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1.
We infused lidocaine intravenously into 13 pregnant ewes at a rate sufficient to maintain plasma levels between 2-4 mugm/ml, which are those commonly seen with regional anaesthesia. These levels did not change maternal blood pressure, pulse rate, cardiac output, stroke volume, total peripheral resistance, uterine blood flow or intra-amniotic pressure. Foetal blood pressure and pulse rate remained stable as did both maternal and foetal blood gases and acid-base values.  相似文献   

2.
OBJECTIVE: To determine placental transfer of ketanserin and to assess the effect of serotonin-2 receptor blockade by ketanserin on serotonin- and phenylephrine-induced vasoconstriction. STUDY DESIGN: Five chronically instrumented pregnant ewes at 120 days gestation were injected with 20 mg ketanserin i.v., and fetal and maternal arterial samples were obtained at predetermined intervals to assess placental transfer. Maternal and fetal responses of blood flows and pressures were determined after injected of serotonin (20 micrograms/kg) or phenylephrine (10 micrograms/kg) before and after ketanserin (0.75 mg/kg). RESULTS: In the ewe, ketanserin is transferred across the placenta and reaches measurable levels in the fetal lamb. Ketanserin blocks the maternal and fetal serotonin-induced rise in arterial pressure, but not the serotonin-induced reduction in uterine blood flow. CONCLUSION: In the pregnant ewe, the serotonin-induced rise in maternal and fetal blood pressure is effectively antagonized by ketanserin, whereas the serotonin-induced reduction in uterine blood flow is not.  相似文献   

3.
Resistance exercise has been suggested to increase blood volume, increase the sensitivity of the carotid baroreceptor cardiac reflex response (BARO), and decrease leg compliance, all factors that are expected to improve orthostatic tolerance. To further test these hypotheses, cardiovascular responses to standing and to pre-syncopal limited lower body negative pressure (LBNP) were measured in two groups of sedentary men before and after a 12-week period of either exercise (n = 10) or no exercise (control, n = 9). Resistance exercise training consisted of nine isotonic exercises, four sets of each, 3 days per week, stressing all major muscle groups. After exercise training, leg muscle volumes increased (P < 0.05) by 4-14%, lean body mass increased (P = 0.00) by 2.0 (0.5) kg, leg compliance and BARO were not significantly altered, and the maximal LBNP tolerated without pre-syncope was not significantly different. Supine resting heart rate was reduced (P = 0.03) without attenuating the heart rate or blood pressure responses during the stand test or LBNP. Also, blood volume (125I and 51Cr) and red cell mass were increased (P < 0.02) by 2.8% and 3.9%, respectively. These findings indicate that intense resistance exercise increases blood volume but does not consistently improve orthostatic tolerance.  相似文献   

4.
We investigated the influence of the maternal heart rate on the uterine artery pulsatility index in pregnant ewes. We used an external pacemaker to alter the heart rate of 5 pregnant ewes at 16-17 weeks of pregnancy and examined the effect of changes in the maternal heart rate on the uterine artery flow velocity waveforms and the pulsatility index, as determined by Doppler velocimetry. The uterine artery pulsatility index showed a significant negative correlation with the maternal heart rate. There were no significant changes in other hemodynamic parameters. The maternal heart rate had a significant influence on the uterine artery pulsatility index.  相似文献   

5.
Exercise in the water offers several physiological advantages to the pregnant woman. The hydrostatic force of water pushes extravascular fluid into the vascular spaces, producing an increase in central blood volume that may lead to increased uterine blood flow. This force is proportional to the depth of immersion. The increase in blood volume is proportional to the woman's edema. A marked diuresis and natriuresis accompanies the fluid shifts. The buoyancy of water supports the pregnant women. Water is thermoregulating. Studies of pregnant women exercising in the water have shown less fetal heart rate changes in the water than on land in response to exertion. Pregnant women's heart rates and blood pressures during water exercise are lower than on land exercise, reflecting the immersion-induced increase in circulating blood volume. The physiology of water exercise offers some compensation for the physiological changes of exercise on land that may beneficially affect pregnancy.  相似文献   

6.
Ways of knowing     
BACKGROUND: Although it has become clear that habitual exercise in older individuals can partially offset age-associated cardiovascular declines, it is not known whether the beneficial effects of exercise training in older individuals depend on their prior fitness level. METHODS AND RESULTS: Ten sedentary men (S), age 60.0 +/- 1.6 years (mean +/- SEM), who were carefully screened to exclude cardiac disease underwent exercise training for 24 to 32 weeks, and eight age-matched endurance-trained men (ET) stopped their exercise training for 12 weeks. All underwent treadmill exercise and rest and maximal cycle exercise upright gated blood pool scans at baseline and after the lifestyle intervention. Before the intervention, the treadmill maximum rate of oxygen consumption (Vo2max) was 49.9 +/- 1.9 and 32.1 +/- 1.4 mL.kg-1.min-1 in ET and S, respectively. During upright cycle exercise at exhaustion, although heart rate did not differ between groups, cardiac index, stroke volume index, ejection fraction, and left ventricular contractility index (systolic blood pressure/end-systolic volume index) all were significantly higher, and end-systolic volume index, diastolic blood pressure, and total systemic vascular resistance all were significantly lower in ET versus S. After the partial deconditioning of ET men, Vo2max fell to 42 +/- 2.2 mL.kg-1.min-1, and training of S increased Vo2max to 36.2 +/- 1.6 mL.kg-1.min-1. Training of S had effects on cardiovascular function that were similar in magnitude but directionally opposite those of detraining ET. All initial differences in cardiovascular performance at peak work rate between S and ET were abolished with the intervention. Across the broad range of fitness levels encountered before and after change in training status (Vo2max of 26 to 58 mL.kg-1.min-1), cardiac index, stroke volume index, end-systolic volume index, ejection fraction, and the left ventricular contractility index were all linearly correlated with Vo2max. CONCLUSIONS: Exercise training or detraining of older men results in changes in left ventricular performance that are qualitatively and quantitatively similar, regardless of the initial level of fitness before the intervention.  相似文献   

7.
AIMS: Most secundum atrial septal defects, once diagnosed, are corrected at a young age. The evidence to justify early vs delayed or even non-closure is equivocal and little is known regarding long-term effects of later closure. This is particularly pertinent to those patients awaiting transcatheter closure of their defect for whom a device is only just becoming available. We examined the exercise cardiorespiratory physiology of children surgically treated for an isolated secundum defect. METHODS AND RESULTS: One hundred and six healthy control children and 22 children more than 6 months after surgical repair for an isolated secundum atrial septal defect were studied. All were asymptomatic. Measurements of effective pulmonary blood flow, stroke volume, arteriovenous oxygen difference, minute ventilation, heart rate, oxygen consumption and carbon dioxide production were made using a quadrupole mass spectrometer during rest and graded exercise. Data from the normal children allowed calculation of z scores for the atrial septal defect group matched for age, sex, pubertal stage and surface area. Maximal exercise performance was equal between control and atrial septal defect groups, however, the atrial septal defect group had a significantly greater effective pulmonary blood flow and stroke volume but a lower heart rate than controls at a given exercise stage. Stroke volume abnormalities were most closely related to duration of follow-up (29% of the variance explained, P < 0.01) rather than age at surgery. CONCLUSIONS: We were unable to show a medium term benefit from early surgery for an asymptomatic secundum atrial septal defect during exercise. The clinical relevance of the haemodynamic differences that do exist remains unclear.  相似文献   

8.
1. Hypertension secondary to renal disease was studied in non-pregnant and pregnant ewes to determine whether there were any changes in arterial pressure and the distribution of cardiac output and, in particular, whether uteroplacental blood flow was affected. 2. In six non-pregnant, chronically catheterized, uninephrectomized ewes, a reduction in renal blood flow (RBF) to 40-50% of control caused hypertension within 3 h. This was maintained for as long as RBF was reduced (72 h) and returned to control 24 h after the occluder around the renal artery was released. When this experiment was repeated in 16 uninephrectomized pregnant ewes (118-134 days gestation) hypertension occurred within 3 h and was sustained for as long as RBF was reduced (between 24 and 72 h). Arterial pressure returned to control within 24-72 h of restoring RBF. 3. Compared with non-pregnant ewes, pregnant ewes had similar arterial pressures, higher cardiac outputs (CO; P < 0.001) and heart rates (HR; P < 0.001), lower total peripheral resistances (TPR; P < 0.001) and similar blood flows to brain, ovary, pancreas, kidney and spleen. Splenic vascular resistance (VR) was greater (P = 0.006), gut blood flow was greater (P < 0.05) and gut VR was less (P < 0.05). Myoendometrial blood flow/g was greater (P < 0.005) and myoendometrial VR was less (P = 0.006). 4. In pregnant sheep with renal clip hypertension, there was no change in CO and HR, but TPR increased (P < 0.01), as did plasma renin activity. Gut, brain, pancreatic and myoendometrial VR were increased as long as RBF was reduced; in addition, myoendometrial VR remained high for the rest of the experiment. Placental blood flow was unchanged at 3 h; 24-72 h later it was reduced (P < 0.05) and remained low. Placental VR was increased 24-72 h after RBF was restored when ewes were again normotensive. 5. Thus, one-clip, one-kidney renal hypertension in the pregnant ewe was due to increased TPR associated with a fall in uteroplacental blood flow that persisted even when RBF was restored and ewes were normotensive. This reduction in uteroplacental blood flow could account for the high foetal morbidity and mortality that occurs in pregnant women with renovascular hypertension.  相似文献   

9.
During dynamic exercise in warm environments, requisite increases in skin and active muscle blood flows are supported by increasing cardiac output (Qc) and redistributing flow away from splanchnic and renal circulations. To examine the effect of age on these responses, six young (Y; 26 +/- 2 yr) and six older (O; 64 +/- 2 yr) men performed upright cycle exercise at 35 and 60% of peak O2 consumption (VO2peak) in 22 and 36 degrees C environments. To further isolate age, the two age groups were closely matched for VO2peak, weight, surface area, and body composition. Measurements included heart rate, Qc (CO2 rebreathing), skin blood flow (from increases in forearm blood flow (venous occlusion plethysmography), splanchnic blood flow (indocyanine green dilution), renal blood flow (p-amino-hippurate clearance), and plasma norepinephrine concentration. There were no significant age differences in Qc; however, in both environments the O group maintained Qc at a higher stroke volume and lower heart rate. At 60% VO2peak, forearm blood flow was significantly lower in the O subjects in each environment. Splanchnic blood flow fell (by 12-14% in both groups) at the lower intensity, then decreased to a greater extent at 60% VO2peak in Y than in O subjects (e.g., -45 +/- 2 vs. -33 +/- 3% for the hot environment, P < 0.01). Renal blood flow was lower at rest in the O group, remained relatively constant at 35% VO2peak, then decreased by 20-25% in both groups at 60% VO2peak. At 60% VO2peak, 27 and 37% more total blood flow was redistributed away from these two circulations in the Y than in the O group at 22 and 36 degrees, respectively. It was concluded that the greater increase in skin blood flow in Y subjects is partially supported by a greater redistribution of blood flow away from splanchnic and renal vascular beds.  相似文献   

10.
The present study was designed to characterize effects of inhibiting PG production by infusing nimesulide (CAS 51803-78-2) on PGE2 production and expression of uterine labor-related genes in pregnant sheep. Myometrium, endometrium, and placenta were collected following 6 h of i.v. nimesulide or vehicle infusion. Infusions were commenced 9 h after onset of spontaneous term labor. Tissues were also collected from term control ewes not in labor. PGE2 was measured in fetal plasma by RIA. ER, OTR, Hsp 70 and 90, cPLA2, and PGHS-2 messenger RNA (mRNA) abundance in myometrium, endometrium, and PGHS-2 in placenta were quantified by Northern blot analysis. Fetal plasma PGE2 decreased during nimesulide infusion (P < 0.05). ER, OTR, Hsp 70, and Hsp 90 mRNA increased during spontaneous term labor in vehicle infused ewes in both myometrium and endometrium. In myometrium after nimesulide infusion, OTR and Hsp 70 mRNA decreased significantly (P < 0.05) compared with vehicle infused animals, but the decrease in Hsp 90 and ER mRNA fell outside the level of significance. In the endometrium, nimesulide produced a decrease in ER and OTR mRNA (P < 0.05) compared with vehicle infused animals, but the changes in Hsp 90 and 70 mRNA fell outside the level of significance. Nimesulide reversed the up-regulation of PGHS-2 mRNA that occurred in myometrium, endometrium, and placenta during vehicle infusion (P < 0.05). cPLA2 was only elevated in the endometrium in vehicle infused ewes and did not change in either endometrium or myometrium after nimesulide infusion. CONCLUSIONS: Inhibition of PG production resulted in decreased fetal plasma PGE2. The decreased abundance of mRNA for several of the well described cassette of utero-placental labor-related genes following nimesulide inhibition may result from altered PG production.  相似文献   

11.
A randomized crossover study was designed using the chronically instrumented pregnant sheep preparation to study the possible effects of epidural injection of adrenaline as a single compound on the circulation of mother and fetus. Three consecutive identical doses of adrenaline were administered epidurally with a 30 min interval between treatments. In a randomized crossover fashion two dosages (10 and 15 micrograms) were tested on different days. The day after the last epidural experiment the same doses of adrenaline were given intravenously (i.v.). Between the two i.v. doses a 30 min interval was allowed for values to return to baseline. Twenty-seven experiments were performed in eight ewes. Epidural administration of adrenaline did not affect maternal mean arterial pressure, maternal heart rate, uterine blood flow, fetal mean arterial pressure, fetal heat rate, or maternal and fetal blood gases and acid-base status. After i.v. administration of adrenaline the uterine blood flow decreased in a dose-dependent fashion, but the other haemodynamic variables were not affected. In conclusion, this study indicates that consecutive epidural injections of adrenaline have no significant effect on maternal and fetal haemodynamic responses, uterine blood flow, blood gases and acid-base status in the gravid ewe. However, an i.v. injection of 10 or 15 micrograms adrenaline decreases the uterine blood flow and could compromise the fetus.  相似文献   

12.
Whole body O2 uptake (VO2) during maximal and submaximal exercise has been shown to be preserved in the setting of beta-adrenergic blockade at high altitude, despite marked reductions in heart rate during exercise. An increase in stroke volume at high altitude has been suggested as the mechanism that preserves systemic O2 delivery (blood flow x arterial O2 content) and thereby maintains VO2 at sea-level values. To test this hypothesis, we studied the effects of nonselective beta-adrenergic blockade on submaximal exercise performance in 11 normal men (26 +/- 1 yr) at sea level and on arrival and after 21 days at 4,300 m. Six subjects received propranolol (240 mg/day), and five subjects received placebo. At sea level, during submaximal exercise, cardiac output and O2 delivery were significantly lower in propranolol- than in placebo-treated subjects. Increases in stroke volume and O2 extraction were responsible for the maintenance of VO2. At 4,300 m, beta-adrenergic blockade had no significant effect on VO2, ventilation, alveolar PO2, and arterial blood gases during submaximal exercise. Despite increases in stroke volume, cardiac output and thereby O2 delivery were still reduced in propranolol-treated subjects compared with subjects treated with placebo. Further reductions in already low levels of mixed venous O2 saturation were responsible for the maintenance of VO2 on arrival and after 21 days at 4,300 m in propranolol-treated subjects. Despite similar workloads and VO2, propranolol-treated subjects exercised at greater perceived intensity than subjects given placebo at 4,300 m. The values for mixed venous O2 saturation during submaximal exercise in propranolol-treated subjects at 4,300 m approached those reported at simulated altitudes >8,000 m. Thus beta-adrenergic blockade at 4,300 m results in significant reduction in O2 delivery during submaximal exercise due to incomplete compensation by stroke volume for the reduction in exercise heart rate. Total body VO2 is maintained at a constant level by an interaction between mixed venous O2 saturation, the arterial O2-carrying capacity, and hemodynamics during exercise with acute and chronic hypoxia.  相似文献   

13.
14.
The hypothesis that the rapid increases in blood flow at the exercise onset are exclusively due to the mechanical effects of the muscle pump was tested in six volunteers during dynamic handgrip exercise. While supine, each subject completed a series of eight different exercise tests in which brachial artery blood pressure (BP) was altered by 25-30 mmHg (1 mmHg = 133.3 Pa) by positioning the arm above or below the heart. Two different weights, corresponding to 4.9 and 9.7% of maximal voluntary isometric contraction, were raised and lowered at two different contraction rate schedules (1s:1s and 2s:2s work-rest) each with a 50% duty cycle. Beat-by-beat measures of mean blood velocity (MBV) (pulsed Doppler) were obtained at rest and for 5 min following step increases in work rate with emphasis on the first 24 s. MBV was increased 50-100% above rest following the first contraction in both arm positions (p < 0.05). The increase in MBV from rest was greater in the below position compared with above, and this effect was observed following the first and subsequent contractions (p < 0.05). However, the positional effect on the increase in MBV could not be explained entirely by the approximately 40% greater BP in this position. Also, the greater workload resulted in greater increases in MBV as early as the first contraction, compared with the light workload (p < 0.05) despite similar reductions in forearm volume following single contractions. MBV was greater with faster contraction rate tests by 8 s of exercise. It was concluded that microvascular vasodilation must act in concert with a reduction in venous pressure to increase forearm blood flow within the initial 2-4 s of exercise.  相似文献   

15.
Spaceflight induces a cephalad redistribution of fluid volume and blood flow within the human body, and space motion sickness, which is a problem during the first few days of spaceflight, could be related to these changes in fluid status and in blood flow of the cerebrum and vestibular system. To evaluate possible changes in cerebral blood flow during simulated weightlessness, we measured blood velocity in the middle cerebral artery (MCA) along with retinal vascular diameters, intraocular pressure, impedance cardiography, and sphygmomanometry on nine men (26.2 +/- 6.6 yr) morning and evening for 2 days during continuous 10 degrees head-down tilt (HDT). When subjects went from seated to head-down bed rest, their heart rate and retinal diameters decreased, and intraocular pressures increased. After 48 h of HDT, blood flow velocity in the MCA was decreased and thoracic impedance was increased, indicating less fluid in the thorax. Percent changes in blood flow velocities in the MCA after 48 h of HDT were inversely correlated with percent changes in retinal vascular diameters. Blood flow velocities in the MCA were inversely correlated (intersubject) with arterial pressures and retinal vascular diameters. Heart rate, stroke volume, cardiac output, systolic arterial pressure, and at times pulse pressure and blood flow velocities in the MCA were greater in the evening. Total peripheral resistance was higher in the morning. Although cerebral blood velocity is reduced after subjects are head down for 2 days, the inverse relationship with retinal vessel diameters, which have control analogous to that of cerebral vessels, indicates cerebral blood flow is not reduced.  相似文献   

16.
The effect on the middle cerebral artery blood flow velocity (VMCA) of moderate and hard physical exercise on an ergometer cycle was examined in 10 healthy volunteers using transcranial Doppler sonography (TCD). During exercise, the heart rate increased by 136% and the systolic blood pressure by 37% (mean values). During initial moderate exercise, VMCA increased by 51%; in a following period of maximal physical work, VMCA decreased again by 20% in 9 of 10 volunteers although the heart rate continued to increase by 10% and the systolic blood pressure by 5% (mean values). Constriction of the MCA may explain the initial increase of VMCA, suggesting a role for large cerebral arteries in autoregulation. Our data indicate that the subsequent decrease of VMCA is caused by arteriolar constriction, a likely cause of which was hyperventilation during the excessive work period.  相似文献   

17.
It is known that a compensatory reduction and diversion of renal flow occurs in severe exercise in humans but not in dogs. We investigated this in miniature swine by measuring changes in total renal blood flow (TRF) and intra-renal blood flow (IRBF) distribution with tracer microspheres (15 +/- 5 mum) at rest and during steady-state exercise at 4.8-7.2 kph and 0% grade, and during severe exercise at 4.8-7.2 kph and 10% grade. We measured heart rate and cardiac output (Q) via implanted probes. TRF was determined as a percent of Q and as ml/100 g per min. IRBF was determined for the outer cortex, inner cortex, outer medulla, and inner medulla. Our results show that renal blood flow is significantly (P less than 0.05) reduced in pigs with exercise. Steady-state exercise reduced flow to about 66% of control and severe exercise reduced renal flow to 30% of control. IRBF was unchanged throughout. These results show that the exercising pig augments blood flow to skeletal muscle by reducing blood flow to kidneys, a response known to occur in man.  相似文献   

18.
OBJECTIVE: To determine the effect of physical activity on pulmonary, cardiovascular and metabolic activity in paraplegics. PATIENTS AND METHODS: Eight male paraplegics (average age 35.7 [range 25-47] years) had been selected from a pool of training members of the German Sport Union for the Disabled. They performed graded arm crank training for 8.3 +/- 3.1 h/week. Left ventricular volume (LVV), stroke volume (SV), wall thickness (WT), heart rate (HR) as well as serum lactate concentration were measured after different levels of the graded exercise. Results were compared with those obtained in 11 male sport students (average age 26.4 [23-30] years), who had similarly trained for 5.6 +/- 1.3 h/week. RESULTS: The paraplegics had a significantly smaller LVV than the controls (771 +/- 84 ml vs 976 +/- 84 ml) and smaller SV (83 +/- 13 ml vs 104 +/- 11ml), with comparable WT. Paraplegics achieved significantly lower maximal exercise (145 +/- 23.7 vs 160 +/- 28.2) and maximal HR (177 +/- 12 vs 170 +/- 9) were not significantly different at the various exercise steps. CONCLUSION: Paraplegia decreases cardiac dimensions and function. Long-term physical exercise achieves results comparable with those of untrained but not of trained healthy controls. Physically active paraplegics showed physiological cardiovascular and metabolic reactions to exercise.  相似文献   

19.
Measuring haemodynamic performance in children is either invasive, and thus unacceptable, or noninvasive when the measured variable is often remote from the true variable. Measuring only maximum performance variables relies too heavily on motivation, especially in disease groups. We describe a method for the measurement of haemodynamic performance using respiratory mass spectrometry during rest, exercise and recovery therefrom. One hundred and six healthy children (55 male, 51 female) aged 8-16.9 yrs underwent an identical exercise protocol. Following studies at rest, they initially bicycled at 25 W x m(-2), increasing every 3 min by 15 W x m(-2) until exhaustion, after which measurements were made during recovery. Effective pulmonary blood flow, stroke volume, oxygen consumption, arteriovenous oxygen difference and functional residual capacity (FRC) together with estimates of pulmonary capillary blood volume and transit time were assessed at every exercise stage using inert gas rebreathing techniques. Haemodynamic performance is highly dependent on surface area, age, gender and pubertal stage. Many parameters, for example transfer factor, demonstrate pubertal stage-dependent differences at identical workloads even after correction for size. Females have a lower capillary blood volume at rest compared to age and size-matched males, but it is equalized during exercise. FRC unexpectedly rose with exercise, and peak exercise was associated with a falling stroke volume in 91% (95% CI 84-96%) of children, a possible demonstration of Starling's law of the heart. Oxygen pulse (oxygen consumption/cardiac frequency) is a very poor marker for pulmonary blood flow. Normal values are provided for all haemodynamic parameters for rest and every exercise stage for all subgroups of children. This should allow accurate comparison of normal and disease groups in future.  相似文献   

20.
In order to evaluate the effects of physical activity on seric lipoproteins and coagulation parameters, an 8-week clinical trial was performed. Fifteen healthy young subjects (average age 23 years) with no history of previous agonistic physical activity, entered the study. Each subject underwent a physical programme consisting of three times a week bicycle ergometer exercise with progressive increases in work rate by using stages of 3 min duration until the 85% of the predictive heart rate was reached. Each individual was subjected to four blood drawings according to the following schedule: at the beginning of the study, after 4 weeks, after 8 weeks (at the end of the programme) and 4 weeks after the interruption of training. As far as the seric lipoproteins are concerned, the following parameters were monitored: total cholesterol, HDL-C, LDL-C, VLDL-C, triglycerides, Apo-A1, Apo-B100, NEFA and phospholipids. On the other hand the following coagulation parameters were monitored: fibrinogen PT, aPtt, coagulation factors (II-XII), red cells, leucocytes, platelets, hemoglobin and hematocrit. From the analysis of the data, the following statistically significant results were observed: HDL-C increased by 14%, LDL-C decreased by 13%, Apo-A1 increased by 6%, fibrinogen increased by 31.7%, Ptt decreased by 3.7% and leucocytes increased by 15%. Four weeks after exercise was terminated, all monitored parameters turned into the basal range. Our data seem to demonstrate a positive effect of physical exercise on seric lipoproteins in the short period. Nevertheless they provide evidence of an hypercoagulability condition demonstrated by the important fibrinogen increase and the Ptt decrease.  相似文献   

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