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Biomedical subjects

C C Michel

Publications and source records attributed to C C Michel.

At least 73 records · Page 4Linked to original sources
PubMed1979

The investigation of capillary permeability in single vessels.

Measurements of filtration coefficients (Lp) and osmotic reflexion coefficients (sigma) of single capillaries in the frog mesentery suggest that fluid flows through the walls of these vessels in two types of channel. One channel type (representing about 10% of Lp) appears to be exclusively available for water whereas the other channels appear available for both water and hydrophilic solutes though they severely restrict the passage of albumin (sigma = 0.81). The effects of proteins in the perfusate upon Lp and studies on the passage of ferritin into the surface vesicles of the endothelial cells, suggest that an important component of capillary permeability may reside in an endocapillary layer.

Animals↗
PubMed1978

The effects of position and skin temperature on the capillary pressures in the fingers and toes.

1. Direct measurements of the capillary pressure (P(c)) were made in capillaries at the base of the nails of the fingers and toes of two subjects (the authors of this paper).2. With the hand or foot at heart level, P(c) varied over the range of 7-70 cm H(2)O with mean values of 43 cm H(2)O in both the fingers and the toes. P(c) was higher in the arterial limb (mean 49 cm H(2)O) than in the venous limb (mean 34 cm H(2)O) of the capillary loops. The plasma colloid osmotic pressures for the two subjects were 33 and 34 cm H(2)O.3. For capillaries at heart level there was a strong positive correlation between P(c) and skin temperature when the latter was varied over the range 23-36 degrees C.4. When the hand or foot was lowered, P(c) increased less than the local arterial (P(a)) and venous pressures (P(v)). Furthermore the variation in P(c) was reduced. In fourteen measurements of P(c) made on capillaries in the toes of standing subjects, P(c) was no more than 10 cm H(2)O greater than P(v). It is argued that the increase in the ratio (P(a) - P(c))/(P(c) - P(v)) with hydrostatic load represents an increase in the ratio of pre- to post-capillary resistance.5. When P(v) was increased by inflating a sphygmomanometer cuff around the upper arm, (P(a) - P(c))/(P(c) - P(v)) increased in the hand held at heart level. These changes were similar to those seen with changes in position.6. The implications of the results are discussed with respect to fluid balance between the blood and tissues. It is argued that since P(c) in the warm hand was never less than the plasma colloid osmotic pressure, fluid is not reabsorbed from the tissues into the capillaries of the warm skin of the hand even at heart level. Compensatory changes in the circulation appear to minimise the filtration of fluid into the feet of the standing subject but the mechanism of these changes remains obscure.

Blood Pressure↗
PubMed1977

Variations in permeability along individually perfused capillaries of the frog mesentery.

When single capillaries in the exposed transilluminated frog mesentery were perfused with solutions containing patent blue V (molecular radius 0-7 nm), unbound T1824 (molecular radius 1-3 nm) and T1824-albumin (molecular radius 3-6 nm), the coloured molecules initially appeared to enter the extracapillary tissues more easily at some places than at others along the length of the vessels. Three patterns of extravascular distribution were observed: (1) High frequency unevenness: patent blue V and unbound T1824 first appeared outside the capillary as spots, bars or bands set at intervals 30-80 mum apart along the length of the vessel. (2) Low frequency unevenness: at later times, the extravascular dye was seen to be unevenly distributed on a much larger scale, with lengths of vessel of up to 400 mum surrounded by little extravascular dye separating similar lengths around which much dye had accummulated. This pattern of distribution was seen for all three solutes. (3) Arteriovenous gradient: perfusions with all three solutes resulted in more extracapillary colouration accumulating around the venous ends of the capillaries. Reasons are given for believing that the distribution of extracapillary solute reflected the distribution of permeability along the length of the capillary. The variations in permeability were attributed to an uneven distribution of small pores along the capillary rather than to presences of large pores.

Animals↗
PubMed1976

Osmotic reflextion coefficients of capillary walls to low molecular weight hydrophilic solutes measured in single perfused capillaries of the frog mesentery.

1. Individual capillaries of the transilluminated frog mesentery have been perfused with suspensions of human red cells in frog Ringer solution containing 1-0 g albumin 100 ml.-1. The outer surface of the mesentery has been washed with normal frog Ringer solution and with frog Ringer solutions made hypertonic by addition of one of the following solutes: sodium chloride (100 m-mole. 1.-1); urea (100 m-mole.1.-1); sucrose (20-50 m-mole. 1.-1); cyanocobalamin (8-5 m-mole. 1.-1). The temperature of the mesentery was between 14 and 16 degrees C in all experiments. 2. Wtih the mesentery superfused with normal Ringer, the filtration coefficient was determined from measurements of the rate of fluid filtration across the capillary wall, at a series of known capillary pressures (Michel, Mason, Curry & Tooke, 1974). Filtration coefficient varied from 0-69 X 10(-3) to 4-45 X 10(-3) mum. sec-1 .cm H2O-1 with an average value of 1-87 X 10(-3) mum. sec-1. cm H2O-1. 3. When the superfusate was made hypertonic by the addition of a test solute, the osmotic reflextion coefficient (sigma) of the capillary wall to test solute was calculated from the additional rate of filtration, the concentration of test solute in the superfusate and the filtration coefficient. Average values for sigma were: sodium chloride, 0-068 +/- 0-03 (three capillaries); urea, 0-071 +/- 0.015 (four capillaries); sucrose, 0-115 +/- 0-023 (seven capillaries); cyanocobalamin, 0-100 +/- 0-03 (three capillaries). 4. In further experiments, the osmotic reflextion coefficients to sodium chloride, urea and sucrose were determined in the same capillary. Five technically acceptable experiments were carried out. Although there were differences in the value of sigma between different capillaries, in any one capillary values of sigma were of the same magnitude and there appeared to be no significant trend with the molecular size of the test solute. 5. Our findings are inconsistent with the hypothesis that there is a single pathway for water and small hydrophilic molecules across the capillary wall. 6. Our results may be interpreted in terms of an exclusive channel for water in parallel with a channel shared by both water and small hydrophilic molecules. It is suggested that the exclusive water channel may be the membranes and cytoplasm of the endothelial cells and the shared channel may be located in the intercellular junctions. 7. Our data suggest the exclusive water channel represents about 10% of the total filtration coefficient in frog mesenteric capillaries. The shared channel shows relatively little restriction to the molecules investigated. Estimates of the volume flow throught the two channels are made for conditions where hydrostatic pressure differences and osmotic pressure differences are the driving forces.

Animals↗