Cardiac interbeat interval dynamics from childhood to senescence : comparison of conventional and new measures based on fractals and chaos theory.

BACKGROUND: New methods of R-R interval variability based on fractal scaling and nonlinear dynamics ("chaos theory") may give new insights into heart rate dynamics. The aims of this study were to (1) systematically characterize and quantify the effects of aging from early childhood to advanced age on 24-hour heart rate dynamics in healthy subjects; (2) compare age-related changes in conventional time- and frequency-domain measures with changes in newly derived measures based on fractal scaling and complexity (chaos) theory; and (3) further test the hypothesis that there is loss of complexity and altered fractal scaling of heart rate dynamics with advanced age. METHODS AND RESULTS: The relationship between age and cardiac interbeat (R-R) interval dynamics from childhood to senescence was studied in 114 healthy subjects (age range, 1 to 82 years) by measurement of the slope, beta, of the power-law regression line (log power-log frequency) of R-R interval variability (10(-4) to 10(-2) Hz), approximate entropy (ApEn), short-term (alpha(1)) and intermediate-term (alpha(2)) fractal scaling exponents obtained by detrended fluctuation analysis, and traditional time- and frequency-domain measures from 24-hour ECG recordings. Compared with young adults (<40 years old, n=29), children (<15 years old, n=27) showed similar complexity (ApEn) and fractal correlation properties (alpha(1), alpha(2), beta) of R-R interval dynamics despite lower spectral and time-domain measures. Progressive loss of complexity (decreased ApEn, r=-0.69, P<0.001) and alterations of long-term fractal-like heart rate behavior (increased alpha(2), r=0.63, decreased beta, r=-0.60, P<0.001 for both) were observed thereafter from middle age (40 to 60 years, n=29) to old age (>60 years, n=29). CONCLUSIONS: Cardiac interbeat interval dynamics change markedly from childhood to old age in healthy subjects. Children show complexity and fractal correlation properties of R-R interval time series comparable to those of young adults, despite lower overall heart rate variability. Healthy aging is associated with R-R interval dynamics showing higher regularity and altered fractal scaling consistent with a loss of complex variability.

Intraindividual variability of infant whole-body plethysmographic measurements: effects of age and disease.

The intraindividual variability of whole-body plethysmographic measurements was studied in a large series of consecutive infants (N = 144), divided into two groups: a group of infants born very prematurely (PM, N = 63), with (N = 28) or without (N = 35) a history of bronchopulmonary dysplasia (BPD), and a group of infants with persistent respiratory symptoms (PRS, N = 81), i.e., wheezing (N = 53) or cough (N = 28). The intraindividual variability was determined within each test and between tests, separated by a 10-min interval. In both study groups, the between-test variability was significantly larger than that within tests. Expressed as the median coefficient of variation (CV), the between-test repeatabilities in the PRS group were 8.0% for thoracic gas volume (TGV), 17.5% for airway resistance (Raw), and 18.4% for specific airway conductance (sGaw), and in the PM group, 8.9% for TGV, 20.4% for Raw, and 20.7% for sGaw. However, the individual range of CVs was large, ranging from 3 to 19% for TGV and from 5 to 55% for sGaw. With respect to TGV, the difference between the groups was statistically significant (P = 0.03). In infants with a history of BPD, there was also a significant negative age dependency in CVs of sGaw (r = -0.50, P = 0. 009), showing larger variation among younger individuals. The presenting symptom (wheezing or cough) in the PRS group did not influence the measurement variability significantly, and neither did the degree of bronchial obstruction. We conclude that on a group basis, the repeatability of infant body plethysmographic measurements may be satisfactory for scientific studies demonstrating pharmacodynamic effects; however, the intraindividual measurement variability should be reported for each test conditions and for infant groups in each study. Due to the large range in individual variation and the influence of age and disease processes on the variation, for an individual child there is only questionable benefit from a given measurement, unless the intrasubject, between-test variability is assessed individually before interventions, such as a bronchodilation test.

Heart rate and cardiac arrhythmia during high-Gz flight.

Twenty-four pilots (age 20-32 years) were monitored with a Holter monitor during 26 hours including a high-Gz flight in order to evaluate heart rate (HR) and cardiac rhythm. Flight experience did not predict the mean in-flight HR (range 69-121 beats/minute), which decreased with increasing age and correlated to the maximum HR during sleep. We recorded maximally 27 ventricular and 97 supraventricular ectopic beats, 10 junctional rhythms, 5 gray-out, 1 vestibular symptom, and 1 instance of numbness of the feet during the flight. No causal relationship between HR, cardiac arrhythmia, or symptoms was found. Adaptation to in-flight +Gz stress takes place without significant arrhythmia and at a submaximal age-related HR.

Comparative analysis of tilting disc and ball valve prosthesis in aortic position.

In a retrospective analysis, comparison was made between the Cutter-Smeloff ball valve (n = 63) and the Lillehei-Kaster tilting disc valve (n = 256) in the aortic position. No significant intergroup difference was found as regards rate of thromboembolism (0.6/100 patient years for both valve types), endocarditis (0.2 for Cutter-Smeloff and 0.5 for Lillehei-Kaster/100 patient years) and paraprosthetic leak (0.9 and 0.5, respectively/100 patient years). The actuarial curve of cumulative survival was similar for both valves until 6 years postoperatively. Thereafter the outcome was less favourable for the patients with Cutter-Smeloff valve (actuarial survival 79 +/- 5% than for those with Lillehei-Kaster valve (91.2 +/- 2%). The reason for this, statistically significant, difference may be associated with the difference in valve profiles.

Long-term follow-up of Björk-Shiley mitral valve replacement. 10 years' experience.

Retrospective analysis was made of 176 patients who received a Björk-Shiley mitral valve replacement in the period 1973 through 1982. Actuarial cumulative curves showed the 10-year and 5-year survival rates to be 79 +/- 3.4%. The functional status at follow-up was better than preoperatively in 77.1% of the patients. The hospital mortality was 9.1% and the late mortality was 3.6/100 patient years. Early complications included disc entrapment against the ventricular wall in three cases, wedging of chorda between disc and valve rim in two and posterior perforation of the left ventricle in three patients. There was no structural valve damage. Calculated per 100 patient years, the incidence of thromboembolism was 2.5, endocarditis 1.4 and prosthetic leak 1.8. One thrombosed valve was successfully replaced by a new prosthesis 11 years after the initial implantation. Jamming of the disc by tissue over-growth necessitated a new valve implantation in one case. The incidence of early valve-related complications was high, but the long-term results were comparable with those from other mechanical valves. One early complication--disc entrapment against the ventricular wall--may be avoided by use of a sufficiently small valve if the ventricle is small and thickened.

Distal pulse palpation: is it reliable?

The aim of this study was to evaluate the reliability of distal pulse palpation. The dorsalis pedis and the tibialis posterior arteries of 25 patients with suspected lower limb arterial disease were independently palpated by three vascular surgeons and three medical students in the outpatient clinic and by two vascular nurses and one physician in the vascular laboratory. The palpation findings were compared to the ankle/brachial index (ABI). Palpable and unpalpable pulses were best separated with ABI 0.76 as the cutoff point. The degree of misdiagnosis was unacceptably high, with an underdiagnosis of more than 30%. The agreement was highest (kappa 0. 68, good) among the vascular laboratory personnel in the peaceful vascular laboratory and lowest (kappa 0.38, fair) among the vascular surgeons in the busy outpatient clinic. The poor agreement and the high proportion of misdiagnosis obtained in the outpatient clinic argue against the use of pulse palpation as a single diagnostic method. Palpable pulses with low ABIs clearly state the need for more objective measurements whenever ischemia is suspected. Yet, by carefully palpating both pedal arteries under good, nonhurried conditions the reproducibility and accuracy of pulse palpation can be tolerable.