Thermal inertia associated with ultrapulse technology in phacoemulsification.

PURPOSE: To determine whether very short pulses of ultrasound (5 to 6 milliseconds) have less heat propagation in biological tissue (thermal inertia) than traditional pulses (50 milliseconds). SETTING: Department of Ophthalmology and Visual Sciences, University of Utah Health Sciences Center, Salt Lake City, Utah. METHODS: Thermal testing was done in balanced salt solution (BSS) and in eye-bank eyes. In the same fresh human eye-bank eye, net temperature increase after 20 seconds of ultrasound (50 milliseconds on and 50 milliseconds off) was compared with the increase after 6 milliseconds on and 12 milliseconds off with the same phacoemulsification unit. The same experiment and setting was run in BSS and the eye-bank ratios compared with the BSS ratios. Twenty runs were done at each power setting in BSS and 22 in the eye-bank eye. RESULTS: There was 10.9% less heat generated with 6-millisecond pulses of ultrasound in limbal tissue than in BSS compared with 50-millisecond pulses of ultrasound (P = .0002). CONCLUSION: Very short pulses of ultrasound (5 to 6 milliseconds) propagated less thermal energy in limbal tissue than in BSS compared with 50-millisecond ultrasound pulses.