Background: Spinal cord stimulation (SCS) is an established treatment option for chronic pain. Prior to permanent implantation, temporary trials are performed to evaluate the SCS treatment. During the trial period, it is common for the patients to experience changes in paresthesias. However, it is unclear what the role of lead migration is, if any, in the changes in paresthesia. Objective: To evaluate the role of lead migration on the effect of postural stimulation changes during SCS trials. Study Design: Case series. Setting: University pain management center. Methods: X-rays of the patients with successful trials, in sitting and standing position, were obtained at the end of a 7 day SCS trial. Data were collected based on the need for adjustment of the stimulation settings due to changes in paresthesias with postural change of sitting versus standing. Results: The average lead migration was 3.05 mm inferiorly from a standing to sitting position for all subjects. The average migration was 2.85 mm in subjects requiring adjustment of the SCS setting due to change in paresthesia compared to 3.24 mm for those who did not require adjustment regardless of position. The results were insignificant based on P = 0.17. Limitations: Small sample size, case series. Conclusions: This case series demonstrates continued support for the role of the width of the cerebral spinal fluid space as the significant factor on paresthesia changes in SCS with respect to postural changes, even during the trial period. Key words: Spinal cord stimulation, postural change, lead migration, paresthesia, neurostimulation, chronic pain, dorsal column

Current in vitro models of the left heart establish the pressure difference required to close the mitral valve by sealing and pressurizing the ventricular side of the valve, limiting important access to the subvalvular apparatus. This paper describes and evaluates a system that establishes physiological pressure differences across the valve using vacuum on the atrial side. The subvalvular apparatus is open to atmospheric pressure and accessible by tools and sensors, establishing a novel technique for experimentation on atrioventricular valves. Porcine mitral valves were excised and closed by vacuum within the atrial chamber. Images were used to document and analyze closure of the leaflets. Papillary muscle force and regurgitant flow rate were measured to be 4.07 N at 120 mmHg and approximately 12.1 ml/s respectively, both of which are within clinically relevant ranges. The relative ease of these measurements demonstrates the usefulness of improved ventricular access at peak pressure/force closure. Graphical abstract