Comparison of nifedipine and isosorbide dinitrate when added to maximal propranolol therapy in stable angina pectoris

Phase-rectified signal averaging for the detection of quasi-periodicities and the prediction of cardiovascular risk

We present the phase-rectified signal averaging (PRSA) method as an efficient technique for the study of quasi-periodic oscillations in noisy, nonstationary signals. It allows the assessment of system dynamics despite phase resetting and noise and in relation with either increases or decreases of the considered signal. We employ the method to study the quasi-periodicities of the human heart rate based on long-term ECG recordings. The center deflection of the PRSA curve characterizes the average capacity of the heart to decelerate (or accelerate) the cardiac rhythm. It can be measured by a central wavelet coefficient which we denote as deceleration capacity (DC). We find that decreased DC is a more precise predictor of mortality in survivors of heart attack than left ventricular ejection fraction, the current "gold standard" risk predictor. In addition, we discuss the dependence of the DC parameter on age and on diabetes.

Analysis of cardiovascular oscillations: a new approach to the early prediction of pre-eclampsia

Pre-eclampsia (PE) is a serious disorder with high morbidity and mortality occurring during pregnancy; 3%-5% of all pregnant women are affected. Early prediction is still insufficient in clinical practice. Although most pre-eclamptic patients show pathological uterine perfusion in the second trimester, this parameter has a positive predictive accuracy of only 30%, which makes it unsuitable for early, reliable prediction. The study is based on the hypothesis that alterations in cardiovascular regulatory behavior can be used to predict PE. Ninety-six pregnant women in whom Doppler investigation detected perfusion disorders of the uterine arteries were included in the study. Twenty-four of these pregnant women developed PE after the 30th week of gestation. During pregnancy, additional several noninvasive continuous blood pressure recordings were made over 30 min under resting conditions by means of a finger cuff. The time series extracted of systolic as well as diastolic beat-to-beat pressures and the heart rate were studied by variability and coupling analysis to find predictive factors preceding genesis of the disease. In the period between the 18th and 26th weeks of pregnancy, three special variability and baroreflex parameters were able to predict PE several weeks before clinical manifestation. Discriminant function analysis of these parameters was able to predict PE with a sensitivity and specificity of 87.5% and a positive predictive value of 70%. The combined clinical assessment of uterine perfusion and cardiovascular variability demonstrates the best current prediction several weeks before clinical manifestation of PE.

Long-term invariant parameters obtained from 24-h Holter recordings: a comparison between different analysis techniques

Over the last two decades, a large number of different methods had been used to study the fractal-like behavior of the heart rate variability (HRV). In this paper some of the most used techniques were reviewed. In particular, the focus is set on those methods which characterize the long memory behavior of time series (in particular, periodogram, detrended fluctuation analysis, rescale range analysis, scaled window variance, Higuchi dimension, wavelet-transform modulus maxima, and generalized structure functions). The performances of the different techniques were tested on simulated self-similar noises (fBm and fGn) for values of alpha, the slope of the spectral density for very small frequency, ranging from -1 to 3 with a 0.05 step. The check was performed using the scaling relationships between the various indices. DFA and periodogram showed the smallest mean square error from the expected values in the range of interest for HRV. Building on the results obtained from these tests, the effective ability of the different methods in discriminating different populations of patients from RR series derived from Holter recordings, was assessed. To this extent, the Noltisalis database was used. It consists of a set of 30, 24-h Holter recordings collected from healthy subjects, patients suffering from congestive heart failure, and heart transplanted patients. All the methods, with the exception at most of rescale range analysis, were almost equivalent in distinguish between the three groups of patients. Finally, the scaling relationships, valid for fBm and fGn, when empirically used on HRV series, also approximately held.

Introduction: Cardiovascular physics

The number of patients suffering from cardiovascular diseases increases unproportionally high with the increase of the human population and aging, leading to very high expenses in the public health system. Therefore, the challenge of cardiovascular physics is to develop high-sophisticated methods which are able to, on the one hand, supplement and replace expensive medical devices and, on the other hand, improve the medical diagnostics with decreasing the patient's risk. Cardiovascular physics-which interconnects medicine, physics, biology, engineering, and mathematics-is based on interdisciplinary collaboration of specialists from the above scientific fields and attempts to gain deeper insights into pathophysiology and treatment options. This paper summarizes advances in cardiovascular physics with emphasis on a workshop held in Bad Honnef, Germany, in May 2005. The meeting attracted an interdisciplinary audience and led to a number of papers covering the main research fields of cardiovascular physics, including data analysis, modeling, and medical application. The variety of problems addressed by this issue underlines the complexity of the cardiovascular system. It could be demonstrated in this Focus Issue, that data analyses and modeling methods from cardiovascular physics have the ability to lead to significant improvements in different medical fields. Consequently, this Focus Issue of Chaos is a status report that may invite all interested readers to join the community and find competent discussion and cooperation partners.

Characteristics of heart period variability in intubated very low birth weight infants with respiratory disease

BACKGROUND

Heart period variability provides a measure of balance between the sympathetic nervous system (SNS) and parasympathetic nervous system (PNS). Since the PNS develops during the final weeks of gestation, premature infants have an overriding SNS. Spectral power analysis of heart period variability reveals two main frequency regions, the low frequency region (LF) representing primarily SNS activity and the high frequency region (HF) representing PNS activity.

OBJECTIVES

To identify the characteristics of heart period power in the LF and HF regions in very low birth weight (VLBW) infants in the neonatal intensive care unit across gestational age groups and between sleep and awake states.

METHODS

Data were collected from 16 intubated and mechanically ventilated VLBW infants with respiratory disease. Using spectral analysis techniques, heart period power in the two main frequency regions was extracted.

RESULTS

HF power did not improve with gestational age as expected. LF power did increase with age, albeit nonsignificantly. LF and HF power were not significantly different between awake and sleep states.

CONCLUSIONS

The results of this preliminary study suggest that PNS tone does not improve with gestational age in VLBW infants with respiratory disease. The intensive care environment may stimulate a sympathetic response in these infants and disrupt normal PNS development.

Interactions of a new beta-blocker, celiprolol, with the calcium antagonists, diltiazem and nifedipine, on atrioventricular conduction

The influence of a new beta-blocker, celiprolol, on the direct dromotropic effects of the Ca antagonists, diltiazem and nifedipine, on atrioventricular (AV) conduction was estimated in the canine isolated, blood-perfused AV node preparation. Diltiazem (1-10 micrograms) and nifedipine (0.3-3 micrograms) injected i.a. into the AV node artery dose dependently prolonged the atrio-His (AH) interval (5-39 msec and 7-51 msec) in the AV mode preparation. When celiprolol (1 and 10 mg/kg) was given i.v. in the support dog, the AH interval in the AV node preparation was transiently shortened and then maintained constant as a control. These doses of i.v. celiprolol completely abolished the isoproterenol-induced decrease in the AH interval (28 msec at 0.03 microgram, i.a.) and AV nodal tachycardia. In the presence of celiprolol, the same doses of i.a. diltiazem and nifedipine increased the AH interval by the same amounts (6-43 msec and 8-53 msec) as the control. The incidence of second degree AV conduction block produced by diltiazem (2 in 5 AV node preparations at 10 micrograms) and nifedipine (2 in 6 preparations at 3 micrograms) was not changed by celiprolol. In the second experiments, diltiazem (30-300 micrograms/kg) and nifedipine (3-30 micrograms/kg), given i.v. in an open-chest in situ vagotomized dog, dose dependently increased AV conduction time (AVCT; 2-30 msec and 1-12 msec). Celiprolol 1 and 10 mg/kg i.v., which suppressed the isoproterenol-induced decrease in AVCT (32 msec at 0.3 mu/kg i.v.) and AV nodal tachycardia (4 in 6 in situ hearts), potentiated the prolongation of AVCT by the same doses of diltiazem (11-50 msec) and nifedipine (3-40 msec). The incidence of second degree AV conduction block produced by i.v., diltiazem (1 in 5 in situ hearts at 300 micrograms/kg) and nifedipine (0 in 6 in situ hearts at 30 micrograms/kg) was aggravated (4 in 5 and 3 in 6 in situ hearts) after i.v. celiprolol. These results indicate that although celiprolol does not affect the direct negative dromotropic effects of the Ca antagonists, AV block could easily be produced when celiprolol eliminates tonic adrenergic influences in vivo.

Efficacy of a single dose of slow-release isosorbide dinitrate in the treatment of silent or painful myocardial ischemia in stable angina pectoris

A double-blind study was performed in 32 patients with stable angina pectoris to assess the effects of slow-release isosorbide dinitrate (ISDN) (a single dose of 120 mg/day) on the frequency and duration of painless and painful ischemic episodes, and on electrocardiographic changes and exercise tolerance. Forty-eight-hour electrocardiographic monitoring and treadmill exercise tests were performed before, and at 20 and 21 days of therapy. Holter monitoring showed a significant decrease in the frequency of painful and silent episodes (p less than 0.001), and in the duration of painful (1,623 +/- 664 seconds vs 323 +/- 161 seconds; p less than 0.001) and silent episodes (2,818 +/- 1,496 seconds vs 223 +/- 102 seconds; p less than 0.001). The magnitude of painful and silent ST-segment depression was significantly reduced (2.7 +/- 0.9 mm to 0.7 +/- 0.7 mm and 2.0 +/- 1.1 mm to 0.7 +/- 0.5 mm, respectively; p less than 0.001). Time of exercise testing to the onset of ST-segment depression (442 +/- 137 seconds vs 858 +/- 110 seconds; p less than 0.001) or anginal pain was doubled (461 +/- 128 seconds vs 830 +/- 130 seconds; p less than 0.001). The work load increased from 6 to 10 METs (p less than 0.001). ISDN in a single dose of 120 mg/day is a valuable drug for stable angina pectoris, decreasing the frequency of silent and painful ischemic episodes and the magnitude of ST-segment depressions, and increasing exercise tolerance. It particularly shortened the duration of silent episodes. For patients' compliance, a once-daily dose of ISDN could be advantageous.

Evaluation of the antianginal effect of nifedipine: influence of formulation dependent pharmacokinetics

Nifedipine capsules t.d.s. and an extended release formulation of nifedipine, nifedipine-ER tablets, given once daily in corresponding daily doses, have been compared with placebo in a double-blind, three-way cross-over study in 24 patients with stable angina pectoris. The objective was to study the influence on the antianginal effect of the different pharmacokinetics of several preparations of nifedipine. All patients received concomitant treatment with beta-adrenoceptor blockers. Antianginal efficacy was assessed by a dynamic exercise test at the end of the dosage intervals, i.e. 8 and 24 h after nifedipine capsules and nifedipine-ER, respectively, as well as 6 h after dosing. Six h after dosing the time of onset of chest pain and total exercise time were longer and total work was significantly higher during both nifedipine-ER (plasma concentration 260 nmol/l) and placebo treatment than after nifedipine capsules (plasma concentration 78 nmol/l). Time to 1 mm ST depression was longer during nifedipine-ER than during nifedipine capsule treatment. No significant difference was seen between nifedipine-ER and placebo. At the end of the dosage interval (24 and 8 h after nifedipine-ER and nifedipine capsules, respectively), no significant difference was found between nifedipine-ER (plasma concentration 75 nmol/l) and the other two treatments. However, placebo was superior to nifedipine capsules (plasma concentration 58 nmol/l) both in the time to onset of chest pain and total exercise time. The lack of effect at the end of the dosage interval was probably due to the subtherapeutic plasma nifedipine level.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of nifedipine on total ischemic activity and circadian distribution of myocardial ischemic episodes in angina pectoris

A randomized, double-blind, crossover study was conducted in 10 patients to assess the effect of nifedipine versus placebo on total ischemic activity and circadian distribution of ischemic episodes. After baseline exercise treadmill testing and 48-hour ambulatory electrocardiographic ST-segment monitoring, patients received either nifedipine (mean dose, 80 mg/day) or placebo administered 4 times per day, with the initial dose taken immediately upon arising in the morning. Patients were maintained on a stable dose of each study drug for 7 days, after which they underwent repeat exercise treadmill testing and 48-hour ambulatory electrocardiography. During exercise treadmill testing, greater exercise duration was achieved by patients receiving nifedipine than by those receiving placebo (421 +/- 121 vs 353 +/- 155 seconds, respectively; p less than 0.05). Time to greater than or equal to 1 mm ST depression was significantly greater with nifedipine (282 +/- 146 seconds) than at baseline (130 +/- 72 seconds, p less than 0.003) and with placebo (150 +/- 98 seconds, p less than 0.0005). During ambulatory electrocardiographic monitoring, nifedipine reduced both the total number of ischemic episodes (18 vs 54 at baseline and 63 with placebo; p less than 0.02 for both) and the total duration of ischemia (260 vs 874 at baseline and 927 minutes with placebo; p less than 0.02 for both). The surge of ischemia between 06:00 and 12:00 noted at baseline and during placebo therapy was nearly abolished during nifedipine treatment. Nifedipine at this dosage, administered in this manner, is effective in reducing total ischemic activity and may prevent morning surges of ischemic episodes.

The role of nitrates, beta blockers, and calcium antagonists in stable angina pectoris

Numerous controlled studies have shown that nitrates, beta blockers, and calcium antagonists are effective in the treatment of stable angina pectoris. The pharmacokinetics, pharmacodynamics, and hemodynamic effects of these agents are different, and thus combination therapy offers additive improvement and also counterbalancing of the undesirable side effects of each drug. The choice of therapy depends on the severity of symptoms, associated diseases, compliance, side effects, and status of left ventricular function. The main mechanism of improvement is a decrease in myocardial oxygen consumption, though an increase in coronary blood flow is another potential reason for the use of calcium blockers. This review considers the properties of these drugs, their mechanism of action, and the results of randomized studies.