. We made the elastic sacculus compression system to compress in different diameter (4mm; 5.5mm; 7mm), the ventrolateral medulla oblongata of New Zealand rabbits which were randomly divided into group A (left) and group B (right). Rabbits underwent posterior medial craniotomy. We recorded and statistically analyzed the heart rates before and after ventrolateral medulla oblongata compression in different pressure on both sides. The average heart rates of pre-compression, 4mm, 5.5mm, and 7mm elastic sacculus compression system compression were respectively 132.6±5.83，114.74±9.27，110.93±10.59，105.84±5.87 beat per minute in group B. The heart rates had significant statistic difference (P＜0.01) when right ventrolateral medulla oblongata is compressed by elastic sacculus compression system in different diameter. The post-compression heart rates were lower than that of pre-compression. The average heart rates of pre-compression, 4mm, 5.5mm, and 7mm elastic sacculus compression system compression were respectively 131.85±7.8，129.49±6.4，130.2±3.9，128.58±5.43 beat per minute in group A. The heart rates had no statistic difference when left ventrolateral medulla oblongata is compressed by elastic sacculus compression system in different diameter. Compression at right ventrolateral medulla oblongata can lead to heart rate decrease. Compression at left ventrolateral medulla oblongata can’t lead to heart rate decrease. Animal experiments results supported our hypotheses. Compression at right ventrolateral medulla oblongata might be one of the reasons of sinus bradycardia in human being.
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