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C A Swenne

Publications and source records attributed to C A Swenne.

At least 19 recordsLinked to original sources
PubMed2004

Phase-averaged characterization of respiratory sinus arrhythmia pattern.

A method for the accurate time-domain characterization of respiratory sinus arrhythmia (RSA) pattern is presented and applied to two groups of healthy subjects to lay the baseline of RSA patterns and to underlay their features: response to standing, stability in successive recordings, and individuality of the shape of RSA pattern. RSA pattern is evaluated by selective averaging of heart rate (HR) changes from multiple respiratory cycles over the respiratory phase and represents the complete modulating function of HR by respiration. The RSA pattern is evaluated with free respiration and even in cases of severe arrhythmia. Estimation error is 6-8% in magnitude, phase resolution is 0.2 rad, and sensitivity margin for respiratory-related HR variability (HRV) components is 1%. RSA magnitude, phase lag, and expiration-to-inspiration time ratio are derived in addition to the entire pattern. In a group of 10 healthy young adults, a phase lag difference of 11.4 +/- 8.5% (mean +/- SD, P < 0.004) was observed between supine and standing postures, possibly ascribed to breathing mechanics. A second group of 15 healthy young adults at supine rest showed stability of the RSA pattern in successive recordings (several weeks apart) as well as individuality among subjects. This may suggest a nonscalar individual long-term index for cardiorespiratory coupling. The method is complementary to the existing statistical and spectral methods. It allows the complete characterization of the primary RSA components and may provide new insight into the effects of vagal activity and changes in clinical conditions.

Adult↗
PubMed2001

Within-subject electrocardiographic differences at equal heart rates: role of the autonomic nervous system.

Various combinations of sympathetic and vagal tone can yield the same heart rate, while ventricular electrophysiology differs. To demonstrate this in humans, we studied healthy volunteers in the sitting position with horizontal legs. First, heart rate was increased by lowering the legs to 60 degrees and back. Thereafter, heart rate was increased by handgrip. In each subject, a leg-lowering angle was selected at which heart rate matched best with heart rate in the third handgrip minute. Thirteen subjects had a heart rate match better than 1%. Heart rate (control: 65.2+/-9.0 bpm) increased to 72.1+/-8.7 (leg lowering) and to 72.1+/-8.8 (handgrip) bpm. QRS azimuth, QRS duration, maximal T vector, T azimuth, T elevation, ST duration, QRS-T angle and QT interval differed significantly (P<0.05) between leg lowering and handgrip (QT interval 418+/-15 versus 435+/-21 ms). Also, septal dispersion of repolarization, assessed as the time difference between the apex and the end of the T wave in the V2 and V3 leads, differed significantly (V2: 96.7+/-19.3 versus 110.0+/-23.3 ms, P<0.01; V3: 88.7+/-19.3 versus 97.3+/-23.3 ms; P<0.01). Hence, leg lowering and handgrip cause different ventricular depolarization and repolarization. The hypertensive handgrip manoeuvre entails a longer QT interval and probably an increased septal dispersion of repolarization.

Adaptation, Physiological↗
PubMed2001

Changes in frequency of premature complexes and heart rate variability related to shift work.

OBJECTIVES: To investigate whether an increased risk of cardiovascular disease might be caused by increased arrhythmogeneity and by unfavourable changes in autonomic cardiac control the changes in the occurrence of premature complexes (PVCs) and in heart rate variability (HRV) were studied in subjects who started to work in shifts. METHODS: 1 Year changes in frequency of PVCs and HRV were measured in 49 shift workers and 22 control subjects working in daytime. All respondents were starting in a new job in integrated circuit or waste incinerator plants. RESULTS: The incidence of PVC increased significantly in shift workers over the 1 year follow up, compared with daytime workers. The frequency of ventricular extrasystoles increased in 48.9% of the shift workers, and in 27.3% of the daytime workers. The Spearman correlation coefficient between the number of nights worked and the change in PVCs was 0.33 (p=0.004). A small non-significant unfavourable change in HRV was found in both the shift and daytime workers. CONCLUSIONS: A change in arrhythmogeneity, but not in cardiac autonomic control, might explain the increased risk of cardiovascular disease in shift workers.

Adult↗
PubMed2000

Low heart rate variability in a 2-minute rhythm strip predicts risk of coronary heart disease and mortality from several causes: the ARIC Study. Atherosclerosis Risk In Communities.

BACKGROUND: Low heart rate variability (HRV) is associated with a higher risk of death in patients with heart disease and in elderly subjects and with a higher incidence of coronary heart disease (CHD) in the general population. METHODS AND RESULTS: We studied the predictive value of HRV for CHD and death from several causes in a population study of 14 672 men and women without CHD, aged 45 to 65, by using the case-cohort design. At baseline, in 1987 to 1989, 2-minute rhythm strips were recorded. Time-domain measures of HRV were determined in a random sample of 900 subjects, for all subjects with incident CHD (395 subjects), and for all deaths (443 subjects) that occurred through 1993. Relative rates of incident CHD and cause-specific death in tertiles of HRV were computed with Poisson regression for the case-cohort design. Subjects with low HRV had an adverse cardiovascular risk profile and an elevated risk of incident CHD and death. The increased risk of death could not be attributed to a specific cause and could not be explained by other risk factors. CONCLUSIONS: Low HRV was associated with increased risk of CHD and death from several causes. It is hypothesized that low HRV is a marker of less favorable health.

Aged↗
PubMed2000

Occupational determinants of heart rate variability.

OBJECTIVES: Analysis of HRV has been suggested as a way to study the effects of work-related stresses on cardiovascular autonomic regulation. The aim of this study was to evaluate the use of HRV in the investigation of work-related stressors. METHODS: Cross-sectional data from an ongoing cohort study were used to analyse the relationship of the potential workplace stressors of job-strain, noise and shift work, with HRV. Mean HRV values during sleep and work were calculated in 135 24-h EKG recordings. RESULTS: Shift workers displayed significantly decreased SDNNi levels during sleep, compared with those of the daytime workers (adjusted least square mean values: 69.3 and 85.8 ms, respectively, P < 0.05). Compared with the control group reporting low job demands and high work control (mean: 73.2), we found significantly elevated %LF means during work adjusted for sleep in the low demands, low control group (77.9, P < 0.01), high demands, high control group (77.7, P < 0.05) and high demands, low control group (77.7, P < 0.05). Workers reporting a high noise level compared with a low work noise level also displayed an elevated adjusted mean %LF during work (78.0 and 75.3 respectively, P < 0.06). CONCLUSIONS: The finding of a decreased SDNNi level during sleep in shift workers compared with day workers indicated a less favourable cardiovascular autonomic regulation, which may explain in part the excess cardiovascular disease risk in shift workers. The elevated %LF during work in employees exposed to high job strain or high noise levels indicated a direct shift in the autonomic cardiac balance towards sympathetic dominance. We concluded that the analysis of HRV may provide a useful tool in the study of the physiological effects of work-related stresses.

Adult↗
PubMed2000

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.

Adult↗
PubMed2000

Correlated neurocardiologic and fitness changes in athletes interrupting training.

PURPOSE: We studied nine male Dutch top marathon skaters during a 1-month interruption of their training schedules after their last contest in the winter to investigate a possible decline in baroreflex sensitivity. METHODS: Before and after this period, a maximal exercise test was done, and at days 0, 4, 7, 14, and 28 neurocardiologic measurement sessions--heart rate and noninvasive baroreflex sensitivity, recumbent and tilt--were performed. RESULTS: Interruption of training resulted in a significant and relevant decrease in the maximal oxygen uptake (from 65.7 +/- 5.8 to 61.6 +/- 4.7 mL O2 x kg(-1) x min(-1); P = 0.03), most likely associated with decreased competitive possibilities. Resting heart rate modestly increased (from 54.6 +/- 7.2 to 58.8 +/- 7.5 bpm), however, not significantly. Heart rate during 60 degrees tilt increased considerably (from 70.1 +/- 6.1 to 80.1 +/- 9.1 bpm; P = 0.01), possibly due to a decrease in blood volume and an increase in cardiopulmonary baroreflex gain. Arterial baroreflex sensitivity decreased significantly in the recumbent (from 13.3 +/- 5.4 to 9.8 +/- 3.8 ms x mm Hg(-1), P = 0.04), but not in the 60 degrees tilt position (from 6.7 +/- 2.0 to 6.0 +/- 2.5 ms x mm Hg(-1)). The relative decrease in baroreflex sensitivity and maximal oxygen uptake correlated significantly (r = 0.71, P = 0.02). CONCLUSIONS: In summary, our data show that correlated detrimental changes in fitness and baroreflex sensitivity are measurable in these athletes after a month of interruption of training.

Adult↗
PubMed1999

Exercise training and heart rate variability in older people.

PURPOSE: Heart rate variability (HRV), a characteristic that is potentially increased by physical activity, has been associated with incidence of cardiac events and total mortality. Since the incidence of cardiac events among older people is high and their physical activity levels and HRV are generally low, it is important to investigate whether regular physical activity can modify HRV in this age group. The purpose of the study was to investigate the effect of regular physical activity on HRV in older men and women. METHODS: In a randomized controlled trial, the effect of six months' training on HRV was investigated in a group of 51 older men and women (67.0 +/- 5.1 yr). The training group gathered three times per week for 45 min supervised training. RESULTS: At the end of the intervention period, HRV was higher primarily during the day. During daytime, the SD of all normal intervals (+6%) as well as the low frequency component (+ 15%) and the very low frequency component (+ 10%) of HRV were significantly increased (P < 0.05) as compared with the control group. Effects of training were most pronounced in subjects inactive in sports at baseline. CONCLUSION: This study demonstrates that regular physical activity increases HRV (specifically in the very low and low frequency components) in older subjects. Hence, in older subjects, physical training may be an effective means to modify positively a factor that is associated with increased incidence of cardiac events.

Aged↗
PubMed1999

Correlation of heart rate variability with cardiac functional and metabolic variables in cyclists with training induced left ventricular hypertrophy.

OBJECTIVE: To examine the correlation between heart rate variability and left ventricular mass in cyclists with an athlete's heart. METHODS: Left ventricular mass and diastolic function were determined at rest and myocardial high energy phosphates were quantified at rest and during atropine-dobutamine stress in 12 male cyclists and 10 control subjects, using magnetic resonance techniques. Ambulatory 24 hour ECG recordings were obtained, and time and frequency domain heart rate variability indices were computed. RESULTS: In the cyclists, the mean of all RR intervals between normal beats (meanNN), the SD of the RR intervals, and their coefficient of variation were significantly greater than in control subjects (p < 0.01, p < 0.01, and p < 0.05, respectively). For cyclists and control subjects, only meanNN correlated with left ventricular mass (r = 0.48, p = 0.038). The heart rate variability indices that correlated with functional or metabolic variables were: meanNN v E/A peak (the ratio of peak early and peak atrial filling rate) (r = 0.48, p = 0.039); the root mean square of successive differences in RR intervals among successive normal beats v E/A area (ratio of peak early and peak atrial filling volume) (r = 0.48, p = 0.040); percentage of successive RR intervals differing by more than 50 ms v the phosphocreatine to ATP ratio at rest (r = 0.54, p = 0. 017); and the SD of the average RR intervals during all five minute periods v the phosphocreatine to ATP ratio during stress (r = 0.60, p = 0.007). CONCLUSIONS: Highly trained cyclists have increased heart rate variability indices, reflecting increased cardiac vagal control compared with control subjects. Left ventricular mass has no major influence on heart rate variability, but heart rate variability is significantly correlated with high energy phosphate metabolism and diastolic function.

Adult↗
PubMed1997

Heart rate variability from short electrocardiographic recordings predicts mortality from all causes in middle-aged and elderly men. The Zutphen Study.

Low heart rate variability is associated with high risk of sudden death in myocardial infarction patients. This has been attributed to unfavorable autonomic cardiac control. In the present study, the predictive value of heart rate variability for sudden death, mortality from coronary heart disease, and from all causes was investigated in the general population, using brief electrocardiographic recordings. From 1960 to 1985, 878 middle-aged Dutch men, aged 40-60 years, were followed and repeatedly examined as part of the Zutphen Study. In 1985 the remaining cohort was extended to 885 elderly men, aged 65-85 years, and followed until 1990. Heart rate variability (standard deviation of duration of normal RR intervals) was determined from the resting 12-lead electrocardiogram. The 5-year age-adjusted relative rate of total mortality of men with heart rate variability of < 20 milliseconds (msec) compared with men with heart rate variability of 20-39 msec was 2.1 (95 percent confidence interval 1.4-3.0) in middle-aged men and 1.4 (95% confidence interval 0.9-2.2) in elderly men. Death from noncoronary causes, especially cancer, contributed significantly to this elevated risk. The association of low heart rate variability with sudden death or coronary heart disease mortality was less consistent. In conclusion, in middle-aged men and probably in elderly men, low heart rate variability is predictive of mortality from all causes. This suggests that low heart rate variability is an indicator of compromised health in the general population.

Adult↗
PubMed1996

Heart rate variability during repeated incremental head-up tilt discloses time dependence of individual autonomic dynamics.

According to the Rosenblueth-Simeone model, the heart rate (HR) is proportional to the sympathovagal balance. The individual proportionality constant is the intrinsic HR, which can be determined only invasively. The percentage low-frequency spectral HR variability power, relative to the low- plus high-frequency spectral power (%LF) has been raised as a noninvasive alternative. We previously studied young healthy male subjects, in whom gradual autonomic changes were induced by incremental head-up tilt (0-10-20-30-40-45-50-55-60-65-70-75-80 degrees). At each tilt angle we computed HR and %LF. Linear regressions of %LF on HR, characterizing individual autonomic dynamics, confirmed that, within a subject, changes in %LF were proportional to changes in HR. For the current study, we made repeated measurements in 19 subjects after 1 to 8 months. In six subjects, the session 1 and session 2 regression lines differed significantly (t-test, p < 0.05), demonstrating the time dependence of the autonomic dynamics. In such cases, similar HR values on different days are to be associated with different %LF values. We also determined the reproducibility of the supine HR and %LF values. For all 19 subjects, the coefficients of variation were 7 and 22%, respectively: HR reproduces better than %LF. Hence, time-dependent autonomic dynamics contribute systematically to the inferior reproducibility of %LF.

Adult↗
PubMed1996

Intravenous instrumentation alters the autonomic state in humans.

Intravascular instrumentation may induce syncope or presyncope. It is not known whether asymptomatic subjects also have autonomic reactions, albeit concealed. We addressed this issue by studying 44 healthy young male subjects of various levels of fitness, ranging from inactivity to athletic [mean maximal oxygen uptake was 49.1 (SD 10.7) ml*kg(-1)*min(-1), range 28.7-71.9 ml*kg(-1)*min(-1)]. The autonomic response to venous cannulation was quantified by measuring heart rate before cannulation (HR(1)), after cannulation (HR(2)), and after complete pharmacological autonomic blockade (HR(0) = the intrinsic heart rate). The sympathovagal balance before and after cannulation was computed as HR(1)/HR(0) and HR(2)/HR(0), respectively. The group means of heart rate and sympathovagal balance decreased significantly (paired Student's t-test P <0.01) from 62.5 to 59.9 beats*min(-1), and from 0.71 to 0.68, respectively. The maximal decrease in heart rate was 8.8 beats*min(-1), and in the sympathovagal balance was 0.11. Our study demonstrated that the asymptomatic subjects responded to intravenous instrumentation with a concealed autonomic reaction. Thus, from our findings it would seem that intravenous instrumentation interferes with measurements relating to autonomic nervous system activity.

Adult↗
PubMed1995

Similar orthostatic defense in active, healthy young adult and late middle-aged men.

Orthostatic defense is commonly validated with a 60 degrees to 80 degrees head-up tilt test, addressing the step response rather than the response to permanent orthostatis. During the initial phase of tilt, neural factors predominate, while later, the slower humoral factors fade in. It has been demonstrated that, during adaptation of the circulatory system to the standing conditions, overshoot and undershoot occur. These oscillations hamper straight-forward interpretation of a tilt test, and may contribute to the inconclusiveness of current studies regarding the aging of orthostatic defense. Gradual, progressive, orthostatic load testing seems a valuable alternative. We used a novel, incremental, head-up tilt protocol (0 degrees to 80 degrees, 13 increments) to impose graded orthostatic stress on 46 healthy young adult men (mean age +/- SD 25 +/- 3 years), and on 16 healthy late middle-aged men (60 +/- 4 years), while recording the electrocardiogram and the blood pressure. A first-order estimate of the heart rate range associated with the sympathovagal transition was made by combined analysis of heart rate and heart rate variability trends. We observed similar responses in heart rate, heart rate variability, and blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Autonomic, ischaemic, circadian and rhythmic factors as causes of the spontaneous variability of ventricular arrhythmias.

Ventricular arrhythmias present with strongly varying intensity. This spontaneous variability makes it difficult to use one of the existing arrhythmia grading systems for risk or therapy efficacy studies. We attempted to explain the variability by the changing autonomic, ischaemic, circadian, and rhythmic factors. Four (two learning, two test) 24-h Holter tapes were made within one month in 31 patients with chronic frequent ventricular ectopic beats of miscellaneous aetiology and under constant drug regimen. The data were segmented into 5-min episodes, in which ectopy (dependent variable) was measured, together with heart rate, amount of heart rate variability, fraction low-frequency heart rate variability, ST depression, and clock time (independent variables). Forty-three percent of the fluctuations in arrhythmia incidence could be explained with a multiple regression procedure, and more than 50% of the variance in arrhythmia incidence could be explained in 36% of the cases. Our study demonstrates that much of the spontaneous variability of ventricular arrhythmias can be attributed to the varying conditions. This method of dealing with arrhythmia variability might lead to an alternative to the current arrhythmia grading systems used in risk and drug efficacy studies.

Adult↗
PubMed1994

Heart rate and heart rate variability as indexes of sympathovagal balance.

According to the Rosenblueth-Simeone model, the heart rate (HR) is proportional to the sympathovagal balance. The individual proportionality constant is the intrinsic heart rate, which can only be determined invasively. The normalized low-frequency heart rate variability power (LF) has been raised as a calibrated noninvasive alternative. To concrete this assumption, we studied the individual LF-HR relation during incremental head-up tilt (0, 10, 20, 30, 40, 45, 50, 55, 60, 65, 70, 75, and 80 degrees) in 21 young, healthy males. HR (means +/- SD) increased from 61.0 +/- 9.1 beats/min at 0 degree to 85.9 +/- 18.3 beats/min at 80 degrees. LF increased from 45.8 +/- 16.7 nu at 0 degrees to 79.8 +/- 13.8 nu at 80 degrees (nu meaning normalized units). Individual regressions of LF on HR yielded correlation coefficients of 0.80 +/- 0.13 (means +/- SD). The demonstrated linear relation between LF and HR confirms the potential significance of heart rate variability as a noninvasive means of assessing the sympathovagal balance.

Adult↗