Capillary transit time

Goresky CA, Rose CP. Blood-tissue exchange in liver and heart the influence of heterogeneity of capillary transit times. Fed Proc 1977 36 2629-34. 

In addition to providing information on blood flow in large retinal vessels, LTA also permitted assessment of the microcirculation. This was based on the measurement of the capillary transit time. As expected, the capillary transit time changed as a function of blood pressure and, interestingly, showed a twofold variation within the cardiac cycle (3). 

Uneven Maternal and Fetal Capillary Transit Times. The standard values chosen for maternal and fetal blood flow rates are equal. In studying effects of variations of one of the flow rates (15), the maternal and fetal capillary transit times become unequal, and the time steps of the integration, At, do not correspond to the same distance along the capillary on each side. To prevent the integration from getting out of step (diffusion not occurring perpendicular to the membrane), Equation 5 must be modified (14) to ... 

Oxygen makes up 21% of air, with a partial pressure of 21 kPa (158 mm Hg) at sea level. The partial pressure drives the diffusion of oxygen thus, ascent to elevated altitude reduces the uptake and delivery of oxygen to the tissues. air is delivered to the distal airways and alveoli, the PO2 decreases by dilution with carbon dioxide and water vapor and by uptake into the blood. Under ideal conditions, when ventilation and perfusion are well matched the alveolar PO2 will be -14.6 kPa (110 mm Hg). The corresponding alveolar partial pressures of water and CO2 are 6.2 kPa (47 mm Hg) and 5.3 kPa (40 mm Hg), respectively. Under normal conditions, there is complete equilibration ( alveolar gas and capillary blood. In some diseases, the diffusion barrier for gas transport may be increased during exercise, when high cardiac output reduces capillary transit time, full equilibration may not occur, and the alveolar-end-capillary Po gradient may be increased. 

The structure of the blood capillary wall is complex and varies in different organs and tissues. It consists of a single layer of endothelial cells joined together by intercellular junctions. Each endothelial cell, on an average, is 20-40 pm long, 10-15 pm wide, and 0.1-0.5 pm thick, and contains 10,000-15,000 uniform, spherical vesicles called plasmalemmal vesicles. These vesicles range in size between 60 and 80 nm in diameter. About 70% of these vesicles open on the luminal side of the endothelial surface, and the remaining open within the cytoplasm. Plasmalemmal vesicles are believed to be involved in the pinocytic transport of substances across the endothelium. The transition time of pinocytic vesicles across the cell is... 

Using both spallation- and fission-product targets in the LAMPF H beam, we determined that the He-jet technique should work well at LAMPF beam intensities ( 800 iA). Absolute efficiencies for transport of refractory-element activities through a 22-m long capillary were found to average about 60%. Transit time measurements appear convincing that activities as short as 300 ms could be made accessible for study. We found that PbC aerosols provided more efficient transport than KC1 or NaCl aerosols. 

Accuracy) Stability Ruggedness Robustness precision Peak area precision Applied voltage Capillary temperature Injection mechanism pressure/vacuum applied Time of applied pressure/ vacuum Height of vial and transition time treatment, capillary temperature, buffer ionic strength, organic modifiers... 

The vascularization of muscle tissue increases. As the number of capillaries increases, the transit time for blood through muscle increases (i.e., there is increased resistance to flow because of a greater surface area for the exchange of nutrients). The exchange of nutrients and waste products between the blood and muscle fibers is more efficient. 

The normal transit time for blood passing through the pulmonary capillary network is about 0.75 seconds. During this time oxygen must pass through... 

Another extension of HDC is to replace the packed bed with a long capillary (39). Capillary particle chromatography requires 30 kPa pressure and has a separating range of 0.2-200 pm. In such techniques, the particle transit time is a logarithmic function of particle size. 

Since pulmonary arterial blood is poor in oxygen and rich in carbon dioxide, it exchanges excess carbon dioxide for oxygen in the pulmonary capillaries, which are in close contact with alveolar walls. At rest, the transit time for blood in the pulmonary capillaries is computed as... 

A principal difference between lEF in a gel and in a capillary is that, in the latter, mobilization of the focused proteins past the detector has to be carried out if an online imaging detection system is not being used. Mainly three techniques are used chemical and hydrodynamic flow mobilization (in coated capillaries) and mobilization utilizing the EOF (in uncoated or partially coated capillaries). The last approach is troublesome, though, since the transit times of the focused zones change severely from run to run thus, it is preferable to perform cIEF in well-coated capillaries, where EOF is completely suppressed. 

The speed of reaction within the erythrocytes is about 13 000 times faster than in the plasma. This accounts both for the rapid uptake of carbon dioxide by the blood during the short transit time (about one sec.) of blood through the systemic capillary and for the rapid release of carbon dioxide from the blood to the alveolar gas during the transit of the blood through the pulmonary capillaries. Without carbonic anhydrase, carbon dioxide partial pressures in the venous blood, and hence in the tissues would be much higher. Indeed when... 

The time resolution of a photomultiplier is limited mainly by the variations in the paths that electrons take in reaching the anode. Because of the spread in transit times, the anode pulse resulting from the absorptitm of a single photon typically has a width on the order of 10 -10 s. The spread of transit times is smaller in microchannel plate photomultipliers, which work on the same principles as ordinary photomultipliers except that the electronic amplification steps occur along the walls of small capillaries. The anode pulse width in a microchannel plate detector can be as short as 2 x 10 s. 

In an early paper, Sadowski and Bird (1965) recognised that using a bulk viscosity function for the fluid together with a capillary-hydraulic radius model for the porous media in the manner described above did not take into account any time-dependent elastic phenomena. They suggested that, in a tortuous channel of a porous medium, elastic effects would not be seen provided that the fluid s relaxation time was small compared with the transit time through the contraction/expansion. The fluid would have enough time to readjust to the changing flow conditions. However, if the transit time is small compared with the fluid s relaxation time, then the elasticity of the fluid would have an effect. 

Hypoxic exposure is manifested in the brain by a shift to a more disoxygenated capillary hemoglobin profile (2), despite increased blood flow (3,4), greater blood volume (2,5,6), and decreased capillary mean transit times (6). Brain parenchymal oxygen pressiues fall (5,7,8), but local glucose utilization is... 

Shockley RP, LaManna JC. Determination of rat cerebral cortical blood volume changes by capillary mean transit time analysis during hypoxia, hypercapnia, and hyperventilation. Brain Res 1988 454 170-178. 

Figure 2 Two measured pulses from a 25 fim diameter sphere which is reversed back and forth through a 70 /im diameter and 570 m long glass capillary. The particle migrates radially in Poiseuille flow from the axis (short transit time) towards the wall (long transit time) and the pulse height increases when the particle moves closer to the wall. Approximately 20 reversals separate the two realizations.

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