An in vivo histopathological comparison of single and double pulsed modes of a fractionated CO ₂ laser

Introduction Studies examining the histopathological changes that occur in human skin following fractional laser treatment have been performed mainly in animals or abdominal tissue prior to abdominoplasty. This study looks at the effect of double pulse fractional CO ₂ laser compared to single pulse treatments to assess differences in tissue injury in the face and abdomen. Methods Twelve healthy subjects randomized into two groups, had two 1cm ² areas (infraumbilical and forehead) treated with the fractional CO ₂ laser (Deep Fx, Lumenis). Settings used were 15mJ double pulse, and 30mJ single pulse, 300Hz, 10% density and compared to the historic control of 15 patients treated at 15mJ single pulse [Bailey et al. (2011), Lasers Surg Med 43: 99-107]. Treated sites were biopsied and analyzed with H&E and TUNEL staining to measure width and depth of the microthermal zones (MTZ) of ablation. Results When comparing 15mJ double pulse to single pulse there were significant differences both in depth (abdominal skin, P=0.002 and facial skin, P=0.001) and width (facial skin, P=0.0002) of MTZ. When comparing double pulsing at 15mJ with single pulsing at 30mJ there were significant differences between MTZ depths in the abdomen (P<0.01) but not in either the MTZ depth (P=0.69) or the width in the face (P=0.502). Discussion This study demonstrates the differences between histopathological laser injury patterns in the face compared to the abdomen when single pulsing is used. It also demonstrates that double pulsing at 15mJ is statistically similar to single pulsing at 30mJ in the face. We think this could have ramifications for clinical practice where by double pulsing at lower energies may result in better clinical outcomes than increasing energies or using multiple passes at single pulse. Clinical studies needs to be performed to investigate this further.