Uterine blood flow in the pregnant rabbit.
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Two methods are described for the measurement of uterine blood flow in the pregnant rabbit. The first involves the use of a Parks ultrasonic Doppler probe placed over the exposed uterine artery. The second method uses a drop counter system connected between the uterine and jugular veins. The Doppler flowmeter was used to measure uterine arterial blood flow in twenty rabbits on Day 28 or 29 of pregnancy. No significant difference was observed between blood flow on these 2 days and the absolute blood flow to one horn (plus or minus S. E.) was found to be 16.8 plus or minus 1.4 ml/min, equivalent to 27.1 plus or minus 1.8 ml/100 g tissue/min. Using the drop recorder technique, the flow to one uterine horn in eleven rabbits on Day 27 or 28 of pregnancy was 12.5 plus or minus 1.9 ml/min, equivalent to 23.6 plus or minus 3.2 ml/100 g tissue/min. The pressure-flow relationship in the uterine vascular bed was studied using the Doppler flowmeter and graded mechanical occlusion of the arterial supply. Within the range of pressures studied, the flow was found to be linearly related to the arterio-venous pressure difference. This suggests that the uterine vascular bed was fully dilated under the conditions of study. (+info)
Effect of rhythmic tetanic skeletal muscle contractions on peak muscle perfusion.
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The purpose of this investigation was to examine the effect of rhythmic tetanic skeletal muscle contractions on peak muscle perfusion by using spontaneously perfused canine gastrocnemii in situ. Simultaneous pulsatile blood pressures were measured by means of transducers placed in the popliteal artery and vein, and pulsatile flow was measured with a flow-through-type transit-time ultrasound probe placed in the venous return line. Two series of experiments were performed. In series 1, maximal vasodilation of the muscles' vascular beds was elicited by infusing a normal saline solution containing adenosine (29.3 mg/min) and sodium nitroprusside (180 microg/min) for 15 s and then simultaneously occluding both the popliteal artery and vein for 5 min. The release of occlusion initiated a maximal hyperemic response, during which time four tetanic contractions were induced with supramaximal voltage (6-8 V, 0.2-ms stimuli for 200-ms duration at 50 Hz, 1/s). In series 2, the muscles were stimulated for 3 min before the muscle contractions were stopped for a period of 3 s; stimulation was then resumed. The results of series 1 indicate that, although contractions lowered venous pressure, muscle blood flow was significantly reduced from 2,056 +/- 246 to 1,738 +/- 225 ml x kg(-1) x min(-1) when contractions were initiated and then increased significantly to 1,925 +/- 225 ml x kg(-1) x min(-1) during the first 5 s after contractions were stopped. In series 2, blood flow after 3 min of contractions averaged 1,454 +/- 149 ml x kg(-1) x min(-1). Stopping the contractions for 3 s caused blood flow to increase significantly to 1,874 +/- 172 ml x kg(-1) x min(-1); blood flow declined significantly to 1,458 +/- 139 ml x kg(-1) x min(-1) when contractions were resumed. We conclude that the mechanical action of rhythmic, synchronous, maximal isometric tetanic skeletal muscle contractions inhibits peak muscle perfusion during maximal and near-maximal vasodilation of the muscle's vascular bed. This argues against a primary role for the muscle pump in achieving peak skeletal muscle blood flow. (+info)
A rabbit model to study orbital venous pressure, intraocular pressure, and ocular hemodynamics simultaneously.
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PURPOSE: To measure orbital venous pressure (OVP) and determine the effects of changes in mean arterial pressure (MAP) on OVP, intraocular pressure (IOP), episcleral venous pressure (EVP), and ciliary and choroidal blood flows. METHODS: The experiments were performed in anesthetized rabbits. In all animals, MAP, IOP, and OVP were measured by direct cannulation of the central ear artery, the vitreous, and the orbital venous sinus, respectively. Laser Doppler flowmetry was used to measure choroidal blood flow in one group, and ciliary blood flow in a second group. A servonull micropressure system was used to measure EVP in a third group. The protocol for all three groups entailed varying MAP mechanically with occluders on the aorta and vena cava. RESULTS: The OVP and IOP relationship correlated linearly (r = 0.99) during mechanical manipulation of MAP. EVP also correlated well with OVP (r = 0.9). Resistance calculations based on choroidal and ciliary blood flows and the pressure gradients indicate active adjustment of arterial resistance and passive changes in venous resistance in response to changing MAP in both circulations. CONCLUSIONS: The rabbit orbital venous sinus permits continuous measurements of OVP. The present findings show that OVP is not static and suggest that OVP may play an important role in IOP homeostasis and ocular hemodynamics. (+info)
Effect of hindlimb isolation procedure on isogravimetric capillary pressure and transcapillary fluid dynamics in dogs.
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We measured isogravimetric capillary pressure (Pci) and plasma colloid osmotic pressure (pip) in isolated dog hindlimbs. A very rapid isolation technique and a perfusion technique involving no weight change were developed in order to compare the effects of different isolation procedures. Also, a "previous isolation procedure" (PIP) was used to approximate isolation procedures previously reported; this procedure included (A) anesthesia for 1 to 1 1/2 hours before limb isolation, (B) 1/2 hour of denervation before isolation, and (C) perfusion after isolation for 1/2 hour at an arterial pressure of 100 mm Hg and a venous pressure of 6 mm Hg. These different procedures altered average (+/- SE) capillary pressure and fluid dynamics in the hindlimb as shown in the foly pressure in the intact resting dog hindlimb may be 8 mm Hg below plasma colloid osmotic pressure, or about 9 mm Hg, and that many reported values have been heavily influenced by the isolation technique. (+info)
Hepatic venous pressure gradient measurements to assess response to primary prophylaxis in patients with cirrhosis: a decision analytical study.
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BACKGROUND: The measurement of the hepatic venous pressure gradient may identify a suboptimal response to beta-blockers in patients with varices at risk for bleeding. However, the cost-effectiveness of routine hepatic venous pressure gradient measurements to guide primary prophylaxis has not been examined. METHODS: We used decision analysis to evaluate two hepatic venous pressure gradient measurement strategies relative to standard beta-blocker therapy in a hypothetical cohort of patients with high-risk varices: (i) hepatic venous pressure gradient measurement 4 weeks after the initiation of beta-blocker therapy; and (ii) hepatic venous pressure gradient measurement prior to and 4 weeks after the initiation of beta-blocker therapy. The total expected costs, variceal bleeding episodes and deaths were calculated over a 1-year time horizon. RESULTS: Beta-blocker therapy was associated with total costs of $1464, seven variceal bleeding episodes, one variceal bleeding episode-related death and 15 deaths. One hepatic venous pressure gradient measurement was associated with total costs of $5015, four variceal bleeding episodes, one variceal bleeding episode-related death and 15 deaths. Two hepatic venous pressure gradient measurements were associated with total costs of $8657, four episodes of variceal bleeding, one variceal bleeding episode-related death and 15 deaths. Compared with beta-blocker therapy alone, the incremental costs per variceal bleeding episode prevented and death averted were, respectively, $108 185 and $355 100 (one hepatic venous pressure gradient measurement) and $202 796 and $719 300 (two hepatic venous pressure gradient measurements). The results were sensitive to the time horizon of the analysis, the probability of bleeding whilst on beta-blockers and the cost of hepatic venous pressure gradient measurement. CONCLUSION: Hepatic venous pressure gradient measurement to guide primary prophylaxis is an expensive strategy for reducing variceal bleeding or death, especially in patients with limited life expectancy, such as those with advanced, decompensated cirrhosis. (+info)
On-line venous oxygen tensions in rainbow trout during graded exercise at two acclimation temperatures.
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For most teleost fish, the majority of the myocardial oxygen supply is provided by the oxygen reserve remaining in venous blood after other tissues have extracted oxygen. We examined the effect of graded exercise and water temperature on this venous blood oxygen supply to the heart (termed the cardiac circulation) by performing novel on-line measurements of venous partial pressure of oxygen (Pv(O(2))) using a fibreoptic micro-optode implanted in the ductus Cuvier of rainbow trout (Oncorhynchus mykiss). As expected, Pv(O(2)) decreased progressively and significantly as swimming velocity approached the critical swimming speed (U(crit)). Unsteady swimming behaviours during the graded exercise, however, caused abrupt and generally short-lived decreases in Pv(O(2)). For the cold-acclimated (6-10 degrees C) fish, Pv(O(2)) reached a minimum plateau value of 15.3+/-3.7 torr (1 torr=133.3 Pa) before U(crit) was reached, and so increased swimming effort near to U(crit) did not reduce Pv(O(2)) further. Warm-acclimated fish had a significantly higher Pv(O(2)) (28.9+/-3.5 torr) at U(crit). Despite this difference in the Pv(O(2)) at U(crit), we estimated that there was little difference between warm- and cold-acclimated fish in terms of oxygen supply in the cardiac circulation because of a right-shift in the haemoglobin-oxygen dissociation curve at warm temperatures. Furthermore, although Pv(O(2)) decreased significantly at U(crit), our estimates suggest that the expected increase in cardiac output would easily maintain the oxygen supply in venous blood at a level similar to that found in resting fish. Although unsteady swimming behaviours decreased Pv(O(2)), unsteady swimming rarely decreased the minimum Pv(O(2)) value observed at U(crit) by more than 10%. The findings are discussed in terms of a threshold Pv(O(2)) required to maintain adequate rates of oxygen diffusion from the cardiac circulation to the myocardial tissues. (+info)
Influence of leg position and environmental temperature on segmental volume expansion during venous occlusion plethysmography.
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Blood flow determinations by venous occlusion plethysmography applying the strain-gauge technique are frequently used. A problem with the strain-gauge technique is that the relationship between venous volume and transmural pressure is not linear and, furthermore, changes with the sympathetic tone. The present study tests the hypothesis that these factors lead to a redistribution of venous blood, which may impair the accuracy of the technique. The relative volume expansion rates of four leg segments were studied with the leg in different positions and at disparate temperatures, thereby inducing varying venous pressures and sympathetic tone ( n =6). With elevated leg and relaxed veins (at 50 degrees C), the distal thigh showed a relatively low expansion rate (25.8+/-4.5 ml.min(-1).l(-1)), whereas values in the calf segments were higher (34.5-39.0 ml.min(-1).l(-1)). With lower initial transmural pressure, calf segments can increase their volume much more during occlusion compared with the distal thigh. In a higher transmural pressure region (lowered leg), the difference in compliance between limb segments is less. In this case, compliance and volume expansion rate was higher in the distal thigh (14.2, 13.5 and 22.2 ml.min(-1).l(-1) at 10, 20 and 50 degrees C respectively) than in the calf segments (for the distal calf: 6.4, 7.7 and 16.2 ml.min(-1).l(-1) respectively). There was a significant interaction ( P <0.001) between temperature and leg position, indicating a higher degree of sympathetic vasoactivity in the calf. It is concluded that blood flow determination by strain-gauge plethysmography is less accurate, due to a potential redistribution of the venous blood. Therefore possible influences of variations in sympathetic tone and venous pressure must be considered even in intra-individual comparisons, especially in interventional studies. (+info)
The jugular foramen in complex and syndromic craniosynostosis and its relationship to raised intracranial pressure.
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BACKGROUND AND PURPOSE: Complex and syndromic craniosynostosis can be complicated by raised intracranial pressure (ICP), which in the absence of other identifiable origins, is probably caused by venous hypertension. Children with these conditions have been shown to have narrowing of the sigmoid sinus-jugular vein complex. Evidence of bony narrowing of the jugular foramina in children with complex or syndromic craniosynostosis and raised ICP compared with that in children with craniosynostosis without raised ICP would provide support for the theory that venous hypertension occurs in the former children. METHODS: Measurements of the jugular foramina were obtained from reformatted helical CT scans obtained in 12 children with complex or syndromic craniosynostosis and raised ICP (group 1) and in two control groups of children with normal ICP. The first control group comprised 10 children with simple nonsyndromic synostosis of one or two sutures (group 2), and the second control group included nine children with complex or syndromic craniosynostosis (group 3). RESULTS: Children with raised ICP had narrower jugular foramina than did the age-matched control subjects. For group 1, the mean diameter of jugular foramina was 6.5 mm; group 2, 11.5 mm (P <.01); and group 3, 10 mm (P <.05). No significant difference existed between the two control groups. CONCLUSION: Significantly narrower jugular foramina in children with raised ICP is further evidence of the role of venous outflow obstruction and intracranial venous hypertension in the development of raised ICP in complex and syndromic craniosynostosis. (+info)