The Skin as a Barrier in Physiotherapy

Clijsen, Ron (2013) The Skin as a Barrier in Physiotherapy. PhD thesis, Vrije Universiteit Brussels.

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Although little evidence exists for the long term effectiveness of physical therapy applications, its use in the management of musculoskeletal disorders is widespread. Local heat applications such as paraphango are used in the treatment of ischaemic muscle pain. The vasodilation induced by local heat increases the blood flow in the muscle tissue, reducing the ischaemia and pain sensation. As the redistribution of blood towards the heated area could have an impact on the patients cardiovascular system, cardiovascular problems are often considered as a contraindication for local heat application. Although it is claimed that local heat application influences the perfusion in the underlying soft tissue, the physiological mechanisms controlling vasomotion and thermoregulation are not well understood and information on heat induced changes in skin parameters is limited. Evaluation and quantification of the changes in ST and the local effects on the arterial and venous microcirculation of the skin could provide important insights and define contraindications for paraphango therapy. Cardiovascular adaptations such as heart rate, DBP and SBP in reaction to paraphango could also provide insights in the impact of blood redistribution on the cardiovascular system and to define possible contraindications. Topical transdermal applications are commonly used in the treatment of various (rheumatic) inflammatory dysfunctions and acute soft tissue injuries. In physiotherapy various transdermal enhancements techniques, such as sonophoresis, iontophoresis and occlusion are used in order to decrease the skin barrier and to achieve a clinical effective drug concentration in the target tissues. Although several clinical studies claim an advanced healing process after the use of transdermal techniques, the evidence related to the effectiveness is controversially discussed in the literature and basic principles of transdermal penetration are not always taken into account. Screening the literature on iontophoretic delivery as used in the physiotherapy revealed that most human in- vivo studies take no account of the basic principles of percutaneous penetration. The effectiveness of iontophoretic delivery of an active substance is usually only compared with placebo iontophoresis without an active substance, which provides no proof for the penetration enhancement effect of a current. Studies investigating clinical outcome of iontophoretic drug delivery did not compare the effect of iontophoresis with the effect of passive penetration. To obtain valid results on the enhancement factor of a current, data of iontophoretic delivery should be compared with data of passive drug penetration, as iontophoretic delivery can be substantially influenced by passive penetration. Beside its function as a barrier, the human stratum corneum has the property to store previously topically applied substances during a prolonged time. A stratum corneum reservoir is an accumulation of a topically applied compound within the skin or within a skin layer for a longer period of time. The building up of a SC reservoir is an important component of the pharmacodynamics of topically applied substances. Rougier et al. (1985) used the reservoir effect of the stratum corneum after 30 minutes of application to predict the total amount absorbe. Up to now there is little information concerning the reservoir properties of DF on different application modalities as used in physiotherapy. In the treatment of musculoskeletal disorders, ultrasound is one of the most frequently used physical treatment modalities in physiotherapy. When ultrasound is used in combination with topical treatment of NSAIDs or corticosteroids a sonophoretic drug enhancement is aimed. In physiotherapy, sonophoresis is applied to the skin in a pre-treatment modus and a simultaneous treatment. Although low frequency sonophoresis (frequencies 20-100 KHz) is up to three order of magnitude more effective in enhancing skin permeability compared to the 1MHz ultrasound, the most common sonophoretic application in physiotherapy involves the use of high frequency or therapeutic sonophoresis (frequencies ≥ 0.7 MHz). In recent years, several in vivo studies revealed the clinical effectiveness of high frequency sonophoresis with NSAID’s and corticosteroids in the treatment of musculoskeletal disorders. As hypothesized in the review of Polat et al. (2011), the pre-treatment method causes enhancement of the drug transport mainly due to structural changes in the skin (cavitation) whereas the simultaneous technique enhances the skin permeability by structural changes and through convention-related mechanisms (thermal radiation, pressure effects, etc.). Evidenced based practice in physiotherapy is relatively new, the positive impacts of which are just becoming to be validated. Within the context of evidence based practice, continued research in physiotherapy is essential to improve the effectiveness of treatment strategies. In this doctoral thesis we investigated aspects of physiological processes related to physical applications in physiotherapy from the point of view of the skin as a limiting barrier. Within the paradigm of evidence based practice, the results of this research support the competence of the physiotherapist as a clinical practitioner to optimize the efficacy of his/her treatment strategies.

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