Determination of circulating blood volume by measurement of indocyanine green dye in hemolysate: a preliminary study

In 8 emergency care patients blood volume was determined using Cr5I labelled erythrocytes and indocyanine green (ICG). Prior to measurement of ICG in blood with a spectrophotometer, the blood was hemolyzed with Triton-X. A close correlation of r = 0.97 between the Cr51 and the ICGTR-X estimates was found; the ICGTR-X volume was about 3% lower than the Cr51 volume. In five additional in vitro experiments the ICGTR-X method was found to reflect real volumes with an insignificant error of less than 1%. Blood volume determination with ICGTR-X cannot be applied in cases of circulatory failure. ICG should be administered in a dose of 0.5 mg/kg of body weight. For calibration purposes, a two point calibration curve (point 1: point of intersection of x and y axis; point 2: 5 mg ICG/1 of blood) is sufficient. From these preliminary experiments it is concluded that the ICGTR-X method is a rapid and simple technique of blood volume determination with multiple reproducibility which can be carried out in any clinical laboratory.     

Measurement of cerebral blood volume using near-infrared spectroscopy and indocyanine green elimination.

Methods for measuring cerebral blood volume (CBV) have traditionally used radioisotopes. More recently, near-infrared spectroscopy (NIRS) has been used to measure CBV by using a technique involving O(2) desaturation of cerebral tissue, where the observed change in the concentration of oxygenated hemoglobin is a marker of the volume of blood contained within the brain. A new integration method employing NIRS is described by using indocyanine green (ICG) as the intravascular marker. After bolus injection, concentration-time integrals of cerebral tissue ICG concentration ([ICG](tissue)) measured by NIRS are compared with corresponding integrals of the cerebral blood ICG concentrations ([ICG](blood)) estimated by high-performance liquid chromatography of peripheral blood samples with allowance for cerebral-to-large-vessel hematocrit ratio. It is shown that CBV = integral [ICG]tissue/[ICG]blood. Measurements in 10 adult volunteers gave a mean value of 1.1 +/- 0.39 (SD) ml/100 g illuminated tissue. This result, although lower than previous NIRS estimations, is consistent with the long extracerebral path of light in the adult head. Scaling of results is required to take into account this component of the optical pathlength.     

Optimal back-extrapolation method for estimating plasma volume in humans using the indocyanine green dilution method

Background

The indocyanine green dilution method is one of the methods available to estimate plasma volume, although some researchers have questioned the accuracy of this method.

Methods

We developed a new, physiologically based mathematical model of indocyanine green kinetics that more accurately represents indocyanine green kinetics during the first few minutes postinjection than what is assumed when using the traditional mono-exponential back-extrapolation method. The mathematical model is used to develop an optimal back-extrapolation method for estimating plasma volume based on simulated indocyanine green kinetics obtained from the physiological model.

Results

Results from a clinical study using the indocyanine green dilution method in 36 subjects with type 2 diabetes indicate that the estimated plasma volumes are considerably lower when using the traditional back-extrapolation method than when using the proposed back-extrapolation method (mean (standard deviation) plasma volume?=?26.8 (5.4) mL/kg for the traditional method vs 35.1 (7.0) mL/kg for the proposed method). The results obtained using the proposed method are more consistent with previously reported plasma volume values.

Conclusions

Based on the more physiological representation of indocyanine green kinetics and greater consistency with previously reported plasma volume values, the new back-extrapolation method is proposed for use when estimating plasma volume using the indocyanine green dilution method.

     

Microwave sensing of physiological movement and volume change: a review.

The ability non-invasively to detect and monitor the movement of tissues and organs from outside the body provides many worthwhile areas of potential biomedical applications. Several non-invasive microwave techniques for contact and remote sensing of circulatory and respiratory movements and volume changes have been developed. In general, these systems consist of a microwave generator, a sampling device, a transmitting-receiving antenna, a set of signal-conditioning and processing devices, and a display unit. They operate at continuous-wave frequencies between 1 and 35 GHz and make use of amplitude and phase information derived from the received signal. The average power density of energy radiated by present systems ranges from approximately 0.001-1.0 mW/cm2. These systems are capable of registering instantaneous changes in fluid volume, pressure pulse, heart rate, and respiration rate in contact with body surface or at distances greater than 30 m, or behind thick layers of non-conductive walls.     

Human respiratory muscle blood flow measured by near-infrared spectroscopy and indocyanine green.

Measurement of respiratory muscle blood flow (RMBF) in humans has important implications for understanding patterns of blood flow distribution during exercise in healthy individuals and those with chronic disease. Previous studies examining RMBF in humans have required invasive methods on anesthetized subjects. To assess RMBF in awake subjects, we applied an indicator-dilution method using near-infrared spectroscopy (NIRS) and the light-absorbing tracer indocyanine green dye (ICG). NIRS optodes were placed on the left seventh intercostal space at the apposition of the costal diaphragm and on an inactive control muscle (vastus lateralis). The primary respiratory muscles within view of the NIRS optodes include the internal and external intercostals. Intravenous bolus injection of ICG allowed for cardiac output (by the conventional dye-dilution method with arterial sampling), RMBF, and vastus lateralis blood flow to be quantified simultaneously. Esophageal and gastric pressures were also measured to calculate the work of breathing and transdiaphragmatic pressure. Measurements were obtained in five conscious humans during both resting breathing and three separate 5-min bouts of constant isocapnic hyperpnea at 27.1 +/- 3.2, 56.0 +/- 6.1, and 75.9 +/- 5.7% of maximum minute ventilation as determined on a previous maximal exercise test. RMBF progressively increased (9.9 +/- 0.6, 14.8 +/- 2.7, 29.9 +/- 5.8, and 50.1 +/- 12.5 ml 100 ml(-1) min(-1), respectively) with increasing levels of ventilation while blood flow to the inactive control muscle remained constant (10.4 +/- 1.4, 8.7 +/- 0.7, 12.9 +/- 1.7, and 12.2 +/- 1.8 ml 100 ml(-1) min(-1), respectively). As ventilation rose, RMBF was closely and significantly correlated with 1) cardiac output (r = 0.994, P = 0.006), 2) the work of breathing (r = 0.995, P = 0.005), and 3) transdiaphragmatic pressure (r = 0.998, P = 0.002). These data suggest that the NIRS-ICG technique provides a feasible and sensitive index of RMBF at different levels of ventilation in humans.     

Intradermal indocyanine green for in vivo fluorescence laser scanning microscopy of human skin: a pilot study

Background

In clinical diagnostics, as well as in routine dermatology, the increased need for non-invasive diagnosis is currently satisfied by reflectance laser scanning microscopy. However, this technique has some limitations as it relies solely on differences in the reflection properties of epidermal and dermal structures. To date, the superior method of fluorescence laser scanning microscopy is not generally applied in dermatology and predominantly restricted to fluorescein as fluorescent tracer, which has a number of limitations. Therefore, we searched for an alternative fluorophore matching a novel skin imaging device to advance this promising diagnostic approach.

Methodology/Principal Findings

Using a Vivascope®-1500 Multilaser microscope, we found that the fluorophore Indocyanine-Green (ICG) is well suited as a fluorescent marker for skin imaging in vivo after intradermal injection. ICG is one of few fluorescent dyes approved for use in humans. Its fluorescence properties are compatible with the application of a near-infrared laser, which penetrates deeper into the tissue than the standard 488 nm laser for fluorescein. ICG-fluorescence turned out to be much more stable than fluorescein in vivo, persisting for more than 48 hours without significant photobleaching whereas fluorescein fades within 2 hours. The well-defined intercellular staining pattern of ICG allows automated cell-recognition algorithms, which we accomplished with the free software CellProfiler, providing the possibility of quantitative high-content imaging. Furthermore, we demonstrate the superiority of ICG-based fluorescence microscopy for selected skin pathologies, including dermal nevi, irritant contact dermatitis and necrotic skin.

Conclusions/Significance

Our results introduce a novel in vivo skin imaging technique using ICG, which delivers a stable intercellular fluorescence signal ideal for morphological assessment down to sub-cellular detail. The application of ICG in combination with the near infrared laser opens new ways for minimal-invasive diagnosis and monitoring of skin disorders.     

Lamarckism and epigenetic inheritance: a clarification

Since the 1990s, the terms “Lamarckism” and “Lamarckian” have seen a significant resurgence in biological publications. The discovery of new molecular mechanisms (DNA methylation, histone modifications, RNA interference, etc.) have been interpreted as evidence supporting the reality and efficiency of the inheritance of acquired characters, and thus the revival of Lamarckism. The present paper aims at giving a critical evaluation of such interpretations. I argue that two types of arguments allow to draw a clear distinction between the genuine Lamarckian concept of inheritance of acquired characters and transgenerational epigenetic inheritance. The first concerns the explanandum of the processes under consideration: molecular mechanisms of transgenerational epigenetic inheritance are understood as evolved products of natural selection. This means that the kind of inheritance of acquired characters they might be responsible for is an obligatory emergent feature of evolution, whereas traditional Lamarckisms conceived the inheritance of acquired characters as a property inherent in living matter itself. The second argument concerns the explanans of the inheritance of acquired characters: in light of current knowledge, epigenetic mechanisms are not able to drive adaptive evolution by themselves. Emergent Lamarckian phenomena would be possible if and only if individual epigenetic variation allowed the inheritance of acquired characters to be a factor of unlimited change. This implies specific requirements for epigenetic variation, which I explicitly define and expand upon. I then show that given current knowledge, these requirements are not empirically grounded.     

Synthesis and characterization of bovine serum albumin-coated nanocapsules loaded with indocyanine green as potential multifunctional nanoconstructs

We have synthesized and characterized bovine serum albumin (BSA)-coated polymeric nanocapsules (NCs) loaded with indocyanine green (ICG), an FDA-approved near infrared chromophore. Poly(allylamine) hydrochloride was electrostatically crosslinked with phosphate anions to form nanoconstructs encapsulating ICG. BSA was conjugated onto the polymeric NCs via glutaraldehyde. BSA-coated ICG-containing nanocapsules (BSA-ICG NCs) were characterized by FTIR and optical spectroscopy, SEM, and zeta-potential measurements. Using normal human endocervical epithelial cells, we demonstrate the effectiveness of BSA-ICG NCs for intracellular optical imaging in vitro. These nanoconstructs may potentially serve as a multifunctional platform for combined optical imaging, phototherapy, and drug delivery.