Ventilation is not constant during steady-state prolonged hypoxia. This raises questions as to the role of the carotid body (CB) in sustained hypoxia. Studies in awake goats using an extracorporeal CB circuit to allow separation of systemic (CNS) and CB blood gases provided evidence that prolonged hypoxia isolated to the ...

BACKGROUND AND PURPOSE: Acetazolamide is commonly used with single-photon CT to assess the cerebrovascular reserve in patients with internal carotid artery stenosis or occlusion. In this study we wanted to evaluate the effects of adenosine, a well-known vasodilatatory compound with a short biological half-life, on brain circulation in humans and ...

PURPOSE: The present study outlines a novel in situ technique to assess the regulation of vascular resistance in the penile vascular bed of the Wistar rat. MATERIALS AND METHODS: The isolation and perfusion of the pudendal artery were achieved by ligating all branches of the external iliac artery not directly ...

To investigate the relation between the tissue renin-angiotensin system (RAS) and the local vasomotor tone of large arteries, we used in vitro isolated carotid arteries from 14-week-old Wistar-Kyoto rats (WKY; n = 80) and spontaneously hypertensive rats (SHR; n = 80). Diameters were measured with the use of an ultrasonic ...

Assessing the adequacy of collateral circulatory pathways has become increasingly important in the investigation of cerebral circulation. Using transorbital Doppler ultrasonography (TOD), we examined the ophthalmic artery (OA) in patients with hemodynamic significant internal carotid artery (ICA) occlusive disease. The velocity and the direction of flow in the OA were ...

Reduction of the retinal blood flow by occlusion of both common carotid arteries suppressed the b-wave of the rat's electroretinogram. Transient occlusion of the carotids for 45 min reduced the b-wave by 46% without affecting the amplitude of the a-wave. The normal ERG activity returned 30 min after restoration of ...

Blood velocity changes in the internal carotid artery were estimated using Doppler ultrasound before, during and after injection of indometacin or placebo in 7 healthy adults. Upon injection of the active substance there was a rapid reduction in blood velocities in the internal carotid artery, increasing with increasing doses of ...

Near-infrared spectroscopy was used to monitor changes in the cerebral oxygenation state in 13 patients during carotid endarterectomy. Variations in the levels of the chromophores (oxygenated hemoglobin (HbO2), deoxygenated hemoglobin (Hb), and oxidized cytochrome (CytO2)), and the total hemoglobin content (tHb) were compared with changes in middle cerebral artery flow ...

1. The role of nitric (NO) in the regulation of capillary and arteriovenous anastomotic blood flow was evaluated in the carotid circulation of the pig. For this purpose, the effect of intracarotid (i.c.) infusions of saline and two NO donors, nitroprusside sodium (NPR) and S-nitroso-N-acetylpenicillamine (SNAP) in concentrations of 3-100 ...

The optimum flow rate and pressure for selective cerebral perfusion during moderate hypothermia (25 degrees C) were investigated in 36 mongrel dogs. Cerebral perfusion was performed for 90 minutes at a flow rate of 100% (the physiologic flow rate), 50%, 25%, and 0%, or no flow (cerebrocirculatory arrest). Somatosensory evoked ...

Patients with carotid body tumors require accurate preoperative assessment of vessel involvement and the probable impact of interrupting blood flow through the internal carotid artery. Recent developments in imaging, methods of measuring cerebral blood flow, balloon occlusion testing, and techniques to maintain vascular flow when a graft is required have ...

Ophthalmic artery blood flow pattern and the pulsatile ocular blood volume changes in patients with hemodynamically significant carotid occlusive disease are described. Using transorbital Doppler ultrasonography and dynamic tonometry 45 patients with high-grade internal carotid artery stenosis or occlusion and 15 healthy controls were examined. The measurements were performed under ...

A comparison of two volumetric blood flow measurement techniques, CVI-Q (based on time domain correlation) and ultrasonic flowmetry, has been performed in vitro and in vivo. A pulsatile flowpump was used to simulate carotid and femoral type waveforms which were measured simultaneously using the two methods. Five dogs had their ...

The unidirectional gas-flow pattern through the avian lung is thought to result from 'aerodynamic valves'; support for this hypothesis lies mainly in the failure to find any evidence for anatomical valves. During expiration, air flows from the caudal air sacs through the major exchange area of the lung, the paleopulmonic ...

The Huatuo reconstruction pill (HTRP) is a Chinese traditional herbal preparation which has been used for hundreds of years with remarkable effect on the cerebral palsy. The significant increase in both the common and internal carotid blood flow and the positive inotropic action on the heart were observed in anesthetized ...

Different methods have been used in the evaluation and monitoring of the cerebral oxygen supply during neuro-interventional therapies. Attenuation of near-infrared light by the chromophores oxyhemoglobin and deoxyhemoglobin have shown to be useful in the study of the cellular oxygen metabolism and oxygen delivery to the brain. Transcranial cerebral oximetry ...

A simple bedside test has been developed to assess the state of autoregulation in subarachnoid haemorrhage patients. Transcranial Doppler was used to measure blood flow velocity in the middle cerebral artery after a brief common carotid compression. Acceleration of blood flow postcompression was interpreted as evidence of intact cerebral autoregulation. ...

BACKGROUND AND PURPOSE: Blood flow can be evaluated non-invasively using magnetic resonance phase-contrast flow quantification. The purpose of this prospective study was to assess the feasibility of this method and to evaluate the hemodynamic effects of carotid endarterectomy. METHODS: Volumetric flow rates and peak systolic velocities of the internal and ...

The objective of the present study was to determine whether or not the neuropeptide, oxytocin, can move by counter current transfer from venous blood of the perihypophyseal cavernous sinus into arterial blood of the carotid rete supplying the brain and hypophysis, and also whether this exchange depends on the day ...

BACKGROUND AND PURPOSE: Evaluating cerebrovascular vasomotor reactivity seems to be of prognostic relevance for patients with occlusive internal carotid artery disease. To evaluate its clinical usefulness, the recently introduced breath-holding maneuver as a carbon dioxide-dependent vasodilatory stimulus was compared with the acetazolamide challenge by means of transcranial Doppler ultrasound and ...

By providing a non-invasive method for continuous display of mean flow velocity (Vmean) in the cerebral arteries, transcranial Doppler (TCD) ultrasound supplements evaluation of cerebral perfusion. Dynamic exercise increases middle cerebral artery (MCA) Vmean from approximately 55 to 65 cm s-1 dependent on work rate, and even more when corrected ...

Ultrasound-derived volumetric flow analysis may be useful in answering questions of basic physiological interest in the cerebrovascular circulation. Using this technique, the authors have sought to describe quantitatively the complete concurrent flow relations among all four arteries supplying the brain. The aim of this study of normal subjects was to ...

BACKGROUND AND PURPOSE: The aim of this study is to elucidate the effect of orthostatic hypotension on changes in cerebral blood flow. METHODS: Blood flow velocities of both the common carotid artery and vertebral artery were measured using duplex ultrasonography in 12 patients: 6 with familial amyloidotic polyneuropathy, 3 with ...

In order to establish whether or not the cerebral autoregulation is still effective at blood pressure rates in those who experience a chronic cerebral hypotension 37 patients were subjected to noninvasive CO2 enhanced transcranial Doppler (TCD) and ocular pneumoplethysmographic (OPG-GEE) studies of the middle cerebral and ophthalmic arteries. The patients ...

Transit-time ultrasound methods were used to measure blood flow in 37 patients undergoing carotid endarterectomy. Internal carotid flow before (ICFbef) and after (ICFaft) endarterectomy was measured with a 6 mm perivascular probe, and Javid shunt flow (SF) was measured with a clamp-on probe. For the entire group ICFbef averaged 117 ...

Redundant length of the cervical part of the internal carotid artery (ICA) is a clear angiographic entity although the clinical significance is uncertain. Transcranial Doppler sonography (TCD) examinations were performed on 15 patients with 23 elongated ICAs. The recordings were obtained with the use of flat 2 MHz probe from ...

Cerebral blood flow measurement has been an important investigative tool in newborns at risk for perinatal brain damage. The validity of Doppler cerebral blood flow velocity measurements depends on a constant vessel diameter. We have validated Doppler against the electromagnetic flowmeter (EM) using a modified common carotid artery model in ...

Fifty-eight patients with subclavian artery stenosis were classified as having definite or probable vertebrobasilar symptoms, carotid symptoms or no symptoms. The vertebral artery flow pattern was graded as no subclavian steal (Grade 0), systolic deceleration (Grade 1), alternating flow (Grade 2), or reversed flow (Grade 3). We found a statistically ...

Near infrared spectroscopy is a non-invasive method for continuous monitoring of tissue oxygenation. In 11 patients undergoing unilateral carotid endarterectomy, changes in cerebral oxygenation following carotid cross-clamping and declamping detected by a near infrared spectrometer were compared with corresponding changes in ipsilateral middle cerebral artery flow velocity measured by transcranial ...

Blood perfusion of systemic circulation is influenced by the physical characteristics of artery. Several investigations proposed that the physical parameters of vessels are determined by neurological factors, hormonal factors, and physical properties of arteries among others. In this study, arterial impedance was estimated because it may express the condition of ...

PURPOSE: The effect of occlusion of the external carotid system on blood flow of the internal maxillary artery was investigated in 16 dogs. METHODS: The external carotid system was occluded by ligation or clamping at different levels separately or simultaneously and the blood flow of the internal maxillary artery was ...

Hemodynamic theories of atherogenesis suggest that flow disturbances (departures from laminar flow including high and low shear) and increases in heart rate may be important in the initiation, progression, and complications of atherosclerosis such as dissection and embolism. It is therefore desirable to evaluate the effects of antihypertensive drugs on ...

BACKGROUND: The relationship between preoperative stenosis and the effect of carotid endarterectomy (CEA) upon internal carotid blood flow (ICF) is not well understood. With the intention of better characterizing this, we compared intraoperative measurements of internal carotid blood with the maximum single diameter stenosis found in preoperative angiograms. METHODS: Fifty-two ...

Haemodilution in nine neonates resulted in significant mean (SEM) decrease of packed cell volume (0.67 (0.01) to 0.55 (0.01)) and increases in cardiac output (250 (16) to 308 (25) ml/min/kg) and blood flow velocities of the internal carotid artery and the coeliac artery (+20%). However, red cell flows in the ...

This study was undertaken to examine further the effects of hypocapnia and the contribution of hypotension to the haemodynamic consequences of cerebral arteriovenous fistula ablation in the rat chronic carotid-jugular fistula model. Regional cerebral blood flow (rCBF) was measured by the (14)C-iodoantipyrine technique under halothane anaesthesia 12 weeks after the ...

This study had two purposes. First, the use of Transonic flowprobes placed on the common carotid and internal carotid arteries of seven male baboons was evaluated for measuring cerebral blood flow (BF) during +Gz stress. The approach was to compare BF's obtained with these flowprobes to microsphere measurements of total ...

1. We measured plasma concentrations of arginine vasopressin (AVP), arterial, venous and amniotic pressures, and carotid and femoral blood flows in fifteen chronically instrumented fetal sheep at 119-125 days of gestation. In eight of the fetuses the carotid sinus nerves were cut (denervated fetuses); the other seven remained intact and ...

BACKGROUND AND PURPOSE: Thromboembolic stroke is likely to occur in patients with a restricted cerebral blood flow reserve. Our aims were to determine (1) whether symptomatic patients had any significant hemodynamic restriction ipsilateral to carotid occlusive disease compared with patients whose carotid stenosis is asymptomatic and (2) whether patients with ...

Transcranial Doppler ultrasound measurement of the velocity of blood flow in the middle cerebral artery (MCA) was performed in 24 consecutive patients undergoing carotid endarterectomy. Measurements were performed preoperatively at rest, following common carotid artery compression, and continuously during surgery. In addition, internal carotid artery stump pressures were measured and ...

1. The influence of the trigeminal ganglion on the carotid circulation has been investigated by measuring electrical stimulation-induced alterations in carotid arterial blood flow and resistance in anaesthetized guinea-pigs. The effects of several receptor antagonists were assessed to determine which neurotransmitters are involved in regulating carotid blood flow. 2. Arterial ...

By means of Doppler spectral analysis, it was shown that internal carotid artery stenosis has a dynamic component that determines the possibility of changes in the area of stenosis under various influences. It was demonstrated that cold pressor test may increase the area of stenosis in some patients for up ...

To study facial flush after systemic administration of human corticotropin-releasing hormone (hCRH) we injected 100 micrograms hCRH intravenously to ten healthy young men. The increase in facial temperature was measured by infrared camera. A significant increase in facial temperature of 1.39 degrees C +/- 0.3 was found within 7 min ...

BACKGROUND AND PURPOSE: Homocystinuria due to cystathionine beta-synthase deficiency and familial hypercholesterolemia are inherited disorders of metabolism that are associated with premature development of cardiovascular disease. This study addresses the possibility that different patterns of carotid wall damage and cerebral blood flow hemodynamics are present in these two metabolic diseases. ...

Intracerebral haemorrhage is a serious complication after carotid endarterectomy. We tried to identify predictors of this event. Two-hundred-and-thirty-three operations were selected from a total of 280 because of reliable intraoperative transcranial Doppler data with regards to the increase of peak blood flow velocities and pulsatility indices in the ipsilateral middle ...

PURPOSE: To determine the utility of [15O]H2O positron emission tomography (PET) for the quantitative determination of cerebral blood flow in patients undergoing balloon test occlusion of the internal carotid artery. METHODS: Twenty-two [15O]H2O PET cerebral blood flow studies were completed on 20 patients for whom temporary or permanent occlusion of ...

Eighty healthy male subjects (age range: 47 to 87) with hematocrits of 48% or greater and no vascular or hematologic pathology were studied. In each subject, the following values were determined: hematocrit, blood pressure (measured in both arms by sphygmomanometry), and the calibers and blood flow velocities of both internal ...

BACKGROUND AND PURPOSE: We compared relative changes in middle cerebral artery velocity and internal carotid artery flow during autoregulation testing to test the validity of using transcranial Doppler recordings of middle cerebral artery velocity to evaluate cerebral autoregulation in humans. METHODS: Seven human volunteers had dynamic autoregulation tested during surgical ...

A study was performed to evaluate immediate changes in carotid artery blood flow after carotid endarterectomy using a Doppler ultrasonographic flowmeter. Forty-seven consecutive patients aged 49-78 (median 64) years with symptomatic internal carotid artery (ICA) stenosis underwent carotid endarterectomy. Volume flow, resistance and pulsatility index were measured in the common ...

The purpose of this experiment is to investigate the effect of arterial mechanics on carotid blood pressure and blood flow waveforms using an animal model. Blood pressure and blood flow waves were recorded from the carotid artery of the rabbit under different physiological and pharmacological conditions. The basic mechanism of ...

The purpose of this study was to measure antegrade and retrograde flow in the aorta and the major arterial pathways in the body noninvasively with cine magnetic resonance (MR) velocity mapping, to determine the hemodynamic significance of retrograde flow in arteries. Two hundred forty cine velocity maps for blood flow ...