Autonomic impact of venous needling

The authors studied 34 young healthy male subjects (age 26.2/spl plusmn/3.5 yrs) in supine position, measuring heart rate (HR) in 3 six-minute episodes. Prior to the first episode, the subjects were supine for stabilization during 20 minutes. Prior to the second episode, a venous needle was introduced in the left underarm. Prior to the third episode, complete autonomic blockade was accomplished by metoprolol and atropine. The sympathovagal balance before and after needling was computed by division of HR in episodes 1 and 2 by HR in episode 3 (the intrinsic heart rate). Needling caused a significant decrease in the sympathovagal balance from 0.71/spl plusmn/0.09 (range 0.50 to 0.89) to 0.68/spl plusmn/0.10 (range 0.49 to 0.91). The average decrease was -0.03/spl plusmn/0.04, range -0.11 to +0.04. This study demonstrates that intravascular instrumentation has a major autonomic impact; which imposes a methodological problem on invasive autonomic studies.<>