Noninvasive estimation of human tissue respiration with wavelet-analysis of oxygen saturation and blood flow oscillations in skin microvessels

Laser Doppler flowmetry, laser spectrophotometry of oxygen saturation, and the fluorescence determination of the NADH/FAD ratio were carried out in 30 subjects in the upper limb skin zones with and without arteriolovenular anastomoses (AVAs). It was demonstrated that the wavelet-analysis of oxygen saturation and blood flow oscillations in microvessels was an efficient approach to noninvasive estimation of the skin oxygen extraction (OE) and oxygen consumption (OC) rates. OE = (SaO₂ ? SvO₂)/SaO₂, where SaO₂ (%) and SvO₂ (%) are the oxygen saturations of arterial and venular blood, respectively. If the cardiac (A_c, perfusion units, p.u.) to respiratory rhythm amplitude (A_r, p.u.) ratio A_c/A_r ?? 1, SvO₂ = SO₂. If A_c/A_r > 1, SvO₂ = SO₂/(A_c/A_r). OC = M _nutr (SaO₂ ?? SvO₂) in p.u. · %O₂, where M _nutr is the nutritive blood flow value in p.u. M _nutr = M/SI, where SI is the shunting index of blood flow in microvessels. The perfusion, OE, and OC values were higher in the skin with AVAs than in the skin without AVAs. The perfusion and oxygen saturation values were more variable in the skin with AVAs. The oxygen diffusing from the tiniest arterioles and capillaries is the most important for tissue metabolism. The contribution of the total perfusion and the oxygen diffusion from arterioles to tissue metabolism increased under the tissue ischemia conditions.     

Evaluation of the parameters of total,nutritive, and shunt blood flows in the skin microvasculature using laser Doppler flowmetry

Examination of 28 healthy subjects and 66 patients was performed using laser Doppler flowmetry (LDF) of the skin of fingers in the red and infrared ranges and wavelet analysis of microvascular blood flow oscillations. Formulas were suggested for the total (TF), nutritive (NF), and shunt (SF) local blood flows. TF = MI × A_c × A_n /(P_m × ), where MI is the microcirculation index in perfusion units (PU), A_n and A_c are the averaged maximum amplitudes of the neurogenic and cardiac rhythms (in PU), P_m is the mean arterial pressure (in mm Hg), and is the mean square deviation of the amplitude of blood flow oscillations (in PU). NF = TF/SP, where SP is the shunting parameter. SP = A_n/A_m, where A_m is the averaged maximum amplitude of the myogenic rhythm (in PU). SF = TF - NF. Significant positive relationships between the skin oxygenation and NF (red), temperature and TF (red), and blood flow measured by hydrogen clearance and TF (infrared) were revealed by comparison of the LDF parameters with polarographic and thermographic data. The advantages of the LDF parameters compared with the MI were shown, especially in skin denervation syndromes. The TF decreased in the case of complete anatomic rupture of the median nerve and increased in reflex sympathetic dystrophy, with both cases being accompanied by a deficit of the NF (red).Translated from Fiziologiya Cheloveka, Vol. 31, No. 1, 2005, pp. 114–119.Original Russian Text Copyright © 2005 by Krupatkin.     

Dynamic oscillatory circuit of regulation of capillary hemodynamics

We used laser Doppler flowmetry with wavelet analysis of blood flow oscillations, computer capillaroscopy, and thermometry of the nail bed in 30 subjects to show an important role of the oscillatory circuit in the regulation of capillary hemodynamics, number of functioning capillaries, and linear and volumetric velocity of blood flow. The number of functioning capillaries is regulated by oscillations of myogenic and sensory peptidergic origin. The appearance of sensory oscillations, especially high-amplitude oscillations, is an adaptive neurotrophic mechanism that significantly increases the number of functioning capillaries and intensity of blood flow from arterioles to capillaries. The linear velocity of blood flow depends on both the tone of microvessels and changes in the dynamic component of blood pressure. Under conditions of skin hypoperfusion, the mean linear velocity of capillary blood flow may be inversely related to the extracapillary perfusion, including the amplitude of heart rate (A _h) and oscillations of the tone of precapillary sphincters, whereas under conditions of vasodilation and increased skin perfusion, it may be inversely related to the amplitude of arteriolar oscillations of endothelial or neurogenic sympathetic origin (A _maxe + n) and the shunting index. The A _h affects the linear velocity of blood flow in the arterial part of capillaries, whereas the A _maxe + n influences the same factor in the venous part. The contribution of oscillations to the regulation of the linear velocity varies depending on the perfusion and skin temperature. The resultant tone of distributing microvessels is determined by the competition between the stationary and oscillatory components. In addition to changes in the amplitude, the frequency of vasomotions may also be important. The regulatory importance of the oscillatory circuit is increased with a decrease in the skin blood flow.     

Hypoxia and Exercise Increase the Transpulmonary Passage of 99mTc-Labeled Albumin Particles in Humans

Intrapulmonary arteriovenous anastomoses (IPAVs) are large diameter connections that allow blood to bypass the lung capillaries and may provide a route for right-to-left embolus transmission. These anastomoses are recruited by exercise and catecholamines and hypoxia. Yet, whether IPAVs are recruited via direct, oxygen sensitive regulatory mechanisms or indirect effects secondary to redistribution pulmonary blood flow is unknown. Here, we hypothesized that the addition of exercise to hypoxic gas breathing, which increases cardiac output, would augment IPAVs recruitment in healthy humans. To test this hypothesis, we measured the transpulmonary passage of ^99mTc-macroaggregated albumin particles (^99mTc-MAA) in seven healthy volunteers, at rest and with exercise at 85% of volitional max, with normoxic (FIO₂ = 0.21) and hypoxic (FIO₂ = 0.10) gas breathing. We found increased ^99mTc-MAA passage in both exercise conditions and resting hypoxia. However, contrary to our hypothesis, we found the greatest ^99mTc-MAA passage with resting hypoxia. As an additional, secondary endpoint, we also noted that the transpulmonary passage of ^99mTc-MAA was well-correlated with the alveolar-arterial oxygen difference (A-aDO₂) during exercise. While increased cardiac output has been proposed as an important modulator of IPAVs recruitment, we provide evidence that the modulation of blood flow through these pathways is more complex and that increasing cardiac output does not necessarily increase IPAVs recruitment. As we discuss, our data suggest that the resistance downstream of IPAVs is an important determinant of their perfusion.     

Phase synchronization of skin blood flow oscillations in humans under asymmetric local heating

The hypothesis is proposed that an external local stimulus may cause a change in the phase relationships of oscillations in the peripheral skin blood flow of contralateral extremities. To test this assumption, the wavelet phase coherence of skin blood flow oscillations of the left and right forearms of 18 healthy volunteers of both sexes at rest and in response to unilateral local heating was investigated. An area of the skin of the left forearm was exposed to heat and the native blood perfusion in an area of the skin of the right forearm was recorded simultaneously. It was shown that an asymmetric local change of skin perfusion led to a significant change in the phase relationships of the blood flow oscillations in all the analyzed frequency ranges. A significant reduction of phase synchronization of oscillations of skin blood flow in the range of endothelial, neurogenic, and myogenic activity, as well as in the range of respiratory rhythm was revealed. In contrast, in the range of the cardiac rhythm, a significant increase in phase synchronization of the oscillations of the blood flow of contralateral skin areas of the forearm was detected.     

The Kinetics of Distribution of the Fat-Soluble Inert Gas Cyclopropane in the Body

A kinetic analysis is made of the experimentally measured time course of respiratory uptake of the highly fat-soluble, inert gas cyclopropane by normal human subjects. The analysis is based on the well-known perfusion-limited model in which a number of body compartments are arranged in parallel with the lungs via the circulating blood. Three distinct body compartments are derived from the data. These are tentatively identified as: (a) adipose tissue (b) fat-poor tissue of low perfusion such as resting muscle, skin, and connective tissue (c) fat-poor tissue of high perfusion such as brain, heart, gut, liver, and kidney. Blood flow rates to the several compartments are also derived from the data. The rates to compartments (a) and (b) are each approximately 10 per cent of the estimated total cardiac output. The derived perfusion (blood flow rate/compartment weight) of the three compartments are in the range, respectively, (a) 2 to 4, (b) 1 to 2.5, (c) 25 to 75 ml/min/100 gm. Uncertainties arising from the experimental data and from simplifications of the model (neglect of lung fill-up phase of uptake and gross diffusion of cyclopropane from one tissue into another) are discussed. The present type of uptake experiment is significant for the problems of total body fat determination, of gross body composition in relation to weight change, of gross shunting of blood flow from one compartment to another, of anesthesia by fat-soluble substances, and of decompression sickness.     

Cardiovascular responses to thoracic skin cooling: comparison of incubating and non-incubating Bantam hens

Summary Body temperatures, metabolic rate, haemostatic parameters, and cardiovascular reactions to thoracic skin cooling were compared between incubating (broody) and non-broody Bantam hens. Under resting conditions, without thoracic skin cooling, cardiac output of broody hens was twice that of non-broody hens. However, their metabolic rate was increased by only one-third over that of non-broody hens, and the arteriovenous difference in oxygen concentration was smaller for broody birds. This indicates a higher rate of non-nutrient blood flow during incubation. A higher thoracic skin temperature (T _ths) for broody hens compared to non-broody hens suggests that brood patches are the probable site of this increased flow through arteriovenous anastomoses (AVAs). Thoracic skin cooling increased metabolic rate and significantly more in broody hens, but did not increase AVA blood flow. The relation between metabolic rate and total peripheral resistance indicated more intense vasodilation for broody hens at the relatively low metabolic rates during moderate cooling, and more intense vasoconstriction for the broody hens at the high metabolic rates during stronger cooling. This corresponds to T _ths measurements indicating dilation of brood patch AVAs with moderate cooling and AVA constriction with severe cooling. During moderate cooling, vasoconstriction in the feet and wattles of broody hens (but not of non-broody hens) freen non-nutrient blood flow for redistribution to the brood patches. Thus, the cardiovascular system of the hen seems to adjust to the special demands of incubation by a permanent increase of AVA flow in the brood patch, and by an additional capacity for brood patch vasodilation induced by cold stimuli in the range from 35 to 25°C. This corresponds well to the temperature range for development of galliform embryos.Abbreviations AVAs arteriovenous anastomoses - BP arterial blood pressure - CaO₂ and CvO₂ arterial and venous oxygen concentrations, respectively - HR heart rate - MAP mean arterial blood pressure - cardiac output - SV stroke volume - T _bs back skin temperature - T _c cofon temperature - T _f foot temperature - T _ths thoracic skin temperature - TPR total peripheral resistance - T _w wattle temperature - oxygen consumption     

Inspiratory and expiratory muscle perfusion in maximally exercised ponies

The present study was carried out on seven healthy ponies to examine the extent of blood flow in various inspiratory and expiratory muscles at rest and during maximal exertion as well as to determine the proportion of cardiac output needed to perfuse respiratory muscles during these conditions. Tissue blood flow was studied with 15 micron-diameter radionuclide-labeled microspheres injected into the left ventricle during steady conditions. The inspiratory and expiratory muscles comprised 2.41 and 3.05% of body weight, respectively, and received 6.17 and 3.75% of the cardiac output at rest. With maximal exercise, heart rate (from 55 +/- 3 to 218 +/- 4 beats/min), mean aortic pressure (from 125 +/- 5 to 170 +/- 6 mmHg), and cardiac output (from 96 +/- 11 to 730 +/- 78 ml.min-1.kg-1) increased markedly. During exercise blood flow increased significantly in all respiratory muscles (P less than 0.0001) as vascular resistance decreased precipitously. Marked heterogeneity of perfusion existed among various inspiratory as well as expiratory muscles during exercise. Among the inspiratory muscles, the highest perfusion occurred in the diaphragm followed by serratus ventralis, and among the expiratory muscles, the highest perfusion occurred in the internal oblique abdominis and the transverse thoracis (triangularis sterni). Collectively, the inspiratory (8.44%) and expiratory (6.35%) muscle blood flow comprised 14.8 +/- 1.2% of the cardiac output during maximal exercise, a significant increase above resting value, whereas renal fraction of cardiac output decreased from 21% (at rest) to 0.72%.     

Blood flow oscillations at a frequency of about 0.1 Hz in skin microvessels do not reflect the sympathetic regulation of their tone

Wavelet analysis of blood flow oscillations recorded with laser Doppler flowmetry in finger glabrous skin microvessels was carried out in 82 subjects with different variations in the syndromes of hand and foot sympathectomy and denervation. As distinct from the 0.02–0.046-Hz (about 0.03–0.04 Hz) blood flow oscillations in skin microvessels of sympathetic thermoregulatory origin, no relationship was found between the presence of 0.07–0.015 Hz (about 0.1 Hz) vasomotions in the wavelet spectrum and intactness of sympathetic innervation in the tissue region. The use of the myogenic band oscillation parameters, in particular, the amplitudes of vasomotions, for assessing the state of sympathetic thermoregulatory innervation determining the neurogenic tone of skin microvessels is not physiologically correct. The influence of local environmental factors on the vasomotion parameters confirms their local origin. The local perfusion pressure value significantly influenced the amplitude but not the frequency of vasomotions. The amplitude dominance of vasomotions was observed upon a decrease in perfusion pressure, whereas a marked increase in perfusion pressure or venous congestion resulted in a sharp depression of their amplitudes. Under the sympathectomy conditions, the oscillatory dynamic component of the arteriolar myogenic tone in the glabrous skin of the extremity acral zones is involved in the blood flow’s autoregulation. The presence of fine sensory fibers is necessary to carry out the dynamic autoregulation of the blood flow. Sensory nonmyelinated fibers and the trophic neuropeptides secreted by them not only initiate independent oscillations in the low-frequency (0.047–0.069 Hz) myogenic band, but also contribute to the normalized amplitudes of vasomotions being increased. At the same time, no appreciable influence of the sympathetic vasomotor activity and the corresponding influence of catecholamines on the amplitude and frequency of vasomotions was observed.     

Effect of furosemide on pulmonary blood flow distribution in resting and exercising horses.

We determined the spatial distribution of pulmonary blood flow (PBF) with 15-micron fluorescent-labeled microspheres during rest and exercise in five Thoroughbred horses before and 4 h after furosemide administration (0.5 mg/kg iv). The primary finding of this study was that PBF redistribution occurred from rest to exercise, both with and without furosemide. However, there was less blood flow to the dorsal portion of the lung during exercise postfurosemide compared with prefurosemide. Furosemide did alter the resting perfusion distribution by increasing the flow to the ventral regions of the lung; however, that increase in flow was abated with exercise. Other findings included 1) unchanged gas exchange and cardiac output during rest and exercise after vs. before furosemide, 2) a decrease in pulmonary arterial pressure after furosemide, 3) an increase in the slope of the relationship of PBF vs. vertical height up the lung during exercise, both with and without furosemide, and 4) a decrease in blood flow to the dorsal region of the lung at rest after furosemide. Pulmonary perfusion variability within the lung may be a function of the anatomy of the pulmonary vessels that results in a predominantly fixed spatial pattern of flow distribution.     

Effect of circulatory congestion on the components of pulmonary diffusing capacity in morbid obesity

Objective: Obese patients without clinically apparent heart disease may have a high output state and elevated total and central blood volumes. Central circulatory congestion should result in elevated pulmonary diffusing capacity (D_LCO) and capillary blood volume (V_c) reflecting pulmonary capillary recruitment; however, the effect on membrane diffusion (D_m) is uncertain. We examined D_LCO and its partition into V_c and D_m in 13 severely obese subjects (BMI = 51 ± 14 kg/m²) without manifest cardiopulmonary disease before and after surgically induced weight loss. Research Methods and Procedures: D_LCO and its partition into V_c and D_m [referenced to alveolar volume (V_A)] as described by Roughton and Forster, total body water by tritiated water, and fat distribution by waist‐to‐hip ratio were performed. Results: Despite normal D_LCO (mean 98 ± 16% predicted), V_c/V_A was increased (mean 118 ± 30% predicted), and D_m/V_A was reduced (mean 77 ± 34% predicted). Nine of 13 subjects were restudied after weight loss (mean 52 ± 43 kg); V_c/V_A decreased to 89 ± 18% predicted (p = 0.01), and D_m/V_A increased to 139 ± 30% predicted (p < 0.01). Increasing total body water was associated with both increasing V_c (r = 0.74, p = 0.01) and increasing waist‐to‐hip ratio (r = 0.65, p = 0.02), indicating that circulatory congestion increases with increasing central obesity. Discussion: Severely obese subjects without manifest cardiopulmonary disease may have increased V_c indicating central circulatory congestion and reduced D_m suggesting associated alveolar capillary leak, despite normal D_LCO. Reversibility with weight loss is in accord with reversibility of the hemodynamic abnormalities of obesity.     

Nasal mucosal vasodilatation in response to passive hyperthermia in humans

The present study was conducted to measure nasal mucosal blood flow (NMBF) during body warming. Five subjects [mean (SD) 24 (2) years], wearing only shorts and a thick felt hat with ear flaps, were immersed to the neck in a bath at 40 (0.5)°C. Tympanic (T _ty), esophageal (T _es), mean unweighted skin (T _sk), nose skin and ear pinna skin were recorded at 1-min intervals. NMBF on the lower septal wall was estimated using a laser Doppler flow meter. At rest T _ty and T _es were both 36.5°C. T _ty dropped significantly below T _es during body warming, despite impeded heat loss from the head due to the felt hat. T _ty increased to 37.3°C and T _es increased to 37.5°C during the immersion. During the immersion all skin temperatures were steady or increasing, ruling out the possibility of a contamination of T _ty from (T _sk), Body warming significantly (P = 0.001) increased NMBF by approximately three times from resting values at the end of immersion. During the period of increasing core temperatures NMBF was significantly correlated to T _ty (r = 0.93, P = 0.0001) and T _es (r = 0.97, P = 0.0001), suggesting the blood flow change in this tissue was a thermo-regulatory response. The increased NMBF during hyperthermia supports the hypothesis of respiratory cooling involvement in selective brain cooling of humans.     

Estimation of the microcirculation state in cerebrovascular disorders using laser doppler flowmetry data and hemorheological parameters

The microcirculation state was assessed in the group of patients with ischemic stroke (n = 30) and the control group of healthy individuals (n = 27) using laser Doppler flowmetry and the wavelet analysis of the amplitude-frequency range of microvascular blood flow oscillations combined with absorption spectroscopy. The hemorheological parameters (blood and plasma viscosity, the degree of red blood cell aggregability and deformability) were assessed in both groups, as were their correlations with the microcirculation parameters. Decreased tissue perfusion (by 25%) and specific oxygen consumption (by 21%) were revealed in a cerebrovascular accident. Changes in the tone-forming regulatory mechanisms of microcirculation of vasodilating nature (decreased microvascular tone, activation of the secretory function of endothelium) may be regarded as a compensatory reaction aimed at maintaining the blood supply of organs and tissues in stroke. The blood viscosity increase in patients due to the plasma viscosity increase and increased red blood cell aggregability and their decreased deformability cause the blood flow to slow down and the wall shear stress to increase, which activates the endothelial secretory function and vasodilation of microvessels. Correlation between the rheological parameters and the passive (respiratory and cardiac) rhythm amplitudes was observed in the control group. In patients, the hemorheological parameters were correlated with the characteristics of the active factors of microvascular blood flow modulation (endothelial, neurogenic, and myogenic), which confirms the role of changed blood properties and regulatory tone-forming mechanisms in the maintenance of tissue perfusion in cerbrovascular accidents.     

Vascular resistance and vasoactivity of gills and pulmonary artery of the salamander,Ambystoma tigrinum

Summary In order to understand the blood flow patterns and their regulation in the gills and pulmonary artery ofAmbystoma tigrinum, the vascular resistance and vasoactivity of the two major branchial perfusion pathways and a vascular plexus in the pulmonary artery were investigated using an isolated-tissue perfusion method. Acetylcholine and epinephrine were both pressor agents in all three vascular segments. Angiotensin II also constricted the branchial respiratory vasculature. Norephinephrine was primarily a vasodilator in the branchial respiratory vasculature, however, it had no effect on the shunt vessels of the gill or the pulmonary arterial plexus. Both gill circulations were insensitive to alterations in CO₂ and pH. Anoxia produced a slight vasodilation of the branchial respiratory vessels but had no effect on the shunt vasculature. Mild hypoxia had no effect on either branchial circulations. The results suggest that: (1) blood flow through the respiratory section of the gill may vary between 8 and 47% of total gill flow, (2) the major perfusion pathway to the lung is probably from the efferent artery of the third gill through the ductus arteriosus and then into the pulmonary artery, (3) O₂, CO₂ and pH exert no local control of branchial perfusion, (4) both cholinergic and adrenergic regulation of branchial and proximal pulmonary arterial vascular resistance is possible, (5) a rise in circulating norepinephrine should increase blood flow to the respiratory section of the gill.Abbreviations AII angiotensin II - ACh acetylcholine - EPi epinephrine - NE norepinephrine     

Baroreflex participation in redistribution of cardiac output at onset of exercise

The distribution of cardiac output and systemic vascular conductance was measured in five rabbits. Cardiac output was measured by ascending aortic flowmetry and was partitioned according to the distribution of 15-micron radiolabeled microspheres injected into the left atrium. The rabbits were studied under four conditions: at rest and after 20 s of treadmill exercise, both before and approximately 5 min after acute barodenervation of the conscious animal. During exercise in the baroinnervated state, approximately 40% of the increased blood flow to skeletal and cardiac muscle was contributed by diversion from the splanchnic organs, kidneys, systemic arteriovenous anastomoses, and skin. This diversion of blood flow during exercise was absent after arterial barodenervation. We conclude that at the onset of exercise in rabbits the mismatch between cardiac output and the metabolic demands of skeletal and cardiac muscle is accommodated by vasoconstriction in other vascular beds. We suggest that the vasoconstriction in the splanchnic organs and skin may be caused by transient suppression of the reflex effects of arterial baroreceptor input at the onset of exercise.     

Hemodynamic responses to heat stress in the resting and exercising human leg: insight into the effect of temperature on skeletal muscle blood flow

Heat stress increases limb blood flow and cardiac output (Q) in humans, presumably in sole response to an augmented thermoregulatory demand of the skin circulation. Here we tested the hypothesis that local hyperthermia also increases skeletal muscle blood flow at rest and during exercise. Hemodynamics, blood and tissue oxygenation, and muscle, skin, and core temperatures were measured at rest and during exercise in 11 males across four conditions of progressive whole body heat stress and at rest during isolated leg heat stress. During whole body heat stress, leg blood flow (LBF), Q, and leg (LVC) and systemic vascular conductance increased gradually with elevations in muscle temperature both at rest and during exercise (r(2) = 0.86-0.99; P < 0.05). Enhanced LBF and LVC were accompanied by reductions in leg arteriovenous oxygen (a-vO(2)) difference and increases in deep femoral venous O(2) content and quadriceps tissue oxygenation, reflecting elevations in muscle and skin perfusion. The increase in LVC occurred despite an augmented plasma norepinephrine (P < 0.05) and was associated with elevations in muscle temperature (r(2) = 0.85; P = 0.001) and arterial plasma ATP (r(2) = 0.87; P < 0.001). Isolated leg heat stress accounted for one-half of the increase in LBF with severe whole body heat stress. Our findings suggest that local hyperthermia also induces vasodilatation of the skeletal muscle microvasculature, thereby contributing to heat stress and exercise hyperemia. The increased limb muscle vasodilatation in these conditions of elevated muscle sympathetic vasoconstrictor activity is closely related to the rise in arterial plasma ATP and local tissue temperature.     

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.     

Innervation and neurokinin receptors during angiogenesis in the rat sponge granuloma

Summary Angiogenesis is an essential component of wound healing and inflammation. In the rat subcutaneous sponge implantation model, angiogenesis can be enhanced by administration of the sensory neuropeptide, substance P. We have used quantitativein vitro receptor autoradiography and immunohistochemistry to investigate the development of endogenous neurovascular regulatory systems in the newly-formed granulation tissue of this model. The fraction of endothelial cells immunoreactive for proliferating cell nuclear antigen, endothelial fractional area, and¹³³Xe clearance were used as measures of endothelial proliferation, neovascularization, and blood flow, respectively. Endothelial proliferation occurred predominantly in tissues surrounding the sponge, and peaked before neovascularization of sponge stroma and the establishment of sponge blood flow. Substance P-containing sensory nerves and specific, high affinity substance P binding sites with characteristics of neurokinin receptors of the NK₁ subclass, were localized to microvessels surrounding the sponge at all time points. Lower density substance P binding sites were localized to newly formed microvessels within the sponge stroma, progressively increasing in density from day 4 to day 14. Nerve fibres were observed in the stroma of only 2 of 6 sponges at day 14, and none at earlier time points. These data support the hypothesis that substance P-enhanced angiogenesis in this model results from a direct action on microvascular NK₁ receptors. Neovascularization is a sequential process, with early endothelial proliferation followed by new vessel formation and increased blood flow, with maturation of endogenous neurovascular regulatory systems occurring late in this process in inflamed tissues.     

Endothelial dysfunction in aged humans is related with oxidative stress and vascular inflammation

Vascular endothelial dysfunction occurs during the human aging process, and it is considered as a crucial event in the development of many vasculopathies. We investigated the underlying mechanisms of this process, particularly those related with oxidative stress and inflammation, in the vasculature of subjects aged 18–91 years without cardiovascular disease or risk factors. In isolated mesenteric microvessels from these subjects, an age‐dependent impairment of the endothelium‐dependent relaxations to bradykinin was observed. Similar results were observed by plethysmography in the forearm blood flow in response to acetylcholine. In microvessels from subjects aged less than 60 years, most of the bradykinin‐induced relaxation was due to nitric oxide release while the rest was sensitive to cyclooxygenase (COX) blockade. In microvessels from subjects older than 60 years, this COX‐derived vasodilatation was lost but a COX‐derived vasoconstriction occurred. Evidence for age‐related vascular oxidant and inflammatory environment was observed, which could be related to the development of endothelial dysfunction. Indeed, aged microvessels showed superoxide anions (O₂^?) and peroxynitrite (ONOO^?) formation, enhancement of NADPH oxidase and inducible NO synthase expression. Pharmacological interference of COX, thromboxane A₂/prostaglandin H₂ receptor, O₂^?, ONOO^?, inducible NO synthase, and NADPH oxidase improved the age‐related endothelial dysfunction. In situ vascular nuclear factor‐κB activation was enhanced with age, which correlated with endothelial dysfunction. We conclude that the age‐dependent endothelial dysfunction in human vessels is due to the combined effect of oxidative stress and vascular wall inflammation.     

Troglitazone‐Induced Changes in Adiponectin Do Not Affect Endothelial Function in Diabetes

Objective: Adiponectin has been proposed to be related to endothelial function. We have examined the relationship between the increase in adiponectin levels that is associated with troglitazone treatment and endothelium‐dependent vasodilation in type 2 diabetic patients. Research Methods and Procedures: Seventy‐two patients participated in this randomized, placebo‐controlled, double‐blinded study. High‐resolution ultrasound images were used to measure the flow‐mediated dilation (endothelium‐dependent) and nitroglycerin‐induced dilation (endothelium‐independent) of the brachial artery. Laser Doppler perfusion imaging was employed to measure the vascular reactivity in the forearm skin. Results: Troglitazone treatment resulted in an average 75% increase in the adiponectin levels, but no changes were observed in the endothelium‐dependent vasodilation, any other measurement of vascular reactivity, or any other markers of endothelial activation. Also, no changes were observed in the expression of the receptor for advanced glycation end‐products in skin biopsies taken from the forearm. Significant correlations were observed during troglitazone treatment between the changes in the adiponectin levels and the changes in fasting plasma glucose (r = ?0.29, p < 0.05), hemoglobin A_1c (r = ?0.30, p < 0.05), total cholesterol (r = 0.25, p < 0.05), and low‐density lipoprotein‐cholesterol (r = 0.34, p < 0.01). Discussion: The increase in adiponectin levels after troglitazone treatment is not associated with an improvement in the endothelium‐dependent vasodilation, indicating that adiponectin is not a major determinant of endothelial function. In addition, receptor for advanced glycation end‐products expression in the skin microcirculation is not affected by troglitazone treatment.