Pierre-François Migeotte

Ballistocardiography and Seismocardiography: A Review of Recent Advances

In the past decade, there has been a resurgence in the field of unobtrusive cardiomechanical assessment, through advancing methods for measuring and interpreting ballistocardiogram (BCG) and seismocardiogram (SCG) signals. Novel instrumentation solutions have enabled BCG and SCG measurement outside of clinical settings, in the home, in the field, and even in microgravity. Customized signal processing algorithms have led to reduced measurement noise, clinically relevant feature extraction, and signal modeling. Finally, human subjects physiology studies have been conducted using these novel instruments and signal processing tools with promising results. This paper reviews the recent advances in these areas of modern BCG and SCG research.

A study of the dynamic interactions between sleep EEG and heart rate variability in healthy young men

OBJECTIVE We investigated the interactions between heart rate variability and sleep electroencephalogram power spectra. METHODS Heart rate and sleep electroencephalogram signals were recorded in 8 healthy young men. Spectral analysis was applied to electrocardiogram and electroencephalogram recordings. Spectral components of RR intervals were studied across sleep stages. The cross-spectrum maximum was determined as well as coherencies, gains and phase shifts between normalized high frequency of RR intervals and all electroencephalographic frequency bands, calculated over the first 3 NREM-REM cycles. RESULTS RR intervals increased from awake to NREM and decreased during REM. Normalized low frequency decreased from awake to NREM and increased during REM while normalized high frequency evolved conversely. Low to high frequency ratio developed in opposition to RR intervals. Coherencies between normalized high frequency and power spectra were high for all bands. The gain was highest for delta band. Phase shift between normalized high frequency and delta differed from zero and modifications in normalized high frequency preceded changes in delta by 41+/-14 degrees. CONCLUSIONS Our study demonstrates that: (1) all electroencephalographic power bands are linked to normalized high frequency; (2) modifications in cardiac vagal activity show predominantly parallel changes and precede changes in delta band by a phase shift corresponding to a lead of 12+/-5 min.

The impact of chronic primary insomnia on the heart rate ― EEG variability link

OBJECTIVE To determine if chronic insomnia alters the relationship between heart rate variability and delta sleep determined at the EEG. METHODS After one night of accommodation, polysomnography was performed in 14 male patients with chronic primary insomnia matched with 14 healthy men. ECG and EEG recordings allowed the determination of High Frequency (HF) power of RR-interval and delta sleep EEG power across the first three Non Rapid Eye Movement (NREM)-REM cycles. Interaction between normalized HF RR-interval variability and normalized delta sleep EEG power was studied by coherency analysis. RESULTS Patients showed increased total number of awakenings, longer sleep latency and wake durations and shorter sleep efficiency and REM duration than controls (p<.01). Heart rate variability across first three NREM-REM cycles and sleep stages (NREM, REM and awake) were similar between both groups. In each group, normalized HF variability of RR-interval decreased from NREM to both REM and awake. Patients showed decreased linear relationship between normalized HF RR-interval variability and delta EEG power, expressed by decreased coherence, in comparison to controls (p<.05). Gain and phase shift between these signals were similar between both groups. CONCLUSIONS Interaction between changes in cardiac autonomic activity and delta power is altered in chronic primary insomniac patients, even in the absence of modifications in heart rate variability and cardiovascular diseases. SIGNIFICANCE This altered interaction could reflect the first step to cardiovascular disorders.

Interdependency between heart rate variability and sleep EEG: linear/non-linear?

OBJECTIVE To investigate whether the interdependency between heart rate variability (HRV) and sleep electroencephalogram (EEG) power spectra is linear or non-linear. METHODS Heart rate and sleep EEG signals were recorded in 8 healthy young men. Spectral analysis was applied to electrocardiogram and EEG sleep recordings. Synchronization likelihood was computed over the first 3 non-rapid eye movement-rapid eye movement sleep cycles between normalized high frequency of RR intervals (RRI) and all electroencephalographic frequency bands. Comparison to surrogate data of different types was used to attest statistical significance of the coupling between RRI and EEG power bands and its linear or non-linear character. RESULTS Synchronization likelihood values were statistically greater than univariate surrogate synchronization for all sleep bands both at the individual and the group levels. With reference to multivariate surrogates, synchronization values were statistically greater at the group level and, in a majority of cases, for individual comparison except for sigma and beta bands. CONCLUSIONS While all electroencephalographic power bands are linked to normalized high frequency RRI band, this interdependency is non-linear for delta, theta and alpha bands. SIGNIFICANCE Non-linear description is required to capture the full interdependent dynamics of HRV and sleep EEG power bands.

Three dimensional ballistocardiography: Methodology and results from microgravity and dry immersion

Balistocardiography was recorded in 3-D on a free floating astronaut in space as well as on healthy volunteers participating to a dry immersion study in a terrestrial laboratory. We demonstrate a new technique suitable for the analysis of 3-D BCG. The spatial curve of the displacement vector is analyzed instead of the three components of acceleration. The technique presented is invariant from the axis of representation and provides important novel physiological information.

Progressive aging does not alter the interaction between autonomic cardiac activity and delta EEG power.

OBJECTIVE We tested the hypothesis that the reductions of the changes in the respective influence of the cardiac sympathetic and vagal activity control and delta EEG activity with aging alter the interactions between the heart rate variability (HRV) and the delta sleep EEG power band. METHODS A polysomnography was performed on 16 healthy young men and 19 healthy middle-aged men across the first 3 NREM-REM cycles. Spectral analysis was applied to electrocardiogram and electroencephalogram recordings. High Frequency (HF(nu)) of HRV as well as the maximum of cross-spectrum, coherency, gain and phase shifts between HF(nu) and delta sleep EEG power band were compared between both groups. RESULTS Young men experienced more deep sleep than middle-aged men (P<0.001). In middle-aged subjects, HF(nu) was lower than the HF(nu) of their younger counterparts (P<0.001), but they showed similar increases during NREM sleep and similar decreases during REM sleep as the young subjects. Cross-spectrum values, coherency, gain and phase shifts between HF(nu) and delta were identical between the two groups. Modifications in HF(nu) show parallel changes and precede changes in delta EEG band by a similar leads of 11+/-6min in young men and 9+/-7 min in middle-aged men (P=0.23). CONCLUSIONS Reduced changes in the respective influence of the cardiac sympathetic and vagal activity and delta EEG activity with progressive aging do not alter the relationship and phase difference between changes in the relative predominant cardiac vagal activity and delta power in middle-aged men. SIGNIFICANCE Interaction between the cardiac sympathetic and vagal activity with delta EEG activity is maintained in middle-aged men.

Dysfunctional vestibular system causes a blood pressure drop in astronauts returning from space

It is a challenge for the human body to maintain stable blood pressure while standing. The body’s failure to do so can lead to dizziness or even fainting. For decades it has been postulated that the vestibular organ can prevent a drop in pressure during a position change – supposedly mediated by reflexes to the cardiovascular system. We show – for the first time – a significant correlation between decreased functionality of the vestibular otolith system and a decrease in the mean arterial pressure when a person stands up. Until now, no experiments on Earth could selectively suppress both otolith systems; astronauts returning from space are a unique group of subjects in this regard. Their otolith systems are being temporarily disturbed and at the same time they often suffer from blood pressure instability. In our study, we observed the functioning of both the otolith and the cardiovascular system of the astronauts before and after spaceflight. Our finding indicates that an intact otolith system plays an important role in preventing blood pressure instability during orthostatic challenges. Our finding not only has important implications for human space exploration; they may also improve the treatment of unstable blood pressure here on Earth.

Comparing real-life and laboratory-induced stress reactivity on cardio-respiratory parameters: Differentiation of a tonic and a phasic component

To recreate stress in laboratory conditions, the nature of the elicited physiological reactions to the presentation of mental tasks has been extensively studied. However, whether this experimental response is equivalent to real-life stress reactivity is still under debate. We investigated cardio-respiratory reactivity to a sequential protocol of different mental tasks of varying difficulties, some of them involving emotional material, and repeated the measures in a baseline and in a real-life stress situation. R-R interval (RRI), breathing frequency and volumes, and respiratory sinus arrhythmia (RSA) were computed. Baseline results showed a superior sensitivity of respiratory parameters to mental task load over RRI and RSA, no effect of task difficulty or emotional material, and a habituation response of all parameters along the protocol. Stress results showed a dual effect: first, a decreased RRI and RSA in rest values, and second, a decreased reactivity in RRI in response to mental tasks. These findings are discussed through the interaction of activation, considered to be a tonic variable, and arousal, as a phasic response.

A New Model for Utricular Function Testing Using a Sinusoidal Translation Profile during Unilateral Centrifugation

The utricle plays an important role in orientation with respect to gravity. The unilateral centrifugation test allows a side-by-side investigation of both utricles. During this test, the subject is rotated about an earth-vertical axis at high rotation speeds (e.g. 400°/s) and translated along an interaural axis to consecutively align the axis of rotation with the left and the right utricle. A simple sinusoidal translation profile (0.013 Hz; amplitude = 4 cm) was chosen. The combined rotation and translation induces ocular counter rolling (OCR), which is measured using 3-D video-oculography. This OCR is the sum of the reflexes generated by both the semicircular canals and the utricles. In this paper, we present a new physiological model that decomposes this total OCR into a canal and a utricular contribution, modelled by a second-order transfer function and a combination of 2 sine functions, respectively. This model yields parameters such as canal gain, cupular and adaptation time constants and a velocity storage component for the canals. Utricular gain, bias, phase and the asymmetry between the left and the right utricle are characteristic parameters generated by the model for the utricles. The model is presented along with the results of 10 healthy subjects and 2 patients with a unilateral vestibular loss due to acoustic neuroma surgery to illustrate the effectiveness of the model.

A Method for the Analysis of Respiratory Sinus Arrhythmia Using Continuous Wavelet Transforms

A continuous wavelet transform-based method is presented to study the nonstationary strength and phase delay of the respiratory sinus arrhythmia (RSA). The RSA is the cyclic variation of instantaneous heart rate at the breathing frequency. In studies of cardio-respiratory interaction during sleep, paced breathing or postural changes, low respiratory frequencies, and fast changes can occur. Comparison on synthetic data presented here shows that the proposed method outperforms traditional short-time Fourier-transform analysis in these conditions. On the one hand, wavelet analysis presents a sufficient frequency-resolution to handle low respiratory frequencies, for which time frames should be long in Fourier-based analysis. On the other hand, it is able to track fast variations of the signals in both amplitude and phase for which time frames should be short in Fourier-based analysis.