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  • 1
    Electronic Resource
    Electronic Resource
    Effects of thiopentone, etomidate and propofol on beat-to-beat cardiovascular signals in man (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Anaesthesia 48 (1993), S. 0 
    Details
    ISSN: 1365-2044
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Analysis of beat-to-beat fluctuations of heart rate and blood pressure is a promising new approach to the clinical diagnosis and management of alterations in cardiovascular regulation. We investigated the effects of three induction agents on beat-to-beat heart rate and blood pressure fluctuations in man. Beat-to-beat fluctuations were analysed by spectral analysis. Two spectral areas are of main interest. One area is centred on the respiratory frequency and shifts with changes in respiratory rate (High Frequency area). These high frequency flucuations in heart rate are caused by respiratory-induced blood pressure fluctuations, mediated by the vagus nerve through the baroreflex mechanism. Variability in the Low Frequency area, which occurs between 0.06 and 0.12 Hz is considered to be related to haemodynamic fluctuations due to the sympathetic baroreflex control loop of vasomotor activity and heart rate. Results from our study indicate that thiopentone, etomidate and propofol show considerable differences in their effects on beat-to-beat variability of heart rate and blood pressure. These differences can be explained by their specific effects on the cardiovascular system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2044.1993.tb07412.x
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  • 2
    Electronic Resource
    Electronic Resource
    The effect of oxprenolol dosage time on its pharmacokinetics and haemodynamic effects during exercise in man (1993)
    Springer
    European journal of clinical pharmacology 44 (1993), S. 171-176 
    Details
    ISSN: 1432-1041
    Keywords: Oxprenolol ; β-adrenoceptor blockade ; circadian rhythm ; haemodynamics ; pharmacokinetics ; exercise ; healthy volunteers ; kinetic-dynamic model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary We have studied the effect of dosage time of oxprenolol (Trasicor®) on its pharmacokinetics and pharmacodynamics in six healthy volunteers. The drug effects measured were heart rate and systolic blood pressure during exercise. Oxprenolol was taken orally at 08.00 h, 14.00 h, 20.00 h, and 02.00 h in randomized order, with 1 week between successive doses. There were differences in the pharmacokinetics of oxprenolol for the ratio between the apparent volume of distribution and systemic availability (P=0.04) and for elimination half-life (P=0.006). Both were lowest after administration at 14.00 h (163 (77) l and 1.2 (0.6) h; mean (SD)) and highest after administration at 02.00 h (229 (100) l, and 1.7 (0.6) h). The systolic blood pressure during exercise before oxprenolol did not vary with dosage time, but heart rate during exercise before intake was lowest before dosage time 08.00 h and highest before dosage time 20.00 h (P=0.03). The time-course of heart rate during exercise after oxprenolol was described by a model that incorporated the factors drug concentration and spontaneous diurnal variation. EC50 and Emax did not vary between dosage times. The spontaneous diurnal variation in heart rate during exercise was unaffected by oxprenolol, leading to an apparently greater effect of oxprenolol during the night than during the day.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00315476
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  • 3
    Electronic Resource
    Electronic Resource
    A simplified sliding-filament muscle model for simulation purposes (1973)
    Springer
    Biological cybernetics 12 (1973), S. 94-101 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract A muscle model based on the sliding filament concept is put forward. The model is simplified in such a way that it may easily be simulated on a computer (analog or digital). The model shows quite a few muscle properties rather well e.g. Hill's relation, quick-stretch and quick-release series elasticity and some dynamic transfer properties. It is found that, using an antagonistic muscle model pair and an appropriate load, realistic arm movements can be simulated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00272465
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  • 4
    Electronic Resource
    Electronic Resource
    Pharmacokinetic-pharmacodynamic modelling of oxprenolol in man using continuous non-invasive blood pressure monitoring (1988)
    Springer
    European journal of clinical pharmacology 34 (1988), S. 395-400 
    Details
    ISSN: 1432-1041
    Keywords: oxprenolol ; beta-blockade ; concentration-effect relationship ; non-invasive monitoring ; exercise test ; blood pressure monitoring ; healthy volunteers ; predictive model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The relationship between the plasma concentration of oxprenolol and its haemodynamic effects during physical exercise was studied in 6 healthy volunteers, in whom BP and heart rate (HR) were continuously monitored by non-invasive techniques (Fin-A-Press-Tonometer) during repeated three-minute exercise periods for 8 h after treatment. Using the fitted pharmacokinetic curve, the drug effect was related to its plasma concentration using the Emax model. The mean EC50 for the relationship between drug concentration and heart rate during exercise (HRex) was 73.1 ng/ml, and for systolic blood pressure during exercise (SBPex) it was 112.7 ng/ml. Emax was 29.0% for HRex, and 33.2% for SBPex. There were no consistent differences between the parameters for the effects on HRex and SPBex. Thus, using a new, non-invasive technique for continuous measurement of blood pressure, the effect of a beta-adrenoceptor blocking drug on SBPex was described with similar accuracy as its effect on HRex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00542442
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  • 5
    Electronic Resource
    Electronic Resource
    Differences in circulatory control in normal subjects who faint and who do not faint during orthostatic stress (1993)
    Springer
    Clinical autonomic research 3 (1993), S. 117-124 
    Details
    ISSN: 1619-1560
    Keywords: Blood pressure ; Pulse contour method ; Spectral analysis ; Standing up ; Syncope
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We have determined if there are differences in normal subjects who fainted and those who did not faint during prolonged standing. We studied the short-term orthostatic responses in relation to heart rate, blood pressure measured by Finapres, left ventricular stroke volume analysed by pulse contour method, cardiac output and systemic vascular resistance, and also postural blood pressure and heart rate variability as assessed by spectral analysis. Thirteen healthy males without a history of syncope were studied. Three fainted after 10–13 min standing; the ten non-fainters remained upright for 20 min. The initial (first 30 s) postural circulatory adjustment was comparable for blood pressure but the rebound bradycardia was smaller in the fainters (heart rate at 22 s amounted to +13 ±10 beats/min above control vs. +1 ±5 beats/min in the non-fainters). Upright heart rate at 2 min standing was higher in the fainters (+31 ±2 beats/min vs. +20 ±5 beats/min), and blood pressure at 7 min standing was lower (−2/+5/+8 ± 5/5/5 mmHg vs. +11/+13/+16 ± 10/6/5 mmHg). The responses of stroke volume and cardiac output were comparable but systemic vascular resistance gradually decreased in the fainters from 5 min standing to the onset of fainting (+4 ±13% vs. +33 ±19% at 7 min standing). In fainters, the variability in upright blood pressure around 0.1 Hz was larger (8.8 mmHg2/Hz for diastolic blood pressure vs. 5.7 ±1.5 mmHg2/Hz in non-fainters). In conclusion, the circulatory adjustments to active standing in fainters is different from non-fainters, as they lose vasoconstrictor tone after 5 min of standing despite an increase in blood pressure variability and heart rate which suggest increased sympathetic activity. Whether there are other opposing factors, which include vasodilator substances, is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01818996
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  • 6
    Electronic Resource
    Electronic Resource
    Postural dizziness and transient hypotension in two healthy teenagers (1991)
    Springer
    Clinical autonomic research 1 (1991), S. 281-287 
    Details
    ISSN: 1619-1560
    Keywords: Teenage ; Dizziness ; Continuous non-invasive blood pressure determination ; FinapresTM
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Neurocardiovascular control during postural change was investigated in two teenage females with complaints of dizziness almost immediately on standing up. Blood pressure and heart rate were monitored continuously with a FinapresTM device. On standing there was a brief but marked fall in blood pressure between 5–10 s after the onset of the manoeuvre. The maximum fall in systolic and diastolic blood pressure was 65 mmHg and 40 mmHg respectively in the first subject, and 58mmHg and 29 mmHg respectively in the second subject. In both, postural tachycardia was present after 1–2 min of standing with heart rate increasing by up to 39 beats/min in the first subject and 60 beats/min in the second subject. On a follow-up examination 3 years later these changes had disappeared in the first subject while they persisted in the second subject, when she was studied two years later. We conclude that in these patients initial postural dizziness is related to an excessive fall in blood pressure upon standing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01819833
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  • 7
    Electronic Resource
    Electronic Resource
    Spectrum of a series of point events, generated by the integral pulse frequency modulation model (1985)
    Springer
    Medical & biological engineering & computing 23 (1985), S. 138-142 
    Details
    ISSN: 1741-0444
    Keywords: Event series ; IPFM model ; ITT model ; Spectral analysis ; Spike signals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The paper deals with the relationship between the spectra of the input signal and the output signal of the integral pulse frequency modulation (IPFM) model. The IPFM model is a physiologically attractive device for the conversion of a continuous input signal into an output signal, consisting of a series of events (e.g. nerve spikes, heart beats). Two different spectra are used in the analysis of a series of events; the interval spectrum and the spectrum of counts. The latter spectrum is known analytically for the event series belonging to a sinusoidal input signal. An approximation to the interval spectrum of this series is presented. Using data from a simulated IPFM model, it is shown that, for an input signal consisting of the sum of two sinusoids, terms at sum and difference frequencies appear in the interval spectrum but not in the spectrum of counts. However, the spectrum of counts is contaminated by sidebands of the mean repetition frequency. It is concluded that in general the spectral properties of the input signal cannot be recovered fully from the interval spectrum, nor from the spectrum of counts, the more so as physiological series of events will seldom be generated by an ideal IPFM model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456750
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  • 8
    Electronic Resource
    Electronic Resource
    Relationships between short-term blood-pressure fluctuations and heart-rate variability in resting subjects II: a simple model (1985)
    Springer
    Medical & biological engineering & computing 23 (1985), S. 359-364 
    Details
    ISSN: 1741-0444
    Keywords: Baroreflex ; Blood-pressure fluctuations ; Cross-spectrum ; Heart-rate variability ; Mathematical models ; Spectral analysis ; Windkessel model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract A simple model of the beat-to-beat properties of the cardiovascular system is used to interpret the results of spectral analysis of blood-pressure and interval data. The model consists of two equations, one representing the fast regulation of interval by the systolic pressure (baroreflex), the other one representing a Windkessel approximation of the systemic arterial system. The model, when applied to interval and blood-pressure data from resting subjects, explains the lack of respiratory variability in the diastolic pressure values. The baroreflex equation seems to describe the data only in the region of respiratory frequencies. The shape of the phase spectrum of systolic pressures against intervals is modelled by difference equations, but no physiological interpretation of these equations is given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02441590
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  • 9
    Electronic Resource
    Electronic Resource
    Relationships between short-term blood-pressure fluctuations and heart-rate variability in resting subjects I: a spectral analysis approach (1985)
    Springer
    Medical & biological engineering & computing 23 (1985), S. 352-358 
    Details
    ISSN: 1741-0444
    Keywords: Blood pressure ; Blood-pressure fluctuations ; Cross spectrum ; Heart rate ; Heart-rate variability ; Power spectrum ; Spectral analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract A method to attribute the short-term variability of blood pressure and heart rate of resting subjects to their various causes, using spectral techniques, is presented. Power spectra and cross-spectra are calculated for beat-to-beat values of R-R interval and blood pressure from subjects who were seated in a comfortable chair. Interval values as well as systolic, mean and pulse pressures show variations linked to respiration and to the so-called 10 s rhythm. The diastolic pressure values are scarcely influenced by respiration in the normal respiratory range (0·20–0·35 Hz), but do show 10 s variability. Relationships between pressure and interval variability which indicate that the 10 s variability in systolic pressure leads the interval variation by two to three beats become manifest in cross-spectra; however, no such lag is found between the respiration-linked variations in systolic pressure and intervals. It is argued that the technique presented provides a critical test for models of the fast regulation of the cardiovascular system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02441589
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