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Comparative study of pulsed Ho:YAG versus Tm:YAG: impulse-induced pressure in porcine aorta

The goal of this study is to measure the average impulse induced pressure in porcine aorta by one laser pulse for both a free running Tm:YAG (2.014 microns) laser and a free running Ho:YAG (2.1 microns) laser. The pulsed Tm:YAG and Ho:YAG lasers operated at a repetition rate of 2 Hz and a FWHM pulse width of 150 microseconds. The laser energy was delivered to the tissue via a 600 micron core diameter low-OH silica fiber. The impulse pressure induced in the aortic wall was evaluated using tissue samples (n equals 50) mounted on a pendulum to measure the transferred momentum from the laser pulse to the tissue. The impulse induced pressure was determined using a contact mode, where the fiber tip and tissue surface are within 0.5 mm of each other. The impulse induced pressure was studied over a fluence range of 35 - 350 J/cm2, fifteen measurements were taken at each fluence level. The results showed that the average impulse induced pressure of the Ho:YAG pulsed laser in the fiber contact mode was 2 - 6 times greater than in the non-contact mode, where the energy at the fiber tip was imaged onto the tissue surface. The results also showed that both the Ho:YAG and the Tm:YAG average impulse induced pressure, in the contact mode, increased linearly at lower fluences, reaching a peak at approximately 13 - 14 atm.