Heart rate variability and fractal dimension during orthostatic challenges

1993 ◽  
Vol 75 (6) ◽  
pp. 2602-2612 ◽  
Author(s):  
G. C. Butler ◽  
Y. Yamamoto ◽  
H. C. Xing ◽  
D. R. Northey ◽  
R. L. Hughson
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
Spectral Analysis ◽  
Fractal Dimension ◽  
Cardiovascular System ◽  
Lower Body Negative Pressure ◽  
Broad Band ◽  
Coarse Graining ◽  
Noise Spectrum ◽  
Four Levels

Heart rate variability (HRV) spectral analysis has been used as a tool for short-term assessment of parasympathetic (PNS) and sympathetic nervous system (SNS) control of heart rate. However, it has been suggested that the PNS and SNS indicators are superimposed on a broad-band noise spectrum in which the power spectral densities are inversely proportional to their frequency (1/f beta). In this study, we have used coarse-graining spectral analysis to extract the harmonic components for calculation of PNS and SNS indicators and to obtain the slope (beta) of the 1/f beta component to estimate fractal dimension (DF) of a trail of HRV. DF was regarded as an indicator of cardiovascular system complexity. Ten healthy young subjects (6 women and 4 men) were studied in supine rest and with sequential applications of four levels of lower body negative pressure (LBNP; -10, -20, -30, and -50 mmHg) and head-up tilt (HUT; 10, 20, 30, and 70 degrees). In the 20 tests, there were six occurrences of presyncopal symptoms that required the test to be terminated before the planned end point. At low levels of LBNP or HUT, arterial pulse pressure (PP) was not changed from rest, and calculated DF was very high (beta approximately 1.00). At the higher levels of LBNP and HUT, PP decreased. Coincident with this reduction in PP, PNS activity decreased, SNS activity increased, and DF was reduced, each with a significant linear relationship to the change in PP (PNS: r = 0.56; SNS: r = 0.57; DF: r = 0.70, P < 0.01). Each occurrence of presyncope was associated a low PNS indicator as well as DF < 2.50 (beta > or = 1.80). These data indicate that the cardiovascular system is operating at a reduced level of complexity and further suggest that reduced complexity might not be compatible with cardiovascular homeostasis.

scholarly journals Power spectral analysis of heart rate in hypothyroidism

2000 ◽  
pp. 327-333 ◽  
Author(s):  
V Cacciatori ◽  
ML Gemma ◽  
F Bellavere ◽  
R Castello ◽  
ME De Gregori ◽  
...  
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
Spectral Analysis ◽  
Spectral Density ◽  
Cardiovascular System ◽  
Power Spectral Density ◽  
Power Spectral Analysis ◽  
Control Subjects ◽  
Power Spectral ◽  
Hypothyroid Patients

OBJECTIVE: The aim of the present study was to evaluate the impact of hypothyroidism on the autonomic regulation of the cardiovascular system by analysing separately sympathetic and parasympathetic influences on the heart. DESIGN: In seven newly diagnosed untreated hypothyroid patients we analysed power spectral density of heart rate cyclic variations at rest, while lying, and while standing. The same protocol was repeated after the induction of stable euthyroidism by levothyroxine (L-T(4)) treatment. The results were also compared with those obtained from seven age-, sex- and body mass index-matched control subjects. METHODS: Heart rate variability was evaluated by autoregressive power spectral analysis (PSA). This method allows reliable quantification of low frequency (LF) and high frequency (HF) components of the heart rate power spectral density. These are considered to be under mainly sympathetic and purely parasympathetic control respectively. In addition, heart rate variations during deep breathing, lying to standing, and Valsalva's manoeuvre were assessed. RESULTS: PSA showed a sharp reduction in the HF (parasympathetic) component in hypothyroid subjects compared with controls (lying, 29.4+/-5.4 vs 47.7+/-6.3 normalized units (NU) (means +/- s.e.m.), P<0.05; standing, 14.0+/-3.5 vs 32.1+/-3.6NU, P<0.005). Conversely, the LF (mainly sympathetic) component was higher in hypothyroid subjects than in controls (lying, 61.6+/-6.4 vs 45.4+/-6.7 NU; standing, 71.7+/-8.0 vs 53.1+/-5.6NU), this difference being significant in the standing position. Hence, the LF/HF ratio, which is considered an index of sympathovagal balance, was increased in hypothyroid subjects while both lying (2.75+/-0.6 vs 1.16+/-0.3; P<0.05) and standing (10.0+/-3.7 vs 1.85+/-0.3; P<0. 02). Total heart rate variability, expressed as total power spectral density, was lower in hypothyroid patients than in control subjects, this difference being significant in the lying position (574+/-126 vs 2302+/-994ms(2), P<0.05). In patients re-examined after L-T(4) therapy, complete normalization of cardiovascular parameters was observed (LF/HF ratio, lying, 1.26+/-0.4; standing, 2.56+/-0.8, both P<0.01 vs baseline values). The response to conventional cardiovascular autonomic tests was not significantly different between hypothyroid patients and healthy controls, and did not change in patients after therapy. CONCLUSIONS: These results suggest that, contrary to the clinical picture, thyroid hormone deficiency is associated with an increased sympathetic influence on the autonomic cardiovascular system. The changes in sympathetic function could be explained by a secondary adaptation to an altered cardiovascular responsiveness.

scholarly journals Even slight movements disturb analysis of cardiovascular dynamics

1999 ◽  
Vol 277 (1) ◽  
pp. H261-H267 ◽  
Author(s):  
Jacques-Olivier Fortrat ◽  
Cédric Formet ◽  
Jean Frutoso ◽  
Claude Gharib
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Heart Rate Variability ◽  
Spectral Analysis ◽  
Low Frequency ◽  
Coarse Graining ◽  
Spectral Exponent ◽  
Spontaneous Movements ◽  
Frequency Components ◽  
Fractal Noise

We hypothesized that spontaneous movements (postural adjustments and ideomotion) disturb analysis of heart rate and blood pressure variability and could explain the discrepancy between studies. We measured R-R intervals and systolic blood pressure in nine healthy sitting subjects during three protocols: 1) no movement allowed, 2) movements allowed but not standing, 3) movements and standing allowed. Heart rate and blood pressure were not altered by movements. Movements with or without standing produced a twofold or greater increase of the overall variability of R-R intervals and of the low-frequency components of spectral analysis of heart rate variability. The spectral exponent β of heart rate variability (1.123 at rest) was changed by movements (1.364), and the percentage of fractal noise (79% at rest) was increased by standing (91%, coarse-graining spectral analysis). Spontaneous movements could induce a plateau in the correlation dimensions of heart rate variability, but they changed its nonlinear predictability. We suggest that future studies on short-term cardiovascular variability should control spontaneous movements.

Frequency characteristics of long-term heart rate variability during constant-routine protocol

2003 ◽  
Vol 285 (1) ◽  
pp. R171-R176 ◽  
Author(s):  
Naoko Aoyagi ◽  
Kyoko Ohashi ◽  
Yoshiharu Yamamoto
Keyword(s):  
Physical Activity ◽  
Heart Rate ◽  
Heart Rate Variability ◽  
Spectral Analysis ◽  
Core Body Temperature ◽  
Coarse Graining ◽  
Daily Routine ◽  
Crossover Frequency ◽  
Behavioral Factors

The effects of such behavioral factors as physical activity, food intake, and circadian rhythm on long-term heart rate variability (HRV) in humans remain poorly understood. We therefore studied their effects on HRV using a constant-routine protocol that included simultaneous core body temperature (CBT) correction. Seven healthy subjects completed the constant-routine and daily-routine protocols, during which HRV and CBT were continuously monitored. During the constant routine, subjects were kept awake for 27 h in a semirecumbent posture with minimal physical activity; small isocaloric meals were provided every 2 h. During the daily routine, subjects carried on their lives normally. Data were analyzed using generic spectral analysis based on a fast Fourier transform; coarse-graining spectral analysis was also used to eliminate periodicity due to the regular meals for raw HRV and for the CBT-corrected HRV without circadian and/or low-frequency ultradian components. The results showed that 1) the power spectra of HRV in the constant routine and daily routine had similar power-law scalings at frequencies above ∼10-3.5 Hz, while 2) below that crossover frequency, HRV was smaller in the constant routine than in the daily routine, with the difference becoming significant ( P < 0.05) at <10-4 Hz, 3) coarse-graining spectral analysis eliminated diet-induced peaks in generic spectral analysis-based HRV spectra during the constant routine and emphasized the crossover at ∼10-3.5 Hz, and 4) CBT correction did not alter the results. Below a frequency of ∼10-3.5 Hz (a period >1 h), HRV is strongly influenced by behavioral factors; above that crossover frequency, HRV is behavior independent, possibly reflecting an intrinsic regulatory system.

Blunted Cardiac Autonomic Responsiveness to Hypoxemic Stress in Healthy Older Adults

2003 ◽  
Vol 28 (4) ◽  
pp. 518-535 ◽  
Author(s):  
S. Deborah Lucy ◽  
John M. Kowalchuk ◽  
Richard L. Hughson ◽  
Donald H. Paterson ◽  
David A. Cunningham
Keyword(s):  
Older Adults ◽  
Heart Rate ◽  
Heart Rate Variability ◽  
Spectral Analysis ◽  
Spectral Power ◽  
Coarse Graining ◽  
Key Words Heart ◽  
Key Words Heart Rate ◽  
Age Related ◽  
End Tidal

Supine resting cardiac dynamics and responses to steady-state hypoxemia were investigated in six healthy older (59-72 yrs) adults using coarse-graining spectral analysis of heart rate variability (HRV) and were compared to six young (22-29 yrs) adults studied previously (Lucy et al<normal + trebuchet ms char,12 pt char, black char, condensed by 0.05 pt char>.,</normal + trebuchet ms char,12 pt char, black char, condensed by 0.05 pt char> 2000). End-tidal carbon dioxide pressure (PETCO2) was clamped at 1-2 mmHg above the usual resting value for 11 min of euoxia (PETO2100 mmHg), followed by 22 min of hypoxia (PETO2 55 mmHg). During euoxia, vagally mediated harmonic and fractal power of HRV of older adults was minimal. Hypoxia induced an increase in ventilation, p < 0.01, and heart rate, p < 0.05. The heart rate increase (mean ± SE) of 0.23 ± 0.08 beats•min−1 per 1% decrease in arterial O2 saturation was 25% of that demonstrated previously by young subjects, p < 0.001. In older adults, HRV spectral power remained unchanged during hypoxia, providing further evidence of an age-related blunting of cardiac autonomic function. Key words: heart rate variability, coarse-graining spectral analysis, cardiac vagal control, acute isocapnic hypoxia, dynamic end-tidal forcing (DEF) technique

scholarly journals Role of increased sympathetic activity in the genesis of ambulatory ischemia: Spectral analysis of heart rate variability

1996 ◽  
Vol 27 (2) ◽  
pp. 398-399
Author(s):  
Tohru Kaji ◽  
Tetsuro Kohya ◽  
Fumishi Tomita ◽  
Tomohide Ono ◽  
Akira Kitabatake
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
Spectral Analysis ◽  
Sympathetic Activity
Sign in / Sign up

Export Citation Format

Share Document