Biomedical subjects

J Calpe

Publications and source records attributed to J Calpe.

3 recordsLinked to original sources

PubMed1998

Quantification of the modifications in the dominant frequency of ventricular fibrillation under conditions of ischemia and reperfusion: an experimental study.

The characteristics of ventricular fibrillatory signals vary as a function of the time elapsed from the onset of arrhythmia and the maneuvers used to maintain coronary perfusion. The dominant frequency (FrD) of the power spectrum of ventricular fibrillation (VF) is known to decrease after interrupting coronary perfusion, though the corresponding recovery process upon reestablishing coronary flow has not been quantified to date. With the aim of investigating the recovery of the FrD during reperfusion after a brief ischemic period, 11 isolated and perfused rabbit heart preparations were used to analyze the signals obtained with three unipolar epicardial electrodes (E1-E3) and a bipolar electrode immersed in the thermostatized organ bath (E4), following the electrical induction of VF. Recordings were made under conditions of maintained coronary perfusion (5 min), upon interrupting perfusion (15 min), and after reperfusion (5 min). FrD was determined using Welch's method. The variations in FrD were quantified during both ischemia and reperfusion, based on an exponential model deltaFrD = A exp (-t/C). During ischemia deltaFrD is the difference between FrD and the minimum value, while t is the time elapsed from the interruption of coronary perfusion. During reperfusion deltaFrD is the difference between the maximum value and FrD, while t is the time elapsed from the restoration of perfusion. A is one of the constants of the model, and C is the time constant. FrD exhibited respective initial values of 16.20 +/- 1.67, 16.03 +/- 1.38, and 16.03 +/- 1.80 Hz in the epicardial leads, and 15.09 +/- 1.07 Hz in the bipolar lead within the bath. No significant variations were observed during maintained coronary perfusion. The fit of the FrD variations to the model during ischemia and reperfusion proved significant in nine experiments. The mean time constants C obtained on fitting to the model during ischemia were as follows: E1 = 294.4 +/- 75.6, E2 = 225.7 +/- 48.5, E3 = 327.4 +/- 79.7, and E4 = 298.7 +/- 43.9 seconds. The mean values of C obtained during reperfusion, and the significance of the differences with respect to the ischemic period were: E1 = 57.5 +/- 8.4 (P < 0.01), E2 = 64.5 +/- 11.2 (P < 0.01), E3 = 80.7 +/- 13.3 (P < 0.01), and E4 = 74.9 +/- 13.6 (P < 0.0001). The time course variations of the FrD of the VF power spectrum fit an exponential model during ischemia and reperfusion. The time constants of the model during reperfusion after a brief ischemic period are significantly shorter than those obtained during ischemia.

Animals↗

PubMed1994

[The spectral analysis of heart rate variability. The methodological aspects].

OBJECTIVES: A study is made of the influence of methodology on the analysis of cardiac cycle variability in terms of frequency and time domains. METHODS: Twenty-five individuals were divided into three groups: 1) non-smokers (n = 10); 2) smokers (n = 8); and 3) non-smokers without guided respiratory frequency (n = 7). An analysis was made of RR variability during 5 min intervals in time domain (standard deviation, variation coefficient, and difference between maximum and minimum RR), and frequency domain (spectral analysis, Fast Fourier Transform algorithm using 5 types of data windows). RESULTS: On comparing the results obtained in the 25 individuals with the 5 data windows, significant differences were observed (ANOVA; p < 0.001) in maximum and total amplitudes of the spectrum (in absolute terms) in the low frequency band (0.04-0.15 Hz). No significant differences were found between the normalized values or between the low/high (0.15-0.40 Hz) frequency ratio: W1 = 1.63 +/- 0.30; W2 = 1.62 +/- 0.29; W3 = 1.65 +/- 0.31; W4 = 1.52 +/- 0.26, and W5 = 1.55 +/- 0.27 (X +/- SE). On averaging the RR intervals each 5 cycles, significant differences were encountered for great part of the parameters studied. No significant differences were encountered for great part of the parameters studied. No significant differences were noted between the non-smokers as regards the use or non-use of a metronome (low/high frequency ratio in group 1 = 1.85 +/- 0.39 vs group 3 = 1.78 +/- 0.43; NS). The linear regressions between the variability parameters in terms of time and frequency domains (absolute values), and age (group 1) were significant, with greater regression coefficients on using the linear transformation of an exponential model. On comparing groups 1 and 2, a non statistically significant trend towards smaller maximum and total amplitudes (absolute values) was noted in group 2 for both frequency bands. CONCLUSIONS: 1) The type of data window (Fourier analysis) introduces significant modifications of some parameters expressed in absolute values, but not between normalized values; 2) signal averaging greatly modifies the information obtained; 3) the decrease in variability parameters observed with age fits better to an exponential model; 4) no differences were detected on guiding or not respiratory frequency, and 5) smoking appears to induce a tendency towards reducing cardiac cycle variability.

Adult↗

PubMedDate not supplied

[Pacemaker activation by muscular movement].

In recent years impressive progress was achieved in the field of cardiac stimulation. Sometimes atrial systole is not available to increase stroke volume in patients with pacemakers for complete atrioventricular block. We describe a new model of heart pacemaker (Activitrax), which is activated by muscle movement and is responsive to metabolic demands, increasing the pacemaker's firing rate according to exercise. The result which allowed a better quality of life was highly satisfactory.

Adult↗