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R Aaslid

Publications and source records attributed to R Aaslid.

52 records · Page 3Linked to original sources
PubMed1984

Evaluation of cerebrovascular spasm with transcranial Doppler ultrasound.

The use of an ultrasonic transcranial Doppler technique for noninvasive evaluation of cerebral vasospasm is described. Middle cerebral arteries (MCA's), classified as spastic on angiography, demonstrated blood-flow velocity between 120 and 230 cm/sec. The flow velocities in these arteries had a clear inverse relationship to the diameter as measured from angiograms in 38 patients with recent subarachnoid hemorrhage. This relationship in the proximal anterior cerebral artery (ACA) was found to be more complicated to assess, due to the collateral channels in the anterior part of the circle of Willis. The authors conclude, however, that the new method of measuring vasospasm will also detect spasm in the ACA if it has a hemodynamically significant effect upon flow resistance.

Blood Flow Velocity↗
PubMed1982

Noninvasive transcranial Doppler ultrasound recording of flow velocity in basal cerebral arteries.

In this report the authors describe a noninvasive transcranial method of determining the flow velocities in the basal cerebral arteries. Placement of the probe of a range-gated ultrasound Doppler instrument in the temporal area just above the zygomatic arch allowed the velocities in the middle cerebral artery (MCA) to be determined from the Doppler signals. The flow velocities in the proximal anterior (ACA) and posterior (PCA) cerebral arteries were also recorded at steady state and during test compression of the common carotid arteries. An investigation of 50 healthy subjects by this transcranial Doppler method revealed that the velocity in the MCA, ACA, and PCA was 62 +/- 12, 51 +/0 12, and 44 +/- 11 cm/sec, respectively. This method is of particular value for the detection of vasospasm following subarachnoid hemorrhage and for evaluating the cerebral circulation in occlusive disease of the carotid and vertebral arteries.

Adult↗
PubMed1982

Toxicity of phospholipase C in rabbits.

Tissue thromboplastin is the most potent physiological trigger of blood coagulation and is probably involved in the pathogenesis of several forms of intravascular coagulation. Phospholipase C from Bacillus cereus is an effective inhibitor of thromboplastin. As part of an investigation into the possible use of phospholipase C as a therapeutic or prophylactic agent in thrombosis and other forms of intravascular coagulation, we have previously studied its effect in rats. We now report on the toxicity in rabbits (along with some data on cats and monkeys). Estimated LD50 for rabbits was about 0.45-0.65 mg/kg (as compared to 1.70 mg/kg for rats). No respiratory or circulatory changes were observed, but phospholipase C caused a significant increase of several plasma enzymes in rabbits.

Acid-Base Equilibrium↗
PubMed1981

Accuracy of an ultrasound Doppler servo method for noninvasive determination of instantaneous and mean arterial blood pressure.

A new noninvasive method for determining arterial blood pressure is presented. Using a fast servo system, the pressure in the arm cuff is controlled so that the flow is maintained at a low value. Transcutaneous ultrasound Doppler techniques are used to detect flow to the artery. Comparison with invasive pressure measurements demonstrated that the servo method reproduced beat-to-beat variations in arterial blood pressure faithfully. Mean arterial blood pressure was determined from the noninvasive recordings using the same mathematically valid procedure as was used for the invasive recordings. The deviation between the invasive and the noninvasive determinations of this measurement was -0.6 +/- 2.2 mm Hg (mean +/- SD) in 23 subjects.

Arteries↗
PubMed1977

Intracranial pulse pressure dynamics in patients with intracranial hypertension.

The pulsative inflow of blood to the brain causes fluctuations in the cerebral blood volume, and this is considered to be the main cause of the pulsations of the intracranial pressure (ICP). This statement allows discrimination between two different factors that influence the pulse amplitude of the ICP: 1. The pulsatile pattern of the cerebral arterial blood flow. 2. The slope of the intracranial pressure-volume curve. In order to clarify the relative contributions of the two factors we have developed a simulation model of the intracranial pressure-volume curve and the cerebral blood flow. Measurements from clinical practice and data from other authors can be interpreted with reference to this model. The increase in the pulse amplitude due to a moderate increase in the ICP is mainly explained by the decrease of the intracranial compliance. However, it is recognized that, when the ICP approaches the arterial blood pressure, the ICP amplitude increases disproportionally with increasing ICP. In this situation the transmural pressure of the cerebral arteries approaches zero, and the compliance relevant to the arterial flow system is no longer that of the vessel wall but the compliance of the craniospinal compartment.

Adult↗
PubMed1977

Determination of effective orifice area in mitral stenosis from non-invasive ultrasound Doppler data and mitral flow rate.

Ten patients with mitral stenosis, but without mitral insufficiency, have been studied during cardiac catheterization. The mitral orifice blood velocities, the mitral pressure gradient, and the mitral flow rate were determined with ultrasound, manometry, and the direct Fick method, respectively. The effective orifice area was calculated from the ultrasound data and the mitral flow rate. The geometric orifice area was calculated from the pressure gradient and the mitral flow rate, using a revised Gorlin formula. A comparison of the two methods showed a correlation coefficient of 0.975. The investigation demonstrated that the ultrasound method represents an alternative to the conventional catheterization methods used for the quantification of mitral flow obstruction.

Blood Flow Velocity↗
PubMed1976

Determination of pressure gradient in mitral stenosis with a non-invasive ultrasound Doppler technique.

A 2 MHz continuous waveform non-invasive ultrasound doppler system has been used in the present investigation. With the aid of the audio signals of the frequency shifts, the ultrasound probe was positioned on the external chest so that the axis of the incident ultrasonic beam coincided with the direction of the maximum velocity vectors of the mitral jet. The frequency shifts due to the mitral jet were frequency analyzed and the time course of the maximum frequency shift was determined. The time course of the maximum mitral jet velocity was then determined from the doppler equation and the time course of the mitral pressure gradient from an orifice equation. The usefulness of the technique was evaluated by studying 25 patients with mitral stenosis and 10 without heart disease. The patients with mitral stenosis were studied during cardiac catheterization and the ultrasound data, the pulmonary artery wedge pressure, and the left ventricular pressure were recorded simultaneously. A table is presented where the gradient determined with the ultrasound technique, deltaPU, is compared with the gradient determined from the pressure tracing, deltaPM. Averaged over the 25 patients studied, deltaPU was 1.7 mmHg smaller than deltaPM at 0.08 sec diastolic time and 1.8 mmHg smaller at 0.25 sec diastolic time. The findings in the patients without heart disease differed distinctly from those in the patients with mitral stenosis. The investigation demonstrated that the non-invasive ultrasound technique can be used with confidence to gain an impression of the magnitude of the mitral pressure gradient. The findings also suggest that deltaPU represents the actual pressure gradient more accurately than deltaPM. Another investigation is proposed to assess the accuracy of the technique more completely.

Adult↗
PubMed1975

"In situ" evaluation of the aortic pivoting disc valve prosthesis.

An index of the "in situ" forward flow characteristics of an aortic valve prosthesis is suggested. The effective area index, Ia, is defined as the ratio between the effective orifice area, Aeff, and the area occupied by the valve in the aortic root. Aeff is calculated from a hydraulic formula using peroperative measurements of instantaneous ascending aortic flow, Fao, and the pressure gradient, deltaP. Ia was found to be 0.29 +/- 0.33 (S.D.) for Lillehei-Kaster valves and 0.32 +/- 0.059 (S.D.) for Björk-Shiley valves. The variations in valve performance among the Björk-Shiley valves may partly be due to differences in valve orientation in the aortic root. Attention should therefore be given to the choice of the opening direction of the disc in order to optimize valve performance in the patient.

Aortic Valve Insufficiency↗
PubMedDate not supplied

Cerebral autoregulation during whole-body hypothermia and hyperthermia stimulus.

The purpose of the study contained herein was to investigate the effects of old traditional physiotherapeutic treatments on cerebral autoregulation. Treatment consisted of complete body immersion in cold or warm water baths. Fifteen volunteers were investigated by means of transcranial Doppler sonography and a servo-controlled noninvasive device for blood pressure measuring. One group of 8 volunteers (mean age, 27.2+/-3.5 yr; gender, 3 females/5 males) was subjected to cold baths of 22 degrees C for 20 min Another group of 7 volunteers (mean age, 52.1+/-8.5 yr; gender, 4 females/3 males) took hyperthermic baths at rising water temperatures from 36 degrees to 42 degrees C, increased by 1 degree C every 5 min. Each volunteer in both groups underwent autoregulation tests two to four times before, during, and after the thermic bath. Dynamic autoregulation was measured by the response of cerebral blood flow velocity to a transient decrease of the mean arterial blood pressure, induced by rapid deflation of thigh cuffs. The autoregulation index, i.e., a measure of the speed of change of cerebral autoregulation, was used to quantify the response. Further parameters were core temperature, blood pressure (mm Hg) and CO2et. During hypothermic baths, core temperature decreased by 0.3 degrees C (P = 0.001), measured between preliminary phase and the end of the bath; the autoregulation index decreased significantly (P < 0.05) from 5.3 before the bath to 4.25 during the bath. During hyperthermic baths, the autoregulation index increased from 6.0 to 7.5 and 8.9 (P < 0.001), with an increase of core temperature of 0.4 degrees C. The main cerebral autoregulation system is dependent on changes of core temperature, provoked by hypothermic or hyperthermic whole-body thermostimulus. Application of hyperthermic baths increased the autoregulation index, and hypothermic baths decreased the autoregulation index. Further studies are needed to prove the positive effects of thermo-stimulating water applications on cerebral hemodynamics in patients with cerebral diseases.

Adult↗
PubMedDate not supplied

Visually evoked dynamic blood flow response of the human cerebral circulation.

The dynamics of the metabolic mechanism that regulates cerebral blood flow was studied in 10 normal human subjects using a noninvasive transcranial ultrasonic Doppler method. Flow volume in the posterior cerebral artery, supplying the visual cortex, increased 20.2% in response to light stimulation of the retina, while flow velocity in the same artery increased 16.4%. The regulation of blood flow was very rapid; only 2.3 seconds elapsed from application of the light stimulus to 50% of full response. Full regulation (90% of full response) took 4.6 seconds. The blood flow response adapted slightly after about 10 seconds. Flow velocity in the middle cerebral artery increased significantly, by 3.3%, while flow in the superior cerebellar artery showed no significant change in response to this stimulus. These findings suggest the mechanism of very fast metabolic regulation of cerebral blood flow in humans.

Adult↗
PubMedDate not supplied

Evaluation of cerebrovascular disease by combined extracranial and transcranial Doppler sonography. Experience in 1,039 patients.

Results from 1,039 combined cervical and transcranial Doppler examinations are reported. Satisfactory transcranial signals were not found in 2.7% of the cases. Compared with angiography, the accuracy of transcranial criteria in assessing collateral flow over the circle of Willis was 94 and 88% for anterior and posterior circulation, respectively. The method also appeared very promising for detection of lesions of the intracranial arteries although the number of such cases with angiographic verification was limited in the present series. Arterial narrowing due to cerebral vasospasm was diagnosed with a sensitivity of 80%. In patients with ruptured intracranial aneurysms, an incidence of 93% arterial narrowing in basal cerebral arteries was found. Patients with subarachnoid hemorrhage and no aneurysm on angiography also showed arterial narrowing with an incidence of 56%. It was possible to monitor the time course and severity of cerebral vasospasm. Arteriovenous malformations were characterized by Doppler findings of high velocities and low pulsatilities. These lesions were diagnosed with an accuracy of 95%.

Cerebral Angiography↗
PubMedDate not supplied

Variations in middle cerebral artery blood flow investigated with noninvasive transcranial blood velocity measurements.

Observations on blood velocity in the middle cerebral artery using transcranial Doppler ultrasound and on the ipsilateral internal carotid artery flow volume were obtained during periods of transient, rapid blood flow variations in 7 patients. Five patients were investigated after carotid endarterectomy. A further 2 patients having staged carotid endarterectomy and open heart surgery were investigated during nonpulsatile cardiopulmonary bypass. The patient selection permitted the assumption that middle cerebral artery flow remained proportional to internal carotid artery flow. The integrated time-mean values from consecutive 5-second periods were computed. The arithmetic mean internal carotid artery flow varied from 167 to 399 ml/min in individual patients, with individual ranges between +/- 15% and +/- 35% of the mean flow. The mean middle cerebral artery blood velocity varied from 32 to 78 cm/sec. The relation between flow volume and blood velocity was nearly linear under these conditions. Normalization of the data as percent of the individual arithmetic means permitted a composite analysis of data from all patients. Linear regression of normalized blood velocity (V') on normalized flow volume (Q') showed V' = 1.05 Q' - 5.08 (r2 = 0.898).

Blood Flow Velocity↗