Renal microvascular oxygen tension during hyperoxia and acute hemodilution assessed by phosphorescence quenching and excitation with blue and red light

Mathematical simulations of oxygen delivery to tissue from capillaries that take into account the particulate nature of blood flow predict the existence of oxygen tension (Po2) gradients between erythrocytes (RBCs). As RBCs and plasma alternately pass an observation point, these gradients are manifested as rapid fluctuations in Po2, also known as erythrocyte-associated transients (EATs). The impact of hemodilution on EATs and oxygen delivery at the capillary level of the microcirculation has yet to be elucidated. Therefore, in the present study, phosphorescence quenching microscopy was used to measure EATs and Po2 in capillaries of the rat spinotrapezius muscle at the following systemic hematocrits (Hctsys): normal (39%) and after moderate (HES1; 27%) or severe (HES2; 15%) isovolemic hemodilution using a 6% hetastarch solution. A 532-nm laser, generating 10-μs pulses concentrated onto a 0.9-μm spot, was used to obtain plasma Po2 values 100 times/s at points along surface capillaries of the muscle. Mean capillary Po2 (Pc[Formula: see text]; means ± SE) significantly decreased between conditions (normal: 56 ± 2 mmHg, n = 45; HES1: 47 ± 2 mmHg, n = 62; HES2: 27 ± 2 mmHg, n = 52, where n = capillary number). In addition, the magnitude of Po2 transients (ΔPo2) significantly decreased with hemodilution (normal: 19 ± 1 mmHg, n = 45; HES1: 11 ± 1 mmHg, n = 62; HES2: 6 ± 1 mmHg, n = 52). Results suggest that the decrease in Pc[Formula: see text] and ΔPo2 with hemodilution is primarily dependent on Hctsys and subsequent microvascular compensations.

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Phosphorescence quenching and the microcirculation: An automated, multipoint oxygen tension measuring instrument

Review of Scientific Instruments ◽

10.1063/1.1146133 ◽

1995 ◽

Vol 66 (10) ◽

pp. 5075-5084 ◽

Cited By ~ 30

Author(s):

Ross D. Shonat ◽

Keith N. Richmond ◽

Paul C. Johnson

Keyword(s):

Oxygen Tension ◽

Measuring Instrument ◽

Phosphorescence Quenching

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Impact of accumulated oxygen depletion (AOD) on measurements of oxygen tension (PO2) using phosphorescence quenching microscopy (PQM)

The FASEB Journal ◽

10.1096/fasebj.22.1_supplement.927.1 ◽

2008 ◽

Vol 22 (S1) ◽

Author(s):

Aleksander Sergeevich Golub ◽

Roland Nathan Pittman

Keyword(s):

Oxygen Tension ◽

Oxygen Depletion ◽

Phosphorescence Quenching

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Oxygen tension gradients and heterogeneity in venous microcirculation: a phosphorescence quenching study

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1997.272.5.h2233 ◽

1997 ◽

Vol 272 (5) ◽

pp. H2233-H2240 ◽

Cited By ~ 20

Author(s):

R. D. Shonat ◽

P. C. Johnson

Keyword(s):

Blood Pressure ◽

Oxygen Tension ◽

Systemic Blood Pressure ◽

Systemic Blood ◽

Microvascular Network ◽

Waste Products ◽

Phosphorescence Quenching ◽

Oxygen Gradients ◽

Weakly Dependent ◽

Made In

Localized measurements of intravascular oxygen tension (PO2) at multiple locations in the microvascular network of the rat spinotrapezius muscle were used to study the spatial distribution of PO2 in venular structures. By use of a newly developed phosphorescence system to rapidly and repeatedly measure PO2, 538 individual measurements were made in 18 different networks during rest. Average intravascular PO2 was (in mmHg +/- SD) 33 +/- 9, 21 +/- 9, 26 +/- 10, and 33 +/- 8 in small arcade arterioles, postcapillary venules (PV), 3 degrees venules (3V), and arcade venules, respectively. The coefficient of variation (CV), a descriptive indicator of spatial heterogeneity, was correspondingly 0.28, 0.45, 0.37, and 0.23 for the different vessel groups. PO2 was found to increase significantly (P < 0.001) from PV to 3V, rising 0.009 +/- 0.002 mmHg/microns along the vessel. By linear regression, the slope of PO2 for the vessel difference group, PV-3V as a function of mean systemic blood pressure (BPm; in mmHg) was -0.09 +/- 0.04 (P < 0.05), indicating that the measured longitudinal oxygen gradients and CV are only weakly dependent on BPm. The results support the hypothesis that oxygen can diffuse across the walls of postcapillary vessels and suggest that the venular structures are not merely passive conduits for removing oxygen and waste products but may play an important role in regulating oxygen delivery.

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Microvascular oxygen tension in the rat mesentery

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00861.2007 ◽

2008 ◽

Vol 294 (1) ◽

pp. H21-H28 ◽

Cited By ~ 24

Author(s):

Aleksander S. Golub ◽

Matthew C. Barker ◽

Roland N. Pittman

Keyword(s):

Oxygen Consumption ◽

Oxygen Tension ◽

Oxygen Delivery ◽

Vascular Wall ◽

Spot Size ◽

Vessel Diameter ◽

Primary Site ◽

Phosphorescence Quenching ◽

Rat Mesentery ◽

Mesenteric Microcirculation

Longitudinal Po2 profiles in the microvasculature of the rat mesentery were studied using a novel phosphorescence quenching microscopy technique that minimizes the accumulated photoconsumption of oxygen by the method. Intravascular oxygen tension (Po2, in mmHg) and vessel diameter ( d, in μm) were measured in mesenteric microvessels ( n = 204) of seven anesthetized rats (275 g). The excitation parameters were as follows: 7 × 7-μm spot size; 410 nm laser; and 100 curves at 11 pulses/s, with pulse parameters of 2-μs duration and 80-pJ/μm2 energy density. The mean Po2 (± SE) was 65.0 ± 1.4 mmHg ( n = 78) for arterioles ( d = 18.8 ± 0.7 μm), 62.1 ± 2.0 mmHg ( n = 38) at the arteriolar end of capillaries ( d = 7.8 ± 0.3 μm), and 52.0 ± 1.0 mmHg ( n = 88) for venules ( d = 22.5 ± 1.0 μm). There was no apparent dependence of Po2 on d in arterioles and venules. There were also no significant deviations in Po2 based on d (bin width, 5 μm) from the general mean for both of these types of vessels. Results indicate that the primary site of oxygen delivery to tissue is located between the smallest arterioles and venules (change of 16.3 mmHg, P = 0.001). In conclusion, oxygen losses from mesenteric arterioles and venules are negligible, indicating low metabolic rates for both the vascular wall and the mesenteric tissue. Capillaries appear to be the primary site of oxygen delivery to the tissue in the mesenteric microcirculation. In light of the present results, previously reported data concerning oxygen consumption in the mesenteric microcirculation can be explained as artifacts of accumulated oxygen consumption due to the application of instrumentation having a large excitation area for Po2 measurements in slow moving and stationary media.

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