Measurement of hemoglobin oxygen saturation in capillaries

We present a computer-aided videodensitometric method for the determination of oxygen saturation in red blood cells flowing through capillaries of the hamster cheek pouch retractor muscle. The optical density (OD) of red blood cells is determined at two wavelengths. At the first, 431 nm, there is a maximum difference between absorption by oxygen deoxyhemoglobin. At the second, 420 nm, absorption is equal for the two absorbing species (isosbestic wavelength). In capillaries of the retractor muscle a relationship between oxygen saturation (S) and the following OD ratio was obtained as S = -1.71 (OD431/OD420) + 2.20. The error (95% confidence interval) in oxygen saturation associated with a determination of the OD ratio is estimated to be +/- 4.8%. The computerization of the method employs a frame-by-frame analysis of the light intensity over a selected capillary segment. The light intensity waveform along the segment is digitized and the minimum (I) and maximum (I0) light intensities are used to compute an optical density (OD = log10 [I0/I]). These minimum and maximum intensities correspond to the presence and absence of a red blood cell, respectively. The method permits the off-line analysis of videotaped scenes and provides a means of assessing the extent of temporal and spatial heterogeneity of oxygen saturation in selected capillary networks. The method has been developed for use in capillaries in transilluminated striated muscle but should be generally applicable to the measurement of capillary oxygen saturation in other tissues.

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Determination of red blood cell oxygenation in vivo by dual video densitometric image analysis

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1990.258.4.h1216 ◽

1990 ◽

Vol 258 (4) ◽

pp. H1216-H1223 ◽

Cited By ~ 12

Author(s):

C. G. Ellis ◽

M. L. Ellsworth ◽

R. N. Pittman

Keyword(s):

Oxygen Saturation ◽

Red Blood Cells ◽

Blood Cells ◽

Striated Muscle ◽

Wave Length ◽

Retractor Muscle ◽

Light Intensities ◽

Microscopic Field

We have developed a new video microspectrophotometric system for the in vivo determination of oxygen saturation in red blood cells in striated muscle capillaries. This method allows one to quantify changes in the oxygenation of small groups of red blood cells as they traverse the capillary. Simultaneous images of a single microscopic field are recorded using two silicon-intensified target cameras and high-resolution video recorders. One image is recorded at an oxygen-dependent wave-length (431 nm) and the other at an isosbestic wavelength (420 nm). Light intensities from 10 adjacent pixels aligned along the axis of the capillary from identical 10-s segments of the video-tapes are digitized once per frame. Both sets of data are redisplayed simultaneously as two-dimensional images (10 pixels high x 300 frames wide) using a graphics system. These images show alternating bright and dark bands corresponding to plasma gaps and red blood cells. Light intensities in the presence and absence of red blood cells are determined by positioning a window over the appropriate region of the graphics image. Optical densities of single red blood cells at the two wavelengths, OD431 and OD420, are computed as is their ratio (OD431/OD420), which is linearly related to oxygen saturation. In vivo calibration studies in capillaries of the hamster retractor muscle indicate that the error in measuring oxygen saturation with this technique is approximately 2.7% saturation for a group of 10 cells.

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Arterioles supply oxygen to capillaries by diffusion as well as by convection

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1990.258.4.h1240 ◽

1990 ◽

Vol 258 (4) ◽

pp. H1240-H1243 ◽

Cited By ~ 22

Author(s):

M. L. Ellsworth ◽

R. N. Pittman

Keyword(s):

Oxygen Saturation ◽

Red Blood Cells ◽

Oxygen Transport ◽

Blood Cells ◽

Oxygen Exchange ◽

Cheek Pouch ◽

Retractor Muscle ◽

Hamster Cheek Pouch ◽

Local Oxygen

In the early part of this century, August Krogh proposed a model of oxygen transport in capillaries that assumes that all oxygen is delivered to the capillaries by convection from small terminal arterioles and lost from these capillaries by diffusion. This model and its consequences have been used extensively to interpret whole organ oxygen transport data in terms of diffusion between capillaries and tissues and to relate changes in microvascular hemodynamics to alterations in oxygen transport. We evaluated the appropriateness of such extrapolation by measuring oxygen saturation at discrete locations along the lengths of individual capillaries in the hamster cheek pouch retractor muscle. Our results indicate that the amount of oxygen lost from individual capillaries can be markedly affected by the presence of larger microvessels that frequently cross the capillary path. These larger vessels act either as a diffusive supply of oxygen for the red blood cells within the capillary or as an additional sink for the oxygen depending on the direction of the oxygen tension gradient. This transfer of oxygen between larger microvessels and capillaries attenuates the importance of capillary hemodynamics in oxygen exchange. Therefore, conclusions about local oxygen exchange that utilize only hemodynamic data from whole organ or microvascular experiments and the Krogh model will generally be invalid and should be viewed with caution.

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Measurement of percent oxyhemoglobin in the microvasculature

Journal of Applied Physiology ◽

10.1152/jappl.1975.38.2.321 ◽

1975 ◽

Vol 38 (2) ◽

pp. 321-327 ◽

Cited By ~ 69

Author(s):

R. N. Pittman ◽

B. R. Duling

Keyword(s):

Optical Density ◽

Density Ratio ◽

Optical Path Length ◽

Optical Path ◽

Cheek Pouch ◽

Theoretical Treatment ◽

Hamster Cheek Pouch ◽

Particulate Suspensions ◽

Optical Density Ratio

A new method is applied to the determination of percent oxyhemoglobin (percent saturation) in whole blood. The method is based on a theoretical treatment of light absorption and scattering by particulate suspensions and requires the measurement of optical densities (D) of blood at three closely spaced wavelengths. The optical density of red blood cell (RBC) suspensions was measured with a video microdensitometer and a linear relationship was found between percent saturation and the corrected optical density ratio, (D555 B)/(D546 B). For a given saturation, this ratio was independent of optical path length (12 mum-2 mm), hematocrit (3–50%), and RBC velocity (1.5–17 mm/s). The applicability to microvascular measurements has been assessed through the use of TV microdensitometry on micropipettes with flowing RBCs and on microvessels in the hamster cheek pouch.

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