Local ballistocardiographic spectrum studies from signals obtained from limbs and carotid artery with an EMFi sensor induced with a tilt table.

The purpose of this work is to study the effect of a tilt table test procedure on ballistocardiographic (BCG) signal by using Electromechanical Film (EMFi) strip sensors. The ECG, BCG, carotid pulse (CP) from the neck near the carotid artery and ankle pulse signals were recorded from 7 persons. The spectral components of the recordings during the tilt table test were studied concentrating mainly on heart induced pulsatile signals propagating along the artery to the periphery. The properties of BCG pulse signal changed due to the tilt test in spectral domain. Blood pressure (BP) values and shape of the pulse changed due to the tilt test. According to this study, local BCG measurements with EMFi sensor strips combined with a tilt test can be used as a very simple non-invasive method in hemodynamic studies.

Short and longer term repeatability of ballistocardiography in a sitting position with EMFi sensor.

Short and long-term alterations of ballistocardiographic parameters (BCG) were studied in a sitting position using Electromechanical Film (EMFi) sensors. Several physiological parameters were recorded from 48 men of middle age in consecutive recordings and after a 2-week interval. The duration and amplitudes of the signal components were studied. The repeatability index R, the Pearson correlation, and Bland-Altman (BA) repeatability methods were used to determine how repeatable the studied signals are. In consecutive and during 2 week recordings, the Pearson correlation rates for BCG systolic component values (from 0.88/0.83 (T(RJ)) to 0.97/0.78 (A(IJ)), PWV values for the left 0.97/0.67 and right ankle 0.98/0.76) were detected indicating excellent repeatability during consecutive recordings. Respectively BA T(RJ) was -0.002 ± 0.028/-0.004 ± 0.030. Corresponding R values were T(RJ) 0.90/0.82 and right ankle PWV 0.98/0.81. Quite modest blood pressure R values were obtained between 2 week recordings (systolic 0.63, diastolic 0.75, and heart rate 0.59). BCG and PWV measured with EMFi sensors are highly repeatable in consecutive recordings. In longer time interval recordings, BCG is influenced by hemodynamic instability, but in spite of this the reproducibility of the main parameters of the BCG and PWV were better than measured heart rate and blood pressure values.

Automatic detection of spiking events in EMFi sheet during sleep.

In this paper we present a new method for detection of spiking events caused by the increased respiratory resistance (IRR) from ballistocardiographic (BCG) data recorded with EMFi sheet. Spiking is a phenomenon where BCG wave complexes increase in amplitude during IRR. In this study data from six patients with a total of 1503 visually scored spiking events were studied. The algorithm monitors amplitude levels of BCG complexes and detects large relative increases. In this work 10 different variations of the algorithm were compared in order to find the best variation, which can cope with different recordings. The best variation of the algorithm was able to detect spiking events with 80% true positive and 19% false positive rates. The detection is not dependent on absolute waveform amplitudes and therefore does not require any recording-specific tuning prior to application. It is important to recognize spiking events in order to evaluate the severity of respiratory disturbance during sleep.

Anteroposterior difference in EEG sleep depth measure is reduced in apnea patients.

In the present work, mean frequencies of FFT amplitude spectra from six EEG derivations were used to provide a frontopolar, a central and an occipital sleep depth measure. Parameters quantifying the anteroposterior differences in these three sleep depth measures during the night were also developed. The method was applied to analysis of 30 all-night recordings from 15 healthy control subjects and 15 apnea patients. Control subjects showed larger differences in sleep depth between frontopolar and central positions than the apnea patients. The relatively reduced frontal sleep depth in apnea patients might reflect the disruption of the dynamic sleep process caused by apneas.