Lennon, Robert L.

The current study was conducted to establish a reliable method for the placement of a long (>5 cm) catheter in the axillary neurovascular sheath, and to assess the effect of proximal catheter position on postoperative pain management by continuous bupivacaine infusion. In 20 patients scheduled for upper extremity surgery, a Portex® epidural catheter was advanced a mean distance of 12 cm in the axillary neurovascular sheath and its correct position verified by onset of upper extremity anesthesia and x-ray examination. After operation a continuous infusion of bupivacaine 0.125% was initiated through this catheter. Excellent pain relief (score of 0-1 as evaluated on a visual analogue scale of 0 to 10), and sympathetic blockade was achieved in all patients with an average rate of bupivacaine administration of 7 ml/hr. Additionally administered systemic narcotics were in a mean range of 3-10 mg of morphine/day. Catheters remained in place for an average of 3.7 days. Catheter tips cultured on removal of the catheter (n = 11) yielded negative cultures in eight cases (placement 3.6 ± 0.6 days), and positive cultures in three cases (placement 8.6 ± 2.2 days, mean ± SE). No signs of local or systemic infection were noted in any patient and no specific antibiotic therapy was initiated. This technique is recommended for postoperative analgesia in selected patients. In this study there was a low risk of catheter displacement and no evidence of local anesthetic toxicity. Limiting the duration of continuous axillary catheter infusion to 4 days may minimize the risk of infection.

Dyke, Christopher K., Niki M. Dietz, Robert L. Lennon, David O. Warner, and Michael J. Joyner. Forearm blood flow responses to handgripping after local neuromuscular blockade. J. Appl. Physiol. 84(2): 754–758, 1998.—To test the hypothesis that acetylcholine “spillover” from motor nerves contributes significantly to skeletal muscle vasodilation during exercise, we measured the forearm blood flow responses during attempted handgripping after local paralysis of the forearm with the neuromuscular-blocking drug pipecuronium. This compound blocks postsynaptic nicotinic receptors but has no impact on acetylcholine release from motor nerves. The drug was administered selectively to one forearm by using regional intravenous drug administration techniques in five subjects. Pipecuronium reduced maximum forearm grip strength from 40.0 ± 3.2 kg before treatment to 0.0 kg after treatment. By contrast, drug administration had no effect on maximum voluntary contraction in the untreated forearm (41.3 ± 3.3 vs. 41.4 ± 2.7 kg). During 2 min of attempted maximal contraction of the paralyzed forearm, the forearm blood flow increased from only 3.4 ± 0.8 to 4.8 ± 1.2 ml ⋅ 100 ml−1 ⋅ min−1( P < 0.05). Heart rate increased from 63 ± 3 to 73 ± 8 beats/min ( P > 0.05) during attempted contraction, and only three of five subjects showed obvious increases in heart rate. Mean arterial pressure increased significantly ( P < 0.05) from 102 ± 6 to 109 ± 9 mmHg during attempted contractions. When these increases in flow are considered in the context of the marked (10-fold or greater) increases in flow seen in contracting forearm skeletal muscle, it appears that acetylcholine spillover from motor nerves has, at most, a minimal impact on the hyperemic responses to contraction in humans.

The purpose of this study was to examine the effects of the increased sympathetic activity elicited by the upright posture on blood flow to exercising human forearm muscles. Six subjects performed light and heavy rhythmic forearm exercise. Trials were conducted with the subjects supine and standing. Forearm blood flow (FBF, plethysmography) and skin blood flow (laser Doppler) were measured during brief pauses in the contractions. Arterial blood pressure and heart rate were also measured. During the first 6 min of light exercise, blood flow was similar in the supine and standing positions (approximately 15 ml.min-1.100 ml-1); from minutes 7 to 20 FBF was approximately 3-7 ml.min-1.100 ml-1 less in the standing position (P less than 0.05). When 5 min of heavy exercise immediately followed the light exercise, FBF was approximately 30-35 ml.min-1.100 ml-1 in the supine position. These values were approximately 8-12 ml.min-1.100 ml-1 greater than those observed in the upright position (P less than 0.05). When light exercise did not precede 8 min of heavy exercise, the blood flow at the end of minute 1 was similar in the supine and standing positions but was approximately 6-9 ml.min-1.100 ml-1 lower in the standing position during minutes 2-8. Heart rate was always approximately 10-20 beats higher in the upright position (P less than 0.05). Forearm skin blood flow and mean arterial pressure were similar in the two positions, indicating that the changes in FBF resulted from differences in the caliber of the resistance vessels in the forearm muscles.(ABSTRACT TRUNCATED AT 250 WORDS)