A randomised, blinded, controlled study of the clinical relevance of matching pulse duration to thermal relaxation time when treating facial telangiectasia

Abstract

The theory of selective photo-thermolysis (SP) suggests the occurrence of optimal damage when the laser pulse duration (PD) equals the target thermal relaxation time (Tr). This study examines the clinical relevance of this theory. The study design and methods consisted of prospective, randomised, blinded, controlled study of KTP 532-nm laser treatment of 28 telangiectatic facial vessels. The PD varied from 0.13 to 1.71 times Tr (factor of 13). All vessels achieved marked improvement or clearance. The analysis of proportions reaching clearance over marked improvement for small and large calibre vessels shows a better outcome when the PD is nearer to the Tr (86% vs 57%; P = 0.09, 95% CI for difference -3% to 60%). Logistic regression analysis shows that, as the ratio of PD to Tr increases (PD near to or higher than Tr), the chance of clearing improves (P = 0.169; 95% CI 0.34 to 341). This study has shown that, for the range of vessels investigated: (1) marked improvement or clearance may be achieved using PDs that range between 0.13 and 1.71 times the Tr; and (2) it also reveals an overall trend towards a higher proportion of clearance when the PD is near to or higher than the Tr.