Single-frequency master-oscillator fiber power amplifier system emitting 20 W of power.

We report a master-oscillator fiber power-amplifier system consisting of a diode-pumped monolithic nonplanar ring laser as the master oscillator and a Yb-doped large-mode-area double-clad fiber as the power amplifier. The system emits up to 20.1 W of single-frequency radiation at a wavelength of 1064 nm with diffraction-limited beam quality (M(2)

High-average-power picosecond Yb-doped fiber amplifier.

We report on a cladding-pumped, ytterbium-doped large-core-area fiber amplifier that is capable of generating 51.2 W of average power at a 1064-nm center wavelength, an 80-MHz repetition rate, and a 10-ps pulse duration. In an ytterbium-doped large-mode-area fiber these pulses could be amplified up to 43.2 W with diffraction-limited beam quality (M(2)~1.3) . Power scaling limitations that arise from nonlinear distortions such as self-phase modulation and stimulated Raman scattering are discussed.

Optimized transcranial Doppler technique for the diagnosis of cardiac right-to-left shunts.

Transcranial Doppler sonography (TCD) is a simple method to detect a right-to-left cardiac shunt, although standardized procedures do not exist. In this study 69 patients were tested according to predetermined criteria and procedures (cluster of > 10 microbubbles, duration between injection in the cubital vein and detection in the middle cerebral artery [MCA] < or = 10 sec). Agitated saline solution was compared to oxypolygelatine, a plasma volume expander, as contrast media. Valsalva's maneuver and coughing were used to provoke right-to-left cardiac shunting, detected by TCD, transthoracic echocardiography (TTE), and transesophageal echocardiography (TEE). Oxypolygelatine caused a significantly higher number of microbubbles in the right atrium and MCA than did the saline solution, leading to a greater diagnostic reliability of TCD (paired t test, p < 0.001). Coughing did not provoke right-to-left cardiac shunts (x2 analysis, p < 0.001). The technique used for carrying out Valsalva's maneuver was important for the detection of right-to-left cardiac shunts. Twenty-five right-to-left shunts were diagnosed with TCD and 18 with TTE (36 vs 26%; x2 analysis, p = 0.1). The findings indicate that TCD when properly done is highly sensitive and specific for the diagnosis of right-to-left cardiac shunts.

[Recent developments in the area of Doppler ultrasound imaging]. / Neuere Entwicklungen auf dem Gebiete der Dopplersonographie.

Developments in Doppler Sonography: Review of duplex Sonography with and without ultrasonic contrast media, power Doppler, transcranial Doppler sonography. Duplex sonography for investigating the extracranial brain circulation should always be used in conjunction with unidimensional direction sensitive Doppler sonography.

Doppler monitoring of middle cerebral artery emboli from carotid stenoses.

The aim of this study was to prove the existence of clinically silent embolization arising from carotid stenoses. Simultaneous bilateral transcranial Doppler sonography of the middle cerebral artery was carried out during 10 minutes in 30 patients having ultrasonically demonstrated unilateral (n = 12) or bilateral internal carotid stenoses (n = 18). Twenty-four of the stenoses were clinically considered to be symptomatic and 24 were asymptomatic. Emboli signals were detected in 5 of the 30 patients. All occurred unilaterally on the side of a high-grade carotid stenosis. Four of the 5 lesions were symptomatic, and 1 was asymptomatic.

High-power cw neodymium-doped fiber laser operating at 9.2 W with high beam quality.

We report on a 9.2-W cw, two-times diffraction-limited, neodymium-doped fiber laser operating in the 1.06-microm region. For a silica-based double-clad fiber, slope efficiencies of more than 25% are observed for pumping by a diode-laser system operating near 810 nm.

[A head and transducer holding technique for TCD monitoring of the vertebrobasilar circulation]. / Eine Kopf- und Transducerhalterungstechnik zum TCD-Monitoring am vertebrobasilären Kreislauf.

For monitoring the Doppler spectrum of the vertebral and basilar arteries the authors have used a microball vacuum cushion for fixing the head of the patient in lateral, moderately anteflected position, and a three lockable joint type instrument holder allowing adjustment of the probe suboccipitally. This setting was used for transforaminal vertebrobasilar emboli monitoring in 5 patients having prosthetic heart valves. As an alternative technique a microball filled vacuum collar was tried out for immobilisation of the patient's head, and a snake neck type surgical instrument holder for guiding the probe.

High intensity transcranial Doppler signals (hits) after prosthetic valve implantation.

High intensity transcranial Doppler signals (HITS), assumed to be caused by microemboli, have been reported to occur in many patients with mechanical heart valve prostheses. The aim of our study was to quantify these phenomena and to find possible differences. Furthermore, parameters which might influence the prevalence of HITS were investigated. Monitoring of both middle cerebral artery frequency shift spectra was carried out for 10 minutes in 100 patients having an aortic (n = 64) and (n = 5)/or (n = 31) mitral mechanical heart valve prosthesis. The spectra were off-line screened for HITS by ear. The findings were correlated with the degree of anticoagulation and with the time period since implantation. To examine if platelet aggregates would be the underlying cause, another HITS count was done for 10 minutes prior to and 40 minutes after i.v. injection of 250 mg aspirin (ASA) as well as after four days of 100 mg/day ASA orally in a group of seven patients. Prior to surgery, HITS were present in only one patient. Postoperatively, HITS were detected in 54 of 100 patients. There was no significant difference between left and right sides, no correlation with anticoagulation, and only a borderline correlation with the time interval since implantation. Sixty-six percent of the 50 patients monitored within the first three postoperative weeks had HITS as compared to only 42% in 50 subjects who were examined three months or later after surgery (p < 0.05). With regard to the number of HITS an inverse behaviour was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

[Assessment of cerebral autoregulation using transcranial Doppler sonography under lower body negative pressure]. / Prüfung der zerebralen Autoregulation mittels transkranieller Doppler-Sonographie unter Lower Body Negative Pressure.

A novel technique for transcranial Doppler sonographic assessment of cerebral autoregulation was tried out in 20 healthy volunteers, ten of them right-handed and ten left-handed. A fall in arterial blood pressure was produced through lower body negative pressure (LBNP) of -50 mmHg during 1 min. The Doppler shift signal of both middle cerebral arteries was recorded simultaneously and analyzed digitally to obtain mean Doppler shift frequency and Doppler signal power. Their product, as an index of volume flow, was calculated on-line. By positioning and coupling of the transducers and keeping the position of the head stable throughout the test, spurious readings due to the effects of gravity or head movement were excluded. With an average fall of mean arterial blood pressure of 10.3 +/- 7.7 mmHg, the TCD flow index as averaged over the entire period of LBNP was 103.6 +/- 19.5% of the value measured under atmospheric pressure, demonstrating a physiological autoregulation. In the right-handed subjects the flow index during LBNP was significantly higher on the right than on the left side. In only one of the ten right-handed individuals the side difference was reversed, while this was the case in five of the ten left-handed subjects.

[The transcranial Doppler ultrasound upright posture test for clinical evaluation of cerebral autoregulation]. / Ein TCD-Steh-Test zur klinischen Prüfung der zerebralen Autoregulation.

Description of a TCD test designed for the clinical investigation of cerebral autoregulation. The Doppler shift frequency of the middle cerebral artery is recorded using of a transducer fixed to the patient's head by an elastic ribbon and a ball joint type probe-holder, and on-line digitally analysed to calculate the TCD flow index (signal power times velocity). Blood pressure is measured every 30 seconds at the right index hold at the level of the heart, using a special sphygmomanometer. The patient sits on a foot-stool. After 1.5 minutes of measurement he rises to remain in upright position for another 2 minutes. The flow index normalised to its average over the sitting period quantitatively indicates the evolution of volume flow brought about by the change of the body position. The change in arterial blood pressure is off-line calculated from its periodic measurements. In a pilot study this test has been successfully used in 30 healthy volunteers and 2 patients suffering from orthostatic dysregulation of blood pressure.

Ultrasonic imaging of the internal jugular vein.

The ultrasonographic anatomy of the internal jugular vein is described. Current uses of ultrasonic imaging of this vessel are discussed, with special attention given to its use for calculating volume flow.

Smoking and hypertension: risk factors for carotid stenosis.

The prevalence of smoking, hypertension and diabetes mellitus was assessed in 221 patients suffering from internal carotid stenosis and compared with the prevalences in two sex- and age-matched control groups composed of subjects having normal Doppler findings and from non-neurological outpatients. Of the subjects with carotid stenosis 27.6% were hypertensive smokers in comparison with 9.5% and 17.2% in the two control groups. The difference of the stenosis cohort from the two control groups was significant (P less than 0.01 and P = 0.016 respectively). There was no statistically significant differences between the occurrence of diabetes and hypertension in non-smokers and patients who smoked. In 394 investigated patients suffering from carotid stenosis or occlusion an obstruction index, based on the Doppler shift frequency, was calculated. This index was lowest in the normotensive smokers [corrected]. It was only insignificantly higher in the hypertensive non-smokers but significantly so in the normotensive smokers. The index was highest in the hypertensive smokers [corrected]. It was concluded that cigarette smoking, especially if associated with hypertension, is a determinant risk factor for carotid stenosis and occlusion.

Sex and side differences of cerebral arterial caliber.

The diameter of 261 middle cerebral and 225 anterior cerebral arteries was measured on half axial antero-posterior (ap) view, and the diameter of 217 internal carotid arteries on side view angiograms. Mean diameter was significantly larger by 9.3%, 8.8% and 9.7% respectively in males than in females. In the females the vessels of the left hemisphere were wider but not significantly so than those of the right hemisphere, and the contrary was true for the males. In both sexes the side difference was reversed in the eighth decennium. There was no correlation of vessel diameter with age except for a statistically significant increase by 7.8% of right middle cerebral artery diameter in males from the fifth to the sixth decennium.

Internal jugular venous flow measurement by means of a duplex scanner.

Using a special probe holder, cross-sectional area and time-averaged mean spatial velocity of the internal jugular vein were measured by means of a duplex scanner and multiplied to calculate volume flow. In a cohort of 100 subjects ages 21 to 70 years, average right plus left flow was 740 +/- 209 mL/min. Flow was 8.7% lower in females than in males. Normalization of flow to 100 g brain tissue by dividing it through the mean sex specific brain weight resulted in no significant sex difference. Within the age range investigated, there was no decrease of flow with age.

[A method for the determination of continuous contraction ability of the hand-arm muscles]. / Eine Methode zur Bestimmung der Dauerkontraktionsfähigkeit der Hand-Arm-Muskulatur.

Suppositions concerning the technique of tools were performed for recording the so-called mechanogram, which is intended for wide objective estimation of function of the handgrip-musculature. Based on an explorative study in 44 probands the first results and experiences may be reported.

[Doppler sonography measurement of jugular vein blood flow]. / Dopplersonographische Messung des Jugularvenenflusses.

By multiplying mean cross section determined with a linear array scanner by time averaged mean spatial velocity measured with a single gated pw Doppler device, internal jugular venous volume flow was computed in 50 healthy male and 50 female volunteers aged 21 to 70 years with even age distribution within this range. Right plus left flow was 793 +/- 276 ml/min in males and 799 +/- 288 ml/min in females. There was no correlation between flow and age.