Mapping the myoglobin concentration, oxygenation, and optical pathlength in heart ex vivo using near-infrared imaging

Noninvasive cardiac hemodynamics monitoring of acute myocardial ischemia in rats using near-infrared spectroscopy: A pilot study

Noninvasive and real-time optical detection of cardiac hemodynamics dysfunction during myocardial ischemia remains challenging. In this study, we developed a near-infrared spectroscopy device to monitor rats' myocardial hemodynamics. The well-designed system can accurately reflect the hemodynamics changes by the classic upper limb ischemia test. Systemic hypoxia by disconnecting to the ventilator and cardiac ischemia by coronary artery slipknot ligation was conducted to monitor myocardial hemodynamics. When systemic hypoxia occurred, ΔHbR and ΔtHb increased significantly, whereas ΔHbO decreased rapidly. When coronary blood flow was obstructed by slipknots, cardiothoracic ΔHbO immediately begins to decline, while ΔHbR also significantly increases. Simultaneously, SpO2 did not show any obvious changes during myocardial ischemia, while SpO2 decreased significantly during systemic hypoxia. These results demonstrated that cardiothoracic hemodynamics stemmed from myocardial ischemia. This pilot study demonstrated the practicality of noninvasive, low-cost optical monitoring for cardiac oxygenation dysfunction in rats.

Development of a Tissue Oxygenation Flow-Based Index Toward Discerning the Healing Status in Diabetic Foot Ulcers

Objective: The objective of this study is to characterize breath-hold (BH)-induced oxygenation changes in diabetic foot ulcers (DFUs) and develop an oxygenation flow index (OFI) to discern nonhealing from healing DFUs. Approach: The imaging approach utilizes an innovative BH stimulus that induces vasoconstriction and measures for altering oxygenation flow in and around the tissues of DFUs and controls. The modified Beer-Lambert law was utilized to calculate hemoglobin-based spatiotemporal oxygenation maps in terms of oxygen saturation. Results: We found controls had synchronous BH-induced oxygenation changes across the dorsal (OFI: 29.0%) and plantar (OFI: 57.6%) aspects of the foot. Nonhealing DFUs, however, had less synchronous BH-induced oxygenation changes (OFI <28%). In addition, two complicated healing DFU cases, or cases with underlying issues or poor long-term healing outcomes, were observed to have OFIs <28%. Innovation: An OFI was developed to differentiate nonhealing DFUs from healing DFUs using a single, noncontact, near-infrared optical scanner for spatiotemporal oxygenation monitoring. The OFI has potential to provide immediate feedback on the microcirculation in DFUs, through hemoglobin-based oxygenation parameters. Conclusion: A preliminary threshold (OFI <28%) could differentiate nonhealing and complicated DFUs from healing DFUs. The overall oxygenation flow pattern was less synchronous (or the OFI value reduced) in the nonwound areas of the feet that were nonhealing. In other words, the reduced OFI value (<28%) in the entire foot, excluding the wound region is a possible indicator that the wound may not heal.

Reversible Oxidative Modifications in Myoglobin and Functional Implications

Myoglobin (Mb), an oxygen-binding heme protein highly expressed in heart and skeletal muscle, has been shown to undergo oxidative modifications on both an inter- and intramolecular level when exposed to hydrogen peroxide (H₂O₂) in vitro. Here, we show that exposure to H₂O₂ increases the peroxidase activity of Mb. Reaction of Mb with H₂O₂ causes covalent binding of heme to the Mb protein (Mb-X), corresponding to an increase in peroxidase activity when ascorbic acid is the reducing co-substrate. Treatment of H₂O₂-reacted Mb with ascorbic acid reverses the Mb-X crosslink. Reaction with H₂O₂ causes Mb to form dimers, trimers, and larger molecular weight Mb aggregates, and treatment with ascorbic acid regenerates Mb monomers. Reaction of Mb with H₂O₂ causes formation of dityrosine crosslinks, though the labile nature of the crosslinks broken by treatment with ascorbic acid suggests that the reversible aggregation of Mb is mediated by crosslinks other than dityrosine. Disappearance of a peptide containing a tryptophan residue when Mb is treated with H₂O₂ and the peptide’s reappearance after subsequent treatment with ascorbic acid suggest that tryptophan side chains might participate in the labile crosslinking. Taken together, these data suggest that while exposure to H₂O₂ causes Mb-X formation, increases Mb peroxidase activity, and causes Mb aggregation, these oxidative modifications are reversible by treatment with ascorbic acid. A caveat is that future studies should demonstrate that these and other in vitro findings regarding properties of Mb have relevance in the intracellular milieu, especially in regard to actual concentrations of metMb, H₂O₂, and ascorbate that would be found in vivo.

Near infrared image processing to quantitate and visualize oxygen saturation during vascular occlusion

The assessment of microcirculation spatial heterogeneity on the hand skin is the main objective of this work. Near-infrared spectroscopy based 2D imaging is a non-invasive technique for the assessment of tissue oxygenation. The haemoglobin oxygen saturation images were acquired by a dedicated camera (Kent Imaging) during baseline, ischaemia (brachial artery cuff occlusion) and reperfusion. Acquired images underwent a preliminary restoration process aimed at removing degradations occurring during signal capturing. Then, wavelet transform based multiscale analysis was applied to identify edges by detecting local maxima and minima across successive scales. Segmentation of test areas during different conditions was obtained by thresholding-based region growing approach. The method identifies the differences in microcirculatory control of blood flow in different regions of the hand skin. The obtained results demonstrate the potential use of NIRS images for the clinical evaluation of skin disease and microcirculatory dysfunction.

Myoglobin functions in the heart

The physiological role of myoglobin (Mb) within the heart depends on its oxygenation state. The myocardium exhibits a broad oxygen partial pressure (pO2) spectrum with a transmural gradient from the epicardial to the subendocardial layer, ranging from arterial values to an average of 19.3 mm Hg down to 0 mm Hg. The function of Mb as an O2 storage depot is well appreciated, especially during systolic compression. In addition, Mb controls myocardial nitric oxide (NO) homeostasis and thus modulates mitochondrial respiration under physiological and pathological conditions. We recently discovered the role of Mb as a myocardial O2 sensor; in its oxygenated state Mb scavenges NO, protecting the heart from the deleterious effects of excessive NO. Under hypoxia, however, deoxygenated Mb changes its role from an NO scavenger to an NO producer. The NO produced protects the cell from short phases of hypoxia and from myocardial ischemia/reperfusion injury. In this review we summarize the traditional and novel aspects of Mb and its (patho)physiological role in the heart.

NIR spectroscopic imaging to map hemoglobin + myoglobin oxygenation, their concentration and optical pathlength across a beating pig heart during surgery

The purpose of this paper is to demonstrate that near-infrared (NIR) spectroscopic imaging can provide spatial distribution (maps) of the absolute concentration of hemoglobin + myoglobin, oxygen saturation parameter and optical pathlength, reporting on the biochemico-physiological status of a beating heart in vivo. The method is based on processing the NIR spectroscopic images employing a first-derivative approach. Blood-pressure-controlled gating compensated the effect of heart motion on the imaging. All the maps are available simultaneously and noninvasively at a spatial resolution in the submillimeter range and can be obtained in a couple of minutes. The equipment has no mechanical contact with the tissue, thereby leaving the heart unaffected during the measurement.

Rhodamine 800 as a near-infrared fluorescent deposition flow tracer in rodent hearts

We investigated the use of a near-infrared (NIR) fluorescent dye, Rhodamine 800 (Rhod800, λ(exc) = 693 nm, λ(em) > 720 nm) as a flow-dependent molecular tracer for NIR spectroscopy and high-resolution cardiac imaging. Rhod800 accumulates in isolated mitochondria in proportion to the mitochondrial membrane potential (ΔΨ). However, in the intact myocardium, Rhod800 binding is ΔΨ-independent. Rat hearts were perfused in a Langendorff mode with Krebs-Henseleit buffer containing 45-nM Rhod800 at normal (100%), increased (150%), or reduced (50%) baseline coronary flow (CF) per gram, for 30 to 60 min. In a different group of hearts, the left anterior descending artery (LAD) was occluded prior to Rhod800 infusion to create a flow deficit area. Rhod800 deposition was analyzed by: 1. absorbance spectroscopy kinetics in the Rhod800-perfused hearts, 2. Rhod800 absorbance and fluorescence imaging in the short-axis heart slices, and 3. dynamic epicardial/subepicardial fluorescence imaging of Rhod800 in KCl-arrested hearts, with a spatial resolution of ∼ 200 μm. Rhod800 deposition was proportional to the perfusate volume (CF and perfusion time) and there was no Rhod800 loss during the washout period. In the LAD-ligated hearts, Rhod800 fluorescence was missing from the no-flow, LAD-dependent endocardial and epicardial/subepicardial area. We concluded that Rhod800 can be used as a deposition flow tracer for dynamic cardiac imaging.