Page 44 - Effects of radiotherapy and hyperbaric oxygen therapy on oral microcirculation Renee Helmers

Chapter 2
regarding elevated systolic pressure trends have also been reported during NB hyperoxia in healthy human volunteers.16 Vasoconstriction and reduced microvascular densities mobilize microcirculatory blood volume into systemic circulation and can explain the transient rise in systolic pressures. Although difficult to compare due to different measurement and analytical approaches, decreased PVD outcomes derived from sublingual mucosa using SDFI have also been reported in healthy human volunteers exposed to NB hyperoxia.33
Observations on the presence of scattered circulating microthrombi in the microcirculation during NB hyperoxia corroborate findings on coagulation and platelet events27,30,35 by others. Coagulation during hyperoxia may represent a host defense mechanism for antagonizing oxygen toxicity by limiting the dissemination of excessive oxygen in circulating blood. Although no systematic analysis of microthrombi and white blood cells in the microcirculation were systematically analyzed in this report, TVD and PVD rarefaction in response to NB hyperoxia may have been attributed to a combination of factors including vasoconstriction, activation of coagulation,27 and crawling leukocytes.22 The mechanisms underlying the effects of hyperoxia on regulating microvascular perfusion remain largely elusive and may be potentially different for each type of anatomical compartment or tissue. Anatomic inspection of parameters conveying both oxygen diffusion- (vascular density) and convection-based (blood flow and vessel diameter characteristics) data provide direct visual cues linking cellular with tissue compartmental interactions yielding potential diagnostic information on clinical relevance and therapeutic efficacy of oxygenation.
Previous HBO studies directed at peripheral vascular effects have reported vasoconstriction as a commonly occurring phenomenon from measurements obtained nonspecifically across whole cutaneous tissue >1 mm depth using LDF.36,44 In this regard subsurface microvascular regulation confined to the first 500 μm cannot be separately investigated by LDF to determine the precise nature of subepithelial microvascular perfusion dynamics. HBOm were performed on human nailfold microcirculation using VC and revealed that blood perfusion remained continuous with escalating RBC flow velocities as barometric pressure increased from 1ATA to 3ATA in the presence of transient decreases in HR.50 Our sublingual MFI dataset is in line with these observations as continuous blood perfusion was recorded at all HB hyperoxia time points, despite the different anatomical locations. Both cutaneous nailfold tissue and the sublingual oral mucosa share common embryonic origins and histology
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