Rapid, climate-driven changes in outlet glaciers on the Pacific coast of East Antarctica.

Observations of ocean-terminating outlet glaciers in Greenland and West Antarctica indicate that their contribution to sea level is accelerating as a result of increased velocity, thinning and retreat. Thinning has also been reported along the margin of the much larger East Antarctic ice sheet, but whether glaciers are advancing or retreating there is largely unknown, and there has been no attempt to place such changes in the context of localized mass loss or climatic or oceanic forcing. Here we present multidecadal trends in the terminus position of 175 ocean-terminating outlet glaciers along 5,400 kilometres of the margin of the East Antarctic ice sheet, and reveal widespread and synchronous changes. Despite large fluctuations between glaciers--linked to their size--three epochal patterns emerged: 63 per cent of glaciers retreated from 1974 to 1990, 72 per cent advanced from 1990 to 2000, and 58 per cent advanced from 2000 to 2010. These trends were most pronounced along the warmer western South Pacific coast, whereas glaciers along the cooler Ross Sea coast experienced no significant changes. We find that glacier change along the Pacific coast is consistent with a rapid and coherent response to air temperature and sea-ice trends, linked through the dominant mode of atmospheric variability (the Southern Annular Mode). We conclude that parts of the world's largest ice sheet may be more vulnerable to external forcing than recognized previously.

Velocity profiles in the normal human abdominal aorta: a comparison between ultrasound and magnetic resonance data.

Evolving magnetic resonance (MR) procedures were utilized to validate one-dimensional ultrasonic (US) Doppler profiles in vivo on the basis of this alternative noninvasive method of assessing blood velocity. Corresponding velocity profiles were acquired by both US and MR in the abdominal aorta of 10 healthy volunteers. The ultrasound velocities recorded throughout a cardiac cycle along the anterio-posterior aortic diameter were compared to their spatial and temporal MR counterparts. Correlation coefficients ranging from 0.92 to 0.97 and regression slopes from 0.86 to 1.13 indicate a high degree of correspondence between the two modalities and increase the confidence in the fidelity of velocity profiles obtained with both procedures.

Ultrasonic phased-array scanner with digital echo synthesis for Doppler echocardiography.

For the purpose of the quantitative assessment of subtle disease processes in the cardiovascular system an electronically steered sector scanner that combines echographic imaging and Doppler blood velocity measurements has been developed. The integrated operation of a fast Fourier transform (FFT) Doppler signal processor for the simultaneous blood velocity evaluation of 64 individual gates is among the specific design goals. The instrument incorporates an unusually high degree of digital signal processing, which allows for high integration density, easy manufacturing and high reliability in future designs. The complex Doppler spectra are determined for each of the 64 Doppler gates in real time, and the subsequent computation of the first moment provides a reliable estimate of the mean blood flow velocities at the respective locations. The instantaneous velocity profile along the Doppler beam is displayed together with the calculated volume flow rate and a range-selected complete frequency spectrum. Results of both in vitro and in vivo tests indicate that in the future, a higher degree of digital signal processing could be implemented in complex ultrasonic systems.

Doppler flow determination.

Doppler ultrasound provides a non-invasive alternative to the established methods of blood flow measurement. The standard principle of the Doppler-echographic determination of volume flow rate is based upon the assessment of three quantities: the vascular cross-section, the angle of incidence of the ultrasound relative to the direction of the velocity vector, and the cross-sectional average velocity. In the literature reporting comparisons between Doppler and invasive cardiac output measurements, correlation coefficients ranging from 0.8 to 0.95 are given for adult patients. Error limits of less than 20% for individual measurements, however, require a skillful investigator, a high quality instrument, and an appropriate subject. From a technical point of view, the highest accuracy is achieved by directing the ultrasound beam parallel to the flow, by measuring the true cross-sectional area instead of the diameter, and in the presence of well-behaved transluminal blood velocity distributions.

Ultrasonic Doppler and duplex systems: possibilities and limitations.

In order to utilize Doppler modalities in an optimal manner, one should both be aware of their potential and respect their limitations. To this end, a variety of technical and physical factors affecting the performance of Doppler devices are discussed: (1) the velocity of propagation limiting the temporal resolution of pulsed systems; (2) intervening tissue that may weaken the echo considerably; (3) the size of the sample volume that could be too small to provide a transvascular mean velocity or too large to discriminate flow in adjacent vessels; (4) the principles of continuous wave mode lacking depth resolution, and pulsed mode being prone to aliasing; (5) the additional complexity of duplex/triplex systems; (6) the tight temporal restrictions of 2-dimensional color mappers which cause poor velocity resolution, and (7) the angle of incidence that needs to be assessed in order to measure absolute velocity and the cross-sectional area that must be measured additionally for the calculation of the volume flow rate. Based on this discussion, some hints on selecting instruments or instrument parameters are given.

An improved stochastic approach to rf amplitude analysis in ultrasonic cardiac tissue characterization.

We carried out a series of studies to improve the reproducibility of methods for ultrasonic myocardial tissue characterization using a stochastic approach to amplitude analysis of radiofrequency signals previously reported from our laboratory. Analysis of transducer scanner characteristics, data acquisition and processing, and data display from studies in tissue phantoms permit us to define some features of a parameter for expression of tissue character. The ratio of mean to standard deviation of the amplitude histogram from our system is explored as now implemented in our laboratory for reproducible measurements. The theoretical basis for understanding the utility of this method in defining tissue architecture and pathologic conditions requires further work.

[The value of echocardiography in the diagnosis of cardiac diseases]. / Die Bedeutung der Echokardiographie in der Diagnostik der Herzkrankheiten.

Single beam echocardiography is now an established diagnostic tool in non-invasive cardiology. The principle indications are valvular diseases, pericardial effusion, aneurysm of the ascending aorta, and congenital heart disease. In the absence of regional contraction disorders, left ventricular function can be assessed by the extent of systolic shortening of the left ventricular diameter. More recently, two-dimensional echocardiography has made a very significant contribution to anatomical and functional evaluation of the heart and the great vessels, since the cardiac structures can be visualized in various cross-sections. This technique is especially helpful for the assessment of left ventricular regional contraction disturbances, the diagnosis of dysfunction of artificial valves and bioprotheses, the detection of dissecting aneurysm, and the estimation of mitral valve area in mitral stenosis. Since various left ventricular axes can be determined, the quantitation of left heart volumes appears to be within the capability of the two-dimensional technique.

A comparison between single gate and multigate ultrasonic Doppler measurements for the assessment of the velocity pattern in the human ascending aorta.

The velocity pattern in the ascending aorta of 15 healthy adults was measured quasisimultaneously from the Doppler-shifts produced in 16 gates distributed equally within the cross-section along a narrow ultrasound beam which centrally traversed the vessel upstream of the brachiocephalic trunk. A comparison between the time integrals of the velocities in gates 9 (centre line), 4 and 13 (off centre) and the time integral of the weighted mean of the velocities of all gates correlated with r = 0.90, SEE = 1.05 (gate 9), r = 0.90, SEE 0.88 (gate 4) and r = 0.92, SEE 0.94 (gate 13). A better correlation (r = 0.96, SEE = 0.60) was found between the linear mean of all gates and the weighted mean. These results show that Doppler measurements in single small gates are not appropriate to determine the average cross-sectional blood flow velocity in healthy adults.

Dynamics of aortic flow in hypertrophic cardiomyopathy.

The purpose of this study was to reassess left ventricular ejection dynamics in hypertrophic cardiomyopathy, to investigate whether a premature stoppage of ejection occurs, as previously reported, and whether reliable criteria for left ventricular outflow tract obstruction can be established by non-invasive evaluation of aortic flow patterns. In a group of 21 patients with hypertrophic cardiomyopathy, composed of 9 with the obstructive form (HOCM), 9 with the non-obstructive form (HNCM) and 3 with apical hypertrophy (HACM), instantaneous flow velocities across the ascending aorta were determined non-invasively with a 16-gated Doppler 2-D echo instrument. Ten normals served as controls. The 16 flow velocities were averaged over 8 heart beats and the relative volume flow rate was calculated by microprocessor analysis. Ejection time (i.e. flow time) derived from the flow curves was compared with the available ejection period as determined from the carotid pulse tracing. In normals, ejection time amounted to 94 +/- 3% of the available ejection period, in HOCM to 92 +/- 5% and in HNCM to 93 +/- 4% (no significant differences). In HACM, however, ejection time was reduced to 71 +/- 14% of the available ejection period. In contrast to HNCM, aortic flow in HOCM was characterized by an early peak followed by a plateau at a sizably lower flow level for the rest of systole. Flow time of an abnormally short duration was the hallmark of HACM. We conclude that in patients with hypertrophic cardiomyopathy, HOCM and HNCM can be distinguished by the shape of their volume flow curves. A premature stoppage of ejection is only found in patients with HACM.

[A Doppler ultrasound device for determining blood volume flow]. / Ein Doppler-Ultraschall-Gerät zur Bestimmung des Blut-Volumenflusses.

A novel ultrasonic quantitative Doppler procedure has been developed which allows for the measurement of real-time volume flow in large blood vessels. It makes use of a 2D array transducer, which enables parallel sampling of a measuring slice placed in normal position to the sound beam. With this arrangement, volume flow can be computed without measuring the angle of incidence. Moreover, the 2D velocity distribution can be assessed within intervals of 10 to 30 ms.

[Dynamics of cardiac output in patients with hypertrophic obstructive cardiomyopathy]. / Auswurfdynamik bei Patienten mit hypertroph-obstruktiver Kardiomyopathie.

To characterise the duration of aortic flow velocity waveforms in hypertrophic obstructive cardiomyopathy (HOCM) the dynamics of aortic flow were investigated in 10 normals and 11 patients with hypertrophic obstructive cardiomyopathy performing 16-gated Doppler 2D-echocardiography of the ascending aorta. 16 flow velocities were recorded along the Doppler beam axis between the anterior and posterior aortic walls, and averaged over 8 beats. Flow times were derived from the flow curves and normalised by the ejection period as determined from the carotid pulse tracing. Thus, relative ejection time (% SEP) was calculated at the anterior (gate 4) and the posterior aortic wall (gate 13) as well as at the axis of the vessel (gate 9). In normals % SEP was 92 +/- 3% in gate 4, 95 +/- 4% in gate 9 and 93 +/- 3% in gate 13 (NS). In patients with HOCM % SEP was 92 +/- 5% in gate 4 and 83 +/- 4% (NS) in gate 9. At the posterior aortic wall (gate 13) % SEP amounted to 68 +/- 5% and was significantly lower than in gate 9 (P less than 0.05) and in gate 4 (P less than 0.001) respectively. It is concluded that in contrast to normals systolic flow time in hypertrophic obstructive cardiomyopathy varies along the sound beam in the ascending aorta. Flow time recorded at the posterior aortic wall is most abbreviated.

[Doppler sonography assessment of blood flow velocity in the ascending aorta. Problems and possible solutions]. / Doppler-sonographische Erfassung der Blutflussgeschwindigkeit in der aufsteigenden Aorta: Problematik and mögliche Lösung.

Irregularities of the transvascular distribution of blood flow within the human ascending aorta have been documented by means of 16 Doppler gates positioned along one scanline of a sector scanner. The velocity profiles recorded from ten healthy adults, ten patients suffering from hypertrophic obstructive cardiomyopathy, ten patients suffering from hypertrophic nonobstructive cardiomyopathy, and ten patients with severe aortic insufficiency exhibited nonuniformities which varied not only from individual to individual but also between the groups and depending on the phase of the cardiac cycle. These variations prevent any local measurement from being representative for the instantaneous mean velocity in all cases. A reliable mean should therefore be determined by simultaneously taking into account all velocities within the vascular cross-section. A computer simulation in order to indicate a potential solution to this problem demonstrates that an annular array transducer can be excited in such a manner that it produces a homogeneous ultrasound beam of a transverse area a hundred times larger than the one obtained in the conventional maximally focussed mode.

Combined two-dimensional ultrasound Doppler technique. New possibilities for the screening of renovascular and parenchymatous hypertension?

A combination of a real time phased array sector scanner and a range-gated 16-channel pulsed Doppler system was used for the evaluation of renal artery flow patterns in 25 echogenic subjects. Eight of these had renal artery stenosis, 5 an increased peripheral resistance in the kidney, and 12 showed normal renal flow patterns with consistent forward flow during the entire heart cycle. In normals, the ratio of end systolic (S2) versus early peak systolic (S1) velocity was 0.52 +/- 0.11 (range 0.37-0.84). In the patients with renal artery stenosis S2/S1 ranged from 0 to 0.30. Five of the 8 patients with renal artery stenosis could be evaluated before and after percutaneous transluminal dilatation (PTA). After successful PTA (diameter reduction less than 50% and pressure gradient less than 20 mm Hg) S2/S1 returned to normal. The patients with increased peripheral resistance due to an angiographically proven small kidney exhibited a variety of flow patterns with S2/S1 ranging from 0 to 0.29, similar to the ones with renal artery stenosis. The results suggest that the noninvasive determination of the ratio S2/S1 with the aid of ultrasound Doppler measurements permits a differentiation between normal and abnormal flow patterns and can be applied for the follow-up of patients after PTA. In utilizing the described method, neither the angle between the Doppler beam and the vessel axis, nor the vessel diameter must be evaluated.

Human abdominal aorta: comparative measurements of blood flow with MR imaging and multigated Doppler US.

Magnetic resonance (MR) imaging has proved to be a new alternative method for the noninvasive detection and quantification of blood flow in human vessels. By means of standard gradient echo sequences triggered with electrocardiography on a 1.5-T whole-body imaging system, the authors measured the flow-induced phase shift in the abdominal aorta of healthy volunteers. The instantaneous two-dimensional velocity profiles and the integrated flow rate were determined in intervals down to 21 msec throughout the cardiac cycle. The results were validated by means of comparative measurements with a multigated Doppler ultrasound instrument. The velocity values acquired with this instrument in one spatial dimension in the anteroposterior direction of the abdominal aorta agreed to a great extent with the temporal and spatial corresponding values recorded with MR imaging. The same high correlation between the two methods was found for the calculated instantaneous total blood flow.

Determination of the ratio of pulmonary blood flow to systemic blood flow by derivation of amplitude weighted mean velocity from continuous wave Doppler spectra.

Conventional Doppler echocardiographic techniques for the estimation of blood flow ratios depend on the precise measurement of the diameters of the aorta and the pulmonary artery and the mean blood flow velocities in these vessels. A simpler and quicker method is described, based on the calculation of the systolic time integrals of the amplitude weighted mean velocities from continuous wave Doppler spectra within the great arteries. In 30 controls the mean (2 SD) ratio of pulmonary to systemic blood flow averaged 0.952 (0.085). The results of the new technique showed a good agreement with those of quantitative dye dilution and oximetry in 16 patients with intracardiac left to right shunts.

Ultrasonic tissue characterization: detection of acute myocardial ischemia in dogs.

Ultrasonic tissue characterization is a new area of investigation in the field of cardiac ultrasound. The amplitude and frequency of the ultrasound signal are normally altered as the signal penetrates through tissue. It is assumed that the amplitude distribution and frequency shift of diseased or edematous tissue are different than those of normal tissue. A statistical approach to the analysis of the unprocessed radiofrequency signal in the amplitude domain was used to study the effect of acute myocardial ischemia on the parameter mean amplitude/standard deviation of the amplitude (MSR). Ten dogs were anesthetized and underwent left lateral thoracotomy. Baseline mean MSR from the interventricular septum was 1.99 +/- 0.05, but increased by 30 min after coronary artery occlusion and started to plateau at 1 hr (mean 2.24 +/- 0.06). Reproducibility in noninfarcted myocardium (left ventricular inferoposterior wall) was good, with a mean MSR of 2.00 +/- 0.05 at baseline and 1.98 +/- 0.04 3 to 4 hr later. There was no difference in mean MSR when data were obtained through chest wall and when they were obtained directly from the surface of the heart. We conclude that statistical analysis in the amplitude domain of the unprocessed radiofrequency signal can detect acute myocardial ischemia within 30 min after coronary artery occlusion, provides reproducible measurements, and is unaffected by chest wall filtering.