Effect of portal-systemic anastomosis on renal haemodynamics in cirrhosis.
(1/366)
In 12 patients with portal hypertension and repeated bleedings from oesophageal varices the central haemodynamics, portal pressure, and mean renal blood flow (RBF) were investigated immediately before and two to seven months after portal-systemic shunt. Cardiac output increased significantly, whereas arterial pressure was unchanged after operation. RBF, which was initially less than in controls, did not change. As portal pressure decreased significantly, a direct portal-renal, neural, or humoral reflex mechanism does not explain the subnormal RBF in cirrhosis. As plasma volume was large and unchanged after operation a "diminished circulating plasma volume" is an unlikely explanation. Therefore, on the basis of the present observations, previously postulated causes of renal hypoperfusion in cirrhosis need revision. (+info)
Chronic retinal vein occlusion in glaucoma.
(2/366)
Asymptomatic chronic retinal vein occlusion that occurs in chronic simple glaucoma is described. The condition is characterized by marked elevation of retinal vein pressure with collateral vessels and vein loops at the optic disc in cases of central vein occlusion, or retinal veno-venous anastomoses along a horizontal line temporal and nasal to the disc in hemisphere vein occlusion. No patient had visible arterial changes, capillary closure, fluorescein leakage, or haemorrhages. The vein occlusion was not limited to "end stage" glaucoma. The role of increased intraocular pressure and glaucomatous enlargement of the optic cup with retinal vein distortion in the pathogenesis of the condition was stressed. Follow-up of these patients revealed persistence of the retinal vein occlusion shown by elevated retinal vein pressures. This would reduce effective perfusion of the inner retina and optic disc and may affect the long-term visual prognosis. (+info)
Upright posture reduces forearm blood flow early in exercise.
(3/366)
The hypothesis that upright posture could modulate forearm blood flow (FBF) early in exercise was tested in six subjects. Both single (2-s duration) and repeated (1-s work/2-s rest cadence for 12 contractions) handgrip contractions (12 kg) were performed in the supine and 70 degrees head-up tilt (HUT) positions. The arm was maintained at heart level to diminish myogenic effects. Baseline brachial artery diameters were assessed at rest in each position. Brachial artery mean blood velocity (MBV; Doppler) and mean arterial pressure (MAP) (Finapres) were measured continuously to calculate FBF and vascular conductance. MAP was not changed with posture. Antecubital venous pressure (Pv) was reduced in HUT (4.55 +/- 1.3 mmHg) compared with supine (11.3 +/- 1.9 mmHg) (P < 0.01). For the repeated contractions, total excess FBF (TEF) was reduced in the HUT position compared with supine (P < 0.02). With the single contractions, peak FBF, peak vascular conductance, and TEF during 30 s after release of the contraction were reduced in the HUT position compared with supine (P < 0.01). Sympathetic blockade augmented the FBF response to a single contraction in HUT (P < 0.05) and tended to increase this response while supine (P = 0.08). However, sympathetic blockade did not attenuate the effect of HUT on peak FBF and TEF after the single contractions. Raising the arm above heart level while supine, to diminish Pv, resulted in FBF dynamics that were similar to those observed during HUT. Alternatively, lowering the arm while in HUT to restore Pv to supine levels restored the peak FBF and vascular conductance responses, but not TEF response, after a single contraction. It was concluded that upright posture diminishes the hyperemic response early in exercise. The data demonstrate that sympathetic constriction restrains the hyperemic response to a single contraction but does not modulate the postural reduction in postcontraction hyperemia. Therefore, the attenuated blood flow response in the HUT posture was largely related to factors associated with diminished venous pressures and not sympathetic vasoconstriction. (+info)
Studies in calf venous pump function utilizing a two-valve experimental model.
(4/366)
OBJECTIVES: to explore the hydrodynamic mechanisms involved in the regulation of ambulatory venous pressure. DESIGN: an experimental model of calf venous pump was constructed with collapsible tubes and valves. MATERIAL: the model consisted of a conduit and a pump with an intervening competent valve. Another valve that could allow reflux into the pump was mounted above the pump. METHODS: conduit pressure and recovery times were monitored under conditions of different degrees of ejection fraction and reflux into the pump. Model variables included using poorly compliant tubes for the pump, the conduit and for both the pump and conduit. RESULTS: the latex tube exhibited a non-linear volume-pressure relationship and a bi-modal regimen of compliance. This bestowed pressure-buffering properties. Ambulatory venous hypertension resulted when reflux beyond buffering capacity occurred. Substituting less compliant PTFE for latex at the pump had a relatively minor effect on post-ejection pressure and recovery times. Using PTFE at the conduit had a profound but divergent effect on both of these parameters. Conduit capacitance reduction had a similar effect. CONCLUSION: conduit elastance plays a significant role in the regulation of ambulatory venous pressure in this experimental model. The hydrodynamic principles illustrated by the model may enhance our understanding of the human calf venous pump. (+info)
Responses of group III and IV muscle afferents to distension of the peripheral vascular bed.
(5/366)
This study was undertaken to test the hypothesis that group III and IV afferents with endings in skeletal muscle signal the distension of the peripheral vascular network. The responses of these slowly conducting afferents to pharmacologically induced vasodilation and to acute obstruction of the venous drainage of the hindlimbs were studied in barbiturate-anesthetized cats. Afferent impulses arising from endings in the triceps surae muscles were recorded from the L(7) and S(1) dorsal roots. Fifteen of the 48 group IV and 3 of the 19 group III afferents tested were stimulated by intra-aortic injections of papaverine (2-2.5 mg/kg). Sixty-two percent of the afferents that responded to papaverine also responded to isoproterenol (50 microg/kg). Seven of the 36 group IV and 2 of the 12 group III afferents tested were excited by acute distension of the hindlimb venous system. Four of the seven group IV afferents responding to venous distension also responded to papaverine (57 vs. 13% for the nonresponding). Finally, we observed that most of the group IV afferents that were excited by dynamic contractions of the triceps surae muscles also responded either to venous distension or to vasodilatory agents. These results are consistent with the histological findings that a large number of group IV endings have their receptive fields close to the venules and suggest that they can be stimulated by the deformation of these vascular structures when peripheral conductance increases. Moreover, such a mechanism offers the possibility of encoding both the effects of muscle contraction through intramuscular pressure changes and the distension of the venular system, thereby monitoring the activity of the veno-muscular pump. (+info)
Restrictive pericarditis.
(6/366)
BACKGROUND: Pericardial thickening is an uncommon complication of cardiac surgery. OBJECTIVES: To study pericardial thickening as the cause of severe postoperative venous congestion. SUBJECTS: Two men, one with severe aortic stenosis and single coronary artery disease, and one with coronary artery disease after an old inferior infarction. Both had coronary artery bypass grafting surgery. METHODS: Magnetic resonance imaging (MRI), Doppler echocardiography, and cardiac catheterisation. RESULTS: Venous pressure was raised in both patients. MRI showed mildly thickened pericardium, and cardiac catheterisation indicated diastolic equalization of pressures in the four chambers. Jugular venous pulse showed a dominant "Y" descent coinciding with early diastolic flow in the superior vena cava, and mitral and tricuspid Doppler forward flow proved restrictive physiology. The clinical background suggested pericardial disease so both patients had pericardiectomy. This proved the pericardium to be thickened; the extent of fibrosis also involved the epicardium. CONCLUSIONS: Although rare, restrictive pericarditis (restrictive ventricular physiology resulting from pericardial disease) should be considered to be a separate diagnostic entity because its pathological basis and treatment are different from intrinsic myocardial disease. This diagnosis may be confirmed by standard investigational techniques or may require diagnostic thoracotomy. (+info)
Effects of protamine on nitric oxide level in the pulmonary circulation.
(7/366)
Protamine reversal of heparin anticoagulation often causes systemic hypotension by releasing nitric oxide (NO) from vascular endothelium. We investigated the hypothesis that protamine prevents severe pulmonary vasoconstriction by increasing NO. Twenty patients undergoing elective coronary artery bypass graft surgery were included in the study. Nitrite and nitrate levels--as end-metabolites of NO--were measured in blood samples obtained before and after protamine administration. Mean arterial pressure, heart rate, mean pulmonary artery pressure, central venous pressure and left atrial pressure were noted as hemodynamic data. Nitrite levels were 4.64 +/- 0.67 mumol in the right atrium and 4.84 +/- 0.95 mumol in the left atrium before protamine administration. The difference was insignificant statistically. These measurements were 4.85 +/- 0.92 in the right atrium and 5.28 +/- 0.66 mumol in the left atrium after protamine administration. This increase was significant (p < 0.05). The measurements of nitrate levels were completely parallel with those of nitrite. Mean arterial pressures were 78.9 +/- 7.59 mm-Hg before protamine and 74.1 +/- 8.55 mm-Hg after protamine (p = 0.03). The changes in other hemodynamic parameters were not significant. Protamine augments NO production and prevents the pulmonary circulation from possible vasoconstriction. (+info)
The effect of pregnancy on the lower-limb venous system of women with varicose veins.
(8/366)
OBJECTIVES: to assess the effect of pregnancy on the lower-limb venous system of women with varicose veins. Design a longitudinal prospective study of 11 pregnant women, with varicose vein disease. METHODS: eleven pregnant women with varicose veins were recruited as part of a larger study. Veins were assessed in both lower limbs using colour-flow duplex scanning at a 75 degrees head-up tilt. The diameter and velocity and duration of reflux were measured in each vein at 12, 20, 26, 34, 38 weeks gestation and 6 weeks postpartum. RESULTS: eleven women had reflux and varicose veins demonstrated at first scan. All veins dilated with increasing gestation. This was maximal in the superficial system, reaching significance (p+info)