COMPARISON OF RESULTS OF THE NORMAL BALLISTOCARDIOGRAM AND A DIRECT FICK METHOD IN MEASURING THE CARDIAC OUTPUT IN MAN

Closed-Loop Multiscale Computational Model of Human Blood Circulation. Applications to Ballistocardiography

Cardiac mechanical activity leads to periodic changes in the distribution of blood throughout the body, which causes micro-oscillations of the body's center of mass and can be measured by ballistocardiography (BCG). However, many of the BCG findings are based on parameters whose origins are poorly understood. Here, we generate simulated multidimensional BCG signals based on a more exhaustive and accurate computational model of blood circulation than previous attempts. This model consists in a closed loop 0D-1D multiscale representation of the human blood circulation. The 0D elements include the cardiac chambers, cardiac valves, arterioles, capillaries, venules, and veins, while the 1D elements include 55 systemic and 57 pulmonary arteries. The simulated multidimensional BCG signal is computed based on the distribution of blood in the different compartments and their anatomical position given by whole-body magnetic resonance angiography on a healthy young subject. We use this model to analyze the elements affecting the BCG signal on its different axes, allowing a better interpretation of clinical records. We also evaluate the impact of filtering and healthy aging on the BCG signal. The results offer a better view of the physiological meaning of BCG, as compared to previous models considering mainly the contribution of the aorta and focusing on longitudinal acceleration BCG. The shape of experimental BCG signals can be reproduced, and their amplitudes are in the range of experimental records. The contributions of the cardiac chambers and the pulmonary circulation are non-negligible, especially on the lateral and transversal components of the velocity BCG signal. The shapes and amplitudes of the BCG waveforms are changing with age, and we propose a scaling law to estimate the pulse wave velocity based on the time intervals between the peaks of the acceleration BCG signal. We also suggest new formulas to estimate the stroke volume and its changes based on the BCG signal expressed in terms of acceleration and kinetic energy.

[Invasive Cardiopulmonary Exercise Testing: A Review]

Right heart catheterization (RHC) is the internationally standardized reference method for measuring pulmonary hemodynamics under resting conditions. In recent years, increasing efforts have been made to establish the reliable assessment of exercise hemodynamics as well, in order to obtain additional diagnostic and prognostic data. Furthermore, cardiopulmonary exercise testing (CPET), as the most comprehensive non-invasive exercise test, is increasingly performed in combination with RHC providing detailed pathophysiological insights into the exercise response, so-called invasive cardiopulmonary exercise testing (iCPET).In this review, the accumulated experience with iCPET is presented and methodological details are discussed. This complex examination is especially helpful in differentiating the underlying causes of unexplained dyspnea. In particular, early forms of cardiac or pulmonary vascular dysfunction can be detected by integrated analysis of hemodynamic as well as ventilatory and gas exchange data. It is expected that with increasing validation of iCPET parameters, a more reliable differentiation of normal from pathological stress reactions will be possible.

Right Heart Catheterization-Background, Physiological Basics, and Clinical Implications

The idea of right heart catheterization (RHC) grew in the milieu of modern thinking about the cardiovascular system, influenced by the experiments of William Harvey, which were inspired by the treatises of Greek philosophers like Aristotle and Gallen, who made significant contributions to the subject. RHC was first discovered in the eighteenth century by William Hale and was subsequently systematically improved by outstanding experiments in the field of physiology, led by Cournand and Dickinson Richards, which finally resulted in the implementation of pulmonary artery catheters (PAC) into clinical practice by Jeremy Swan and William Ganz in the early 1970s. Despite its premature euphoric reception, some further analysis seemed not to share the early enthusiasm as far as the safety and effectiveness issues were concerned. Nonetheless, RHC kept its significant role in the diagnosis, prognostic evaluation, and decision-making of pulmonary hypertension and heart failure patients. Its role in the treatment of end-stage heart failure seems not to be fully understood, although it is promising. PAC-guided optimization of the treatment of patients with ventricular assist devices and its beneficial introduction into clinical practice remains a challenge for the near future.

Novel blood pressure and pulse pressure estimation based on pulse transit time and stroke volume approximation

BACKGROUND

Non-invasive continuous blood pressure monitors are of great interest to the medical community due to their value in hypertension management. Recently, studies have shown the potential of pulse pressure as a therapeutic target for hypertension, but not enough attention has been given to non-invasive continuous monitoring of pulse pressure. Although accurate pulse pressure estimation can be of direct value to hypertension management and indirectly to the estimation of systolic blood pressure, as it is the sum of pulse pressure and diastolic blood pressure, only a few inadequate methods of pulse pressure estimation have been proposed.

METHODS

We present a novel, non-invasive blood pressure and pulse pressure estimation method based on pulse transit time and pre-ejection period. Pre-ejection period and pulse transit time were measured non-invasively using electrocardiogram, seismocardiogram, and photoplethysmogram measured from the torso. The proposed method used the 2-element Windkessel model to model pulse pressure with the ratio of stroke volume, approximated by pre-ejection period, and arterial compliance, estimated by pulse transit time. Diastolic blood pressure was estimated using pulse transit time, and systolic blood pressure was estimated as the sum of the two estimates. The estimation method was verified in 11 subjects in two separate conditions with induced cardiovascular response and the results were compared against a reference measurement and values obtained from a previously proposed method.

RESULTS

The proposed method yielded high agreement with the reference (pulse pressure correlation with reference R ≥ 0.927, diastolic blood pressure correlation with reference R ≥ 0.854, systolic blood pressure correlation with reference R ≥ 0.914) and high estimation accuracy in pulse pressure (mean root-mean-squared error ≤ 3.46 mmHg) and blood pressure (mean root-mean-squared error ≤ 6.31 mmHg for diastolic blood pressure and ≤ 8.41 mmHg for systolic blood pressure) over a wide range of hemodynamic changes.

CONCLUSION

The proposed pulse pressure estimation method provides accurate estimates in situations with and without significant changes in stroke volume. The proposed method improves upon the currently available systolic blood pressure estimation methods by providing accurate pulse pressure estimates.

Theory and developments in an unobtrusive cardiovascular system representation: ballistocardiography

Due to recent technological improvements, namely in the field of piezoelectric sensors, ballistocardiography - an almost forgotten physiological measurement - is now being object of a renewed scientific interest.Transcending the initial purposes of its development, ballistocardiography has revealed itself to be a useful informative signal about the cardiovascular system status, since it is a non-intrusive technique which is able to assess the body's vibrations due to its cardiac, and respiratory physiological signatures.Apart from representing the outcome of the electrical stimulus to the myocardium - which may be obtained by electrocardiography - the ballistocardiograph has additional advantages, as it can be embedded in objects of common use, such as a bed or a chair. Moreover, it enables measurements without the presence of medical staff, factor which avoids the stress caused by medical examinations and reduces the patient's involuntary psychophysiological responses.Given these attributes, and the crescent number of systems developed in recent years, it is therefore pertinent to revise all the information available on the ballistocardiogram's physiological interpretation, its typical waveform information, its features and distortions, as well as the state of the art in device implementations.

History of right heart catheterization: 100 years of experimentation and methodology development

The development of right heart catheterization has provided the clinician the ability to diagnose patients with congenital and acquired right heart disease, and to monitor patients in the intensive care unit with significant cardiovascular illnesses. The development of bedside pulmonary artery catheterization has become a standard of care for the critically ill patient since its introduction into the intensive care unit almost 40 years ago. However, adoption of this procedure into the mainstream of clinical practice occurred without prior evaluation or demonstration of its clinical or cost-effectiveness. Moreover, current randomized, controlled trials provide little evidence in support of the clinical utility of pulmonary artery catheterization in the management of critically ill patients. Nevertheless, the right heart catheter is an important diagnostic tool to assist the clinician in the diagnosis of congenital heart disease and acquired right heart disease, and moreover, when catheter placement is proximal to the right auricle (atria), this catheter provides an important and safe route for administration of fluids, medications, and parenteral nutrition. The purpose of this manuscript is to review the development of right heart catheterization that led to the ability to conduct physiologic studies in cardiovascular dynamics in normal individuals and in patients with cardiovascular diseases, and to review current controversies of the extension of the right heart catheter, the pulmonary artery catheter.

Non-invasive cardiac output trending during exercise recovery on a bathroom-scale-based ballistocardiograph

Cardiac ejection of blood into the aorta generates a reaction force on the body that can be measured externally via the ballistocardiogram (BCG). In this study, a commercial bathroom scale was modified to measure the BCGs of nine healthy subjects recovering from treadmill exercise. During the recovery, Doppler echocardiogram signals were obtained simultaneously from the left ventricular outflow tract of the heart. The percentage changes in root-mean-square (RMS) power of the BCG were strongly correlated with the percentage changes in cardiac output measured by Doppler echocardiography (R(2) = 0.85, n = 275 data points). The correlation coefficients for individually analyzed data ranged from 0.79 to 0.96. Using Bland-Altman methods for assessing agreement, the mean bias was found to be -0.5% (+/-24%) in estimating the percentage changes in cardiac output. In contrast to other non-invasive methods for trending cardiac output, the unobtrusive procedure presented here uses inexpensive equipment and could be performed without the aid of a medical professional.

A simple ballistocardiographic system for a medical cardiovascular physiology course

Ballistocardiography is an old, noninvasive technique used to record the movements of the body synchronous with the heartbeat due to left ventricular pump activity. Despite the fact that this technique to measure cardiac output has been superseded by more advanced and precise techniques, it is useful for teaching cardiac cycle physiology in an undergraduate practical course because of its noninvasive application in humans, clear physiological and physiopathological analysis, and practical approach to considering cardiac output issues. In the present report, a simple, low cost, easy-to-build ballistocardiography system is implemented together with a theoretical and practical session that includes Newton's laws, cardiac output, cardiac pump activity, anatomy and physiology of the vessel circulation, vectorial composition, and signal transduction, which makes cardiovascular physiology easy to understand and focuses on the study of cardiac output otherwise seen only with the help of computer simulation or echocardiography. The proposed system is able to record body displacement or force as ballistocardiography traces and its changes caused by different physiological factors. The ballistocardiography session was included in our medical physiology course six years ago with very high acceptance and approval rates from the students.

Effects of Chlorothiazide on Systemic Hemodynamics in Essential Hypertension

Nineteen observations were made in 12 patients with early essential hypertension. The comparative effects upon mean arterial blood pressure, cardiac index, and total peripheral resistance of the acute and long-term administration of chlorothiazide were studied.

With acute administration of the drug, a 10 per cent drop in mean arterial blood pressure, a decrease of 18 per cent in cardiac index, and an increase of 7 per cent in peripheral resistance were observed.

With long-term administration, a decrease of 21 per cent in mean arterial blood pressure, an increase of 4 per cent in cardiac index, and a drop of 26 per cent in peripheral resistance were found.

The conclusion is drawn that reduction of mean arterial blood pressure with acute administration of chlorothiazide is due to decrease in cardiac output, whereas with long-term use it is due to reduction in total peripheral resistance.

Physical working capacity of old workers and physiological background for work tests and work evaluations

The worker's fitness for different jobs will be determined by a number of functions of which many are influenced by age. The physical working capacity has undoubtedly a maximum between 20 and 35 years of age. The decline after 35 years will be different in every individual, but certain average figures can be given. The reduction is mainly due to a decrease in the maximal values for circulation and respiration rate, that is, in the oxygen-transport system. Also the muscular strength will be reduced in the higher age-groups. The problem in work rationalization is to determine the maximum rate of work that man can carry on continuously and still retain vigour to an advanced age.The result of several work-analyses shows that actually in manual labour the workmen often utilize up to 50% of their aerobic capacity but avoid exceeding this percentage. As the aerobic capacity decreases with age it is important to know the upper limits and the safety margin for the different age-groups. For that reason one has to determine the working capacity of the man and the physiological stress of the job. It is also important to determine to what degree skill and experience can compensate for age-changes. A superior individual will, even in old age, exceed the average of the young. Age differences may often be of less importance than individual differences.It is still not known what physiological qualifications the different jobs demand, or what age-changes in the physiological functions are of importance for these jobs. The gradual increase in the average age of the population makes investigations in this field important.