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In Vitro Assessment of Dermal Absorption
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
It is generally assumed that the diffusion process terminates at the site of vascular entry, and the dermal microvasculature acts as a “sink”, removing the penetrants.1,2 In the common laboratory animals and in man, the dermis (approximately 2 to 3 mm) compared to the epidermis (approximately 50 to 100 μm) is a relatively thick tissue.1,2 By virtue of its relative volume, the dermis may retain permeating substances so that compounds which penetrate the stratum corneum easily may appear to permeate moderately through the skin due to their long residence time in the dermis. Since the cutaneous microcirculation is situated within the region immediately beneath the epidermis, the use of skin preparations with a full-thickness dermis may not be representative of the in vivo situation. However, it should be noted that evidence is accumulating which indicates that the cutaneous microvasculature does not always remove all of the permeating substances; it is not always a perfect “sink”, and a fraction of the absorbed material may be delivered to the subcutaneous fat and underlying connective and muscular tissues.51 Appreciation of some of these issues would greatly assist in choosing the appropriate skin preparations for in vitro investigations.
The No-Reflow Phenomenon: A Misnomer?
Published in Samuel Sideman, Rafael Beyar, Analysis and Simulation of the Cardiac System — Ischemia, 2020
Lewis C. Becker, Giuseppe Ambrosio, John Manissi, Harlan F. Weisman
The basis for the heterogeneity of ischemia during coronary occlusion remains a mystery. One can speculate about the possibility of random closure of precapillary vessels due to obstruction by blood elements, increased alpha or decreased beta adrenergic receptors, increased smooth muscle tone or decreased endothelial production of smooth muscle relaxing factors, and/or local increase in extravascular compressive forces (possibly explaining greater ischemia in the subendocardium). Another possibility relates to the anatomy of the microvasculature. Certain branching angles or the number of vascular divisions occurring before a given precapillary vessel is reached may determine the pressure drop along its length and thereby influence blood flow.
Evaluation Models for Drug Transport Across the Blood–Brain Barrier
Published in Sahab Uddin, Rashid Mamunur, Advances in Neuropharmacology, 2020
Further, the modification of above model by a synthetic microvasculature model was developed. The model consists of two microchannels separated by microfabricated pillar infused with endothelial cells and astrocyte co-cultured medium through various ports (Prabhakarpandian et al., 2013).
Investigation of Retinal Alterations in Patients Recovered from COVID-19: A Comparative Study
Published in Ocular Immunology and Inflammation, 2023
Mehmet Özbaş, Bengi Demirayak, Aslı Vural, Yunus Karabela, Fadime Ulviye Yigit
Savastano et al. presented no significant difference between 70 early post–COVID-19 patients and 22 controls detected by OCTA, similar to our study.7 Notably, there were patients with systemic vascular disorders that might have affected retinal microvasculature in their study group. We excluded patients with any systemic disorders, as well as smokers, to avoid affecting the results. Savastano et al. detected cotton wool spots in 12% of patients and focal retinal hemorrhage in one patient who had hypertension and coronary artery disease. In our study, we observed retinal hemorrhages in three patients (2.85%), one of whom had flame-shaped hemorrhages and increased vascular tortuosity in both eyes (Figure 2). That patient was hospitalized and had thrombocytopenia secondary to SARS-Cov-2 infection. We deduced that bilateral flame-shaped hemorrhages were related to thrombocytopenia in that patient. Pereira et al. carried out the retinal examination of 18 patients with severe COVID-19 and reported retinal findings including flame-shaped hemorrhages, dot hemorrhages, cotton wool spots, and sectorial pallor in 10 patients.5 The reason for this high percentage of retinal findings may be related to systemic disorders of patients or complications of the COVID-19 disease.
Macular microcirculation characteristics in Parkinson’s disease evaluated by OCT-Angiography: a literature review
Published in Seminars in Ophthalmology, 2022
Evita Evangelia Christou, Ioannis Asproudis, Christoforos Asproudis, Alexandros Giannakis, Maria Stefaniotou, Spiridon Konitsiotis
Neuronal degeneration has been well documented as a key pathological feature in PD.7,8 Recent advances have provided evidence of cerebrovascular alterations and highlighted their critical role in the pathogenesis of the disease. Τhe role of microvasculature involvement has been notably identified both as primary cause of the disease onset and as a contributing factor to its progression. The effect of PD on the cerebral microvasculature is not possible to be directly evaluated. Cerebral vessels share striking similar features with retinal microcirculation. Indeed, the vascular network of the eye could potentially serve as a mirror reflecting the cerebral vasculature.9–12 Pathophysiological processes that affect cerebral vasculature may have a direct profound impact on retinal microcirculation. Thus, examination of the retina may provide the opportunity to directly detect changes in the neuronal tissue and to evaluate microvessels in PD and various neurodegenerative disorders.12–16
Impact of tetraplegia vs. paraplegia on venoarteriolar, myogenic and maximal cutaneous vasodilation responses of the microvasculature: Implications for cardiovascular disease
Published in The Journal of Spinal Cord Medicine, 2022
Michelle Trbovich, Yubo Wu, Wouter Koek, Joan Zhao, Dean Kellogg
Structural remodeling of the macrocirculation occurs as soon as 3–6 weeks after SCI consisting of decreased large vessel diameters and increased arterial stiffness.1–5 While such rapid and extensive remodeling of large conduit vessels is well established, structure and function of the microvasculature, has been less explored. Abnormalities in the microvasculature are demonstrable in the cutaneous microcirculation of persons at high risk of cardiovascular disease (CVD).6 Since the prevalence of CVD is higher in SCI persons than their able-bodied (AB) counterparts and is a leading cause of mortality in persons with SCI, greater understanding of the microvasculature after SCI is essential.6,7 More specifically, whether the microcirculation follows the same pattern as the macrocirculation is unknown. Maximal cutaneous vasodilation occurs when smooth muscle is fully relaxed with local skin heating of 42°C.8,9 Maximal cutaneous vasodilation responses are reduced in persons with microvascular disease from diabetes, hypertension, end organ damage and cardiovascular disease.6,7,10–12 The impact of SCI on maximal cutaneous vasodilation responses is not well defined, however given the cutaneous circulation is easily accessible, examining them is relatively safe and can yield valuable information of their contribution to the high mortality from CVD in this population.