Multiresolution Analysis of Heart Rate Variability as Investigational Tool in Experimental Fetal Cardiac Surgery

Nonlinear analysis of heart rate variability to assess the reaction of ewe fetuses undergoing fetal cardiac surgery

Fetal cardiac surgery (FCS) represents a challenging issue for the in utero treatment of congenital heart defects. However, FCS has still not gained the sufficient reliability for clinical practice due to an incompletely elucidated fetal stress response. For example, blood sampling can contribute to its onset, leading to fetoplacental unit dysfunction, one of the main causes of failure of the surgical procedure. In order to address this issue, the role of the autonomic control system during an experimental procedure of cardiac bypass on ewe fetuses was investigated by means of recurrence quantification analysis (RQA), a well-recognized method for the analysis of nonlinear systems. RQA was applied to time series extracted from fetal arterial pressure recordings before and after the cardiac bypass established by means of an extracorporeal circuit, including an axial blood pump, and taking advantage of the capability of the placenta to work as a natural oxygenator. Statistically significant correlations were found among RQA-based metrics and fetal blood gas data, suggesting the possibility to infer the clinical status of the fetus starting from its hemodynamic signals.This study shows the relevance of RQA as a complementary tool for the monitoring of the fetal status during cardiac bypass.

Blood pressure waveform analysis by means of wavelet transform

The assessment of cardiovascular function by means of arterial pulse wave analysis (PWA) is well established in clinical practice. PWA is applied to study risk stratification in hypertension, with emphasis on the measurement of the augmentation index as a measure of aortic pressure wave reflections. Despite the fact that the prognostic power of PWA, in its current form, still remains to be demonstrated in the general population, there is general agreement that analysis and interpretation of the waveform might provide a deeper insight in cardiovascular pathophysiology. We propose here the use of wavelet analysis (WA) as a tool to quantify arterial pressure waveform features, with a twofold aim. First, we discuss a specific use of wavelet transform in the study of pressure waveform morphology, and its potential role in ascertaining the dynamics of temporal properties of arterial pressure waveforms. Second, we apply WA to evaluate a database of carotid artery pressure waveforms of healthy middle-aged women and men. Wavelet analysis has the potential to extract specific features (wavelet details), related to wave reflection and aortic valve closure, from a measured waveform. Analysis showed that the fifth detail, one of the waveform features extracted applying the wavelet decomposition, appeared to be the most appropriate for the analysis of carotid artery pressure waveforms. What remains to be assessed is how the information embedded in this detail can be further processed and transformed into quantitative data, and how it can be rendered useful for automated waveform classification and arterial function parameters with potential clinical applications.

Optical Vibrocardiography: A Novel Tool for the Optical Monitoring of Cardiac Activity

We present an optical non-contact method for heart beat monitoring, based on the measurement of chest wall movements induced by the pumping action of the heart, which is eligible as a surrogate of electrocardiogram (ECG) in assessing both cardiac rate and heart rate variability (HRV). The method is based on the optical recording of the movements of the chest wall by means of laser Doppler interferometry. To this aim, the ECG signal and the velocity of vibration of the chest wall, named optical vibrocardiography (VCG), were simultaneously recorded on 10 subjects. The time series built from the sequences of consecutive R waves (on ECG) and vibrocardiographic (VV) intervals were compared in terms of heart rate (HR). To evaluate the ability of VCG signals as quantitative marker of the autonomic activity, HRV descriptors were also calculated on both ECG and VCG time series. HR and HRV indices obtained from the proposed method agreed with the rate derived from ECG recordings (mean percent difference <3.1%). Our comparison concludes that optical VCG provides a reliable assessment of HR and HRV analysis, with no statistical differences in term of gender are present. Optical VCG appears promising as non-contact method to monitor the cardiac activity under specific conditions, e.g., in magnetic resonance environment, or to reduce exposure risks to workers subjected to hazardous conditions. The technique may be used also to monitor subjects, e.g., severely burned, for which contact with the skin needs to be minimized.