Haemodynamic changes during human pregnancy

MD ThesisThe aim of this work was to investigate the physiological adaptations that occur in the maternal cardiovascular system during singleton and twin pregnancy. The cardiovascular system has been shown to undergo major adaptations during human pregnancy. Most investigators agreed that cardiac output increased during pregnancy however there was no unanimity regarding the extent and timing of this increase nor about the physiological mechanisms underlying it. Even less was known about the haemodynamic readjustments following delivery and about the alterations in multiple pregnancy. Further study has been limited by the lack of an accurate noninvasive technique which is applicable and reproducible during pregnancy. Cross-sectional echocardiography combined with Doppler ultrasound measurement of blood velocity provides a noninvasive method for measuring cardiac output at a number of locations within the heart and great vessels. Preliminary investigations revealed that cardiac outputs determined by this method correlated closely with those measured by the direct Fick technique in non-pregnant subjects. In addition the method was highly reproducible in both pregnant and nonpregnant subjects. M-mode echocardiography allows accurate and noninvasive measurements of cardiac chamber size and ventricular function. These measurements were also found to be highly reproducible in pregnant and non-pregnant subjects. Using these techniques the aims of this thesis were to investigate the extent, timing and mechanisms of the changes in cardiac output during singleton and twin pregnancy. Echocardiographic investigations were performed prior to and during singleton pregnancy, during the first 6 months after singleton pregnancy, and during and 6 months after twin pregnancy. All subjects were studied in the left semi-lateral position. The results suggested that; (1) During singleton pregnancy cardiac output was increased early in the first trimester and continued to rise until 24 weeks gestation when values were 43-49% above pre-pregnant control values. Thereafter there was no further change. Heart rate and left ventricular function increased during the first trimester. Left atrial and left ventricular end-diastolic dimensions increased during the second trimester suggesting an increase in venous return. Cardiac valve cross-sectional areas and left ventricular wall thickness also increased during pregnancy. After delivery cardiac output had fallen to non-pregnant values by 2 weeks. This was associated with reductions in left ventricular performance and left atrial and left ventricular end-diastolic dimensions. The decrease in valve cross-sectional areas and left ventricular wall thickness was not evident until later in the puerperium. (2) During twin pregnancy cardiac output was increased by 20 weeks gestation and thereafter showed no further change. Maximum cardiac output was 59-62% above postnatal control values. This increase was greater than that recorded during singleton pregnancy due to a relatively greater increase in heart rate. Twin pregnancy was also associated with a greater increase in left atrial dimension. The results of these studies shed light on some of the the unanswered questions in the field of maternal haemodynamics. The noninvasive Doppler techniques used allowed accurate and reproducible measurements of cardiac output in pregnant subjects. This work has important implications for the future investigation of cardiac and hypertensive disorders during pregnancy.Newcastle Health Authority: Birthright

Cuffless Blood Pressure in clinical practice: challenges, opportunities and current limits.

Background: Cuffless blood pressure measurement technologies have attracted significant attention for their potential to transform cardiovascular monitoring.Methods: This updated narrative review thoroughly examines the challenges, opportunities, and limitations associated with the implementation of cuffless blood pressure monitoring systems.Results: Diverse technologies, including photoplethysmography, tonometry, and ECG analysis, enable cuffless blood pressure measurement and are integrated into devices like smartphones and smartwatches. Signal processing emerges as a critical aspect, dictating the accuracy and reliability of readings. Despite its potential, the integration of cuffless technologies into clinical practice faces obstacles, including the need to address concerns related to accuracy, calibration, and standardization across diverse devices and patient populations. The development of robust algorithms to mitigate artifacts and environmental disturbances is essential for extracting clear physiological signals. Based on extensive research, this review emphasizes the necessity for standardized protocols, validation studies, and regulatory frameworks to ensure the reliability and safety of cuffless blood pressure monitoring devices and their implementation in mainstream medical practice. Interdisciplinary collaborations between engineers, clinicians, and regulatory bodies are crucial to address technical, clinical, and regulatory complexities during implementation. In conclusion, while cuffless blood pressure monitoring holds immense potential to transform cardiovascular care. The resolution of existing challenges and the establishment of rigorous standards are imperative for its seamless incorporation into routine clinical practice.Conclusion: The emergence of these new technologies shifts the paradigm of cardiovascular health management, presenting a new possibility for non-invasive continuous and dynamic monitoring. The concept of cuffless blood pressure measurement is viable and more finely tuned devices are expected to enter the market, which could redefine our understanding of blood pressure and hypertension

Critical Investigation of the Pulse Contour Method for Obtaining Beat-By-Beat Cardiac Output

The purpose of this study was to explore the efficacy of two existing pulse contour analysis (PCA) models for estimating cardiac stroke volume from the arterial pressure waveform during kicking ergometer exercise and head-up tilt manoeuvres. Secondly, one of the existing models was modified in an attempt to enhance its performance. In part I, seven healthy young adults repeated two submaximal exercise sessions on a kicking ergometer, each with three different sets of steady-state cardiac output comparisons (pulsed Doppler vs. pulse contour). Across all exercise trials regression results were found to be PCA = 1. 23 x Doppler-1. 38 with an r2 = 0. 51. In part II, eight young and eight older male healthy subjects participated in a head-up tilt experiment. Cardiac output comparisons were again performed during the supine and tilt conditions using pulsed Doppler and pulse contour cardiac output. Regression results revealed that PCA performed best during supine conditions and preferentially on the older subjects. In all instances, impedance-calibrated pulse contour analysis will provide reasonable beat-by-beat cardiac output within very narrow confines and will result in a progressively more significant bias as cardiovascular dynamics change. In addition, it appears that heart rate variability negatively influences beat-by-beat pulse contour cardiac output results, further limiting application of existing models

Bioimpedance as a predictor of survival in renal failure and associated comorbidities.

Background: Renal failure requiring dialysis is associated with a high mortality. One of the contributing causes is overhydration. Overhydration can be assessed by bioimpedance analysis (BIA)– the non-invasive electrical measure of small current through the tissues that estimates the proportion of fluid that is intracellular water (ICW, typically muscle which is healthy) and extracellular (ECW, which in excess causes tissue oedema and is potentially dangerous). Several studies indicate that a extracellular water to total body water (TBW) ratio is associated with increased risk of death in dialysis patients but it is not clear if this is independent of other risk factors for death, namely comorbidity. Aims and objectives: To establish the prognostic value of BIA in the prediction of survival on dialysis in the context of other known predictors of survival or hospitalisation. With further analysis of the applicability of the same scenario to heart failure patients. Methodology: To conduct a systematic review using a standardised approach including a prespecified research question, search terms and criteria for study inclusion. With independent selection for inclusion in the study and quality appraisal by multiple authors with different backgrounds and experience. Results: 2701 studies identified by literature search, plus an additional 4 through reference checking. 38 papers included in final analysis, 4 of which were regarding heart failure cohorts. Analysis of the research shows that BIA is an independent predictor of mortality. Conclusion: BIA shown to be an independent predictor of mortality in dialysis patients, further research needed to extrapolate to heart failure (HF) populations

A feasibility study of the Spatio-temporal analysis of cardiac precordial vibrations

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New concepts in echocardiography

If short pulses of high frequency sound are transmitted through the heart, discontinuities in the tissues will produce reflected sound waves or "echoes". There wil! be a delay between a pulse transmission and the arrival of a correspond·mg echo. Together with knowledge of sound velocity this wi!l enable determination of the distance between the transmitterfreceiver and the reflecting interface, thus providing information about cardiac dimensions. Similarly the Doppler effect can be used to provide further diagnostic information. These applications of ultrasound (echocardiography) for the detection of cardiac (mal)function have recently gained acceptance even though interpretation of the information obtained can be difficult. Major reasons for this acceptance are probably that, while

Aerospace medicine and biology: A continuing bibliography with indexes, supplement 164

This bibliography lists 275 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1977

Computer assisted optimization of cardiac resynchronization therapy

The efficacy of cardiac resynchronization therapy (CRT) through biventricular pacing (BVP) has been demonstrated by numerous studies in patients suffering from congestive heart failure. In order to achieve a guideline for optimal treatment with BVP devices, an automated non-invasive strategy based on an electrophysiological computer model of the heart is presented. The presented research investigates an off-line optimization algorithm based on different electrode positioning and timing delays