Simultaneous fluorometry and phosphorometry of Langendorff perfused rat heart: ex vivo animal studies

Fluorescence imaging of intrinsic fluorophores of tissue is a powerful method to assess metabolic changes at the cellular and intracellular levels. At the same time, exogenous phosphorescent probes can be used to accurately measure intravascular tissue oxygenation. Heart failure is the leading cause of death in America. A rat heart can potentially model the human heart to study failures or other abnormalities optically. We report simultaneous fluorescence and phosphorescence measurements performed on a rat heart. We have used two different optical systems to acquire fluorescence signals of flavoprotein and nicotinamide adenine dinucleotide—the two intrinsic fluorophores of mitochondria—and the phosphorescence signal of an intravascular oxygen probe to extract intracellular and intravascular metabolism loads, respectively

Respiratory muscle deoxygenation during exercise in patients with heart failure demonstrated with near-infrared spectroscopy

AbstractExertional dyspnea in patients with heart failure may be due, in part, to respiratory muscle underperfusion. Near-infrared spectroscopy is a new technique that permits noninvasive assessment of skeletal muscle oxygenation by monitoring changes in nearinfrared light absorption. With use of near-infrared spectroscopy, serratus anterior muscle oxygenation during maximal bicycle exercise was compared in 10 patients with heart failure (ejection fraction 16 ± 5%) and 7 age-matched normal subjects. Oxygen consumption (VO2), minute ventilation (VE) and arterial saturation were also measured. Changes in difference in absorption between 760 and 800 nm, expressed in arbitrary units, were used to detect muscle deoxygenation.Minimal change in this difference in absorption occurred in normal subjects during exercise, whereas patients with heart failure exhibited progressive changes throughout exercise consistent with respiratory muscle deoxygenation (peak exercise: normal 3 ± 6, heart failure 12 ± 4 near-infrared arbitrary units, p < 0.001). At comparable work loads patiente with heart failure had significantly greater minute ventilation and respiratory rate but similar tidal volume when contrasted with normal subjects. However, at peak exercise normal subjects achieved significantly greater minute ventilation and tidal volume with a comparable respiratory rate. No significant arterial desaturation occurred during exercise in either group.These findings indicate that respiratory muscle deoxygenation occurs in patients with heart failure during exercise. This deoxygenation may contribute to the exertional dyspnea experienced by such patients

Time-resolved reflectance measurements on layered tissues with strongly varying optical properties

Most biological tissues consist of layers with different optical properties. A few examples are the skin, the esophagus, the stomach and the wall of arteries. An understanding of how the light propagates in such layered systems is a prerequisite for any light based therapy or diagnostic scheme. In this study we investigate the influence of different kinds of layers on time resolved reflectance measurements. Experiments were performed on layered gel phantoms and the results compared to Monte Carlo simulations and diffusion theory. It is shown that when a low absorbing medium is situated on top of a high absorbing medium, the absorption coefficient of the lower layer is accessible if the differences in the absorption coefficient are only small. In the case of large difference the optical properties of the upper layer dominate the signal and shield information on the lowest layer. The degree of this shielding effect depends on layer thickness as well as optical properties. In the case of an almost absorption and scattering free layer in between two normal tissues, an overall increase of the signal is visible. However, the overall shape of the curve is about preserved. The apparent scattering coefficient is slightly decreased, while the apparent absorption coefficient is unaltered

Near-infrared spectroscopy of a heterogeneous turbid system containing distributed absorbers

In most biological tissues, absorbers such as blood in the blood vessels are localized within a low-absorbing background medium. To study the effect of distributed absorbers on the near infrared reflectance, we developed a Monte Carlo code and performed time-domain measurements on heterogeneous tissue-vessel models. The models were made of low absorbing polyester resin mixed with TiO_2 as scatters. A series of tubes with diameters of 3.2 or 6.4 mm were made in the resin sample. The volume ratio of the tubes to the total sample is about 20%. During the measurement, these tubes were filled with turbid fluids with different absorption coefficients to simulate blood in various oxygenation states. We found that the apparent absorption coefficient of the resin/tube system, determined by using the diffusion equation fit, can be approximated by a volume-weighted sum of the absorption coefficients of the different absorbing components. This approximation has to be replaced by a more complex expression if the difference in absorption between the absorbers and background is very large (approximately 20 times). The results of the tissue phantom study are supported by the Monte Carlo simulation. Possible explanations for the photon migration in this kind of heterogeneous system is also presented