Effect of vacuum and thermal shock on laser treatment of Trichophyton rubrum (toenail fungus)

The eradication of Trichophyton rubrum has been attempted via laser irradiation because it could result advantageous relative to current clinical therapies. Anticipating that the necessary thermal effects could unintentionally damage the underlying toe dermal layer, we have explored two auxiliary approaches: (a) laser irradiation under vacuum pressure, with and without water dousing and, (b) cooling followed by laser heating (thermal shock). The rationale is that at low pressures, the temperature necessary to achieve water evaporation/boiling is significantly reduced, thus requiring lower fluences. Similarly, a thermal shock induced by cooling followed by laser irradiation may require lower fluences to achieve fungus necrosis. For all experiments presented we use a Cooltouch, model CT3 plus, 1320 nm laser to irradiate fungi colonies. The vacuum pressure experiments exposed fungi colonies to a subatmospheric pressure of 84.7 kPa (25 inHg) with and without water dousing for 5 min, followed by irradiation with 4.0 J/cm fluence and 40-90 J total energies. The thermal shock experiments consisted of three sections at 4.8 J/cm: cooling the fungus to 0 C at 0.39 C/min and then irradiating to 45-60 C; cooling to -20 C at 1.075 C/min and irradiating to 45 C; and cooling to -20 C at 21.5 C/min and irradiating to 45 C. Fungus growth rate over a 1-week period assessed the feasibility of these procedures. Results indicated both approaches hamper the growth rate of fungi colonies relative to untreated control samples, especially water dousing under vacuum conditions and slow cooling rate preceding irradiation for thermal shock effect.