Hypertension and the Microcirculation
John H. Barker, Gary L. Anderson, Michael D. Menger in Clinically Applied Microcirculation Research, 2019
However, it must be stressed that the total amount of blood flow entering tissues is not the only factor that determines the quality of tissue perfusion. The homogeneity of blood flow within the tissue is also a key factor to prevent the appearance of areas of local tissue hypoxia. Several authors reported that the degree of blood flow dispersion is larger in hypertensive animals.7 As suggested by Schmid-Schonbein,19 the elevated tone in some arterioles associated with hypertension may increase the heterogeneity of blood flow and red cell distribution at the diverging bifurcations. Such a mechanism would induce a higher degree of plasma skimming, as found in genetic hypertensive rats.92 In addition, it may be remembered that the increased microvascular blood flow heterogeneity found in hypertension can certainly be considerably aggravated by rheological changes, such as changes in red cell or white cell membrane properties that are associated with hypertension or with possible associated diseases (diabetes, hyperlipidemia, etc.).
Assessment of Circulation (C)
Elizabeth Charnock, Angela Lee, Amanda Miller in Nursing & Health Survival Guide, 2014
CRT should be assessed by two methods: Central – press with one finger in the centre of the sternum for 5 seconds and release.Peripheral – elevate a digit to above heart level, press on the digit for 5 seconds and release.CRT should be < 2 seconds. An increase in CRT indicates poor perfusion and can be an early sign of septic shock.PRE-TERMINAL WARNING! Central cyanosis is a pre-terminal sign and cardiorespiratory arrest is imminent.Remember: the ambient temperature must be considered when assessing capillary refill time, particularly following trauma where the child has been exposed to a cold environment.Additional signs of poor perfusion are cold and clammy skin, pallor, mottling and peripheral cyanosis.
Trauma Physiology and Metabolism
Ian Greaves, Keith Porter, Jeff Garner in Trauma Care Manual, 2021
Various resuscitation strategies have been described, of which the most physiological is hybrid resuscitation which aims initially to keep the blood pressure high enough to keep the patient alive, whilst keeping blood pressure below normal levels as there is a theoretical risk of a normal pressure worsening haemorrhage by preventing clot formation on bleeding vessels. Because of the potential adverse effects of prolonged hypotension, resuscitation to normotension is substituted after 60 minutes. Unfortunately, some of the measures used to assess blood pressure, such as the presence of a palpable radial, femoral or carotid pulse do not correlate well with measured blood pressure and shock classification systems4 based on heart rate and blood pressure are also inexact and should be abandoned. Novel measurement techniques may provide a better measure of how well perfusion of tissues and organs is being maintained, for example, continuous microscopic camera or infrared probe examination of blood flow through the capillaries of organ beds.
Bioengineering lungs — current status and future prospects
Published in Expert Opinion on Biological Therapy, 2021
Vishal Swaminathan, Barry R. Bryant, Vakhtang Tchantchaleishvili, Taufiek Konrad Rajab
In order to create an effective environment for cell growth, the bioreactor must be sterile. Moreover, the bioreactor provides access to the vascular and respiratory compartments for perfusion through vasculature and ventilation of the respiratory tree with physiologic parameters [35]. Perfusion of the pulmonary vasculature depends on pressures created by the right ventricle. The repetitive force of the heart pumping blood through the circulatory system, in particular through the lung vasculature, can directly affect the stretch and size of vessel walls [36]. The stress from the stroke volume influences cell alignment and homeostasis [41]. Moreover, perfusion promotes nutrient delivery and waste removal, which is necessary for cell functioning. Perfusion of the cellularized scaffold can be implemented in a constant flow and pressure or a cyclic one. Perfusate composition is another challenge that has yet to be completely addressed. Currently, cell culture media is often used, although considering the many types of cells populating a singular scaffold, choosing a media can be challenging. As bioreactors improve, so will the perfusate.
Retinal Tissue Perfusion in Patients with Multiple Sclerosis
Published in Current Eye Research, 2019
Yi Liu, Silvia Delgado, Hong Jiang, Ying Lin, Jeffrey Hernandez, Yuqing Deng, Giovana Rosa Gameiro, Jianhua Wang
As the decreased tissue thickness resulting from retinal neurodegeneration in patients with MS may change the demand for blood flow, it remains unknown whether the decreased blood flow is a consequence of the decreased tissue volume. Tissue perfusion is important in maintaining the organ function and is defined as a certain blood volume flowing through a given tissue volume over a period of time.5,38 Retinal blood flow in the macula can be measured and decreased retinal blood flow under diseased conditions has been reported.20,39 In addition, macular tissue volume can be readily measured using optical coherence tomography.40–42 With both the blood flow and perfused tissue volume available, retinal tissue perfusion (RTP) can be calculated as the blood flow divided by the tissue volume which the blood flow perfuses.43 We hypothesize that retinal hypoperfusion occurs in MS. The goal of the present study was to determine the RTP in patients with MS.
Thermophysical and mechanical properties of biological tissues as a function of temperature: a systematic literature review
Published in International Journal of Hyperthermia, 2022
Leonardo Bianchi, Fabiana Cavarzan, Lucia Ciampitti, Matteo Cremonesi, Francesca Grilli, Paola Saccomandi
Another fundamental factor affecting the thermal outcome during hyperthermia treatments concerns the blood flow in perfused tissues. Blood perfusion refers to the passage of a certain blood volume through vessels embedded in biological tissues, in order to provide oxygen and deliver important nutrients to tissues, as well as remove waste substances [178]. The blood flow can be expressed as the volume of blood, which is forced to flow within a tissue, per tissue mass per unit of time [179], i.e., mL/100 g/min. Moreover, knowing the tissue density, the blood perfusion rate (i.e., the volumetric rate per unit tissue volume, often expressed in 1/s [180]) can be attained as the product of blood flow and the tissue density [181]. The blood flow has been investigated at both normothermic conditions and at temperatures that do not lie in the physiological range, by imposing a temperature variation to biological media through different methods. Likewise, the temperature sensitivity of the blood perfusion has been assessed in different tissues; preclinical studies on healthy tissues and on tumor models have been set, as well as evaluations on blood flow upon temperature changes during clinical trials.