Radiofrequency ablation in treatment of atrial fibrillation.

Beside heart failure and metabolic syndrome, atrial fibrillation is termed the cardiovascular epidemic of the twenty-first century. Its increased morbidity and mortality is alarming. The present, most effective therapy of atrial fibrillation is catheter ablation. Successful ablation of atrial fibrillation prevents the occurrence and progression of electrical, structural and mechanic myocardium remodelling, improves function of the left ventricle, and prevents the risk of thrombembolism. Onset of sinus rhythm activates the reversal remodelling leading to wall reconstruction and atrium reduction. The paper reviews the technique and presents own experience with catheter ablation.

Reproducibility of blood pressure and inter-beat interval variability in man.

Increased blood pressure variability (BPV) and decreased inter-beat interval (heart rate, respectively) variability (IBIV, HRV respectively) are associated with cardiovascular disorders. The aim of this study was to evaluate the reproducibility of BPV and IBIV (HRV) in young healthy individuals. Blood pressure and inter-beat intervals (instantaneous values of heart rate, respectively) were recorded beat-to-beat at rest (5 min, Finapres, breathing at 0.33 Hz) in 152 subjects (19-24 years) 3 times in periods of one week. Systolic (SBPV(0.1r)/SBPV(0.1a)) and diastolic (DBPV(0.1r)/DBPV(0.1a)) blood pressure variability in relative (r.u.) and absolute (mmHg(2)/Hz) units and inter-beat interval (IBIV(0.1r)/IBIV(0.1a)), or heart rate (HRV(0.1r)/HRV(0.1a)) variability in relative (r.u.) and absolute (ms(2)/Hz, resp. mHz(2)) units were determined by the spectral method as spectral power at the frequency of 0.1 Hz and 0.33 Hz (SBPV(0.33r)/SBPV(0.33a), DBPV(0.33r)/DBPV(0.33a), IBIV(0.33r)/IBIV(0.33a), HRV(0.33r)/HRV(0.33a)). All indices of BPV and IBIV (resp. HRV) revealed a lower intraindividual than interindividual variability (ANOVA; p<0.001). The mean values of all indices in each subject significantly correlated with distribution of individual values in the same subject (Pearson's correlation coefficient; p<0.001). Blood pressure and inter-beat interval (heart rate) variability is an individual characteristic feature.

Logit and fuzzy models in data analysis: estimation of risk in cardiac patients.

The aim of this study was a comparison of risk stratification for death in patients after myocardial infarction (MI) and of risk stratification for malignant arrhythmias in patients with implantable cardioverter-defibrillator (ICD). The individual risk factors and more complex approaches were used, which take into account that a borderline between a risky and non-risky value of each predictor is not clear-cut (fuzzification of a critical value) and that individual risk factors have different weight (area under receiver operating curve - AUC or Sommers' D - Dxy). The risk factors were baroreflex sensitivity, ejection fraction and the number of ventricular premature complexes/hour on Holter monitoring. Those factors were evaluated separately and they were involved into logit model and fuzzy models (Fuzzy, Fuzzy-AUC, and Fuzzy-Dxy). Two groups of patients were examined: a) 308 patients 7-21 days after MI (23 patients died within period of 24 month); b) 53 patients with left ventricular dysfunction examined before implantation of ICD (7 patients with malignant arrhythmia and electric discharge within 11 month after implantation). Our results obtained in MI patients demonstrated that the application of logit and fuzzy models was superior over the risk stratification based on algorithm where the decision making is dependent on one parameter. In patients with implanted defibrillator only logit method yielded statistically significant result, but its reliability was doubtful because all other tests were statistically insignificant. We recommend evaluating the data not only by tests based on logit model but also by tests based on fuzzy models.

Association of A1166C polymorphism in AT(1) receptor gene with baroreflex sensitivity.

The aim of this study was to evaluate the association of A1166C polymorphism in angiotensin II type 1 receptor (AT(1)R) gene with baroreflex sensitivity (BRS in ms/mm Hg; BRSf in mHz/mm Hg) in man. BRS and BRSf were determined by a spectral method in 135 subjects (19-26 years) at a frequency of 0.1 Hz. Genotypes were detected by means of polymerase chain reaction and restriction analysis using enzyme DdeI. We compared BRS and BRSf among genotypes of this polymorphism. The frequency of genotypes of AT(1)R A1166C polymorphism was: 45.9 % (AA, n=62), 45.9 % (AC, n=62), 8.2 % (CC, n=11). Differences in BRS (p<0.05) and BRSf (p<0.01) among genotypes of this single nucleotide polymorphism were found (Kruskal-Wallis: BRS - AA: 7.9+/-3.3, AC: 8.6+/-3.6, CC: 5.9+/-2.3 ms/mm Hg; BRSf - AA: 12.0+/-4.0, AC: 12.0+/-5.0, CC: 8.0+/-3.0 mHz/mm Hg). Compared to carriers of other genotypes (AA+AC) the homozygotes with the less frequent allele (CC) showed significantly lower BRSf (Mann-Whitney: BRSf - AA+AC: 12.0+/-4.0, CC: 8.0+/-3.0 mHz/mm Hg; p<0.01) and borderline lower BRS (BRS - AA+AC: 8.2+/-3.5, CC: 5.9+/-2.5 ms/mm Hg; p=0.07). We found a significant association of A1166C polymorphism in AT(1) receptor gene with baroreflex sensitivity. Homozygosity for the less frequent allele was associated with decreased baroreflex sensitivity.

Comparison of baroreflex sensitivity determined by cross-spectral analysis at respiratory and 0.1 Hz frequencies in man.

Non-invasive methods of determination of baroreflex sensitivity (BRS, ms/mmHg) are based on beat-to-beat systolic blood pressure and inter-beat interval recording. Sequential methods and spectral methods at spontaneous breathing include transient superposition of breathing and 0.1 Hz rhythms. Previously, a cross-spectral method of analysis was used, at constant breathing rate using a metronome set at 0.33 Hz, enabling separate determination of BRS at 0.1 Hz (BRS(0.1Hz)) and respiratory rhythms (BRS(0.33Hz)). The aim of the present study was to evaluate the role of breathing in the spectral method of BRS determination with respect to age and hypertension. Such information would be important in evaluation of BRS at pathological conditions associated with extremely low BRS levels. Blood pressure was recorded by Finapres (5 minutes, controlled breathing at 0.33 Hz) in 118 healthy young subjects (YS: mean age 21.0+/-1.3 years), 26 hypertensive patients (HT: mean age 48.6+/-10.3 years) with 26 age-matched controls (CHT: mean age 46.3+/-8.6 years). A comparison of BRS(0.1Hz) and BRS(0.33Hz) was made. Statistically significant correlations were found between BRS(0.1Hz) and BRS(0.33Hz) in all groups: YS: r=0.52, p<0.01, HT: r=0.47, p<0.05, and CHT: r=0.70, p<0.01. The regression equations indicated the existence of a breathing-dependent component unrelated to BRS (YS: BRS(0.33Hz)=2.63+1.14*BRS(0.1Hz); HT: BRS(0.33Hz)=3.19+0.91*BRS(0.1Hz); and CHT: BRS(0.33Hz)=1.88+ +1.01*BRS(0.1Hz); differences between the slopes and the slope of identity line were insignificant). The ratios of BRS(0.1Hz) to BRS(0.33Hz) were significantly lower than 1 (p<0.01) in all groups (YS: 0.876+/-0.419, HT: 0.628+/-0.278, and CHT: 0.782+/-0.260). Thus, BRS evaluated at the breathing rate overestimates the real baroreflex sensitivity. This is more pronounced at low values of BRS, which is more important in patients with pathologic low BRS. For diagnostic purposes we recommend the evaluation of BRS at the frequency of 0.1 Hz using metronome-controlled breathing at a frequency that is substantially higher than 0.1 Hz and is not a multiple of 0.1 Hz to eliminate respiratory baroreflex-non-related influence and resonance effect on heart rate fluctuations.

Anthracycline therapy and 24-hour blood-pressure profile in long-term survivors of childhood cancer.

In our previous studies, a decreased blood pressure was reported in children treated by anthracycline (AC). The aim of this study was to assess the long-term effects of AC anticancer therapy in 45 subjects aged 13-22 years by repeated 24-hour Holter monitoring of blood pressure. Sixty four aged-matched subjects served as controls. The differences between mean values of systolic (SBP) and diastolic blood pressure (DBP) in each hour of both groups were evaluated by Mann-Whitney test. Also the parameters of the least-squares fit of the sinusoidal curve in each subject were estimated (M - mesor, midline-estimating, a mean value of sinusoidal curve corresponds to 24-hours mean pressure; A - amplitude, double amplitude corresponds to night-day difference; Acr - acrophase is a time of maximal value of a sinusoidal curve). SBP and DBP was significantly lower only during night hours in anthracycline patients 19-22 years old. Also M was lower in this age subgroup of patients comparing to age matched controls (SBP: 112+/-6 mm Hg versus 117+/-7 mm Hg, p<0.05; DBP: 67+/-3 mm Hg versus 69+/-6 mm Hg, p<0.05), A was not different, Acr in patients was shifted one hour earlier (SBP: 2.4 p.m. versus 3.6 p.m., p<0.05; DBP: 2.1 p.m. versus 3.3 p.m., p<0.01). This corresponds to the shift of the morning blood-pressure increase seen on 24-hours blood pressure profiles. M correlated with age in controls (SBP: r=0.374, p<0.01; regression coefficient b=1.34 mm Hg/1 year; DBP: r=0.365, p<0.01; b=0.95 mm Hg/1 year), but not in patients (SBP: r=0.182, DBP: r=0.064). A and Acr were age-independent in all subjects. It is concluded that blood pressure in 19-22 years old AC patients is lower during night hours, the age-dependent increase of blood pressure seen in healthy controls between 13 and 22 years of age does not occur in patients. This finding is consistent with the long-lasting impairment of the sympathetic nervous system caused by anthracyclines.

[The progress of autonomic parameters in patients after myocardial infarction with ST elevation]. / Vývoj autonomních parametru u pacientu po infarktu myokardu s ST elevacemi.

The patients after myocardial infarction with ST elevation (STEMI) are endangered by the development inception of autonomic dysfunction, decreased baroreflex sensitivity, decreased heart rate variability, and increased blood pressure variability as a result of increased sympathetic activity and/or decreased parasympathetic activity. Thanks to direct angioplasty and optimal pharmacotherapy of coronary artery disease and heart failure, we didn't found any significant changes of these parameters within a one-year follow-up, and mortality due to cardiac etiology was very low in this group. Autonomic dysfunction and negative left ventricular remodeling is related only to a small group of patients after STEMI, whose risk stratification will be difficult.

Baroreflex sensitivity and essential hypertension in adolescents.

It has been known for many years that baroreflex sensitivity is lowered in hypertensive patients. There are several known factors implicating this association, e.g. high blood pressure leads to remodeling of the carotid arterial wall, to its stiffness and to a diminished activation of baroreceptors; leptin released from a fatty tissue activates the sympathetic nervous system etc. On the other hand, low baroreflex sensitivity (BRS, usually quantified in ms/mmHg) can be inborn. Studies on primary hypertension in children and adolescents have brought new information about the role of baroreflex in the development of an early stage of primary hypertension. BRS lower than 3.9 ms/mmHg was found in 5 % of healthy subjects. This value approaches the critical value for the risk of sudden cardiac death in patients after myocardial infarction and corresponds to the value present in hypertensive patients. A decreased BRS and BRSf (baroreflex sensitivity expressed in mHz/mmHg, index independent of the mean cardiac interval), was found not only in children with hypertension, but also in those with white-coat hypertension. This is in accordance with a single interpretation. The decrease of BRS/BRSf precedes a pathological blood pressure increase. The contribution of obesity and BRS/BRSf to the development of hypertension in adolescents was also compared. Both factors reach a sensitivity and a specificity between 60 % and 65 %, but there is no correlation between the values of the body mass index and BRS either in the group of hypertensive patients or in healthy controls. If a receiver operating curve (sensitivity versus specificity) is plotted for both values together using logistic regression analysis, a sensitivity higher than 70 % and a specificity over 80 % are reached. This means that low baroreflex sensitivity is an independent risk factor for the development of primary hypertension. Studies demonstrate that adolescents with increased blood pressure and with BRS under 7 ms/mmHg should be given care and intensively motivated to change their lifestyle including a change in diet and increase in physical activity.

Overweight and decreased baroreflex sensitivity as independent risk factors for hypertension in children, adolescents, and young adults.

We studied the relationship between blood pressure (BP), body mass index (BMI, kg/m(2)) and baroreflex sensitivity (BRS, ms/mmHg) in adolescents. We examined 34 subjects aged 16.2+/-2.4 years who had repeatedly high causal BP (H) and 52 controls (C) aged 16.4+/-2.2 years. Forty-four C and 22 H were of normal weight (BMI between 19-23.9), and 8 C and 12 H were overweight (BMI between 24-30). Systolic BP was recorded beat-to-beat for 5 min (Finapres, controlled breathing 0.33 Hz). BRS was determined by the cross-spectral method. The predicting power of BMI and BRS for hypertension was evaluated by sensitivity, specificity, and receiver operating curve (ROC - plot of sensitivity versus specificity). H compared with C had lower BRS (p<0.01) and higher BMI (p<0.05). Multiple logistic regression analysis (p<0.001) revealed that a decreased BRS (p<0.05) and an increased BMI (p<0.01) were independently associated with an increased risk of hypertension. No correlation between BMI and BRS was found either in H or in C. Following optimal critical values by ROC, the sensitivity, specificity and area under ROC were determined for: BMI - 22.2 kg/m(2), 61.8 %, 69.2 %, 66.0 %; BRS - 7.1 ms/mmHg, 67.7 %, 69.2 %, 70.0 %; BMI and BRS - 0.439 a.u., 73.5 %, 82.7 %, and 77.3 %. Decreased BRS and overweight were found to be independent risk factors for hypertension.

Arterial blood pressure and baroreflex sensitivity 1-18 years after completing anthracycline therapy.

UNLABELLED: The analysis of short-term blood pressure regulation in children, adolescents and young adults 1 to 18 years after the treatment with anthracyclines known to have cardiotoxic side effects for oncological diseases was the aim of the present study. Thirty-one subjects treated with anthracyclines (PA) and 11 subjects treated with different antitumour drugs (P0) were investigated twice (the interval between two investigations 1-9 years). Three hundred and thirty-nine healthy subjects served as controls (C). Systolic (SBP), diastolic blood pressures (DBP) in the finger arteries and inter-beat interval (IBI) were recorded beat-to-beat (FINAPRES, Ohmeda, metronome controlled breathing, 5 minute recording); the values were corrected by auscultatory blood pressure measurements. Baroreflex sensitivity (BRS, ms/mmHg) was determined by a spectral method. As the investigated subjects were of different ages, the measured values were standardised on the age of 16 years by linear regression, and only standardised values (IBI16, SBP16, DBP16 and BRS16) were further analysed. No differences were found between PA, P0 and C in BRS16 and IBI16. SBP16 and DBP16 were significantly lower in PA (102.1+/-8.3/59.7+/-7.1 versus C: 114.1+/-12.4/69.0+/-9.5 mmHg; p<0.001/p<0.001; mean from two investigations). SBP16 but not DBP16 was also lower in P0 (102.7+/-12.6/64.5+/-9.7 mmHg; p<0.01/no significant) than in C. The correlation coefficient between SBP16 and period after treatment in PA was -0.11 (no significant) and -0.06 in DBP16 (no significant). Thus, there is not seen a trend to normalisation. CONCLUSION: The anthracycline antitumour therapy in children decreases blood pressure and within 18 years after the treatment there is not observed a trend toward normal values. BRS was not influenced by the anthracycline therapy.

Baroreflex sensitivity as an individual characteristic feature.

The reproducibility of baroreflex sensitivity (BRS in ms/mmHg; BRSf in mHz/mmHg) determined with respect to the coherence between the variability in systolic blood pressure (SBP) and inter-beat intervals (IBI) or heart rate (HR) was tested. SBP and IBI were recorded beat-to-beat for 5 min (Finapres, breathing at 0.33 Hz) in 116 subjects (aged 19-24 years) sitting at rest three times in periods of one week. BRS and BRSf was determined by a cross-spectral method in a frequency range of 0.067-0.133 Hz. Eight indices were evaluated: BRS(0.1 Hz) /BRSf(0.1 Hz) - the value at a frequency of 0.1 Hz; BRS(COHmax)/BRSf(COHmax) - the value at maximum coherence; BRS(Wcoh)/BRSf - weighted value with respect to coherence values in the whole frequency range; BRS(WPcoh)/BRS(WPcoh) - weighted value with respect to coherence for frequencies with coherence above 0.5. All indices revealed a lower intraindividual than interindividual variability (p<0.001). The individual mean values of BRS or BRSf correlated (p<0.001) with standard deviation of their individual values for all indices. Baroreflex sensitivity is an individual characteristic feature with the highest reproducibility at its low values in spite of its resting variation. Reproducibility is not influenced by modification of the spectral method used.

Baroreflex sensitivity in children and adolescents: physiology, hypertension, obesity, diabetes mellitus.

The increased prevalence of obesity in children and its complications have led to a greater interest in studying baroreflex sensitivity (BRS) in children. This review of BRS in children and adolescents includes subtopics on: 1. Resting values of BRS and their reproducibility, 2. Genetics of BRS, 3. The role of a primarily low BRS and obesity in the development of hypertension, and 4. Association of diabetes mellitus, BRS, and obesity. The conclusions specific to this age follow from this review: 1. The mean heart rate (HR) influences the measurement of BRS. Since the mean HR decreases during adolescence, HR should be taken into account. 2. A genetic dependency of BRS was found. 3. Low BRS values may precede pathological blood-pressure elevation in children with white-coat hypertension. We hypothesize that low BRS plays an active role in the emergence of hypertension in youth. A contribution of obesity to the development of hypertension was also found. We hypothesize that both factors, a primarily low BRS and obesity, are partially independent risk factors for hypertension in youths. 4. In diabetics, a low BRS compared to healthy children can be associated with insulin resistance. A reversibility of the BRS values could be possible after weight loss.

Age-dependent relationship between the carotid intima-media thickness, baroreflex sensitivity, and the inter-beat interval in normotensive and hypertensive subjects.

The interrelationship between baroreflex sensitivity expressed in ms/mm Hg (BRS) or in Hz/mm Hg (BRSf), carotid wall thickness (IMT), and age was investigated in hypertensive and normotensive subjects with respect to the mean inter-beat interval (IBI) and blood pressure (BP). BP monitoring was performed in 25 treated hypertensives (Hy; 47.4+/-9.2 years of age) and 23 normotensives (Norm; 44.5+/-8.1 years). IMT was measured by ultrasonography. BRS and BRSf were determined by the spectral method (five-minute non-invasive beat-to-beat recording of BP and IBI, Finapres, controlled breathing at a frequency of 0.33 Hz). Significant differences between Hy and Norm were detected in IMT (Hy: 0.624+/-0.183, Norm: 0.522+/-0.070 mm; p<0.01), BRS (Hy: 3.5+/-1.6, Norm: 5.7+/-2.3 ms/mm Hg; p<0.01), BRSf (Hy: 0.005+/-0.002, Norm: 0.009+/-0.004 Hz/mm Hg; p<0.01), systolic BP (Hy: 131+/-21, Norm: 116+/-17 mm Hg; p<0.01) and diastolic BP (Hy: 77+/-16, Norm: 64+/-12 mm Hg; p<0.01). A significant correlation was found between age and IMT (Norm: 0.523, p<0.05; Hy+Norm: 0.419, p<0.01), age and BRS (Norm: -0.596, p< 0.01; Hy+Norm: -0.496, p<0.01), age and BRSf (Norm: -0.555, p<0.01; Hy: -0.540, p <0.01; Hy+Norm: -0.627, p<0.01), age and IBI (Hy: 0.478, p<0.05), age and diastolic BP (Hy: -0.454, p<0.05), BRS and IMT (Hy+Norm: -0.327, p<0.05) and BRSf and IMT (Hy+Norm: -0.358, p<0.05). Hypertensive patients have increased IMT and decreased BRS and BRSf. The positive correlation between age and IMT and the negative correlation between age and BRS and BRSf are in agreement with the hypothesis that the age-dependent decrease of baroreflex sensitivity corresponds to the age-related structural changes of the carotid wall. Using two indices of baroreflex sensitivity, BRS and BRSf, we could show that baroreflex sensitivity in hypertensives is lower not only due to thickening of the carotid wall, but also due to aging.

[Comparison of the prevalence of non-invasive risk markers of the sudden cardiac death in patients treated by thrombolysis and by percutaneous transluminal coronary angioplasty]. / Srovnání výskytu neinvazivních rizikových znaku náhlé srdecní smrti u nemocných lécených trombolýzou a prímou angioplastikou infarktové tepny.

BACKGROUND: Myocardial infarction survivors may develop a higher risk of sudden cardiac death. The risk markers: left ventricular ejection fraction, ventricular premature beats, late potentials on averaged ECG, baroreflex sensitivity and heart rate variability are used as non-invasive stratification markers. METHODS AND RESULTS: Occurrence of the autonomic and morphologic dysfunction risk markers in the myocardial infarction patients treated by thrombolysis and by primary percutaneous transluminal coronary angioplasty (PTCA) is compared. We studied a cohort of 48 acute myocardial infarction survivors treated by primary PTCA and 96 patients treated by thrombolysis. CONCLUSIONS: Patients treated by primary PTCA had significantly lower occurrence of premature ventricular beats and pathological parameters of the heart rate variability.

Development of causal interactions between systolic blood pressure and inter-beat intervals in adolescents.

Systolic blood pressure (SBP) changes control the cardiac inter-beat intervals (IBI) duration via baroreflex. Conversely, SBP is influenced by IBI via non-baroreflex mechanisms. Both causal pathways (feedback - baroreflex and feedforward - non-baroreflex) form a closed loop of the SBP - IBI interaction. The aim of this study was to assess the age-related changes in the IBI - SBP interaction. We have non-invasively recorded resting beat-to-beat SBP and IBI in 335 healthy subjects of different age, ranging from 11 to 23 years. Using a linear autoregressive bivariate model we obtained gain (Gain(SBP,IBI), used traditionally as baroreflex sensitivity) and coherence (Coh(SBP,IBI)) of the SBP-IBI interaction and causal gain and coherence in baroreflex (Gain(SBP->IBI), Coh(SBP->IBI) and coherence in non-baroreflex (Coh(IBI->SBP)) directions separately. A non-linear approach was used for causal coupling indices evaluation (C(SBP->IBI), C(IBI->SBP)) quantifying the amount of information transferred between signals. We performed a correlation to age analysis of all measures. Coh(IBI->SBP) and C(IBI->SBP) were higher than Coh(SBP->IBI) and C(SBP->IBI), respectively. Gain(SBP,IBI) increased and Coh(SBP->IBI) decreased with age. The coupling indices did not correlate with age. We conclude that the feedforward influence dominated at rest. The increase of Gain(SBP,IBI) with age was not found in the closed loop model. A decrease of Coh(SBP->IBI) could be related to a change in the cardiovascular control system complexity during maturation.

Time versus frequency domain techniques for assessing baroreflex sensitivity.

BACKGROUND: Newer techniques to evaluate baroreflex sensitivity (BRS) are based on the analysis of blood pressure (BP) and heart rate (HR) time series in the time or frequency domain. These novel approaches are steadily gaining popularity, since they do not require injection of vasoactive substances, nor do they rely on a complex experimental set-up. AIM: This review outlines and compares some basic features of the latest methods to assess spontaneous baroreflex function. RESULTS: Modern techniques for the estimation of spontaneous BRS are based on a variety of signal processing schemes and derive information on the baroreflex function from different perspectives. Thus factors such as respiration and other non-stationary agents may have different influences on the estimates provided by each of these approaches. Notwithstanding such individual specificity, however, it has been observed that in several physiological and pathophysiological conditions these techniques often provide comparable information on BRS changes over time, particularly when the estimates are averaged over time windows of a few minutes. CONCLUSIONS: Due to the general agreement in the pattern of BRS among most modern methods, it seems reasonable to employ the most validated of these techniques, for which data obtained in several studies are already available.

The importance of high-frequency paced breathing in spectral baroreflex sensitivity assessment.

OBJECTIVE: Computation of the low-frequency (LF) blood pressure variability (BPV) to heart rate variability (HRV) transfer-index is a common method to assess baroreflex sensitivity (BRS), tacitly assuming that all LF-HRV is caused by baroreflex feedback of LF-BPV. However, respiration may also cause HRV by mechanisms not involving the baroreflex. Application of narrow-band (controlled) high-frequency breathing would keep such non-baroreflex-mediated HRV best out of the LF band. Spontaneous breathing, because of its broad-band character, might cause extra, non-baroreflex-mediated, HRV in the LF band, while paced LF breathing would even concentrate most non-baroreflex-mediated HRV in the LF band. Our study addresses the likely resulting BRS overestimation. DESIGN: We recorded HRV and BPV in 20 healthy young subjects in the sitting position. We varied the sympathovagal balance by gradual leg-lowering from horizontal till 60 degrees . At each angle the subjects performed controlled 0.10 Hz, spontaneous, and controlled 0.25 Hz respiration. RESULTS: Resting BRS values were 15.5(7.2), 13.1 (3.7), and 11.6(6.2) ms/mmHg, respectively. Both the 15/min and the free breathing values differed significantly, P< 0.01 and P= 0.04, from the 6/min breathing value. With lowered legs, the BRS values were 8.2(3.4), 8.3(2.9), and 8.3(3.4) ms/mmHg, respectively. CONCLUSION: Controlled 6/min breathing caused significant BRS overestimation under resting conditions. For the group, spontaneous respiration yielded acceptable BRS values, but individual BRS values deviated sometimes considerably. Conversely, with gravitational load, the respiratory pattern had only minor impact on BRS. Our results demonstrate that the risk of an overestimated BRS value is realistic as long as respiration is not controlled and of high-frequency.

Pressure wave cardiography; cardiac diagnosis by means of noninvasive continuous blood pressure record.

The pulse pressure (PP) is proportional to the preceding interval (T) because of the restitution of contractility and the Starling mechanism, and is inversely proportional to the pre-preceding interval (T-1) because of potentiation of contractility. The aim of the present paper was to find if this relationship can be used for diagnostic purposes. Blood pressure was noninvasively and continuously recorded for 3 minutes (Penáz method), in 26 healthy subjects, in 13 patients with congestive heart failure (NYHA I,II) and sinusoidal rhythms and in 21 patients with atrial fibrillations. By means of multidimensional regression analysis the coefficient D[T] and D[T-1] were calculated in each subject. D[T] expresses the relative role of the preceding, D[T-1] of the pre-preceding interval. The correlation between PP and T was small in subjects with sinusoidal rhythms. Subjects with particular correlation coefficients between PP and T-1 higher than 0.5 were used for further analysis (18 controls, 7 patients). The difference between D[T-1] in controls (0.30 +/- 0.20) and in patients (0.48 +/- 0.19) was significant (Wilcoxon P less than 0.05). In subjects with atrial fibrillations both D[T] and D[T-1] were higher in decompensated patients (Wilcoxon P less than 0.05). The ratio D[T]/D[T-1] was higher in patients with mitral stenosis than in patients with ischaemic heart disease (t-test, P less than 0.05). The test can be usefully employed as a screening test in medical practice.

Noninvasive determination of baroreflex sensitivity in man by means of spectral analysis.

The spectral analysis technique was applied for noninvasive assessment of heart-rate baroreflex sensitivity (BRS). The coherence between fluctuation of blood pressure and heart rate at 0.1 Hz and at respiratory frequency is high. This fact enables the assessment of BRS by means of calculating the modulus (or gain) of the transfer function between variations in blood pressure and heart rate. The noninvasive continuous blood pressure registration according to Penáz was used. During voluntarily controlled breathing intervals, the amplitude of 0.1 Hz and respiratory peaks in the spectra of heart rate and blood pressure changed markedly. Nevertheless, the average sensitivity of the baroreflex (modulus) changed insignificantly. This result indicated that the stability of BRS can be advantageous for the use of BRS in clinical practice. The difference between the modulus at 0.1 Hz and at the breathing rate indicates that baroreflex is only one of the factors causing respiratory arrhythmia. We also compared the determination of BRS by spectral analysis with the following alternative method: both lower extremities were occluded for 5 minutes. The release of pressure in the occluding cuffs decreased blood pressure which was followed by a baroreceptor-mediated increase of heart rate. Both methods correlated, but more detailed analysis revealed the role of the low pressure receptors in BRS determined by spectral analysis.

A dampening effect of pulse interval variability on blood pressure variations with respect to primary variability in blood pressure during exercise.

The correlation between baroreflex sensitivity (BRS) and the spectrum component at a frequency of 0.1 Hz of pulse intervals (PI) and systolic blood pressure (SBP) was studied. SBP and PI of 51 subjects were recorded beat-to-beat at rest (3 min), during exercise (0.5 W/kg of body weight, 9 min), and at rest (6 min) after exercise. BRS was determined by a spectral method (a modified alpha index technique). The subjects were divided into groups according to the spectral amplitude of SBP at a frequency of 0.1 Hz. The following limits of amplitude (in mm Hg) were used: very high > 5.4 (VH); high 5.4 > H > 3 (H); medium 3 > M > 2 (M), low < 2 (L). We analyzed the relationships between 0.1 Hz variability in PI and BRS at rest, during the exercise and during recovery in subgroups VH, H, M, L. The 0.1 Hz variability of PI increased significantly with increasing BRS in each of the groups with identical 0.1 Hz variability in SBP. This relationship was shifted to the lower values of PI variability at the same BRS with a decrease in SBP variability. The primary SBP variability increased during exercise. The interrelationship between the variability of SBP, PI and BRS was identical at rest and during exercise. A causal interrelationship between the 0.1 Hz variability of SBP and PI, and BRS was shown. During exercise, the increasing primary variability in SBP due to sympathetic activation was present, but it did not change the relationship between variability in pulse intervals and BRS.