Oscillatory processes in lymph microcirculation in the human skin

This study was the first to use laser Doppler flowmetry followed by wavelet analysis in order to estimate oscillations in lymph microcirculation in 30 subjects with (n = 13) or without (n = 17) edema of the distal part of the upper limb. Lymph flow in the human skin exhibited clear dominance of pacemaker phase oscillations in the frequency ranges of 0.021–0.042 and 0.016–0.035 Hz in the skin of the palm surface of the finger nail bone and in the skin of the forearm, respectively. Edema was associated with an increase in the peak frequencies and normalized maximum amplitudes (Al/Ml, where Al is the mean value of the maximum amplitude of phase oscillations, and Ml is the value of the averaged lymph flow expressed in perfusion units). Low-amplitude oscillations were recorded rarer in the myogenic, endothelial, and respiratory ranges. We did not find any cardiac pulse rhythm in the wavelet spectrum of the lymph flow. We did not find any interaction between the Al/Ml value and the skin temperature. In the group of subjects without edema, under physiological conditions only, we found a negative correlation between the Al/Ml value and the amplitudes of myogenous proper blood flow oscillations, which reflected the number of functional capillaries and activity of oxidative metabolism in the tissue. In the group with edema, we did not find any correlations between the indices of lymph flow and blood flow. The values of normalized amplitude and frequency of phase oscillations may be used as efficient diagnostic tools in the studies on lymph microcirculation.     

Oxygenation and microcirculation during skin stretching in undermined and nonundermined skin

The aim of this experimental study was to assess the skin microcirculation of undermined and nonundermined wound edges closed with a skin-stretching device. In eight piglets, 9 x 9-cm wounds were created on both flanks by excision of the skin and the subcutaneous layer down to the muscular fascia, with general anesthesia. On one flank, the surrounding skin was completely undermined. For a period of 30 minutes, wound closure was performed with a stretching device, using the principle of load cycling. The device stretched the skin and moved the opposing wound edges toward each other. During this period, laser Doppler flowmetry and transcutaneous oximetry were simultaneously used to monitor microcirculation and oxygenation in the stretched skin of both flanks. Undermining of the surrounding skin produced a 12 percent decrease in the laser Doppler flowmetry signal and a 21 percent decrease in the transcutaneous oximetry value. Skin stretching resulted in decreases in the laser Doppler flowmetry signals and the transcutaneous oximetry values, whether or not the skin was undermined. Releasing the stretching device resulted in rapid normalization of the laser Doppler flowmetry values in undermined and nonundermined skin and a slow return of the transcutaneous oximetry values to close to baseline levels in nonundermined skin. The transcutaneous oximetry values in undermined skin did not return to baseline levels; each period of skin stretching resulted in an additional decrease in the transcutaneous oximetry values. Stretching of undermined skin for 30 minutes produced a significant (p < 0.0001) decrease in skin oxygenation. As a result, 50 percent of the undermined stretched skin demonstrated skin necrosis at the wound edges, which was still present after 1 week. Wound healing in the nonundermined stretched skin proceeded without problems. It is concluded from these experiments that the viability of undermined skin becomes compromised as a result of significantly decreased oxygen availability in the skin during and after stretching. Consequently, it is recommended that skin stretching be performed on nonundermined skin, rather than undermined skin. In addition, when skin is stretched to close a large defect, it is logical to use cyclic loading, so that recuperation of the skin circulation can occur. Furthermore, laser Doppler flowmetry seemed to produce atypical signals in monitoring of skin viability of wound edges closed with a skin-stretching device.     

Kinetic measurements of gas exchange in the intact pulmonary microcirculation.

The kinetics of gas exchange are monitored in an isolated perfused lung preparation contained within a plethysmograph. The lungs are perfused with buffer, and there is no gas exchange until a 2.0-ml bolus of reactant is injected into the perfusion system. Subsequent gas exchange produces a pressure transient that is related to the corresponding volume of exchanged gas. The observed rate of volume change is the result of two separate processes: 1) the rate of gas exchange during transit through the capillary bed and 2) the distribution of vascular transit times between the point of injection and the capillary bed. The latter is assessed by a control injection containing a dissolved inert gas that is liberated in the alveoli as the bolus enters the capillary bed. Analysis of the experimental curves permits the separation of these two processes. A model of exchange kinetics indicates that this method has the capability of measuring kinetic events occurring during gas exchange in the microcirculation under physiological conditions.     

PO2 measurements in the microcirculation using phosphorescence quenching microscopy at high magnification

In phosphorescence quenching microscopy (PQM), the multiple excitation of a reference volume produces the integration of oxygen consumption artifacts caused by individual flashes. We analyzed the performance of two types of PQM instruments to explain reported data on Po2 in the microcirculation. The combination of a large excitation area (LEA) and high flash rate produces a large oxygen photoconsumption artifact manifested differently in stationary and flowing fluids. A LEA instrument strongly depresses Po2 in a motionless tissue, but less in flowing blood, creating an apparent transmural Po2 drop in arterioles. The proposed model explains the mechanisms responsible for producing apparent transmural and longitudinal Po2 gradients in arterioles, a Po2 rise in venules, a hypothetical high respiration rate in the arteriolar wall and mesenteric tissue, a low Po2 in lymphatic microvessels, and both low and uniform tissue Po2. This alternative explanation for reported paradoxical results of Po2 distribution in the microcirculation obviates the need to revise the dominant role of capillaries in oxygen transport to tissue. Finding a way to eliminate the photoconsumption artifact is crucial for accurate microscopic oxygen measurements in microvascular networks and tissue. The PQM technique that employs a small excitation area (SEA) together with a low flash rate was specially designed to avoid accumulated oxygen photoconsumption in flowing blood and lymph. The related scanning SEA instrument provides artifact-free Po2 measurements in stationary tissue and motionless fluids. Thus the SEA technique significantly improves the accuracy of microscopic Po2 measurements in the microcirculation using the PQM.     

Non-invasive measurements of skin pigmentation in situ

Objective in situ measurements of skin pigmentation are needed for accurate documentation of pigmentation disorders, in studies of constitutive and induced skin pigmentation, for testing of the efficacy of pro-pigmentation or de-pigmentation agents, etc. Non-invasive instrumental measurements of skin pigmentation have been used for many decades. All are based on the ability of melanin to attenuate light. However, hemoglobin in dermal capillaries also attenuates light and needs to be accounted for when pigmentation is assessed. The methods under consideration include: (a) single point measurements, in which light reflected from a defined skin area is collected and a pigment index is calculated representing the average pigmentation over the examined area, and (b) imaging methods that attempt to generate a concentration distribution map of melanin pigment for the skin area being imaged. In this article, we describe the potentials and the limitations of the different approaches to both single point and imaging methods.     

High-intensity static magnetic fields modulate skin microcirculation and temperature in vivo

We investigated the acute effect of static magnetic fields of up to 8 T on skin blood flow and body temperature in anesthetized rats. These variables were measured prior to, during, and following exposure to a magnetic field in a superconducting magnet with a horizontal bore. The dorsal skin was transversely incised for 1 cm to make a subcutaneous pocket. Probes of a laser Doppler flowmeter and a thermistor were inserted into the pocket and positioned at mid-dorsum to measure skin blood flow and temperature. Another thermistor probe was put into the rectum to monitor rectal temperature. After baseline measurement outside the magnet, the rat was inserted into the bore for 20 min so that mid-dorsum was exactly positioned at the center, where the magnetic field was nearly homogeneous. Post-exposure changes were then recorded for 20 min outside the bore. Sham-exposed animals were submitted to exactly the same conditions, except that the superconducting magnet was not energized. Skin blood flow and temperature decreased significantly during magnetic field exposure and recovered after removal of the animal from the magnet. The rectal temperature showed a tendency to decrease while the animal was in the magnet. The microcirculatory and thermal reactions in the present study were consistent and agreed with some of the predictions based on mathematical simulations and model experiments.     

Recent Glimpses of the Elusive Spindle Matrix

A stationary spindle matrix has been proposed on theoretical grounds to help mediate force production at the mitotic spindle. Direct molecular evidence for the existence of such a matrix has the potential to profoundly influence our view of the molecular mechanisms leading to chromosome segregation during mitosis. Three recent papers suggest that the spindle matrix may be more than a theoretical idea.

Key Words:

Spindle formation, Spindle matrix, Microtubules, Mitosis     

Morphofunctional characteristics of microcirculation in the skin of girls 5-17 years of age

In 261 girls year-to-year morphofunctional transformations of spatial composition of the skin microcirculatory bed have been studied at rest and after a dynamic local load. By means of biomicroscopy main regularities in development of the skin capillary network have been revealed in the nail torus in the postnatal ontogenesis. Formation of the microvessels reactivity during various age periods and maturation of mechanisms of the compensatory-adaptive reactions are connected with formation of the definitive composition of the microcirculatory bed, that in girls corresponds to 11-12 years. Qualitative transformations in the skin capillary network bring certain quantitative changes in the structural microcirculatory parameters--increasing diameter of microvessels and increasing density of functioning capillaries.     

Study of skin microcirculation by epicutaneous diffusion of 133 xenon]

The diffusion of radioactive inert gas xenon 133 through the epidermis in man was studied by compartimental model with a constant speed injection. From this we deduce the cutaneous and subcutaneous flow.