Local heating of human skin by millimeter waves: Effect of blood flow

Abstract

We investigated the influence of blood perfusion on local heating of the forearm and middle finger skin following 42.25 GHz exposure with an open ended waveguide (WG) and with a YAV mm wave therapeutic device. Both sources had bell-shaped distributions of the incident power density (IPD) with peak intensities of 208 and 55 mW/cm(2), respectively. Blood perfusion was changed in two ways: by blood flow occlusion and by externally applied vasodilator (nonivamide/nicoboxil) cream to the skin. For thermal modeling, we used the bioheat transfer equation (BHTE) and the hybrid bioheat equation (HBHE) which combines the BHTE and the scalar effective thermal conductivity equation (ETCE). Under normal conditions with the 208 mW/cm(2) exposure, the cutaneous temperature elevation (DeltaT) in the finger (2.5 +/- 0.3 degrees C) having higher blood flow was notably smaller than the cutaneous DeltaT in the forearm (4.7 +/- 0.4 degrees C). However, heating of the forearm and finger skin with blood flow occluded was the same, indicating that the thermal conductivity of tissue in the absence of blood flow at both locations was also the same. The BHTE accurately predicted local hyperthermia in the forearm only at low blood flow. The HBHE made accurate predictions at both low and high perfusion rates. The relationship between blood flow and the effective thermal conductivity (k(eff)) was found to be linear. The heat dissipating effect of higher perfusion was mostly due to an apparent increase in k(eff). It was shown that mm wave exposure could result in steady state heating of tissue layers located much deeper than the penetration depth (0.56 mm). The surface DeltaT and heat penetration into tissue increased with enlarging the irradiating beam area and with increasing exposure duration. Thus, mm waves at sufficient intensities could thermally affect thermo-sensitive structures located in the skin and underlying tissue.

Millimeter Wave Induced BioEffects

“…It is noted that water is also the major constituent of skeletal muscle, but because of the mentioned depth of the panniculus camosus muscle, it seems more likely that heat is transferred to blood and then to muscle. This idea is supported by the observations of Alekseev et al [2005] who noted that increased perfusion brought about a local decrease in temperature of irradiated human skin.…”

“…In our study the panniculus carnosus muscle atrophied, despite being deeper than the suggested penetration depth of 94 GHz MMW, suggesting that the vascular system plays a large role in the distribution of heat during MMW exposure. Alekseev et al [2005] showed that tissue heating occurs in layers located deeper than the penetration depth of the MMW suggesting the influence of perfusion in heat distribution. Nelson et al [2000] showed that increased blood perfusion reduces the maximum surface temperature response to MMW exposure of a primate scalp model at 100 GHz.…”

“…MMW bioffects in deeper tissues suggest that the primary response in the skin mediates subsequent reactions into the body by blood flow and/or neural pathways [Walters et al 2004;Xiao-feng and Anying 2003;Gowrishankar et al 2004;Alekseev et al 2005]. Thus, building upon the experience of previous work, we have explored variations in tissue response after different exposure lengths of potentially lethal power densities of 94 GHz MMW and after a 1, 2, or 3 day recovery period.…”

“…The effects of MMW on deeper tissues may be affected by the conduction of heat to surrounding tissue and heat movement through perfusion (blood flow) [Nelson et al 2000;Xiaofeng and Anying 2003;Gowrishankar et al 2004;Alekseev et al 2005]. Studies on heat transfer in biological systems exposed to MMW have shown that the thermal energy delivered by MMW stimulates tissue to increase blood flow by thermoregulation in order to remove the excess heat [Xiao-feng and Anying 2003;Gowrishankar et al 2004].…”

Electromagnetic millimeter wave induced hypoalgesia: Frequency dependence and involvement of endogenous opioids

“…A number of experimental studies, including our present experiments, have clarified the possible biological mechanisms of the treatment [Pakhomov et al, 1998b;Logani et al, 2002;Makar et al, 2003;Radzievsky et al, 2004a;Alekseev et al, 2005;Szabo et al, 2006]. Some clinical studies have demonstrated the effectiveness of MMWT under ''double-blind'' conditions [Korpan and Saradeth, 1995;Megdiatov et al, 1995;Radzievsky et al, 1999;Usichenko et al, 2003].…”