Human in vivo baseline intrarenal pressure, peristaltic activity and response to ureteric stenting.

Objectives: To assess human in vivo intrarenal pressure (IRP) and peristaltic activity at baseline and after ureteric stent placement, using a narrow calibre pressure guidewire placed retrogradely in the renal pelvis.
Patients and Methods: A prospective, multi-institutional study recruiting consenting patients undergoing ureteroscopy was designed with ethical approval. Prior to ureteroscopy, the urinary bladder was emptied and the COMET™ II pressure guidewire (Boston Scientific) was advanced retrogradely via the ureteric orifice to the renal pelvis. Baseline IRPs were recorded for 1-2 min. At procedure completion, following ureteric stent insertion, IRPs were recorded for another 1-2 min. Statistical analysis of mean baseline IRP, peristaltic waveforms and frequency of peristaltic contractions was performed, thereby analysing the influence of patient variables and ureteric stenting.
Results: A total of 100 patients were included. Baseline mean (±SD) IRP was 16.76 (6.4) mmHg in the renal pelvis, with maximum peristaltic IRP peaks reaching a mean (SD) of 25.75 (17.9) mmHg. Peristaltic activity generally occurred in a rhythmic, coordinated fashion, with a mean (SD) interval of 5.63 (3.08) s between peaks. On univariate analysis, higher baseline IRP was observed with male sex, preoperative hydronephrosis, and preoperative ureteric stenting. On linear regression, male sex was no longer statistically significant, whilst the latter two variables remained significant (P = 0.004; P < 0.001). The mean (SD) baseline IRP in the non-hydronephrotic, unstented cohort was 14.19 (4.39) mmHg. Age, α-blockers and calcium channel blockers did not significantly influence IRP, and no measured variables influenced peristaltic activity. Immediately after ureteric stent insertion, IRP decreased (mean [SD] 15.18 [5.28] vs 16.76 [6.4] mmHg, P = 0.004), whilst peristaltic activity was maintained.
Conclusions: Human in vivo mean (SD) baseline IRP is 14.19 (4.39) mmHg in normal kidneys and increases with both hydronephrosis and preoperative ureteric stenting. Mean (SD) peristaltic peak IRP values of 25.75 (17.9) mmHg are reached in the renal pelvis every 3-7 s and maintained in the early post-stent period.
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