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A Grip

Publications and source records attributed to A Grip.

18 recordsLinked to original sources
PubMed1990

Evaluation of blood flow velocity waveform in an animal model.

Blood flow velocity waveforms in the abdominal aorta of three anesthetized pigs were recorded by a combined 3.5-MHz real-time and 2-MHz pulsed-Doppler ultrasound. The flow velocity waveforms were analyzed for pulsatility index, systolic to diastolic ratio, rising slope, descending slope, and the minimum diastolic velocity, and then were compared with volume blood flow measured by electromagnetic flowmeter (Q), mean arterial pressure (MAP), and total peripheral resistance (TPR). Total peripheral resistance was calculated according to the formula TPR = MAP/Q. A total of 111 recordings were performed over a range of heart rate: 90-250 beats/min, of Q: 65-1318 mL/min, of MAP: 72-165 mmHg and of total peripheral resistance 0.10-2.17 mmHg x min/mL. A significant positive correlation was found between pulsatility index and total peripheral resistance (correlation coefficient r ranging 0.64-0.87) and between systolic to diastolic ratio and total peripheral resistance (r: 0.59-0.83). The minimum diastolic velocity showed a negative correlation to TPR(r: -0.68 - -0.76). The pulsatility index was dependent on the heart rate, mean arterial pressure and rising slope; however, the relations were not consistent in all experiments. The results indicate that the pulsatility index is a good indicator of the flow velocity waveform changes depending on changes in the peripheral vascular resistance, and that the relationship between the total peripheral resistance and pulsatility index is linear. The systolic to diastolic ratio proved to be comparable even though it is somewhat less effective in performance than the pulsatility index.

Animals↗
PubMed1986

Cerebral carbon dioxide reactivity during nonpulsatile cardiopulmonary bypass.

Five patients undergoing extensive cerebral monitoring during cardiopulmonary bypass (CPB) procedures were subjected to studies on cerebral CO2 reactivity during nonpulsatile CPB. The cerebral monitoring included recording of arterial blood pressure (BP), central venous pressure (CVP), epidural intracranial pressure (EDP), cerebral electrical activity by a cerebral function monitor (CFM), and middle cerebral artery (MCA) flow velocity by transcranial Doppler technique. The cerebral perfusion pressure (CPP) was thus continuously recorded (CPP = BP - EDP). During steady-state CPB with constant hematocrit, temperature, and arterial carbon dioxide tension (PaCO2), MCA flow velocity varied with changing CPP in a pressure-passive manner, indicating that the cerebral autoregulation was not operative. During moderately hypothermic (28 to 32 degrees C), nonpulsatile CPB, with steady-state hematocrit, temperature, and pump flow, we deliberately and rapidly changed PaCO2 for periods of 1 or 2 minutes by increasing gas flow to the membrane oxygenator, thereby testing the cerebral CO2 reactivity. Nineteen CO2 reactivity tests, performed at CPP levels ranging from 17 to 75 mm Hg, disclosed that the cerebral CO2 reactivity decreased with CPP, especially with CPP levels below 35 mm Hg. In these patients, concomitant changes in CPP during the CO2 reactivity test could be compensated for by adjusting the observed change in MCA flow velocity. The corrected CO2 reactivity values obtained in this way ranged from below 1.0 (observed at CPP levels below 20 mm Hg) to a 3.0 to 4.5% X mm Hg-1 change in PaCO2 (observed at CPP levels above 35 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗
PubMed1986

Gas bubbles in the circulation of divers after ascending excursions from 300 to 250 msw.

The occurrence of intravascular bubbles in arteries and veins has been studied using pulsed Doppler ultrasound in six subjects who performed two ascending excursions each from 300 to 250 meters of seawater (msw) during a heliox saturation dive. Following decompression, high-intensity reflections could be observed not only in the venous system but also in the arteries, most notably in the carotid artery. Intravascular bubbles were more numerous during the first ascent than during the second. The arterial bubbles most probably come from the venous side of the circulation, indicating that the pulmonary filter is not as effective as previously thought during saturation diving.

Adult↗
PubMed1986

Continuous monitoring of cardiac output postoperatively using an implantable Doppler probe.

The authors evolved a Doppler probe which can be attached to the ascending aorta intraoperatively. Using a pulsed echo Doppler flowmeter operating at 2 mHz, cardiac output was continuously measured during the first 2 days after open-heart surgery in 20 patients. The internal diameter of the aorta was assessed with ultrasound echo technique. The probe was fixed to the ascending aorta with a double suture through the adventitia. The suture was tightened by means of a long tourniquet which was passed through an infraxiphoid skin incision, between the two chest drains. A stable position providing adequate signals was achieved by use of probes with stabilizing "side flaps". In 8 cases the method was compared with the thermodilution technique using Swan-Ganz catheters. Analysis of 44 simultaneously performed measurements revealed a highly significant correlation between the two methods, and the results remained comparable throughout the 48-hour test period. There were no complications and all the probes could be easily removed.

Cardiac Output↗
PubMed1985

Dissociation between cerebral autoregulation and carbon dioxide reactivity during nonpulsatile cardiopulmonary bypass.

Five patients undergoing cardiopulmonary bypass (CPB) procedures were extensively monitored because of anticipated high risk for neurological complications. Arterial blood pressure (BP), central venous pressure, and epidural intracranial pressure (EDP) were continuously recorded throughout CPB; thus, information on the cerebral perfusion pressure (CPP) was also continuously available (CPP = BP - EDP). Cerebral electrical activity was recorded by a cerebral function monitor. The flow velocity in the middle cerebral artery (MCA) was recorded using a transcranial Doppler technique. During steady-state CPB (constant hematocrit, constant temperature, and constant flow from the heart-lung machine) partial pressure of arterial carbon dioxide (PaCO2) was repeatedly changed to study the effect of changes in this variable on MCA flow velocity during nonpulsatile bypass. During CPB with constant temperature, hematocrit, and PaCO2, the effect of changes in CPP on MCA flow velocity was recorded and analyzed. During nonpulsatile, moderately hypothermic (28 degrees to 32 degrees C), low-flow (1.5 L/min/m2) CPB, there was no evidence of cerebral autoregulation, with CPP levels ranging from 20 to 60 mm Hg. The CO2 reactivity, however, was clearly present and in the range of 1.9 to 4.1%/mm Hg, indicating that there was a dissociation between cerebral autoregulation and CO2 reactivity under these circumstances.

Aged↗
PubMed1982

Estimation of flow in aortocoronary grafts with a pulsed ultrasound Doppler meter.

A newly developed pulsed ultrasound Doppler meter was used for measurement of blood flow in aortocoronary vein grafts during operation. The results were compared with measurements obtained with conventional electromagnetic flowmetry. In 27 grafts, excellent agreement was found between electromagnetic flow probes thoroughly calibrated for varying hematocrit on fresh veins in vitro, and a clip-on type of Doppler probe (r = 0.86). In vitro calibration showed a close correspondence (r = 0.98) with the Doppler technique with no dependency on hematocrit and no need for zero calibration. The use of a conventional electromagnetic flowmeter showed strong dependency on recent calibration, both for saline and for varying hematocrit. Zero-calibration was necessary for every single graft measurement. The application of ultrasound Doppler meters of high quality together with clip-on probes of proper design proved to be superior to electromagnetic flowmetry for intraoperative blood flow measurements.

Blood Flow Velocity↗
PubMed1980

Pulsed Doppler ultrasound for measuring blood flow velocity in the human ophthalmic circulation.

This study was performed in order to develop a method for studying blood flow in the ophthalmic circulation. Using a pulsed doppler system utilizing an ultrasonic frequency of 10 MHz, blood flow velocities have been measured in the ophthalmic artery and in the arteries behind the eyeball (lateral posterior ciliary arteries) in 40 normal subjects. The mean of the peak systolic velocities were 34 +/- 6 cm/s in the ophthalmic artery, and 14 +/- 3 cm/s in the lateral posterior ciliary arteries. We conclude that blood flow velocities can be measured in defined vessel areas in the orbit.

Adolescent↗
PubMed1980

Hemodynamic aspects of cerebral arteriovenous malformations.

Local hemodynamics were studied in 16 patients undergoing total extirpation of cerebral arteriovenous malformation (AVM). Directional Doppler technique was used for the registration of blood velocities in vessels feeding and draining the AVM. Calculated flow in single feeding arteries ranged from 3 to 550 ml/min (average, 180 ml/min). An estimation of total AVM flow was possible in nine patients, and ranged from 150 to more than 900 ml/min (average, 490 ml/min). Pressure recordings were made from feeding arteries at their entrance to the AVM. This pressure was well below the systemic arterial blood pressure in all cases, and ranged from 40 to 77 mm Hg (average, 56 mm Hg). On temporary occlusion, this stump pressure instantly rose to from 55 to 95 mm Hg (average, 76 mm Hg). Draining vein pressure before occlusion ranged from 8 to 23 mm Hg (average, 15 mm Hg), and fell to zero in all patients when the AVM was occluded. These data and other clinical observations are discussed with regard to adjacent brain-tissue perfusion, and with special emphasis on the circulatory breakthrough that can follow the occlusion of these high-capacity shunts.

Adult↗
PubMed1979

Intraoperative evaluation of cerebral hemodynamics using directional Doppler technique. Part 1: Arteriovenous malformations.

The use of a pulsed echo Doppler technique during surgery for cerebral arteriovenous malformation is described. The equipment and the methods employed are presented. The main advantages are easy determination of flow direction and pattern of the vasculature involved, allowing a precise discrimination between inflow and outflow channels. Deep-seated malformations, not visible at the brain surface, can be located with the Doppler technique. The ultrasound probe was placed on the brain surface with a slight pressure on the intact pia mater. The precise direction and depth of the malformation could be determined in relation to the recording site. This facilitated the planning of cortical incisions, identification of vessels involved, and the vascular procedure to be employed.

Adolescent↗
PubMed1979

Intraoperative evaluation of cerebral hemodynamics using directional Doppler technique. Part 2: Saccular aneurysms.

The use of a pulsed echo Doppler technique during procedures for occlusion of intracranial aneurysms is described. Saccular aneurysms can be located with reference to probe position and depth setting. Tracings of intra-aneurysmal flow are presented, and the characteristic flow pattern is disucssed. Special emphasis has been placed on the parent artery flow, particularly the effect of lumen reduction on flow velocity. Results of flow velocity studies on the cognate (direct) and collateral flow in the middle cerebral artery and the proximal anterior cerebral artery are presented and discussed.

Blood Flow Velocity↗
PubMedDate not supplied

Pulsed Doppler techniques for measuring instantaneous maximum and mean flow velocities in carotid arteries.

A 5 MHz pulsed Doppler instrument measuring instantaneous maximum and mean flow velocities is presented. The maximum velocity estimator is based on the principle of frequency variable filtering controlled by a feedback loop to follow the velocity spectrum envelope. Findings by Doppler and bilateral selective carotid arteriography in 216 patients were compared. Extracranial carotid stenoses were identified by the finding of a vessel segment with locally increased flow velocity. Peak Velocity Ratio (PVR) was calculated from maximum velocities measured in the stenosis and in more distal Internal Carotid Artery (ICA) segments. Using PVR, ICA stenoses greater than 20% were detected with sensitivity 96%, specificity 94%, positive accuracy 94% and negative accuracy 96%. Total ICA occlusions were identified with sensitivity 97% and specificity 99%.

Adult↗
PubMedDate not supplied

Blood flow measurement in PTFE grafts.

In vascular surgery peroperative control of the result of reconstruction is essential. PTFE-grafts have been known to be "resistant" to flow registration with electromagnetic flowmetry because of the electrical isolation. Similarly, intraoperative Doppler registration has been impossible because of the attenuation of the ultrasound in the graft wall. The leading disturbances are obviously caused by air in the graft material and are not caused by the material itself. By squeezing the graft carefully between the thumb and forefinger, blood slowly penetrates the wall colouring it red. The squeezing is performed intermittently to avoid occlusion of the graft. Excellent flow registration is obtained after less than 2 min squeezing of the thin walled graft, while at least 5 min squeezing is necessary to obtain signals from thick walled grafts. To obtain satisfactory ultrasound signals more squeezing is necessary.

Animals↗