A non-invasive measure of changes in blood flow in the human anterior tibial muscle

We used photoplethysmography (PPG) to monitor blood flow changes in the human anterior tibial muscle during arterial occlusion and during isometric and concentric contractions. Single-fibre laser-Doppler flowmetry (LDF) was used as a reference in 12 healthy subjects (5 men, 7 women; mean age 24 years). Post-exercise hyperaemic muscle blood flow (MBF) was measured immediately after isometric dorsiflexion of the ankle joint at maximal contraction for 1 min and full range-of-motion dorsiflexion and plantar flexion of the ankle joint for 1 min. A thigh tourniquet was applied for the evaluation of post-occlusive reactive hyperaemia. The MBF (baseline=100%) was [mean (SD)] 150 (31)% (P=0.003) by PPG (880 nm) and 182 (66)% (P=0.012) by LDF. After 1 min of maximal isometric contraction, MBF increased to 150 (51)% (P=0.003) by PPG (880 nm) and to 169 (43)% (P=0.005) by LDF. After 1 min of maximal concentric contractions, MBF increased to 158 (59)% (P=0.003) by PPG (880 nm) and to 170 (99)% (P=0.008) by LDF. Skin blood flow, PPG (560 nm), did not change significantly after isometric or concentric contractions. The results indicate that reactive hyperaemia after exercise and arterial occlusion can be assessed in the human anterior tibial muscle using PPG. Electronic Publication     

Simplified model of laser Doppler signals during reactive hyperaemia

Laser Doppler flowmetry (LDF) is a non-invasive method to measure tissue blood flow. During reactive hyperaemia, the LDF signal increases to a peak and then returns to a resting value. A simplified model is developed to explain these variations. The emphasis is on simulating the effects occurring rather than on trying to mimic the anatomical structure of the microcirculation. A single blood vessel is therefore analysed. The increasing value of blood velocity is studied, and vasodilatation as well as vasoconstriction are taken into account. The model parameters are calculated using wavelets. For a 2-min occlusion on a healthy subject, the radius of the vessel is initially 15 μm, increasing to 24.6 μm at the peak, reached 14 s after the release of the occlusion. The model shows that the high value of the LDF signal during the initial phase of reactive hyperaemia is produced by an increasing number of erythrocytes in a cross-section, due to vasodilatation rather than an increase in moving blood cell velocities. Moreover, the rapidity of the vasodilatation and vasoconstriction effects determine the rapidity of the signal variations. The paper aims to give a basic solution to develop a numerical model.     

Laser-Doppler measurements of concentration and velocity of moving blood cells in rat cerebral circulation

In brain cortex all capillaries are perfused with plasma at anyone time while the flow of blood cells is heterogenous. Increased blood flow is associated with increased number of moving erythrocytes in the microcirculation, while capillary recruitment in its classical anatomical sense appears not to exist in the brain. Modulation of the concentration of flowing erythrocytes may influence the oxygen supply to the tissue. Therefore, we examined the possibility that laser-Doppler flowmetry (LDF) could be used to quantify changes in the microvascular concentration of moving blood cells (CMBC) and blood cell velocity (< v >) by comparing LDF measurements with electromagnetic flow measurements in vitro, and confocal laser-scanning microscopy in vivo in the brain of anaesthetized male Wistar rats. In vitro measurements showed that CMBC was affected by changes in haematocrit, while < v > correlated almost linearly with blood cell velocity measured electromagnetically within a relevant physiological range. In vivo studies during hypercapnia (Paco ₂ from 39 ± 4 to 66 ± 5 mmHg) with confocal laser scanning microscopy disclosed a 39 ± 10% increase of cortical capillary erythrocytes, while CMBC measured with LDF increased by 37 ± 5%. Erythrocyte flow velocity in brain cortex capillaries increased by 65 ± 17% with confocal microscopy as compared to 72 ± 8% with LDF. Local electrical stimulation of cerebellar cortex, and application of adenosine or sodium-nitroprusside, increased CMBC and < v > simultaneously, while during hypercapnia the < v > increase preceded the CMBC increase by 30 s. The CMBC rise rapidly reached a steady state in response to all types of stimulation, while < v > continued to increase during the major part, or the entire stimulation period. In conclusion, our data support the hypothesis that LDF may be useful for haemodynamic studies of brain microcirculation.     

Coronary reactive hyperaemia and arterial pressure in anaesthetized goats

To study the effects of arterial pressure on coronary reactive hyperaemia, left circumflex coronary artery flow was measured, and reactive hyperaemia was determined after 5, 10 or 20 s of occlusion of this artery in anaesthetized goats during normotension, hypertension and hypotension. During hypertension induced by aortic constriction (mean arterial pressure, MAP = 140 +/- 6 mmHg) coronary vascular resistance (CVR), reactive hyperaemia (ratio of peak in hyperaemic flow to control flow and ratio of repayment to debt) and the decrease in CVR during the peak in hyperaemic flow were comparable to those during normotension. During hypertension induced by noradrenaline (MAP = 144 +/- 6 mmHg) CVR was 16% lower (P < 0.05), reactive hyperaemia was reduced by 14-25% (P < 0.05) and the decrease in CVR during the peak in hyperaemic flow was lower than the values of these parameters during normotension. During hypotension induced by constriction of the caudal vena cava (MAP = 40 +/- 4 mmHg) CVR was 22% lower (P < 0.05), reactive hyperaemia was reduced by 25-65% (P < 0.05) and the decrease in CVR during the peak in hyperaemic flow was less compared to the values of these parameters during normotension. During hypotension induced by isoprenaline (MAP = 45 +/- 4 mmHg) CVR was 59% lower, reactive hyperaemia was reduced by 55-100% (P < 0.01) and the decrease in CVR during the peak in hyperaemic flow was less compared to the values of these parameters during normotension. Arterial pressure is a main determinant of coronary reactive hyperaemia after brief periods of ischaemia, and the relationship between arterial pressure and reactive hyperaemia may depend in part on changes in CVR after variations in arterial pressure. These changes in CVR may be related to the action on coronary vessels of myocardial factors and vascular myogenic mechanisms.     

Myogenic vascular regulation in skeletal muscle in vivo is not dependent of endothelium-derived nitric oxide

The hypothesis, based on in vitro experiments on large conduit arteries, that endothelium-derived nitric oxide is a mediator of vascular myogenic reactivity was tested in cat gastrocnemius muscle in vivo. This was done by comparing, in the absence and presence of effective endothelium-derived nitric oxide blockade by the specific inhibitors N_G-monomethyl-l -arginine or N^G-nitro-l -arginine methyl ester, myogenic responses in defined consecutive vascular sections to dynamic vascular transmural pressure stimuli, to arterial occlusion (reactive hyperaemia), and to arterial pressure changes (autoregulation of blood flow and capillary pressure). The results demonstrated that the myogenic vascular reactivity to quick ramp transmural pressure stimuli was not attenuated by endothelium-derived nitric oxide blockade, but rather reinforced. The amplitude of the reactive hyperaemia response was unaffected by endothelium-derived nitric oxide blockade, but its duration was shortened because of faster myogenic constriction, especially of large-bore arterial resistance vessels > 25 μm, in the recovery phase. Both the improved myogenic responsiveness to transmural pressure stimuli and the shortening of the reactive hyperaemia by endothelium-derived nitric oxide blockade suggested that endothelium-derived nitric oxide released in vivo acts as a ‘metabolic’ factor which certainly does not improve, but rather depresses myogenic vascular reactivity. Autoregulation of blood flow and capillary pressure were well preserved in the presence of endothelium-derived nitric oxide blockade. It was concluded from the results of these multifaceted tests that myogenic vascular regulation in skeletal muscle in vivo seems independent of endothelium-derived nitric oxide. Nor did, endothelium-derived nitric oxide seem to play a role as a ‘metabolic’ mediator of the functional hyperaemia response to muscle exercise, since the magnitude of this response was the same in the absence and presence of endothelium-derived nitric oxide blockade.     

Parameters of Postocclusive Reactive Hyperemia Measured by Near Infrared Spectroscopy in Patients with Peripheral Vascular Disease and in Healthy Volunteers

The main purpose of our study was to determine the parameters of the postocclusive reactive hyperemia test that could help and provide the clinician with information about the tissue oxygenation, the severity of the disease, and the results of the applied therapies. Near infrared spectroscopy (NIRS) proved to be a valid noninvasive trend monitor useful for investigating the physiology of oxygen transport to tissue. Important advantages of NIRS over transcutaneous oximetry (TcpO₂) are: (a) a more dynamic nature of the NIRS signals which reflects more closely the actual response of the peripheral vasculature to the occlusive provocation; (b) larger sampling volume; and (c) the ability of assessing tissue oxygenation at deeper tissue levels. We demonstrated that the time parameters of reactive hyperemia, the rate of reactive hyperemia, and the maximal change during reactive hyperemia, all calculated from the oxyhemoglobin (HbO₂) signal of the NIRS, clearly distinguish between healthy volunteers and patients with vascular disorder. The time parameters of reactive hyperemia were significantly longer (p < 0.01), and the rate of reactive hyperemia (p = 0.01) as well as the maximal change during reactive hyperemia (p = 0.02) were significantly lower in patient group compared to healthy volunteers. These parameters were also in good correlation with the values of ankle brachial index (ABI) and the resting values of oxygen partial pressure (TcpO₂). Values of the chosen parameters obtained from the HbO₂ signal were further compared between groups of diabetic and nondiabetic patients with peripheral vascular disease. Although longer time parameters of reactive hyperemia and lower rates of hyperemic response were detected, the difference between both groups was not statistically significant. © 2001 Biomedical Engineering Society. PAC01: 8764Je, 8719Xx     

Finger arterial compliance as determined by transmission of light during mental stress and reactive hyperaemia

A near-infrared finger photoplethysmogram adopting a wavelength of 810 nm provides data pertaining to the pulsatile a.c. component of finger blood flow (ΔI) superimposed on the transmitted d.c. components in a normal (I: tissue plus blood) and an ischaemic circulatory state (I _t: tissue only). Simultaneous recording of finger blood pressure provides data pertaining to the distending pulse (PP) and mean blood pressure. Based on the Lambert-Beer law, indices of the arterial compliance (CI=ΔI/I/PP) and distensibility [DI=ΔI/I/ln(I _t/I)/PP] are advocated for assessing finger vasculature. The functional relationships between transmural pressure and CI and DI were examined using finger occlusion while performing an arithmetic test (i.e. a mental stress) in 16 females, and during reactive hyperaemia in 5. Gradual occlusion of the finger was conducted at 20-s intervals and the beat-by-beat transmural pressure was determined by calculating mean blood pressure minus the occluding cuff pressure. Logarithmically transformed CI and DI data were linearly associated with the transmural pressure; thus, the estimates obtained at a transmural pressure of 40 mmHg were chosen as an arbitrary reference point (CI40 and DI40). The results indicated that CI40 and DI40 were reduced while performing an arithmetic test, and increased during reactive hyperaemia. Responses were larger for CI40 than for DI40. In conclusion, noninvasive finger occlusion allowed the measurement of the compliance/distending pressure relationship, and CI40 could be utilised to evaluate changes in finger vascular tone. Electronic Publication     

Doppler sonographic examination of reactive hyperemia in the diagnosis of peripheral vascular disease

Summary Fifty-four patients with angiographically confirmed peripheral vascular disease (PVD) were examined in order to find out whether the occlusive form of this disease can be better diagnosed by measuring the reappearance time and mean velocity of the blood flow during reactive hyperemia than by determining the peripheral systolic blood pressure, using Doppler ultrasound for both measurements. It was shown that the Doppler pressure was only reliable for a screening diagnosis of PVD. However, using the reappearance time of reactive hyperemia, it was possible to distinguish specific localization types of sclerosis; while reactive hyperemia already reached its half maximum in controls in 4.6 s this occurred in the stenosis type of PVD after 6.9 s, in the upper leg occlusion type after 21.6 s, in the lower leg occlusion type after 46.6 s, and in the multilevel disease after 70.1 s. The delay in the half-maximum reappearance time was significantly different, not only in comparison with controls (P<0.001) but also in the specific types of occlusive PVD as compared with one another (P<0.01). Regarding the intensity of velocity it could also be shown that the mean velocity of blood flow during reactive hyperemia was lower in all patients with PVD than in controls. Again this alteration during reactive hyperemia was significant, not only in comparison with controls (P<0.001), but also when the specific stages of severity according to Fontaine were compared with one another (P<0.05). On the basis of these findings it can be stated that in addition to providing a screening diagnosis of PVD on the basis of the Doppler pressure, the Doppler ultrasound measurement of reactive hyperemia is useful for a specific diagnosis of the localization and severity of PVD.Abbreviations API ankle pressure index - ATR Achilles tendon reflex - DFI Diabetes-Forschungsinstitut - max/2 half-maximum - PVD peripheral vascular disease - RT reappearance time - SD standard deviation     

Skin perfusion patterns (fluorescein perfusography) during reactive hyperaemia in peripheral arterial occlusive disease.

From the pathophysiological point of view the regional distribution of blood flow is of special importance in ischaemic tissues. Within this study foot sole skin perfusion was investigated by means of fluorescein perfusography at rest and during reactive hyperaemia in patients with peripheral arterial occlusive disease confined to one limb (Fontaine stage II). Ambient temperatures were maintained around 21 degrees C. Mean fluorescein appearance times on the one side and their standard deviations (SD) and coefficients of variation (CV) on the other side were taken as measures of overall blood supply and homogeneity of flow, respectively. At rest no differences in these parameters could be detected between diseased legs and controls. After a 3-min supra-systolic circulatory arrest at the thigh, a significant reduction of fluorescein appearance times was observed for both groups but was statistically more pronounced in the controls. Furthermore, during reactive hyperaemia standard deviations as well as coefficients of variation decreased significantly only in normal limbs whereas they either remained constant (SD) or even increased (CV) in those with arterial obstructions. All effects associated with reactive hyperaemia showed statistically significant correlations with systolic ankle pressure indices. From these results it is concluded that haemodynamically effective arterial obstructions are followed by not only a restriction of overall hyperaemic blood supply but also a failure to homogenize microcirculatory perfusion in the case of increased flow requirements.     

Reactive hyperaemic flow characteristics of the right coronary artery compared to the left anterior descending coronary artery in the open-chest dog

Reactive hyperaemia, the cardiovascular response to transient occlusion of a vessel, was examined and compared in the right coronary artery (RCA) and the left anterior descending coronary artery (LAD) in the same heart of an open-chest dog. First, to study the relationship between reactive hyperaemia and occlusion time in the RCA and LAD, respective flows were measured and reactive hyperaemia was induced with different occlusion times. Occlusion time required for half the maximum peak percentage reactive hyperaemic flow (%PRH), t _1/2, for the RCA was approximately twice that of the LAD: 11.4±2.3 s versus 5.9±1.4 s. Maximum %PRH of the RCA was significantly greater than that of the LAD while the percentage repayment of the RCA was lower than that of the LAD. Augmentation of right ventricular oxygen consumption shortened t _1/2 and increased percentage repayment significantly. Second, to determine critical pressure, which was defined as the perfusion pressure below which reactive hyperaemia was abolished completely, the RCA and LAD were perfused through a shunt from the carotid artery, perfusion pressure was varied in the range of 100 to 20 mmHg and reactive hyperaemia was induced. Critical pressure in the RCA was significantly lower than in the LAD: 32.2±5.7 mmHg versus 41.5±5.0 mmHg. These results suggest that the RCA has a greater flow reserve than the LAD. These results were consistent with the difference of oxygen metabolism between the right and left ventricles. The difference of oxygen metabolism between the two ventricles would, at least partly, account for these results.     

Functional Impairments of Microcirculation in HIV-Positive Patients: A Laser Doppler Fluxometry-Based Investigation

Abstract

Purpose: The aim of our study was to investigate the morphologic and functional characteristics of microcirculation in HIV-positive patients. Microcirculation was investigated by means of capillaroscopy and laser Doppler fluxometry (LDF). The results were compared with those obtained from healthy subjects and patients affected by sclerodermia. Method: We evaluated 140 subjects: 69 HIV-positive, 48 sclerodermic, and 23 healthy individuals. The groups were compared for resting flow (RF), mean flow during cold test, mean flow during the recovery, postocclusive reaction, and time of recovery after reactive hyperaemia. Results: RF (p = .0035), flow during the cold test (p = .008), recovery (p = .03), and postocclusive reaction (p = .007) results were higher in HIV-1 positive patients with respect to the other two groups. Recovery after postocclusive reaction in HIV-positive patients was longer than in healthy individuals. Time from diagnosis and a pathologic electromyography were significantly related to a vasospasm reduction induced by the cold test (p = .022). The recovery was also influenced by the time from disease diagnosis (p = .0016). Conclusions: HIV patients seem to have an altered microcirculation regulation, with increased perfusion of the capillary territory. This could be related to the length of period of infection and a coexisting neuropathy.     

2型糖尿病患者足背皮肤微血流变化及其相关危险因素分析

目的:探讨病程≤5年的2型糖尿病患者是否已经存在皮肤微血流的变化,分析影响2型糖尿病患者皮肤微血流的相关因素。方法:应用激光多普勒血流仪(LDF)对24例病程≤5年的2型糖尿病患者(糖尿病组)和25例非糖尿病对照者(对照组)进行足背皮肤微血流测定。微血流的测定应用阻断后反应性充血(PORH)的方法,通过LDF记录皮肤微血流阻断前基值(PORHrest)、袖带加压阻断后最小值(PORHmin)和减压后反应性充血的微血流峰值(PORHpeak),其它观察指标还有微血流从开始减压到升至峰值的时间(Tp)、PORHmax(=PORHpeak-PORHrest)和PORHmax/Tp[=(PORHpeak-PORHrest)/Tp]。结果:与对照组相比,糖尿病组的PORHrest、PORHpeak、PORHmax均明显下降,而Tp和PORHmax/Tp明显增加。多元逐步回归分析显示,影响PORHrest的因素是空腹血糖(FBG)和舒张压(DBP);影响PORHpeak的因素是DBP;影响PORHmax的因素是DBP和FBG。结论:病程≤5年的2型糖尿病患者已存在下肢皮肤微血流改变,高血压、高血糖是导致其微血管病变的主要危险因素。     

Laser-Doppler and plethysmographic skin blood flow during exercise and during acute heat stress in the sauna

Summary Forearm skin blood flow was measured in six male subjects by laser-Doppler flowmetry (LDF) and venous occlusion plethysmography (VOP) during constant-load (125–200 W) upright bicycle exercise in a warm environment ( + SD,t _a 34.6±0.2‡ C) and during a 15 min sauna bath (t _a 69.0±2.8‡ C). During the sauna test the LDF values correlated well with the VOP measurements in the initial phase of active cutaneous va-sodilation, after which the LDF values almost leveled off in spite of a steady increase in VOP measurements. During the exercise the mean VOP and LDF values rose in parallel with each other to steady state levels. The relationship between the results of the two methods proved to be nonlinear. It was concluded that different parameters were measured by VOP and LDF. The latter measured mainly the integrated velocity of blood flow in the outermost cutaneous tissue, and this velocity seemed to be partly dependent on the level of the arterial inflow (VOP), but also on the prevailing pressure-flow and pressure-volume relations in the cutaneous vascular bed.     

2型糖尿病患者皮肤微血流改变与病程的关系

目的:探讨2型糖尿病患者皮肤微血流改变与其病程的关系。方法:选择2型糖尿病患者中病程≤5年和≥15年者各17例。用皮肤血流阻断后反应性充血(PORH)的方法,以左前臂皮肤为测定点,应用激光多普勒血流仪(LDF)记录阻断前、中、后的皮肤微血流值。结果:短病程组的皮肤微血流最大值明显高于长病程组(27.83±8.83比18.07±6.91,P<0.01);短病程组的皮肤微血管反应性充血速率明显大于长病程组(2.62±1.50比1.57±0.96,P<0.05)。结论:2型糖尿病患者前臂皮肤微血管病变随糖尿病病程延长而加重。     

Fisher information and Shannon entropy for on-line detection of transient signal high-values in laser Doppler flowmetry signals of healthy subjects

Laser Doppler flowmetry (LDF) is an easy-to-use method for the assessment of microcirculatory blood flow in tissues. However, LDF recordings very often present TRAnsient Signal High-values (TRASH), generally of a few seconds. These TRASH can come from tissue motions, optical fibre movements, movements of the probe head relative to the tissue, etc. They often lead to difficulties in signal global interpretations. In order to test the possibility of detecting automatically these TRASH for their removal, we process noisy and noiseless LDF signals with two indices from information theory, namely Fisher information and Shannon entropy. For this purpose, LDF signals from 13 healthy subjects are recorded at rest, during vascular occlusion of 3 min, and during post-occlusive hyperaemia. Computation of Fisher information and Shannon entropy values shows that, when calibrated, these two indices can be complementary to detect TRASH and be insensitive to the rapid increases of blood flow induced by post-occlusive hyperaemia. Moreover, the real-time algorithm has the advantage of being easy to implement and does not require any frequency analysis. This study opens new fields of application for Fisher information and Shannon entropy: LDF 'denoising'.     

Lyapunov Exponents of Laser Doppler Flowmetry Signals in Healthy and Type 1 Diabetic Subjects

The skin of diabetic subjects presents abnormalities in capillary blood flow and its regulation, often leading to the generation of plantar ulcers. In order to gain insight into this pathology for type 1 diabetic patients, Lyapunov exponents (LEs) of signals reflecting microvascular perfusion—laser Doppler flowmetry (LDF) signals—are calculated. The algorithm to compute LEs is first validated on simulated data and LDF surrogates. Then, LDF signals recorded at rest and during the application of local and progressive pressure of 11.1 Pa/s are processed. The exponents appear in pairs and are different for healthy and type 1 diabetic subjects at rest; P = 0.0556 for the 7th, 8th, and 9th LEs. Furthermore, progressive pressure has also a distinct effect on LEs. The difference is more pronounced for diabetic patients, for whom P = 0.0625 for the four LEs of highest absolute value. Because these differences arise from abnormalities in microvascular blood flow, they may help to explain the high prevalence of type 1 diabetic patients developing foot ulcers.     

Endogenous prostaglandins as local regulators of blood flow in man: effect of indomethacin on reactive and functional hyperaemia.

1. The contribution of endogenously formed prostaglandins of the E series (PGE) to the development of reactive and functional hyperaemia was studied in the human forearm. 2. Forearm blood flow was recorded using venous occlusion plethysmography. The concentration of prostaglandin E-like substances (PLS) in the venous effluent from the muscle was analysed using bio-assay. For inhibition of PG biosynthesis, indomethacin (1-25 mg/kg body weight) was administered. 3. Following 5 min of arterial occlusion, a marked hyperaemia developed during the next 150 sec. Indomethacin, while not affecting the resting arterial blood flow, significantly decreased the peak level as well as the duration of the hyperaemia. The total reactive hyperaemia was 25 ml./100 ml. tissue before, and 13 ml./100 ml. tissue after administration of indomethacin. 4. During sustained isometric forearm contraction, and following isometric and dynamic forearm muscle activity, a moderate hyperaemia was observed. This was significantly diminished when indomethacin had been administered, although not to the same extent as the reactive hyperaemia. The total hyperaemia in the absence and presence of indomethacin was 113 and 77 ml./100 ml. tissue, respectively, in connexion with isometric contraction and 206 and 120 ml./100 ml. tissue, respectively, following dynamic work. 5. The venous concentration of PLS was very low at rest. A significantly increased concentration was observed after ischaemia. This increased release of PLS was entirely suppressed by indomethacin. With the present assay method, muscular activity elicited no detectable change in the venous concentration of PLS. 6. It is concluded that reactive hyperaemia depends to a considerable extent on an intact PGE synthesis. It is furthermore suggested that endogenous PGE may contribute to the functional hyperaemia that appears during and after muscle activity.     

Effects of C‐peptide on forearm blood flow and brachial artery dilatation in patients with type 1 diabetes mellitus

Recent studies suggest that C‐peptide increases blood flow in both exercising and resting forearm in patients with type 1 diabetes. Now we have studied the effect of C‐peptide administration on endothelial‐mediated and non‐endothelial‐mediated arterial responses as well as central haemodynamics in 10 patients with type 1 diabetes in a placebo‐controlled double‐blind study. Euglycaemia was maintained with an i.v. insulin infusion before and during the study. A high‐resolution ultrasound technique and Doppler echocardiography were used to assess haemodynamic functions. Brachial artery blood flow and brachial artery diameter were measured in the basal state, 1 and 10 min after reactive hyperaemia and 4 min after sublingual glyceryl trinitrate administration (GTN; endothelial‐independent vasodilatation), both before and after the end of 60‐min C‐peptide (6 pmol kg^–1 min^–1) or saline infusion periods. Echocardiographic measurements were also performed before and at the end of the infusion periods. Seven healthy age‐matched males served as controls for vascular studies. The patients showed a blunted brachial dilatation after reactive hyperaemia in comparison with the healthy controls (2.1 ± 0.5% vs. 9.3 ± 0.3%, P < 0.001), indicating a disturbed endothelial function. C‐peptide infusion compared with saline resulted in increased basal blood flow (33 ± 6%, P < 0.001) and brachial arterial dilatation (4 ± 1%, P < 0.05). Left ventricular ejection fraction seemed to be improved (5 ± 2%, P < 0.05) at the end of C‐peptide infusion compared with placebo. The vascular response to reactive hyperaemia and GTN was not affected by C‐peptide infusion. Our results demonstrate that physiological concentrations of C‐peptide increase resting forearm blood flow, brachial artery diameter and left ventricular systolic function in patients with type 1 diabetes.     

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

Summary 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°. 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. In ten healthy men, regression analyses showed positive correlation between rms-EMG and shoulder torque (r=0.77), negative correlation between MPF and arm elevation angle (r= –0.89) indicating accumulated fatigue, and almost positive correlations between LDF and rms-EMG (r=0.65), and between LDF and shoulder angle (r=0.67) when the right trapezius muscle was examined.     

Effect of long-term beta-adrenergic-blockade on calf blood flow in hypertensive patients

The effect of a four-week treatment with propranolol and metoprolol on blood pressure and regional haemodynamics of the lower extremity at rest, after exercise and during reactive hyperaemia was studied in 34 patients with essential hypertension, but without peripheral arterial disease, in a randomized placebo-controlled trial. No significant difference in side-effects recorded during the trial was observed between these two drugs. Treatment with beta-adrenergic blocking drugs reduced systemic blood pressure. Calf blood flow during vasodilatation was also decreased. The most marked changes were observed during reactive hyperaemia; mean calf blood flow was reduced from about 250 ml/min/litre of tissue to 200 ml/min/litre of tissue (P less than 0.01) by propranolol and to 214 ml/min/litre of tissue (P less than 0.01) by metoprolol. Both drugs caused a significant increase in peripheral resistance above the initial level during reactive hyperaemia (P less than 0.05). No significant difference in peripheral resistance was observed, however, when the active drugs were compared with the placebo. There was no difference between propranolol and metoprolol in any of the parameters. Thus, the flow reduction can mainly be attributed to the diminished perfusion pressure due to the decreased cardiac output caused by beta-blockade of the heart.