Laser Doppler blood flow studies during open muscle biopsy in patients with neuromuscular diseases

Post pressure hyperemia in the rat

In prior studies in man, we have demonstrated that pressure-induced hyperemia lasts for prolonged periods as compared to the short-term hyperemia created by proximal arterial occlusion. We have analyzed this phenomenon in our well-studied rat model of skin blood flow. Skin blood flow was measured using laser Doppler techniques in Wistar Kyoto rats at the back, a nutritively perfused site, and at the plantar surface of the paw, where arteriovenous anastomotic perfusion dominates. A customized pressure feedback control device was used to vary applied pressures. At the back, pressures in excess of 80 mmHg resulted in occlusion, whereas at the paw 150 mmHg was required. The peak hyperemic flow after release of pressure was comparable to that elicited by proximal arterial occlusion with a blood pressure cuff. However, the post pressure hyperemia peak descended to a plateau value, which was 50-100% greater than baseline and continued for up to 20 min while the peak following proximal arterial occlusion returned to baseline within 4 min. At the back, post pressure hyperemia reached a maximum after application of 100 mmHg pressure. The application of higher pressures than required for occlusion produced no greater hyperemic response. At the paw, maximum post pressure hyperemia occurred at 100 mmHg, although this pressure level was not totally occlusive. Higher pressures resulted in no greater hyperemia. At the back, 10 min of occlusion produced a maximal peak value whereas 1 min was sufficient at the paw. The application of pressure to a heated probe with subsequent release, produced a hyperemic response. Normalized to baseline blood flow, there was no difference between the hyperemic responses at basal skin temperature and at 44 degrees C. There is a prolonged hyperemic response following local pressure occlusion compared to a much shorter period following proximal ischemic occlusion. One can presume two different mechanisms, one related to ischemia and the other a separate pressure related phenomenon. The thermal vasodilatory response is additive, not synergistic with the post pressure hyperemia we have demonstrated. This finding suggests that different mechanisms are involved in thermal vasodilation and post pressure hyperemia.

Determination of blood flow in the finger using near-infrared spectroscopy

Wavelengths in the near-infrared range have much better penetrance in organic substances than visible light. We used near-infrared spectroscopy to determine non-invasively blood flow in the fingertip. We used laser Doppler technology to measure skin blood flow as a comparison procedure. We performed several manoeuvres to change blood flow. These included restriction of flow, thermal stimulation and post-occlusion hyperaemia. Near-infrared measurements had coefficients of variation of 10-15% at the various wavelengths, contrasting with variability of 30-40% with laser Doppler measurement. With restriction of blood flow, there was a downward shift in the absorbance curve. With thermal stimulation and with post-occlusion hyperaemia, there was a rise in the curve. The flow-induced shifts in the absorbance curve were particularly pronounced in the range of 850-970 nm. The correlation between absorbance values and laser Doppler-determined blood flow was also highest in this range, averaging about 0.69 (n = 625). Near-infrared spectroscopy can therefore be used to scan the fingertip. The absorbances obtained do reflect changes in blood flow. There is a correlation with skin blood flow, although near-infrared measurements are affected by blood flow in the full breadth of the finger, not just the skin. We can measure this blood flow with significant reproducibility. It may be possible to use near-infrared spectroscopy to measure the concentration of individual blood components.

Post-exercise cutaneous hyperaemia resulting from local exercise of an extremity

Large changes in skin blood flow occur after exercise. Most studies have concentrated on the systemic effects of vigorous exercise on skin blood flow. We were interested in the post-exercise response in the neighbourhood of focal exercise. We used a painless neuromuscular electronic stimulator to exercise the muscles of the forearm, producing flexion of the fingers. There was no change in blood pressure and only a small increase in heart rate during this exercise. We measured blood flow during a 5-min pre-exercise period and a 5-min post-exercise period at the forearm, at the dorsum of the index finger and on the pad of the index finger. We also measured values on the contralateral non-exercised extremity during exercise as well as during matched time periods in control experiments with no exercise. Exercise did elicit an increased blood flow in the post-exercise period at all three sites compared with the control experiments with no exercise and on the contralateral extremity. For example, the increase in blood flow at the finger dorsum was 2.1 +/- 0.1 ml (min 100 g)-1 after exercise compared with -0.08 +/- 0.09 ml min-1 100 g-1 during the control experiment and 0.1 +/- 0.1 ml (min 100 g)-1 on the contralateral arm (all P < 0.01). The local application of heat at the site of blood flow monitoring produced a substantial increase in the post-exercise response at the two finger locations [27.4 +/- 0.4 ml (min 100 g)-1 at the finger dorsum], but not at the arm. This is the first demonstration that highly focal exercise, unaccompanied by a systemic haemodynamic response, can elicit a post-exercise cutaneous hyperaemia. Local heating produced a large synergistic increase in the post-exercise hyperaemia at sites with arteriovenous microvascular perfusion but not at sites with primarily nutritive perfusion. These findings show that local vasoregulatory changes occur in response to exercise, even in the absence of whole-body haemodynamic and thermal change.

Effect of calcium channel blockade on skin blood flow in diabetic hypertension: a comparison of isradipine and atenolol

In previous studies, using laser Doppler techniques, the authors have demonstrated a duration-dependent reduction in skin blood flow reserve at sites of nutritive (NUTR) perfusion that occurs in diabetes and correlates with the presence of diabetic retinopathy and proteinuria. They speculated that it might be possible to reverse this decrease in blood flow by using agents with peripheral vasodilating properties. They chose the calcium channel blocking agent isradipine as a prototype. As a contrast agent, they chose atenolol, which has an equivalent antihypertensive effect but minimal peripheral vasodilating properties. They studied 24 diabetic hypertensive patients in a randomized, two-way crossover design. They assigned patients randomly to one or the other active drug and titrated to a maximum tolerated maintenance dose. Skin blood flow was measured at the end of the titration and maintenance phases. Patients then entered a four-week washout period, followed by crossover to the alternative drug, and measurements were repeated. At baseline, the twenty-four-hour mean ambulatory systolic blood pressure was 150 +/- 2 mm Hg with a twenty-four-hour mean diastolic blood pressure of 93 +/- 1 mm Hg. Thermally stimulated skin blood flow reserve was about 50% lower in these patients as compared with an age-, sex-, and weight-matched group of 28 nondiabetic, nonhypertensive patients. There was no difference in skin blood flow between the two groups at basal skin temperature or at a controlled temperature of 35 degrees C. Both atenolol and isradipine successfully lowered blood pressure in the study patients. There was a slightly greater decrease in systolic blood pressure with isradipine and a greater decrease in heart rate with atenolol. Neither isradipine nor atenolol treatment affected skin blood flow values at the maximal 44 degrees C temperature. However, at basal skin temperature and at 35 degrees C, isradipine-treated patients had substantial increases in skin blood flow at NUTR sites. For example, skin blood flow at the knee at 35 degrees C with isradipine treatment was 3.1 +/- 0.4 mL/min/100 g compared with 1.1 +/- 0.2 with atenolol, 1.3 +/- 0.1 with placebo, and 0.9 +/- 0.1 for the nondiabetic controls (all P < 0.01). The authors found a twofold to threefold increase in basal skin blood flow at NUTR sites with isradipine treatment. This degree of increase is substantially greater than that previously demonstrated by their group using pentoxifylline. Locally reduced skin blood flow is a factor in promoting skin breakdown and delayed healing. Further study is needed to explore the possibility that isradipine treatment may enhance healing of diabetic skin ulcers.

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.

Preservation of cortical microcirculation after kidney ischemia-reperfusion: value of an iron chelator

Treatment of suprarenal aneurysms and renal artery reconstructions are both responsible for normothermic ischemia of the kidney (during clamping) followed by reperfusion (declamping). During reflow through an organ undergoing ischemia the production of free radicals can be associated with cell injury and a no-reflow phenomenon characterized by perfusion defects after a period of transient hyperemia. The objectives of this study were to demonstrate the existence of this phenomenon in the kidney undergoing ischemia followed by reperfusion and to test the potential protection afforded by an iron chelator (desferrioxamine) since free radical reactions are catalyzed by iron. Adult New Zealand white rabbits were divided into the following three groups: group A, 15 minutes of ischemia plus 10 minutes of reperfusion; group B, 60 minutes of ischemia plus 10 minutes of reperfusion; and group C, 60 minutes of ischemia plus 10 minutes of reperfusion combined with infusion of desferrioxamine (50 mg/kg). Cortical microcirculation in the kidney was measured by laser Doppler flowmeter before ischemia and 1, 5, and 10 minutes after reperfusion. Vitamin E content was determined in the cortex of the left kidney after 10 minutes of reperfusion and compared with that of the right (control) kidney. After 1 minute of reperfusion the cortical microcirculatory flow was significantly increased in all three groups (reactive hyperemia). In groups A and C blood flow returned to preclamping values after 10 minutes of reperfusion; however, blood flow in group B remained significantly reduced (29.2% +/- 10.5%) after 5 minutes of reperfusion with a further reduction to 48.5% +/- 5.7% after 10 minutes. These findings were correlated with the dosage of vitamin E since the vitamin E content was greatly reduced by 46.7% +/- 7.8% in group B but did not change significantly in groups A and C. This study shows that 60 minutes of normothermic ischemia is followed by a significant reduction in cortical microcirculatory flow (no-reflow phenomenon). Infusion of an iron chelator (desferrioxamine), however, which decreases the intensity of lipid peroxidation induced by the free radicals, preserves the microcirculatory flow.

Decreased skin blood flow early in the course of streptozotocin-induced diabetes mellitus in the rat

We have previously used laser Doppler technology to demonstrate that skin blood flow is reduced in Type 1 (insulin-dependent) diabetic patients. The possibility of using the skin as an extremely accessible indicator of diabetic microvascular disease is attractive. The streptozotocin diabetic rat is an appealing potential animal model. We performed measurements of skin blood flow in two rat species, nine Sprague Dawley (SD) rats and nine Wistar Kyoto (WKY) rats, observing early changes following the inception of diabetes. Four of the SD rats and five of the WKY rats were made diabetic, the rest serving as controls. There were no significant differences in skin blood flow between the two rat strains. As in man, there appear to be rat skin sites with primarily nutritive capillary supply and those with arteriovenous anastomotic predominance. The back and base of tail, both hair-covered areas, demonstrated low flow characteristics, consistent with nutritive perfusion. In contrast, the plantar surface of the paw behaved similarly to the finger or toe pulps in man, sites of arteriovenous perfusion, with high basal flow and a marked increment with thermal stimulation. In diabetic rats of both species, there was significantly lower flow at the back and base of tail than in non-diabetic animals. The differences were of the order of 30-40%. As a function of time, the decrease in blood flow at the base of tail parallelled the increase in glycohaemoglobin levels in the diabetic rats. In contrast, blood flow at the plantar surface of the paw was unchanged throughout the 3-month post-streptozotocin observation period.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of blood flow in the skin and oral mucosa of the rhesus monkey (Macaca mulatta) using laser Doppler flowmetry

1. It is generally assumed that oral blood flow is higher than that of skin, and invasive methods to measure blood flow support this view. 2. However, it was not known whether this finding would be confirmed by laser Doppler flowmetry, which is a noninvasive method to measure blood flow. 3. The purpose of this study was to compare blood flow in oral and skin regions of the rhesus monkey using laser Doppler flowmetry. 4. The results demonstrated that blood flow was significantly higher in oral regions as compared to facial skin (P < 0.05). 5. This finding is most likely related to the more abundant capillary supply in oral mucosa as compared to skin.

Nonpeptide angiotensin AT1 and AT2 receptor ligands modulate the upper limit of cerebral blood flow autoregulation in rats

We investigated the effect of angiotensin AT1 and AT2 receptor blockade on the upper limit of CBF autoregulation in pentobarbital-anesthetized rats. CBF was measured by laser-Doppler flowmetry from the parietal cortex and MABP was increased by intravenous phenylephrine infusion. Neither the AT1 antagonist losartan nor the AT2 ligand PD 123319 nor angiotensin II (ANG II) in the presence of losartan affected baseline CBF. When the blood pressure was increased in the control group, CBF remained fairly constant up to 145 mm Hg and increased steeply after 150 mm Hg. Both PD 123319 (7-10 mg/kg) and losartan (1-10 mg/kg) shifted the upper limit of CBF autoregulation toward higher pressures. Intravenous infusion of PD 123319 was more effective than bolus injection. The losartan effect was dose dependent. Selective stimulation of AT2 receptors with an intravenous ANG II infusion (0.54 micrograms/min) in the presence of losartan did not reverse the effect of losartan on CBF autoregulation, but, on the contrary, appeared to further shift the upper limit of autoregulation toward higher pressures. The results implicate a role for both AT1 and AT2 angiotensin receptors in the regulation of CBF.

Continuous percutaneous measurement by laser-Doppler flowmetry of skeletal muscle microcirculation at varying levels of contraction force determined electromyographically

Laser-Doppler flowmetry (LDF) and electromyography (EMG) were used simultaneously for measuring skeletal muscle blood perfusion in relation to static load and fatigue. Percutaneous single-fibre LDF and bipolar surface EMG of the trapezius muscle were performed continuously during a 10-min series of alternating periods of static contractions and rest, each of 1-min duration. The muscle was exposed to static load expressed as shoulder torque, by keeping the arms straight and elevated at 30, 60, 90 and 135 degrees. On-line computer processing of the LDF and EMG signals made possible the interpretation of the relationship between the perfusion and the activity of the muscle. The LDF and root mean square (rms)-EMG were normalized by using the average value of the serial examinations of each individual as a reference value. Spectrum analyses of EMG showed the lowest variability for median frequency (MDF) in the frequency range 10-1000 Hz and mean power frequency (MPF) at 2-1000 Hz. The LDF power spectrum density during low (muscle rest) and high (high-force muscle contraction) perfusion indicated that disturbances were small when measurements were performed during sustained static contraction with as little movement as possible. Vasomotion, i.e. rhythmic variations in the blood flow, were present and showed a frequency of 5-6 cycles.min-1. Application of a tourniquet to the upper arm caused an arrest of the microcirculation in the distally situated brachioradial muscle which was followed by a postischaemic hyperaemia upon removal of the torniquet.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic trapezius myalgia. Morphology and blood flow studied in 17 patients

Bilateral open biopsies from the painful upper part of the trapezius muscle were studied in 17 patients with localized chronic myalgia related to static load during repetitive assembly work. Isolated pathologic ragged red fibers were related to the presence of myalgia. The phenomenon indicating disturbed mitochondrial function was confined to the Type 1 fibers. Using a laser-Doppler flowmeter, the muscle blood flow was recorded in the exposed muscle before a biopsy was taken. Pain was assessed and graded as the difference between the two sides, as was the presence of ragged red fibers. The myalgia correlated with reduced local blood flow: the greater the pain difference, the greater the reduction in blood flow. There was a correlation between the presence of mitochondrial changes and reduced muscle blood flow.

Measurement of multiple microcirculatory parameters in human nasal mucosa using laser-Doppler velocimetry

LDV has been modified to measure four microcirculatory responses in human nasal mucosa. Resting nasal blood flow was measured in 115 observations in 23 nonatopic subjects and 111 observations in 21 atopic subjects with allergic nasal disease. Other parameters measured concurrently were the number density of moving red blood cells (RBC), mean RBC speed, and flow pulsatility. Challenges with aerosolized buffered saline or water had no significant effect on any parameter. By contrast, nasal application of alpha-adrenergic agonists, oxymetazoline and phenylephrine, produced significant dose-dependent reductions in flow without any significant change in RBC number density. These results suggest a selective alpha-agonist effect on resistance vessels but not on capacitance vessels. Topical cholinergic stimulation with methacholine selectively reduced the RBC number density without affecting other parameters. These modifications of LDV may prove useful in analyzing nasal responses to provocation and determining the sites of action of vasoactive agents on the microcirculation.

Laser Doppler monitoring of replants using a small prism probe

Eighteen patients admitted to Duke University Medical Center for upper limb replantation or revascularization were studied. A small laser Doppler flow prism probe and a cutaneous temperature probe were attached to the distal pulp of replanted digits. Measurements were recorded hourly for the first 3 postoperative days. In the successful cases, the mean laser Doppler flow measurement was 1.76 units (lower 97% confidence limit 0.5 units) and the mean temperature was 34.1 degrees C (lower 97% confidence limit 32 degrees C). In 4 patients with vascular compromise, the laser Doppler flow correctly identified the problem. The reduced size of the new laser Doppler probe makes monitoring of distal pulp flow technically easier while maintaining accuracy.

Model for photon migration in turbid biological media

Various characteristics of photon diffusion in turbid biological media are examined. Applications include the interpretation of data acquired with laser Doppler blood-flow monitors and the design of protocols for therapeutic excitation of tissue chromophores. Incident radiation is assumed to be applied at an interface between a turbid tissue and a transparent medium, and the reemission of photons from that interface is analyzed. Making use of a discrete lattice model, we derive an expression for the joint probability gamma(n, rho)d2 rho that a photon will be emitted in the infinitesimal area d2 rho centered at surface point rho = (x, y), having made n collisions with the tissue. Mathematical expressions are obtained for the intensity distribution of diffuse surface emission, the probability of photon absorption in the interior as a function of depth, and the mean path length of detected photons as a function of the distance between the site of the incident radiation and the location of the detector. We show that the depth dependence of the distribution of photon absorption events can be inferred from measured parameters of the surface emission profile. Results of relevant computer simulations are presented, and illustrative experimental data are shown to be in accord with the theory.

Continuous and non-invasive quantification of heat-induced changes in blood flow in the skin and RIF-1 tumour of mice by laser Doppler flowmetry

The changes in blood flow in the skin and in the periphery of RIF-1 tumours of C3H mice could be monitored continuously during heating with the use of the laser doppler flowmetry. The laser probe was placed gently on the skin or tumour surface and the change in blood flow was quantified from the output signal from the monitor during the heating of the tissues with temperature-controlled water. The blood flow in the tumour increased significantly during the first 20-30 min of heating at 42.5-44.5 degrees C and then began to decline during the second half of one hour of heating. The skin blood flow either continuously increased or remained elevated during 1 h heating at 42.5-44.5 degrees C. These results were generally similar to the previous reports on the heat-induced changes in blood flow in the skin and tumours measured by other methods.

Laser Doppler flowmetry: muscular microcirculation in anaesthetized horses

Muscular microcirculation was studied in seven halothane anaesthetised horses in lateral recumbency using a laser Doppler flowmeter. A significant difference between the dependent and the uppermost triceps brachii was recorded. In the dependent muscles, microflow at first decreased and then increased up to the starting value. In the uppermost muscles, a significant rise of the microflow was measured.

Effects of synthetic leukotrienes on local blood flow and vascular permeability in porcine skin

The local effects of synthetic leukotrienes (LT) were examined in the skin of the anesthetized pig. Blood flow was measured noninvasively with the use of a laser-Doppler flow meter and changes in vascular permeability were measured using technetium-labeled human serum albumin as a marker for extravasation. LTB4 and the peptidolipid leukotrienes, LTC4, LTD4, LTE4, LTF4, induced vasodilator responses when injected intradermally at a dose of 1 ng. The vasodilator effects of LTB4 and LTF4 were comparable in magnitude to those of prostaglandin E2 (PGE2) and histamine and persisted over a wide dose range. Vascular permeability was induced by histamine, PGE2, and LTB4 but not by the other leukotrienes. The effects of LTB4 were significantly increased in the presence of PGE2. Leukotrienes appear not to produce their effects through the generation of prostaglandins as neither the vasodilator nor the permeability-enhancing effects were affected by treatment with indomethacin. The present investigation demonstrates that the pig is the first animal model to be described which reflects the potent vasodilator actions of leukotrienes in human skin. The porcine skin may thus be a useful model in the study of human skin diseases.

Periodic microcirculatory flow in patients with sickle-cell disease

We have applied the technique of laser-Doppler velocimetry to compare patterns of cutaneous blood flow in the forearms of patients with stable sickle-cell disease, with the patterns in normal subjects matched for age, race, and sex, and in patients with anemia due to beta+-thalassemia. The mean resting blood flow in the patients with sickle-cell disease was comparable to that of the control groups but was associated with large, local oscillations in flow with periods of 7 to 10 seconds and peak-to-trough magnitudes about half the mean flow. Oscillations occurred simultaneously at sites separated by 1 cm but were independent in phase and frequency. Since these laser-Doppler measurements represent the average flow pattern in about 1 mm3 of skin (i.e., in approximately 50 to 70 capillary loops), these results suggest that microcirculatory flow in patients with sickle-cell disease proceeds by synchronization of rhythmic flow in large domains of microvessels. These findings indicate that periodic flow may be a compensatory mechanism to offset the deleterious altered rheology of erythrocytes containing polymerized hemoglobin S, and suggest that laser-Doppler velocimetry may be a useful method to investigate microvascular physiology in patients with sickle-cell disease.

Fiber-optic sensors for biomedical applications

In this article the development of fiber-optic sensors for biomedical applications is reviewed. Light-carrying fibers are potentially useful in oximetry, dye dilution measurements, laser-Doppler velocimetry, and fluorometry; as physical sensors of temperature, pressure, and radiation; and as chemical sensors of pH, partial pressure of blood gases, and glucose. Emphasis is placed on the principles and ideas used in the various devices rather than on detailed descriptions or critical discussions.

Scientists and Congress

Scientists are urged to make their views known to members of Congress. To be effectively heard, they should establish personal contact with their congressmen and senators and their staff. Communication should be frequent, personal, and carefully focused. In the last 2(1/2) years, federal funding of scientific research has been severely cut back, while military research funding has been increased. The selection process for funding research is being politicized. Scientists should concern themselves with what is happening politically because the quality of American scientific research is being threatened.