The pathologic effects of photodynamic therapy on the larynx. Experimental study.

Using an argon pump dye laser at a wavelength of 630 nm, varying amounts of energy (10 to 170 J/cm2) were delivered to the presensitized (hematoporphyrin derivative) canine larynx. There appear to be four energy zones that result in progressive degrees of tissue response. Between 10 and 40 J/cm2 the larynx appears normal, with only mild erythema noted at 60 J/cm2. Above 100 J/cm2 moderate to severe erythema and edema were seen, with two upper-airway deaths observed. Transmission pattern analysis revealed that by either increasing the total energy applied and/or positioning the cylindrical diffuser tip at different levels of the larynx, the entire structure including the undersurface of the vocal cord and subglottic region could be exposed to red light.