In-Suit Doppler Technology Assessment

The objective of this program was to perform a technology assessment survey of non-invasive air embolism detection utilizing Doppler ultrasound methodologies. The primary application of this technology will be a continuous monitor for astronauts while performing extravehicular activities (EVA's). The technology assessment was to include: (1) development of a full understanding of all relevant background research; and (2) a survey of the medical ultrasound marketplace for expertise, information, and technical capability relevant to this development. Upon completion of the assessment, LSR was to provide an overview of technological approaches and R&D/manufacturing organizations

Left ventricular performance during coronary angioplasty

Left ventricular (LV) performance during elective single vessel coronary angioplasty (PTCA) was assessed in 67 patients with intravenous digital subtraction ventriculography. Left ventriculography, following right atrial contrast injection, was well tolerated and produced images suitable for analysis in all cases. During balloon inflation, marked contractile abnormalities developed rapidly in ventricular segments subtended by the treated artery. The degree of contractile dysfunction was lessened in the presence of collateral vessels and was independent of short (20 secs) or long (60 secs) balloon inflation, and the presence or absence of additional coronary disease. During PTCA LV end-diastolic volume remained unchanged and LV end-systolic volume increased. However, ECG R wave amplitude decreased, supporting the view that during ischaemia LV volumes are independent of R wave amplitude. "Reciprocal" ECG changes were examined in patients with single vessel disease undergoing left anterior descending PTCA. Despite the development of inferior ST segment depression, inferior LV segmental contraction remained unaltered while inferobasal contraction was augmented. This confirms that these remote ECG changes did not indicate additional ischaemia but represented only an electrical phenomenon. In patients undergoing PTCA after successful thrombolysis for acute myocardial infarction, balloon occlusion was used to "reproduce" thrombotic coronary occlusion. A deterioration was apparent in global and regional LV performance during balloon inflation which may represent the extent of myocardium salvaged by thrombolytic therapy. In the 37 patients studied after PTCA, segmental contraction had returned to baseline values confirming that multiple balloon coronary occlusions of up to 60 seconds do not produce sustained abnormalities of LV contraction detectable by this method. PTCA allows a unique opportunity to examine the immediate effects of controlled coronary occlusion on LV performance. Intravenous digital subtraction ventriculography provides a valuable method with which to study these changes

The assessment of echocardiographic and tissue Doppler profiles of asymptomatic follow-up patients in cardiology practice

Thesis (M. Tech.) -- Central University of Technology, Free State, 2010This main aim of this study was to assess patients in a general cardiology practice in order to determine the systolic and diastolic profiles of these patients. The aim was also to determine what effect life style and risk factors may have on the echocardiographic variables measured during such an examination. The specific aim of this study was the importance of not only examining the systolic function but the necessity to also examine the diastolic profile of patients. Life-style plays an important role, with the main culprit being obesity. Obesity was the single most important factor that affected the diastolic profile of patients seen in this study. With obesity a combination of other risk factors related to obesity was observed. Most abnormalities found due to these risk factors were associated with diastolic changes in the left ventricle. Echocardiography is routinely used in daily practice, but the diagnostic value of this tool can be enhanced if proper analyses of the systolic as well as the diastolic profiles are determined. Many cardiologists only measure the systolic function of the heart as an indication of the well- being of the left ventricle, although in this study it was proven that systolic function did not alter with ageing or with changes in the risk profile. Hundred-and-twelve patients, divided into three age groups, were evaluated in this study. Both systolic and diastolic variables were measured and analysed for abnormalities. None of these patients had systolic function abnormalities, although they had detectable anatomic changes due to ageing, obesity and hypertension. Several abnormalities were found on the diastolic profile of these patients. Muscle thickness increased due to obesity and hypertension and even with ageing, but with no significant abnormalities in the systolic function of the heart. There was a slight increase in the circumferential shortening of the left ventricle and that both the septal and longitudinal functions decreased with ageing. It is noteworthy that even where the systolic function remained normal in ageing subjects, their diastolic profiles changed significantly. Assessment of left ventricular function required a meticulous and systematic approach. In this study forty- one percent of patients visiting this general practice had abnormalities of their diastolic function although their systolic function was normal. It was found that with ageing, especially in the older age group, important abnormalities occur in their diastolic profile. The most common changes were that the E- peak velocity decreased and that the Apeak velocity of the trans-mitral flow increased. It seemed that passive filling decreased with ageing but that active filling increased simultaneously, causing the cardiac output to remain constant in older subjects. This is important to know because diseases affecting the atrium may have a profound effect on the cardiac output of older patients, even if they have normal systolic function, (due to the decreased passive filling they need their active filling or atrial contraction to support a normal cardiac output). An important marker will be to look at the ratio of the E/A- velocities in older patients to determine the ratio of active against passive filling. Other than that, a relatively new tool in echocardiography called tissue Doppler was used to determine what happened to the muscle with ageing. Here it was demonstrated that the different layers of the left ventricle acted differently with ageing. Results showed that the longitudinal fibres weakened with ageing although the circumferential fibres remained unchanged or even strengthened with ageing. It was apparent in this study that the traditional use of only systolic function may not be adequate when evaluating relative asymptomatic patients presenting at a general cardiology practice. It is important to also evaluate the diastolic profiles of these patients in order to scientifically quantify their heart health, even in asymptomatic patients. It is important to routinely evaluate the diastolic profile of patients so that early detection of these diastolic variables can be detected and timely consideration for its treatment can be given by their cardiologist. It is also important to take note of the significance of the obesity problem and the effect it has on the heart’s health. In conclusion, this study emphasizes the importance of the echocardiographic evaluation of diastolic cardiac function in addition to routine systolic evaluation in asymptomatic patients. This will enable the clinician to detect abnormalities early and tailor therapy accordingly. Lifestyle related risk factors, especially obesity, also have significant effects on diastolic cardiac function

Characterising haemodialysis-associated cardiomyopathy using deformation imaging by cardiovascular magnetic resonance tagging and speckle-tracking echocardiography

Haemodialysis patients represent an extreme phenotype of cardiovascular risk with a pattern of disease distinct from that in the general population. Non-traditional risk factors, specific to chronic kidney disease such as hypervolaemia, arterial stiffness and advanced glycation end-product deposition are increasingly recognised. A previously demonstrated non-traditional risk factor associated with worse outcomes is the presence of uraemic cardiomyopathy. This pattern of cardiac morphology and function has previously been defined as the presence of left ventricular abnormalities, including left ventricular hypertrophy, dilatation and left ventricular systolic dysfunction. For the first time the work in this thesis studies an incident haemodialysis population using multi-parametric strain-based imaging. This uses the accuracy of cardiovascular magnetic resonance imaging of resting cardiac and aortic morphology and function augmented with strain by tagging to longitudinal strain changes during haemodialysis by speckle-tracking echocardiography. The general aim of this thesis was to characterise the relationship of left ventricular function to haemodialysis using strain-based imaging. This might allow characterisation of haemodialysis-associated cardiomyopathy which may be distinct from the traditional definition of uraemic cardiomyopathy and may better define those patients who would benefit from modifications to the process of haemodialysis

Low-cost, highly efficient, and tunable ultrafast laser technology based on directly diode-pumped Cr:Colquiriites

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 335-352).This doctoral project aims to develop robust, ultra low-cost ($5,000-20,000), highly-efficient, and tunable femtosecond laser technology based on diode-pumped Cr:Colquiriite gain media (Cr:LiCAF, Cr3+:LiSAF and Cr:LiSGaF). By using inexpensive single-mode diodes ($150) as the pump source, we have obtained continuous-wave (cw) output powers >250-mW with slope efficiencies >50%. Record cw tuning ranges were demonstrated for Cr:LiSAF (775-1042 nm), Cr:LiSGaF (777-977 nm), and Cr:LiCAF (754-871 nm). For femtosecond pulse generation, semiconductor saturable absorber mirrors (SESAMs/SBRs) were developed, which were used to initiate and sustain mode-locking. Typical performance was ~25-100 fs pulses, with an optical spectrum in the 770-920 nm range, with ~1-2 nJ of pulse energies from ~100-MHz repetition rate cavities. Record electrical-to-optical conversion efficiencies of ~10% were demonstrated in the cw mode-locked regime. A mode-locked tuning range of 767-817 nm, with ~130-fs long pulses was obtained by using Cr:LiCAF as gain medium. With the Cr:LiSAF gain medium, using regular SESAMs/SBRs centered around 800 nm, 850 nm, and 910 nm, mode-locked tuning ranges of 803-831 nm, 828-873 nm, and 890-923 nm were demonstrated, respectively. By using a broadband oxidized SESAM/SBR, a record tuning range of 800-905 nm was demonstrated with ~150-fs long pulses. Using an extended cavity Cr:LiCAF laser, pulse energies >15-nJ with peak powers exceeding 100-kW were obtained. We performed the first cavity-dumping experiments with a Cr:Colquiriite laser and demonstrated pulse energies >100-nJ, and peak powers approaching MW level, at repetition rates up to 50-kHz. Cr:LiCAF gain media were also pumped by single-emitter multimode diodes, where we obtained >2-W output power in cw operation, and ~100-fs pulses with 390-mW of average power at a repetition rate of 140 MHz in cw mode-locked operation. As an example application area for this low cost technology, we performed multiphoton microcopy experiments with a single-mode diode-pumped Cr:LiCAF laser. We also performed attosecond-resolution timing jitter characterization experiments of the femtosecond Cr:LiSAF laser, and measured a record-low upper limit for the integrated timing jitter of the Cr:LiSAF laser (137-attoseconds in 10 kHz-10 MHz range).by Umit Demirbas.Ph.D

Regional myocardial perfusion : experimental and clinical studies in patients with coronary artery disease

Coronary artery disease has become a world wide medical problem. There is an overwhelming association between coronary atherosclerosis, angina pectoris, acute myocardial infarction and sudden death. The narrowing of coronary arteries is thought to damage the heart by limiting appropriate changes in coronary blood flow and by causing myocardial ischemia. This thesis attempts to examine the coronary circulation in patients who present with chest pain with and without coronary artery disease. One of the aims of this thesis is to validate the use of a short-lived radionuclide to study changes in regional myocardial perfusion. This technique has been applied in clinical medicine in an attempt to describe the disturbances of regional myocardial perfusion that occur in patients with coronary artery disease. These disturbances of perfusion have been related to the patients' symptoms, the electrocardiogram and the stenosed arteries seen in the arteriogram. Krypton-81m in solution is an inert freely diffusible gas (half-life 13 seconds) which emits a single 190 kev gamma ray. This tracer, a special catheter and a gamma camera have been developed in experiments to measure changes in regional myocardial perfusion. The systematic and rand-Om errors of the method have been defined in experiments. The results show that the mixing and delivered arterial concentration of krypton-81m are stable within a useful physiological range of changes in heart rate, blood pressure and coronary blood flow. Correlations with a reference technique have shown that the method can measure changes in regional myocardial perfusion between O and 3 ml/ml/min. The invasive method, the planar imaging and the need for calibration with washout at high levels of perfusion are investigated and described as limitations that must be considered. Eighty patients presenting with chest pain have been investigated by routine clinical methods, precordial mapping of the electrocardiogram during exercise and coronary arteriography. Changes in regional myocardial perfusion at rest and during atrial pacing has been measured using krypton-81m. The results have shown that stable mixing and delivered arterial concentration of krypton-81m can be achieved in the patients. Fifteen patients with negative exercise tests all demonstrated uniform increases in regional myocardial perfusion with pacing. The remaining 65 patients with positive exercise tests and significant coronary artery disease all showed both regional increases and decreases in myocardial perfusion during atrial pacing. In 16 of the 65 patients the jeopardized segment of ventricular myocardium showed significant increases in perfusion during the first 4 to 7 minutes of pacing. Th e increase stopped and regional perfusion in the affected segment then decreased progressively until the pacing was stopped. In 23 of the 65 patients the affected segment showed no changes in perfusion for 5 to 7 minutes of atrial pacing and then showed progressive decreases in regional myocardial perfusion until the pacing was stopped. Finally, in 26 of the 65 patients the affected segment showed immediate and progressive decreases of regional myocardial perfusion starting with the commencement of atrial pacing. In all the patients with disturbed perfusion ST segment depression in the electrocardiogram appeared after (140 ± 14 sec) the regional decrease of myocardial perfusion in the affected segment. Chest pain always appeared later at 220 ± 19 sec after the appearance of disturbed myocardial perfusion. Regional myocardial perfusion returned to normal in all the patients after the atrial pacing was stopped. There was a spatial relationship between the region of the ventricles affected by disturbed perfusion and the region of the precordium showing abnormal electrocardiographic signs during the exercise test. In conclusion, this clinical study has shown that patients with chest pain who have coronary artery disease suffer decreases of regional myocardial perfusion in affected segments of the ventricles during episodes of angina pectoris induced by atrial pacing. Regional perfusion may increase, remain stable or decrease in the affected segment following the onset of a stress test such as atrial pacing. This probably represents the amount of reserve function and adaptation left in the diseased coronary circulation and may be a useful physiological indicator of the severity of coronary disease and of patients at high risk. ST segment depression and pain have a close temporal relationship to the decreases of regional myocardial perfusion that occur in these patients. These studies suggest that there is a close relationship between myocardial perfusion and metabolism in health and disease. Both myocardial perfusion and metabolism will have to be affected by any rational therapy for angina pectoris and ischemic heart disease

When Cardiac Biophysics Meets Groupwise Statistics: Complementary Modelling Approaches for Patient-Specific Medicine

This habilitation manuscript contains research on biophysical and statistical modeling of the heart, as well as interactions between these two approaches