Application of an optical clearing agent during noninvasive laser coagulation of the canine vas deferens

Abstract

Development of a noninvasive vasectomy technique may eliminate male fear of complications and result in a more popular procedure. This study explores application of an optical clearing agent (OCA) to scrotal skin to reduce laser power necessary for successful noninvasive laser vasectomy and eliminate scrotal skin burns. A mixture of dimethyl sulfoxide and glycerol was noninvasively delivered into scrotal skin using a pneumatic jet device. Near-infrared laser radiation was delivered in conjunction with cryogen spray cooling to the skin surface in a canine model, ex vivo and in vivo. Burst pressure (BP) measurements were conducted to quantify strength of vas closure. A 30-min application of OCA improved skin transparency by 26+/-3%, reducing average power necessary for successful noninvasive laser vasectomy from 9.2 W without OCA (BP=291+/-31 mmHg) to 7.0 W with OCA (BP=292+/-19 mmHg). Control studies without OCA at 7.0 W failed to coagulate the vas with burst pressures (82+/-28 mmHg) significantly below typical ejaculation pressures (136+/-29 mmHg). Application of an OCA reduced the laser power necessary for successful noninvasive thermal coagulation of the vas by approximately 25%. This technique may result in use of a less expensive laser and eliminate the formation of scrotal skin burns during the procedure.

Figure 1

(a) Madajet (pneumatic jet device) used for noninvasive delivery of small quantities of the OCA through the skin. (Reproduced with permission from Pfenninger Medical Procedures Center P.C., John L. Pfenninger, M.D.). (b) Pattern for delivering the OCA on the treatment site. Four injections were spaced equally around the 3-mm-diam laser spot, and then the OCA was allowed to diffuse into the laser treatment area over time.

Figure 2

(a) Diagram of the vas and vas ring clamp. (b) Photograph of the experimental setup for noninvasive laser vasectomy in dogs, in vivo.

Figure 3

Photograph of experimental setup for measuring vas BP, consisting of a pressure transducer, pressure analyzer unit, and syringe pump.

Figure 4

Optical transmission studies performed in canine scrotal skin, ex vivo, after Madajet delivery of an OCA composed of either 100% DMSO or a 1:3 ratio of DMSO and glycerol. Percent increase in optical transmission is plotted as a function of time. The average and standard deviation was plotted for each data set (n=4 samples).

Figure 5

Gross analysis of vas and scrotal skin conducted immediately after noninvasive laser vasectomy procedure on dogs, in vivo. (a) Thermally coagulated section of canine vas (dotted circle) demonstrating characteristic signatures of blanching and shrinkage along an ∼3-mm-long segment corresponding to laser spot diameter (7.0 W, 0.20 Hz, with OCA). (b) Scrotal skin surface in region of procedure (dotted circle). Swollen area corresponds to where OCA was applied. Two compression marks correspond to where vas ring clamp was applied (7.0 W, 0.20 Hz, with OCA). (c) Thermally coagulated section of canine vas (dotted circle) demonstrating characteristic signatures of blanching and shrinkage along an ∼3-mm-long segment corresponding to laser spot diameter (9.2 W, 0.25 Hz, without OCA). (d) Scrotal skin surface after procedure without OCA (9.2 W, 0.25 Hz, without OCA). Note that image (b) shows more tissue trauma than (d), in part, due to the need to leave vas ring clamp on skin for prolonged period of time as OCA needed 30 min to diffuse into skin. This could easily be eliminated in a human model where vas is much easier to grasp.