Dynamic relationship between cardiac imaging and physiological measurements

PhD ThesisImpedance cardiography (ICG) is a non-invasive technique to measure the dynamic changes in electrical impedance of the thorax. Photoplethymgraphy (PPG) is an optical- based non-invasive physiological measurement technique used to detect the blood volume pulses in the microvascular bed of tissue. These two physiological measurements have potential clinical importance to enable simple and cost-efficient ways to examine cardiovascular function and provide surrogate or additional clinical information to the measures from cardiac imaging. However, because the origins of the characteristic waveforms of the impedance and pulse are still not well understood, the clinical applications of these two techniques are limited. There were two main aims in this study: 1) to obtain a better understanding of the origins of the pulsatile impedance changes and peripheral pulse by linking their characteristic features beat-by-beat to those from simultaneous echocardiograms; 2) to validate the clinical indices from ICG and PPG with those well-established echocardiographic indices. Physiological signals, including ECGs, impedance, the first derivative impedance and finger and ear pulses, were simultaneously recorded with echocardiograms from 30 male healthy subjects at rest. The timing sequence of cardiovascular events in a single cardiac cycle was reconstructed with the feature times obtained from the physiological measurements and images. The relations of the time features from the impedance with corresponding features from images and pulses were investigated. The relations of the time features from peripheral pulses with corresponding features from images were also investigated. Furthermore, clinical time indices measured from the impedance and pulse were validated with the reference to the echocardiograms. Finally, the effects of age, heart rate and blood pressure on the image and physiological measurements were examined. According to the reconstructed timing sequence, it was evident that the systolic waves of the thoracic impedance and peripheral pulse occurred following left ventricular ejection. The impedance started to fall 26 ms and the pulse arrived at the fingertip 162 ms after the aortic valve opened. A diastolic wave was observed during the ventricular passive filling phase on the impedance and pulse. The impedance started to recover during the late ventricular ejection phase when the peripheral pulse was rising up. While the pulsatile impedance changes were mainly correlated with valve movement, the derivative impedance (velocity of impedance change) was more correlated with aortic flow (velocity of blood 2 flow). The foot of the finger pulse was significantly correlated with aortic valve open (R = 0.361, P < 0.05), while its systolic peak was strongly correlated with the aortic valve 2 closing (R = 0.579, P < 0.001). Although the pulse had similar waveform shapes to the inverted impedance waveform, the associations between the time features of these two signals were weak. During the validation of potential clinical indices from ICG, significant correlation was found between the overall duration of the derivative impedance systolic wave (359 ms) and the left ventricular ejection time (LVET) measured by aortic valve open duration from M- 2 mode images (329 ms) (R = 0.324, P < 0.001). The overall duration from the finger pulse foot to notch (348 ms) was also significantly correlated with the LVET from M-mode 2 images (R = 0.461, P < 0.001). Therefore, both ICG and PPG had the potential to provide surrogates to the LVET measurement. Age influenced the cardiovascular diastolic function more than systolic function on normal subjects. With age increasing, the reduction of the left ventricular passive filling was compensated by active filling. The ratio of the passive filling duration to the active 2 filling duration decreased with age (R = 0.143, P < 0.05). The influence of age on the diastolic wave of the impedance signals was striking. The impedance diastolic wave disappeared gradually with age. The effects of age on the peripheral pulse were mainly on the shortened pulse foot transit time (PPT) and prolonged pulse rise time. The large artery f stiffness index (SI) increased with age. Most time intervals were prolonged with heart rate slowing down. The effects of systolic blood pressure were evident on pulse transit time and pulse diastolic rising time. Driven by higher systolic blood pressure, both PPT and rising f time decreased significantly (P < 0.001). In conclusion, from the analysis based on simultaneous physiological measurements and echocardiograms, both the pulsatile impedance changes and peripheral volume pulse were initiated by left ventricular ejection. The thoracic impedance changes reflected volume changes in the central great vessels, while the first derivative impedance was associated with the velocity of blood flow. Both ICG and PPG had the potential to provide surrogates for the measures of cardiac mechanical functions from images. The PPG technique also enabled the assessment of changes in vascular function caused by age.Institute of Cellular Medicine Newcastle Universit

Development and Evaluation of an Impedance Cardiographic System to Measure Cardiac Output and Other Cardiac Parameters, 1 July 1968 - 30 June 1969

Impedance cardiographic system to measure cardiac output and cardiovascular function

Mechanical correlates of the third heart sound

AbstractIn seven chronically instrumented conscious dogs, micromanometers measured left ventricular pressure, and ultrasonic dimension transducers measured left ventricular minor-axis diameter; the latter recording was filtered to examine data between 20 and 100 Hz. Acceptable external heart sounds were recorded with a phonocardiographic microphone in four of the seven dogs. With each dog sedatede, intubated and mechanically ventilated, data were obtained during hemodynamic alterations produced by volume loading, phenylephrine, calcium infusion and vena caval occlusion.Damped oscillations were noted consistently in the left ventricular diameter waveform toward the end of rapid ventricular filling. These wall vibrations, assessed by the Altered diameter, correlated well with the third heart sound (S3) on the phonocardiogram. The peak frequency of the wall vibrations increased with increased diastolic pressure (p = 0.004), probably reflecting an increase in myocardlal wall stiffness. In contrast, the amplitude of the vibrations varid directly with left ventricular filling rate (p = 0.0001).Thus, S3seemed to be related specifically to ventricular wall vibrations during rapid filling, and the spectra of the amplitude-frequency relation shifted toward the audible range with increases in diastolic pressure, wall stiffness or filling rate. Spectral analysis of S3may be useful in assessing pathologic chances in myocardial wall properties

Aerospace medicine and Biology: A continuing bibliography with indexes, supplement 177

This bibliography lists 112 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1978

Arterial pressure changes monitoring with a new precordial noninvasive sensor

<p>Abstract</p> <p>Background</p> <p>Recently, a cutaneous force-frequency relation recording system based on first heart sound amplitude vibrations has been validated. A further application is the assessment of Second Heart Sound (S2) amplitude variations at increasing heart rates. The aim of this study was to assess the relationship between second heart sound amplitude variations at increasing heart rates and hemodynamic changes.</p> <p>Methods</p> <p>The transcutaneous force sensor was positioned in the precordial region in 146 consecutive patients referred for exercise (n = 99), dipyridamole (n = 41), or pacing stress (n = 6). The curve of S2 peak amplitude variation as a function of heart rate was computed as the increment with respect to the resting value.</p> <p>Results</p> <p>A consistent S2 signal was obtained in all patients. Baseline S2 was 7.2 ± 3.3 m<it>g</it>, increasing to 12.7 ± 7.7 m<it>g </it>at peak stress. S2 percentage increase was + 133 ± 104% in the 99 exercise, + 2 ± 22% in the 41 dipyridamole, and + 31 ± 27% in the 6 pacing patients (p < 0.05). Significant determinants of S2 amplitude were blood pressure, heart rate, and cardiac index with best correlation (R = .57) for mean pressure.</p> <p>Conclusion</p> <p>S2 recording quantitatively documents systemic pressure changes.</p