Thoracic Sympathotomy on Heart Rate Variability RESULTS Endoscopic thoracic sympathotomy was performed in 20 patients. The mean recording time was 22.8±1.2 hours (mean±SD). All patients exhibited immediate cessation of palmar hyperhidrosis, without severe complications, such as pneumothorax, hemothorax, atelectasis, Horner Syn- drome, prolonged pain, and so on. Compared with preoperative variables, a significant in- crease in pNN50, rMSSD, SDANN (p<0.05) and a remark- able decrease in LF (p<0.05) was observed after endoscopic thoracic sympathotomy. There was no significant difference in HF, LF/HF, or SDNN before and after thoracic sympa- thotomy (Table 1). DISCUSSION The preganglionic fibers traveling to the upper limb come mainly from the intermediolateral nucleus lacated in the spinal cord lateral horns of the T2-T8 spinal segment, leave the cord at the anterior rootlets of the thoracic nerves, go through the white rami communicates, the ventral roots, and the front branches, enter the sympathetic trunk and then synapse, and then finally reach their target postganglionic neurons in the paravertebral or prevertebral thoracic sym- pathetic ganglia. The postganglionic fibers traveling to the upper limb originate from different ganlions, including the middle cervical ganglion, the stellate ganglion and upper thoracic ganglia; join the thoracic nerves through the gray communicanting rami; enter the brachial plexus; and then travel along different nerves to their end targets. Theoreti- cally, ramicotomy of the white rami communicantes, in- cluding the second to the eighth thoracic nerves and the sympathetic trunk could lead to successful sympathetic sur- gery for treating upper essential hyperhidrosis.11 The aim of surgical treatment of primary hyperhidrosis is to interrupt the thoracic sympathetic chain at the R3-R4 level by resec- tion or electrocautery. However, sympathetic fibers that in- nervate the heart, lungs and other thoracic viscera are also present along the exact same pathway. Therefore, from the theoretic perspective, sympathotomy may impair the sym- pathetic nervous system that innervates the heart and lungs, altering sympathetic or parasympathetic dominance in the autonomic nervous system. In the present study we studied the effect of endoscopic transthoracic sympathotomy (ETS) on the autonomic nerve system via heart rate variability (HRV), which is a non-in- vasive, semi-quantitative assessment of the activity of the autonomic nervous system. Compared with the parameters before ETS, we observed a statistical significant increase in SDANN, reflecting an improvement in global cardiac auto- nomic activity; there was also a remarkable decrease in LF among frequency domain variables, indicating a sympa- thetic withdrawal. pNN50 and rMSSD were also signifi- cantly increased, suggesting increased vagal activity. How- ever, we found no statistical difference in HF, LF/HF and SDNN before and after the surgery. Generally, such occur- rences can be attributed to sympathetic withdrawal and a relative increase in parasympathetic activity after ETS. Heart rate variability is a non-invasive, semi-quantitative assessment of the activity and balance of the sympathetic and vagal components of the autonomous nervous system. Among the statistical parameters, SDNN and SDANN which represent sympathetic and parasympathetic activity can be obtained from long-term records, but there’s a weak point of not distinguishing whether increased sympathetic tone or withdrawal of vagal tone contribute to changes in HRV. The rMSSD and pNN50 indexes are representative of parasympathetic activity. In regards to the frequency domain parameters, HF, an indicator of the performance of the va- gus nerve on the heart, corresponds to respiratory modula- tion; LF reflects the joint action of the vagal and sympathet- ic components on the heart, predominantly the sympathetic ones. VLF indexes are used less in heart rate variability as- sessment without physiological explanation. VLF seems to be involved in the renin-angiotensin-aldosterone system, peripheral vasomotor tone and thermoregulation. LF/HF ra- tio is a sign of sympathetic-vagal balance on the heart re- Table 1. Parameters of Heart Rate Variability before and after Endoscopic Thoracic Sympathotomy LF (ms2/Hz) HF (ms2/Hz) LF/HF SDNN (ms) SDANN (ms) rMSSD (ms) pNN50 (%) Before surgery 6.7±0.8 4.4±0.6 1.5±0.4 98.3±15.3 63.6±25.6 36.3±13.7 6.3±4.3 After surgery 5.1±0.6 4.2±0.7 1.2±0.3 107.2±32.6 93.2±32.6 57.1±21.5 19.7±8.9 p value 0.015 0.059 0.552 0.123 0.038 0.023 0.008 LF, low frequencies; HF, high frequencies; rMSSD, root mean square difference; SDANN, standard deviation of the average normal RR interval for all 5-min segments of a 24-hour recording; SDNN, standard deviation for all normal RR intervals for the entire 24-hour recording. Yonsei Med J http://www.eymj.org Volume 53 Number 6 November 2012 1083