An electro-myographic study of the distal porcine ureter

Purpose: The accumulation of urine in the renal pelvis causes depolarisatio n of non-specific muscular pace-maker cells. The wave of depolarisation spr eads distally in the ureteric smooth muscle cells via gap junctions. This w ave of excitation causes a coordinated peristaltic contraction which transp orts the urine bolus distally to the bladder. The EMG activity in the dista l porcine meter was studied and analyzed to establish the characteristics o f ureteric excitation. Materials and Methods: Ten female New Yorkshire pigs (50 to 60 kg.) were st udied in two groups under light halothane anesthesia (5% at induction and 1 % for maintenance anesthesia). In both groups each pig was studied in two s eparate sessions at a week's interval. In group I (n = 5), bipolar needle e lectrodes (empty set: 0.09 mm.) were implanted through a lower mid-line abd ominal incision in the posterior bladder wall, the trigone and the pelvic u reter at intervals of 3 and 8 cm., respectively, from the ureteric orifice. In group II (n = 5), EMG spike burst activity was studied using a twin bip olar ring-electrode attached to an endoluminal ureteric catheter, EMG compl exes were recorded using 0 to 30 Hz filters. The duration of spike burst co mplexes and their intervals were analyzed using a Nicollet, Pathfinder II(R ) machine and a Poly(R) 4.9 digital signal processing program. Results: Two types of spike burst activity could be distinguished between t he electrodes: A, the migrating type and B, the non-migrating type. Frequen cy distribution analysis of spike burst duration revealed two main classes in experimental group II, a short spike burst (96%) which lasted 4.5 +/- 1. 8 seconds and a longer one lasting 13.4 +/- 1.5 seconds. The conduction vel ocity of the migrating spike bursts (n = 177, 42% of total) between the pro ximal and the distal electrode had an average of 2.3 +/- 1.3 cm./sec. No re lationship was found between the duration of the proximal spike burst and t he conduction velocity. Data from experimental group I correlated well with data from group II. Conclusions: The results of our EMG study in the distal ureter reveal an ap proximately 9 cm. long electrically active zone in greater than or equal to 90% of EMG activity recordings. The duration of activity was approximately 5 seconds. Such an excited segment of meter led to a contraction which occ luded the ureter and could prevent retrograde leakage of intraluminal conte nts.