Stable laser-Doppler flow-motion patterns in the human cutaneous microcirculation: Implications for prospective geroscience studies.

Microvascular function has been assessed by determining the rhythmic oscillations in blood flow induced by the vasomotion of resistance vessels. Although laser-Doppler flowmetry (LDF) allows simple, non-invasive evaluation of this flow-motion in the cutaneous microcirculation, the temporal and spatial reproducibility of such assessments remains unclear.In the present study, we investigated cutaneous flow-motion in three consecutive years in eight skin regions using LDF in six healthy young volunteers. The characteristic flow-motion frequency was determined using fast-Fourier transformation. Additionally, in two years a more traditional measure of microvascular reactivity, postocclusive reactive hyperemia (PORH) was evoked in the forearm after transient brachial artery occlusion (1-2-3 min) induced by cuff inflation.Well-defined flow-motion was found in six regions showing significant differences in frequency: the highest flow-motion frequency was found in the frontal and temporal regions (8.0 ± 1.1 and 8.5 ± 1.0 cycles/min, cpm, respectively, mean ± SD) followed by the scapular, infraclavicular and coxal regions (7.5 ± 1.3; 6.7 ± 1.1 and 6.5 ± 1.2 cpm, respectively). The lowest, stable flow-motion was found in the posterior femoral region (5.5 ± 1.0 cpm), whereas flow-motion was detectable only sporadically in the limbs. The region-dependent flow-motion frequencies were very stable within individuals either between the body sides, or among the three measurements, only the infraclavicular region showed a small difference (114 ± 17%∗, % of value in 1st year; ∗P < 0.05). However, PORH indices differed after 2-3 min occlusions significantly in consecutive years.We report that flow-motion frequencies determined from LDF signals show both region-specificity and excellent intra-individual temporal and spatial reproducibility suggesting their usefulness for non-invasive follow-up of microvascular reactivity.

Molecular hydrogen affords neuroprotection in a translational piglet model of hypoxic-ischemic encephalopathy.

Hypoxic-ischemic encephalopathy (HIE) is the major consequence of perinatal asphyxia (PA) in term neonates. Although the newborn piglet is an accepted large animal PA/HIE model, there is no consensus on PA-induction methodology to produce clinically relevant HIE. We aimed to create and to characterize a novel PA model faithfully reproducing all features of asphyxiation including severe hypercapnia resulting in HIE, and to test whether H2 is neuroprotective in this model. Piglets were anaesthetised, artificially ventilated, and intensively monitored (electroencephalography, core temperature, O2 saturation, arterial blood pressure and blood gases). Asphyxia (20 min) was induced by ventilation with a hypoxic-hypercapnic (6%O2 - 20%CO2) gas mixture. Asphyxia-induced changes in the cortical microcirculation were assessed with laser-speckle contrast imaging and analysis. Asphyxia was followed by reventilation with air or air containing hydrogen (2.1%H2, 4 hours). After 24 hours survival, the brains were harvested for neuropathology. Our PA model was characterized by the development of severe hypoxia (pO2 = 27 ± 4 mmHg), and combined acidosis (pH = 6.76 ± 0.04; pCO2 = 114 ± 11 mmHg; lactate = 12.12 ± 0.83 mmol/L), however, cortical ischemia did not develop during the stress. Severely depressed electroencephalography (EEG), and marked neuronal injury indicated the development of HIE. H2 was neuroprotective shown both by the enhanced recovery of EEG and by the significant preservation of neurons in the cerebral cortex, hippocampus, basal ganglia, and the thalamus. H2 appeared to reduce oxidative stress shown by attenuation of 8-hydroxy-2'-deoxyguanosine immunostaining. In summary, this new PA piglet model is able to induce moderate/severe HIE, and the efficacy of hydrogen post-treatment to preserve neuronal activity/function in this PA/HIE model suggests the feasibility of this safe and inexpensive approach in the treatment of asphyxiated babies.

Comparison of cerebrocortical microvascular effects of different hypoxic-ischemic insults in piglets: a laser-speckle imaging study.

The newborn pig is a widely accepted large animal model of hypoxic/ischemic (H/I) encephalopathy (HIE) of the term neonate appropriate for translational research. The methodology of the induction of H/I stress shows extensive variability of the literature, and little is known how these affect study outcome. The purpose of the present study was to determine the cerebrocortical microvascular effects of different H/I insults used in current HIE piglet models. For the semiquantitative study of cerebrocortical blood flow, we developed a methodological innovation: an operating microscope was converted into a custom-designed laser-speckle imager. Anesthetized, air-ventilated newborn pigs (n=7) were fitted with a closed cranial window. Speckle image series (2 ms, 1 Hz) were collected during baseline conditions, during transient bilateral carotid artery occlusion (BCAO), hypoxic (FiO(2)=0.1) hypoxia, hypoxia + BCAO, and asphyxia induced by suspending ventilation. Laser-speckle contrast analysis was performed off-line over parenchymal and arteriolar regions of interests, and pial arteriolar diameters were also determined for detailed analysis of cortical perfusion changes. Under normoxic conditions, transient BCAO did not affect parenchymal perfusion or pial arteriolar diameters. Hypoxia induced marked cortical hyperemia in 5 out of 7 piglets, with simultaneous increases in pial arteriolar diameters and arteriolar flow velocity, however, BCAO could not even affect these hypoxia-induced perfusion changes. In contrast to hypoxia or hypoxia + BCAO, asphyxia inevitably led also to severe cerebrocortical ischemia. In summary, acute reversible BCAO does not reduce cerebrocortical blood flow in the piglet, and thus it likely does not exacerbate the effect of hypoxic ventilation. Asphyxia elicits not only severe hypoxia, but also severe brain ischemia. These microcirculatory effects must be taken into consideration when assessing results obtained in the various HIE piglet models.