Laser Doppler Technique Research Articles

Laser Doppler techniques for the combined measurement of inlet flow and valve motion in IC engines

A measurement methodology and a test set-up for the experimental investigation of internal combustion engines are presented. This system is based on a laser Doppler anemometer and a laser Doppler vibrometer which measure in a co-ordinated or simultaneous mode both the velocity of the intake flow and the motion of the inlet poppet valve. A synchronized data acquisition procedure allows the use of two optical instruments to analyse the effects of valve jumps and bounces on the inlet flow field. At high rpm, anomalous valve behaviour may appear. Fluid velocity measurements are taken inside the cylinder and the manifold of a motored automotive engine head at different rpm, up to a speed at which anomalous valve behaviour regularly occurs. Velocity data are processed in both time and frequency domains. This measurement system also represents a valuable tool to study resonance phenomena in ducts.

Splanchnic ischemia during laparoscopic cholecystectomy.

Experimental studies have shown that elevation of intraabdominal pressure by means of gas insufflation produces hemodynamic disturbances in the peritoneal viscera, leading to splanchnic ischemia. The purpose of this clinical investigation is to reproduce the experimental data in humans undergoing laparoscopic cholecystectomy. Sixteen females participated in this study. Eight of them (the control group) were subjected to open laparotomy for biliary surgery, while on the remaining eight laparoscopic cholecystectomy was performed. In all patients hepatic microcirculation was registered during the time of operation using the laser-Doppler technique. A single-fiber laser-Doppler microprobe was introduced transcutaneously within the hepatic parenchyma, through a Chiba needle, under direct or laparoscopic vision. Additionally, gastric intramucosal/intramural pH, a low level of which indicates tissue ischemia, was assessed by means of a tonometric nasogastric catheter. Hepatic microcirculation and gastric intramucosal/intramural pH were assessed between controls and pneumoperitoneum-subjected patients, and within the laparoscopic surgery group, i.e., during pneumoperitoneum and after abdominal deflation. Hepatic microcirculation was found to be significantly decreased in laparoscopic surgery patients in relation to controls (22.21 +/- 5.48 vs 57.52 +/- 18.06 perfusion units of flow, P = 0.0001) as was gastric intramural pH (7.15 +/- 0.16 vs 7.37 +/- 0.02, P = 0.003). Similarly, immediately after abdominal deflation, hepatic microcirculation exhibited a sudden elevation (22.21 +/- 5.48 vs 67.49 +/- 7.93 perfusion units of flow, P = 0.0001), while gastric intramural pH return to its normal values (7.15 +/- 0.16 vs 7.43 +/- 0.07, P = 0.0001). It is concluded that during laparoscopic cholecystectomy abdominal organs are hypoperfused, leading to a splanchnic ischemia environment. The clinical significance of these events remains to be clarified.

Attractors and quasi-attractors in the cutaneous perfusion in human subjects and patients: “Chaotic” or adaptive behaviour?

The causes of the aperiodic fluctuations in the perfusion of the skin (volar hand, measured by the Laser-Doppler (LD) technique) of healthy human subjects were studied by simultaneous recording of the fluctuations of local blood content (reflectiophotoplethysmography (rPPG)) and those in the skin of the glabella. Various thermoregulatory situations were provoked by exposing 12 subjects to 18, 21, 24 and 27°C ambient temperature; in addition, the hands were placed at, below and above heart level. In mentally relaxed subjects (evidenced by a stable approx. 0.015-Hz rhythm in the glabellar rPPG signal), there was perfect temporal correlation between aperiodic LDA and rPPG signal under all thermoregulatory conditions. Clearly identifiable episodes of retardation associated with skin bleaching, asymmetrical shape of LDA and rPPG signals were taken as indicators of episodic sympathetic skin constrictor (SSC) activity. In synergetic terms, the modulated SSC activity operates as transient ‘quasi-attractor’. A notable exception occurred: when the hand was placed below heart at 27°C ambient temperature, a sinusoidal periodic fluctuation (approx. 0.03 Hz) in the LDA evolved. These were not seen the rPPG signal, i.e., coherence between LDA and rPPG dynamics was lost). Lack of coherency between LDA-rPPG, also observed in patients with autonomic neuropathy and decompensated forms of peripheral arterial disease, suggesting predominance of spontaneously oscillating myogenic vasomotion after removal of temporally variable SSC drive. Stable vasomotion is regarded as a synergetically stereotyped reaction rather than as ‘well-ordered’ stable attractor mode of operation.

Effect of nitric oxide and renal nerves on renomedullary haemodynamics in SHR and Wistar rats, studied with laser Doppler technique.

The threshold for activation of the humoral renal antihypertensive system, presumably residing in the renomedullary interstitial cells (RIC), is substantially reset upwards in the spontaneously hypertensive rat (SHR). Depressor reactions, normally elicited by an increased renal perfusion pressure, can be inhibited either by high frequency renal nerve stimulation or blockade of nitric oxide synthesis, i.e. manoeuvres decreasing renal blood flow at this high perfusion pressure. The present study was designed to explore the effects on regional renal haemodynamics of blocking NO synthesis with N-omega-nitro-L-arginine (L-NNA) in chloralose anaesthetized SHR and Wistar rats. Mean arterial blood pressure (MAP), heart rate (HR), renal blood flow (RBF), cortical blood perfusion (CBP) and papillary blood perfusion (PBP) were measured in renally innervated and denervated SHR (Si n = 8, Sd n = 8) and in Wistar rats (Wi n = 10, Wd n = 10). An innervated non-treated Wistar group served as control (Ci n = 12). The laser Doppler technique was used to record CBP and PBP. MAP increased in all groups receiving L-NNA while HR, RBF and CBP simultaneously decreased. The relative decreases in RBF were more marked into the two SHR groups than in the corresponding Wistar groups. After L-NNA PBP also decreased in all four groups despite the increased MAP and more so in the Si group; Wi -19 +/- 8 (P < 0.05), Wd -17 +/- 6 (P = 0.07), Si -50 +/- 9 (P < 0.01) and Sd -25 +/- 9% (P < 0.05). We conclude that NO is important for maintaining PBP especially in SHR. The more marked decrease in PBP in the innervated SHR suggests a NO/renal nerve interaction in the control of renomedullary blood flow in SHR. This finding may be of importance for the regulation of the humoral renal depressor mechanism.

Spatial and Temporal Evaluation of Locally Induced Skin Trauma Recorded with Laser Doppler Techniques

The single-fiber laser Doppler flowmetry (SF-LDF) technique has been used to study perfusion within tissues. The insertion of the SF-LDF probe into human skin locally alters microcirculation for more than 70 min after positioning. In this study the SF-LDF and a newly developed laser Doppler imager (LDI) were used to describe the spatial distribution, the intensity, and the temporal course of the trauma following intracutaneous insertion of the probe. The LDI scanned a human skin area of 6 × 6 cm (36 × 36 pixels). A flexible SF-LDF probe was inserted intradermally in the same measuring region. Recordings were performed for 120 min with the two techniques simultaneously. With the SF-LDF probe maximal hyperemia was recorded after 5–30 min. After a gradual and slow decrease most of the subjects reached a steady-state level within 80–100 min. A 3-min tourniquet occlusion test was performed 120 min after SF probe positioning. A significant hyperemic response was recorded, indicating that almost no posttraumatic activity was present at this time. The area of increased perfusion recorded with the LDI had an oval to circular configuration with a maximal extension after 5–10 min (radius 1.5–2 cm, area 8.9 cm2). The zone of maximal hyperemia was distributed adjacent to the intradermal probe, gradually decreasing toward the periphery. No significant hyperemia was shown with LDI after 100 min. There was a concordance between the time courses of the hyperemic response obtained with the two techniques.

Retinal hemodynamics in middle-aged normal subjects.

The laser Doppler technique and monochromatic photography were used to measure the total retinal blood flow, temporal/nasal differences in blood flow and the relationship between blood flow and vessel diameter in 5 healthy subjects, aged 54-58 years. Systemic blood pressure (BP) and intraocular pressure were also measured, and the retinal perfusion pressure was calculated. The measurements were compared to those previously obtained from a younger group of 7 healthy subjects, aged 25-38 years. Total retinal blood flow was 73 +/- 13 microliters/min in the middle-aged subjects and was not significantly different from the value measured in young subjects (80 +/- 12 microliters/min). Retinal perfusion pressure was significantly higher in the older subjects, primarily due to elevated systemic BP. The similarity in total flow between the two groups, even though the retinal perfusion pressures were higher in the older group, is an indication of an increased vascular resistance to flow. The increase may be an aging phenomenon or an indication of a well-functioning autoregulatory capacity in the retinal vasculature of the older subjects.

Octreotide and Pancreatic Perfusion on the Outcome of Experimental Acute Pancreatitis

Objective: Pancreatic ischemia plays an important role in the initiation and outcome of acute pancreatitis. Somatostatin, widely used for its treatment, is also given for gastrointestinal bleeding control, since it operates by decreasing the splanchnic blood flow. The present study was thus conducted in rats to evaluate the influence of the somatostatin analogue, octreotide, given as prophylaxis or treatment, on pancreatic tissue perfusion during recovery from experimental acute pancreatitis. <i>Method: </i>32 rats were divided into 4 groups: sham operation plus octreotide (group O, n = 8), pancreatitis induction (group P, n = 8), pancreatitis induction plus octreotide (group P+O, n = 8), and octreotide prior to pancreatitis induction (group O+P, n = 8). Acute pancreatitis was induced by sodium taurocholate infusion in a closed duodenal loop and pancreatic tissue perfusion was assessed by means of the laser-Doppler technique at 0, 30, 60 min and 12 h after the initial measurement. <i>Results: </i>All animals exhibited an equal reduction in pancreatic tissue perfusion of about 45% the initial value at 30 min, having either been subjected to pancreatitis (groups P and P+O) or octreotide treatment only (groups·and O+P). At 60 min both groups O+P and P+O exhibited a further reduction (p < 0.001) to 31.61 ± 8.78 and 32.42 ± 5.44% the initial values, while groups·and P remained at 44.18 ± 2.77 and 44.12 ± 2.58% the initial values. At 12 h group·presented pancreatic perfusion equal to 33.37 ± 14.38% the initial value and group P a perfusion of 23.16 ± 3.78%, while groups O+P and P+O exhibited an extreme decline in pancreatic perfusion, the diminution being 11.08 ± 3.77 and 10.97 ± 1.79% the initial values, respectively (p < 0.0001). <i>Conclusions: </i>Octreotide, given either as prophylaxis or treatment, seems to aggravate the already decreased pancreatic perfusion due to the onset of pancreatitis.

Gut ischemia, oxidative stress, and bacterial translocation in elevated abdominal pressure in rats.

The purpose of this experimental study was to investigate whether the increased intraabdominal pressure due to gas insufflation creates intestinal ischemia leading to oxygen free radical production and bacterial translocation. A group of 88 rats were studied, 40 of which were subjected to a 15 mmHg pressure pneumoperitoneum for 60 minutes, with the following parameters being studied: mean arterial pressure after carotid catheterization; intestinal microcirculation by means of the laser-Doppler technique; gut metabolic activity (O2 extraction) by blood sampling from portal vein and carotid artery; intestinal, hepatic, splenic, and lung free radical production (malondialdehyde); and bacterial translocation toward the mesenteric lymph nodes, liver, and spleen at 3 and 18 hours after pneumoperitoneum deflation. The mean arterial pressure exhibited no alterations, whereas the jejunal mucosa microcirculation was significantly decreased (p = 0.0001), as was the gut metabolic activity (p = 0.025). Malondialdehyde was increased in gut mucosa (p = 0.0002), liver (p = 0.02), spleen (p = 0.03), and lung (p = 0.017). Bacterial translocation toward the mesenteric lymph nodes (p = 0.002), spleen (p = 0.002), and liver (p = 0.05) was increased in the 3-hour group; in the 18-hour group bacteria were not found in mesenteric lymph nodes but were in liver (p = 0.008) and spleen (p = 0.035). It is concluded that elevated intraabdominal pressure in the rat leads to intestinal ischemia, oxygen free radical production, and bacterial translocation. These results must be reproduced in humans and their clinical significance clarified.

Optic nerve head circulation in untreated ocular hypertension.

The laser Doppler technique was used to compare the capillary blood speed measured at localised sites of the optic nerve head in stable, untreated ocular hypertensive patients with that measured in healthy normal subjects. The stereophotogrammetric technique was also used to measure the retinal nerve fibre layer thickness at the disc margin in the eyes of the patients. Doppler broadening measurements were made at superior and inferior temporal disc sites in 18 eyes of 10 ocular hypertensive patients and in 12 eyes of seven age and sex-matched normal subjects. On average, Doppler broadening and, hence, capillary blood speed were significantly higher (p = 0.018) in the patients than in the normal subjects. The largest values of Doppler broadening in the patients were measured at sites adjacent to the thinnest retinal nerve fibre layer. Linear regression analysis showed a significant inverse relation (p = 0.0004) between Doppler broadening and nerve fibre layer thickness in left eyes, and a nearly significant relation (p = 0.06) in right eyes. At temporal sites of the optic nerve head there is a compensatory relation between a thinning nerve fibre layer and a locally increasing blood supply to the optic nerve head. Together with previous observations of fluorescein filling defects in similar patients, these results indicate that there is spatial heterogeneity of blood flow in the optic nerve head in stable, untreated ocular hypertensive patients.

Effects of Substance P and Methacholine on Mucosal Blood Flow in the Upper Airways

The aims of the present investigation were to examine the in vivo effects of substance P (SP) and methacholine on blood flow measured by laser Doppler technique in the maxillary sinus of the rabbit and in the human nasal mucosa. In the rabbit, the test substances were administered by intra-arterial catheter, and the laser Doppler probe was inserted into the maxillary sinus through a trepanation in the anterior wall. In the human nose, the laser Doppler probe was directed toward the nasal septum at the level of the anterior margin of the middle turbinate, and the test substances were administered as aerosols into the ipsilateral nostril. In the rabbit maxillary sinus, both SP and methacholine increased the blood flow, the maximum increases obtained being 13.5 ± 3.1% and 39.0 ± 5.6% after challenges with SP at 0.1 μg/kg and methacholine at 0.5 μg/kg, respectively. The rabbits displayed a decrease in blood flow after challenges at higher dosages of both SP and methacholine, accompanied by a simultaneous fall in systemic blood pressure. Atropine given IV five minutes before methacholine abolished the effects of this compound in the rabbit. The blood flow in the human nose was unaffected by saline controls, whereas it was increased both by SP and by methacholine, the increases being 34.9 ± 6.0% after challenges with SP 1.0 nmol and 119.2 ± 15.1% after challenges with methacholine 5.0 μmol. According to acoustic rhinometry, neither SP nor methacholine had, at the doses used, any effect on human nasal patency. Pretreatment with lidocaine hydrochloride spray into the human nose did not affect the increase in nasal blood flow induced by SP, but abolished the methacholine-evoked blood flow increase. Pretreatment with ipratropium bromide spray into the human nose abolished the increase in blood flow induced by methacholine. The results of the present study indicate that blood flow in the upper airways of humans and rabbits may increase due to release of SP or acetylcholine in vivo, an event that occurs after exposure to airway irritants. The vasodilation in the human nose produced by acetylcholine may be due to a neurogenic reflex, in contrast to the effect of SP.

The effect of polycythemia on skin blood flow in hypertensive rats

Polycythemia has marked effects on blood flow through large arteries, but there has been little study of microvascular flow properties, particularly in the hypertensive state. We have previously shown that skin blood flow in the rat had properties very similar to those in man. We used laser Doppler techniques to determine the effect of erythropoietin-induced polycythemia on skin blood flow in 12 Spontaneously Hypertensive Rats (SHR) as compared with 12 normotensive Wistar-Kyoto (WKY) rats. We contrasted flow values at the back and base of tail, nutritively (NUTR) perfused skin sites, with those at the plantar surface of the paw, a site with substantial arteriovenous anastomotic (AVA) perfusion. Erythropoietin treatment produced a substantially greater hematocrit response in the SHR rats, rising from 47 ± 1 to 64 ± 1, than in the WKY animals, who showed an increase from 46 ± 1 to 55 ± 1. Blood pressure was higher in the EPO-treated WKY and SHR rats: 157 ± 4 mm Hg as compared to 148 ± 2 mmg Hg in the WKY animals and 228 ± 4 mm Hg as compared to 201 ± 3 mm Hg, respectively (both p < 0.03). Erythropoietin treatment had very little effect on basal skin blood flow in either WKY or SHR rats. However, there was significantly lower heat-stimulated flow at the plantar surface of the paw in the EPO treated rats (WKY: 27.3 ± 1.9 ml/min/100 gm vs 35.5 ± 1.5 ml/min/100 gm in the untreated state; p < 0.02; SHR: 32.7 ± 2.6 ml/min/100 gm vs 45.4 ± 2.3 ml/min/100 gm in the untreated state; p < 0.01). In contrast, there was little difference at the back or tail. We conclude that erythropoietin-induced polycythemia affects flow in AVA rather than NUTR microvessels. Although raised vascular pressure has produced microvascular flow in our previous studies, the rise in pressure associated with high hematocrit appears to result from an increase in microvascular resistance, decreasing flow. Our study helps clarify clinical observations on the hemodynamic consequences of hematocrit elevation.

Influence of intense sound stimuli on skin microcirculation

Sound influences not only the organ of hearing but also other systems including the circulation. The purpose of the present study was to investigate the effect of strong sound on the skin microcirculation of the palmar area of the hand and of the plantar area of the foot, which are areas of dense microvasculature and rich sympathetic innervation. The laser Doppler technique was used for measuring cutaneous red cell flux (RCF). Eighteen normal subjects were studied. The results indicate that a pure tone sound of 1500 Hz, with an intensity of 100 dBA and duration 5 s, applied by earphones caused a significant decrease in RCF in 14 out of 18 subjects in the finger but not in the foot skin. A higher intensity (110 dBA) tone caused a stronger decrease of RCF in the finger. The latency and the duration of the reaction showed a dependence on the intensity of the sound, i.e. the reaction to the stronger stimulus was of shorter latency (p < 0.01) and longer duration (p < 0.05). The duration of the reaction did not show significant change when a longer stimulus of 30 s was applied. Repetitive stimuli evoked habituation (p < 0.05).

Glucagon increases medullary interstitial electrolyte concentration in rat kidney.

In anesthetized rats, tissue electrical admittance of the inner medulla (a measure of total ion concentration in the interstitium), medullary blood flow (laser Doppler technique), and renal clearances were measured simultaneously before and during i.v. infusion of glucagon at 110 and 330 ng.min-1.kg-1 body weight. Admittance increased modestly, 5.4% after a large glucagon dose (p < 0.01), whereas medullary blood flow was stable. Glomerular filtration rate increased transiently and then fell during high-dose glucagon infusion. The increase in tissue electrolyte (mostly NaCl) concentration in the medulla observed with stable medullary blood flow and decreasing glomerular filtration rate indicates that stimulation of NaCl reabsorption in the medullary ascending limb of Henle's loop by glucagon was the mechanism underlying augmentation of medullary ionic hypertonicity. This suggests that glucagon can contribute to the urine concentration process.

Optical amplification of diffraction-free beams by photorefractive two-wave mixing and its application to laser Doppler velocimetry

The Fraunhofer diffraction pattern of a narrow annular slit is recorded holographically to generate a beam that approximates a diffraction-free Bessel beam. The experimental limitations resulting from the annular-slit parameters such as the opening width and the transmission coefficient are discussed. The reconstructed Bessel beam is amplified by two-wave mixing in a photorefractive crystal. Thus the efficient conversion of a relatively large beam with a constant (or Gaussian) intensity distribution into a nondiffracting beam is achieved entirely by direct physical interference. We show that diffraction-free beams reproduced and amplified in this way can be applied to the measurement of the velocity of small objects by the use of the laser Doppler technique. In addition, the advantages of Bessel beams, especially in measuring the velocity of solids, are discussed.

Simultaneous measurement of digital artery and skin perfusion pressure by the laser doppler technique in healthy controls and patients with peripheral arterial occlusive disease

To assess feasibility of a new technique for simultaneous measurement of digital artery and skin perfusion pressure at the same digit using the laser Doppler method and to measure the pressure gradient between the two vessel compartments in controls and patients with peripheral arterial occlusive disease. A pressure cuff wrapped around the basis of the toe and connected to a Statham transducer is covered by a special plastic capsule. A hole at the distal end of the capsule permits positioning of a laser Doppler probe at the pulp. A second laser Doppler probe is placed on the skin beneath the pressure cuff. Reappearance of pulsatile flux during cuff pressure release detected by the two laser Doppler probes indicated digital artery pressure and skin perfusion pressure on the corresponding pressure curve. Results in patients with intermittent claudication were compared to results of a group of normal controls. University Hospital, Zürich, Switzerland. Eleven healthy volunteers and 14 patients with intermittent claudication due to peripheral arterial occlusive disease were studied. Digital artery pressure (DAP), skin perfusion pressure (SPP) and pressure gradient between DAP and SPP. Significantly lower mean DAP (95.8 +/- 23.2 mmHg vs. 49.8 +/- 20.4 mmHg; p < 0.01) and mean SPP (81.4 +/- 18.8 mmHg vs. 38.4 +/- 21.7 mmHg; p < 0.01) were observed in the patients. Mean pressure gradients and ratios between DAP and SPP did not differ significantly between the two groups. There was a linear correlation between DAP and SPP (r = 0.82, p < 0.01). The laser Doppler method provides the possibility to measure digital artery and skin perfusion pressure simultaneously at the same digit in an easy and non-invasive way. Pressure gradients between DAP and SPP are similar in controls and patients with claudication.

The effect of aging on skin blood flow in the Wistar-Kyoto rat.

Using laser Doppler techniques in man, we have previously demonstrated that skin blood flow decreases linearly with age. In previous work, we have shown similarities in skin blood flow properties between man and the rat. Our goal was to assess a possible aging effect of skin blood flow in the rat. We determined skin blood flow sequentially in 13 Wistar-Kyoto rats, beginning at 3 months of age, then at 6, 12, 15, and 18 months. We measured flow on the back, the base of the tail, the upper leg, all nutritively (NUTR) perfused sites, and on the plantar paw surface, which is perfused chiefly by arteriovenous anastomotic (AVA) capillaries. We measured flow, microvascular volume and red blood cell velocity at basal temperature and also heated the skin locally to 44 degrees C, to elicit maximal vasodilation. Skin blood flow declined in a linear fashion with increasing age. The decrease was in the order of 15% over 18 months and occurred at both NUTR sites and the paw. The decrease was due to reduced microvascular volume, presumably representing loss of skin capillaries. Red blood cell velocity was not reduced; in fact, it was significantly increased at several NUTR sites. The WKY rat provides an excellent model of aging of the skin microvasculature. The changes we have demonstrated, while not identical to those we have previously demonstrated in man, are sufficiently similar to permit further exploration of the mechanisms of these changes.

Involvement of Substance P in Ultraviolet Irradiation‐induced Inflammation in Rat Skin

The possible involvement of substance P released from primary afferents in rat skin was investigated in cutaneous inflammation following ultraviolet (UV) irradiation. Recordings from c-fibres innervating the UV-exposed hindpaw skin showed long-lasting low-frequency (0.8-1.25 Hz) spontaneous activity. Spontaneously active c-fibres increased to constitute 35.3% of the total population 72 h after UV exposure. Immunohistochemical analysis of substance P-containing nerve fibres in hindpaw skin revealed a significant increase in substance P immunoreactivity 24 h after UV irradiation. Average length of substance P-immunolabelled nerve fibres was about two times higher in UV-exposed compared to control skin. UV-induced oedema was investigated in rat ears using an ear-swelling test. Intradermal injection of either peptide (Spantide) or nonpeptide (CP-96,345) substance P antagonists and epicutaneous application of CP-96,345 reduced UV-induced oedema significantly in the late phase of sunburn (> 12 h after UV exposure). The UV-induced increase in skin blood flow was investigated in hindpaw skin up to 72 h by the laser Doppler technique. Epicutaneous application of CP-96,345 reduced erythema significantly between 12 and 72 h after UV exposure. Thus, our findings suggest the involvement of neurogenic substance P as a proinflammatory mediator in the late phase of UV-induced cutaneous inflammation in rats.

Efferent renal sympathetic nerve stimulation in vivo. Effects on regional renal haemodynamics in the Wistar rat, studied by laser-Doppler technique.

Intrarenal blood flow regulation probably affects long-term blood pressure homeostasis. We have previously shown that 5 Hz renal sympathetic stimulation inhibits a humoral renal depressor mechanism, otherwise activated when increasing perfusion pressure to an isolated kidney in a cross-circulation set-up. This inhibition was suggested to occur as a result of a reduction of renomedullary blood flow. Little is known about nervous blood flow regulation within the medulla. Therefore in this study, total renal (RBF), cortical (CBF) and papillary (PBF) blood flows were separately measured by ultrasonic and laser-Doppler techniques in Wistar rats during graded renal sympathetic stimulations. Periods of 15 min stimulation at 0.5, 2 and 5 Hz were performed in random order. RBF decreased at 0.5 Hz by 1%, at 2 Hz by 16% (P < 0.001) and at 5 Hz by 49% (P < 0.001). In a similar fashion (r = 0.73, P < 0.001), CBF decreased by 1%, 10% (P < 0.001) and 37% (P < 0.001), respectively. By contrast, PBF increased by 2% at 0.5 Hz and 4% at 2 Hz, while it decreased at 5 Hz, by 4% (P < 0.05, compared with 2 Hz). It seems therefore, that superficial renocortical and total renal blood flows are closely regulated by renal sympathetic nerves with increasing vasoconstriction at higher frequencies, while medullary blood flow, on the other hand, seems to be under strong local control, tending to offset neurogenic flow restrictions.

Hyaluronan, heterogeneity, and healing: The effects of ultrapure hyaluronan of defined molecular size on the repair of full‐thickness pig skin wounds

The extracellular matrix macromolecule, hyaluronan, is thought to modulate wound healing. However, the molecular size of hyaluronan and contaminating associated proteins may be important determinants of these effects. We have examined the results of seven daily topical treatments of full-thickness skin wounds in pigs with ultrapure hyaluronan of defined molecular size. High molecular weight hyaluronan (>1000 kd) enhanced, whereas low molecular weight hyaluronan decreased, the rate of early wound contraction as compared with intermediate hyaluronan (molecular weight = 100 kd) and saline solution controls. Fracture strength at 21 days was reduced by high and intermediate molecular weight hyaluronan but not by low molecular weight hyaluronan. Wound perfusion, measured by means of a scanning laser-Doppler technique as a noninvasive indicator of angiogenesis, showed depression by high and intermediate molecular weight hyaluronan on day 3, but all forms of hyaluronan caused elevated blood flow on day 7. The architecture of granulation tissue in this wet healing model was highly organized, but no gross histologic differences were seen because of treatment. Different molecular species of hyaluronan have differential effects on contraction, angiogenesis, and the evolution of wound strength. Where hyaluronan is used as a treatment or vehicle for wounds, its precise composition should be specified.

Laser Vibrometry Measurements of Rotating Blade Vibrations

One of the most important design factors in modern turbomachinery is the vibration of turbomachinery blading. There is a need for developing an in-service, noncontacting, noninterfering method for the measurement and monitoring of gas turbine, jet engine, and steam turbine blade vibrations and stresses. Such a technique would also be useful for monitoring rotating helicopter blades. In the power generation industry, blade failures can result in millions of dollars of downtime. The measurement of blade vibrations and dynamic stresses is an important guide for preventive maintenance, which can be a major contributor to the availability of steam turbine, gas turbine, and helicopter operations. An experiment is designed to verify the feasibility of such a vibration monitoring system using the reference beam on-axis laser-Doppler technique. The experimental setup consists of two flat, cantilever blades mounted on a hub attached to the shaft of a dc motor. The motor rests on a linear bearing permitting motion only in the direction of the motor shaft. The motor and blade assembly is then excited via an electrodynamic shaker at the first natural frequency of the blades. The resulting blade vibration is then detected using a laser vibrometer. The vibration frequencies and amplitudes of the two rotating blades are successfully measured.