Curve registration for study of P-wave morphing during exercise
The P-wave shape analysis remains an interesting objective in various situations. In this paper, the aim is to investigate how the P-wave morphology changes during time-varying effort. To perform this task, a method, Self-Modeling Registration (SMR), derived from the Curve Registration (CR) theory is used. This method permits to link different shapes by mean of time warping functions. First, using the SMR method, significant P-wave shapes are extracted from two ECG records under maximal and graded exercise test where the effort is released abruptly. Then, the selected shapes are linked by warping functions estimated by SMR method. The obtained warping functions show a reversible evolution of the P-wave shape independently of the possible superimposition of the T-wave. To give a physiological explanation of this P-wave morphing, an atrial contribution evolution scenario under exercise is proposed and validated by simulation.
Functional Data Analysis applied to biomedical signal variability
The variability of a set of biomedical signals is analysed following some criterions. Firstly, when the signal source is unique, the variability may be, for one sensor in function of the time occurrence of the signals, for several sensors at the same time, a spatial variability. The case of several sources corresponds to the inter subject variability. Then the distinction between amplitude variability, time variability and shape variability is introduced. Functional Data Analysis is viewed as modelling variability through time warping functions. These functions are either composed with the signals, leading to a lot of curve registration techniques, or composed with the normalised integral functions of the signals when assumed to be positive. The later case is well suited to shape analysis and shape variability estimation around an averaged shape. The Integral Shape Averaging (ISA) and Corrected Integral Shape Averaging (CISA) algorithms are recalled. Two applications are then presented, including shape clustering. The first one concerns the correlation between the occurrence of an obstructive sleep apnoea and a shape change of the ECG P-waves. The second one is related to the Ensemble Spontaneous Activity (ESA) recorded near the cochlea. It is shown, by simulation, that the shape of the histogram of the ESA amplitude is very sensitive to a localised correlated firing of the fibres, possibly associated to Tinnitus, on the contrary of the PSD amplitude at 1 kHz.
Ventricular rate control and exercise performance in chronic atrial fibrillation: effects of diltiazem and verapamil.
The effects of two calcium channel blockers, diltiazem (270 mg/day) and verapamil (240 mg/day), were studied in 18 patients with chronic atrial fibrillation. During 24 h Holter electrocardiographic monitoring, mean ventricular rate (beats/min) decreased from 88 +/- 14 with placebo to 76 +/- 13 (p less than 0.001) with diltiazem and 80 +/- 11 (p less than 0.01) with verapamil. Maximal symptom-limited exercise tolerance (W) increased from 127 +/- 39 during the placebo period to 136 +/- 42 (p less than 0.01) with diltiazem and 137 +/- 39 (p less than 0.01) with verapamil. Ventricular rate and rate-pressure product were lower at rest and during exercise with diltiazem and verapamil than with placebo (p less than 0.001), with the drugs being similarly effective. Ventricular rate at maximal exercise (beats/min) was 179 +/- 13 with placebo compared with 159 +/- 21 with diltiazem and 158 +/- 23 with verapamil. Maximal oxygen uptake (ml/kg per min) was 22.3 +/- 4.5 with placebo, 23.7 +/- 4.9 (p less than 0.05) with diltiazem and 22.9 +/- 4.5 with verapamil (p = NS). Respiratory gas exchange anaerobic threshold was reached at a work load (W) of 76 +/- 21 with placebo, 84 +/- 27 (p less than 0.05) with diltiazem and 85 +/- 23 (p less than 0.01) with verapamil. In conclusion, patients with chronic atrial fibrillation have modestly improved exercise tolerance with calcium channel blockade therapy. The dromotropic responses and the effects on physical performance are of similar magnitude for diltiazem and verapamil.