Physical Characteristics Of Radiofrequency

RFL generates heat in a controlled and minimally invasive manner to damage nerve fibers selectively with the goals of attaining asymptomatic relief and minimizing the risk of complications. Key elements of successful RFL include

From: Minimally Invasive Neurosurgery, edited by: M.R. Proctor and P.M. Black © Humana Press Inc., Totowa, NJ

heat control and localization in the lesion process. Clinical observations support the physical principles of RFL that small 5 and poorly myelinated c-fibers are more susceptible to heat than are heavily myelinated a- and P-fibers (8). Regarding the concept of selective sensitivity of fiber types to heat, however, in vivo animal experiments have demonstrated no difference in heat sensitivity among fiber types and equal destruction of all fiber types within a lesion (9). In temperature-controlled studies in dogs using a 2-min duration and range of 45-85°C in 10° increments, histological studies found no differential effect in lesioning between unmyelinated and myelinated fibers (10).

The RFL technique relies on controlled thermocoagulation of tissues to create a predictable and reproducible size without boiling or carbonization (11-13). Variables in controlling the lesion include tissue impedance, electrode type (i.e., unipolar, monopolar), temperature, and time interval of coagulation. In vitro and in vivo studies have characterized the methods of lesion production by radiofrequency techniques. Monopolar electrodes generate lesions that enlarge in direct relation to temperature increases; bipolar electrodes generate lesions that plateau in size at 85°C (14). In relation to time, lesion size stabilizes at 60-s durations (15). Lesion size increases in direct proportion to electrode size (14,15). The most significant control parameter is temperature monitoring in real time. Real-time temperature monitoring at the electrode tip eliminates the variable of tissue impedance and maintains constant temperature with continual feedback that produces reliable, predictable lesions without boiling or carbonization (15). In summary, radiofrequency ablation is a form of thermocoagulation controlled by electrode size, duration of coagulation, and constant temperature control that allows the optimal tissue lesioning.

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