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Modulation of pulmonary arterial input impedance during transition from inspiration to expiration
No full textWe investigated whether respiration influences pulmonary arterial input impedance during transition from inspiration to expiration in five anesthetized, spontaneously breathing dogs. Impedance (Z) was separately assessed for heart beats occurring in inspiration, in expiration, and during the transition from inspiration to expiration (transitional beat). Transitional beats were scored by the ratio between the fraction of beat falling in expiration and the total beat duration [expiratory fraction (E-fr)] to quantify their position within the transition. In transitional beats, input resistance linearly increased with Es; Z modulus at the heart-rate frequency (f(HR)) decreased up to -50% for E-fr = 50%. Z phase at f(HR) was greater than in inspiration for E-fr 50%. Unlike blood flow velocity, mean value and first harmonic of pulmonary arterial pressure were correlated to E-fr and paralleled the changes of input resistance and Z at f(HR). This indicates that respiration influences Z through modifications in arterial pressure. The evidence of important respiratory influences on Z function may help the pathophysiological interpretation of dysfunctions of the right heart pumping action, such as the so-called cor pulmonale
Effects of sino-aortic denervation on spectral characteristics of blood pressure and pulse interval variability: A wide-band approach
No full textSino-aortic denervation (SAD) is employed in cats to evaluate the baroreflex influence on blood pressure (BP) and pulse interval (PI) spectral components from 0 . 00008 to 0 . 9 Hz as assessed by FFT wide-band spectra and their 1/f modelling; and the linear coupling between BP and PI and between systolic and diastolic BP as assessed by coherence analysis. Specific procedures have been developed to obtain an effective smoothing of spectra and coherence functions. SAD induced an increase in BP powers from 0 . 03 to 0 . 0006 Hz and a power reduction of most of the remaining BP components; a reduction of PI powers at all frequencies; marked deviations of BP spectra from the 1/f trend; a reduction of the coherence between BP and PI from 0 . 12 to 0 . 5 Hz and a coherence enhancement at lower frequencies. These findings indicate that the arterial baroreflex modulates both fast and slow spectral components of BP and PI; homogeneously enhances PI fluctuations at all frequencies; produces differentiated effects on BP fluctuations along the frequency axis; and at low frequencies exerts the buffering action on BP through strategies which reduce the BP-PI linear link
Dynamic detection of rhythmic oscillations in heart-rate tracings: A state-space approach based on fourth-order cumulants
No full textThis paper presents a new procedure specifically aimed at providing a dynamical detection of the oscillations occurring in long-term heart-rate (HR) tracings. The procedure is based on a time-variant state-space modelling of the fourth-order cumulants of the HR signal. The state-space estimator was selected because of its demonstrated capability to distinguish between deterministic and stochastic components of the signal, while the fourth-order cumulants of the signal were used as input of the model to further reduce adverse effects of coloured, white and 1/f Gaussian noise possibly present in the input data. The procedure was tested by the analysis of simulated signals and its performance was compared with the results obtained by state-space modelling applied directly on the test signals (instead of on the fourth-order cumulants of the signals) and by the more traditional auto-regressive modelling. The comparison has shown a clear superiority of the proposed procedure over the other techniques in discriminating deterministic oscillations from coloured noise. Finally, the applicability of the procedure to biological data was verified by analysing five experimental HR tracings recorded in normal subjects during laboratory and daily life conditions
Broadband spectral analysis of blood pressure and heart rate variability in very elderly subjects
No full textSystolic blood pressure (SEP) variability is increased and R-R interval variability is reduced in the elderly. Little is known, however, about how SEP and R-R interval variabilities change in the very elderly. More important, however, it is not known which frequency components of SEP and R-R interval variability are affected significantly. We addressed this issue in subjects older than 70 years by broadband spectral analysis, which allows all variability components from the lowest to the highest frequency to be considered. In 20 very elderly normotensive subjects (mean+/-SD age, 78.1+/-6.8 years) and 28 normotensive adult subjects (36.1+/-7.1 years), noninvasive finger blood pressure and R-R intervals were recorded continuously for 30 minutes in the supine position and 15 minutes in the upright position. SEP and R-R interval power spectral densities were computed over the entire frequency region between 0.005 Hz (0.007 Hz in the upright position) and 0.5 Hz. Overall SEP variability (SD) was greater and overall R-R interval variability was less in very old subjects than in adult subjects. All spectral R-R interval powers were reduced significantly in very elderly individuals. The spectral SEP powers were greater in the very elderly group than in the adult group only in the very-low-frequency range (<0.04 Hz). This was true in the supine and the standing positions. With subjects in the standing position, the shape of the broadband spectra differed in the very old and adult subjects because in the former group the increase in SEP and R-R interval power around 0.1 Hz that was seen in the latter was blunted. Therefore, in very elderly subjects a reduction in overall R-R interval variability is accounted for by a reduction in all of its frequency components. The accompanying increase in overall BP variability, however, results from a nonhomogeneous behavior of its frequency components, which consists of an increase in the very low frequency and a concomitant reduction in the higher frequency powers. The mechanisms responsible for these changes may be complex, but at least they may in part reflect the baroreflex impairment and autonomic dysfunction that characterize aging
REDUCED BAROREFLEX SENSITIVITY WITH AGING - DYNAMIC EVALUATION BY COMPUTER-ANALYSIS OF 24-H CONTINUOUS BLOOD-PRESSURE RECORDINGS IN HUMANS
No full textBroad band spectral analysis in the evaluation of blood pressure and heart rate variability in the very elderly
No full textEFFECTS OF BETA-BLOCKADE ON BAROREFLEX SENSITIVITY - DYNAMIC EVALUATION BY ANALYSIS OF 24-H INTRAARTERIAL AMBULATORY BLOOD-PRESSURE RECORDINGS IN HYPERTENSIVE SUBJECTS
No full textDoes spontaneous respiration alter pulmonary artery input impedance?
No full textThe aim of this study was to determine whether spontaneous respiration influences pulmonary artery input impedance, a question that has received little attention in the literature. Impedance values were assessed during three different phases of the respiratory cycle, namely inspiration, expiration and postexpiration (i.e. the null respiratory flow period between expiration and the next inspiration) in five anaesthetized spontaneously breathing dogs, Firstly, impedance values during postexpiration were taken as the reference baseline, and compared with values obtained during inspiration and expiration, Then, differences between values in inspiration and in expiration were tested, taking impedance during inspiration as the baseline, Differences with respect to postexpiration were found for three parameters of input impedance: input resistance, characteristic impedance, and the frequency at the first zero-crossing of the impedance phase from negative to positive values (fcross), Input resistance was significantly lower in inspiration (85% of the baseline), characteristic impedance was significantly greater in inspiration and in expiration (112 and 119% respectively), and fcross was significantly lower in expiration (89%), By contrast, only input resistance differed significantly when inspiration was compared to expiration. Therefore, spontaneous respiration was shown to influence input impedance significantly, The observed changes in characteristic impedance and fcross might be explained by a stiffening of the pulmonary artery wall, due to neural and/or mechanical factors, during inspiration and expiration
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