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P B Persson

Publications and source records attributed to P B Persson.

At least 55 records · Page 3Linked to original sources
PubMed1997

Frequency-response characteristics of autonomic nervous system function in conscious rats.

To characterize the efferent pathway from the hypothalamic paraventricular nucleus (PVN) to peripheral autonomic neurons and finally to selected effector organs, we stimulated the PVN in 10 conscious rats at frequencies ranging from 0.05 to 2.0 Hz. Simultaneously, blood pressure, heart rate, splanchnic sympathetic nerve activity, and mesenteric artery blood flow were measured. The sinus node of the heart responded to PVN stimulation via the parasympathetic pathway (during beta 1-adrenergic blockade) up to a stimulation frequency of 2.0 Hz, whereas the sympathetically mediated response (during muscarinic blockade) was limited to stimulation frequencies < 0.5 Hz. The splanchnic nerve responded to PVN stimulation with synchronous discharges up to stimulation frequencies of 2.0 Hz, whereas the oscillatory component of the vasoconstrictor response of the mesenteric artery was negligible beyond stimulation frequencies of 1.0 Hz. We conclude that sympathetic transmission to the heart is at least four times slower than parasympathetic transmission. In addition, the time-limiting step in sympathetic transmission from the hypothalamus to vascular smooth muscle contraction and pacemaker activity of the sinus node may be located at the site of synaptic transmission to the adrenergic receptors.

Animals↗
PubMed1997

Very low frequency oscillations in arterial blood pressure after autonomic blockade in conscious dogs.

The aim of this study was to investigate spontaneous variability of arterial blood pressure in conscious foxhounds in the absence of direct sympathetic and parasympathetic influences. Autonomic blockade was achieved by administration of the ganglionic blocking agent hexamethonium (n = 7). In contrast to the control group (n = 7), marked oscillations with a cycle length of 100 s (0.01 Hz) were observed. The relationship of the power densities of the oscillation band (0.01 +/- 0.005 Hz) to the total power increased threefold (0.213 +/- 0.007 vs. 0.057 +/- 0.005; P < 0.01). The 0.01-Hz oscillations typically commenced after some delay. To test whether the absence of the mechanoreceptor afferents was responsible for these fluctuations, we investigated an additional group of foxhounds that were subjected to total baroreceptor and cardiopulmonary receptor denervation (n = 7). Neither in this protocol, nor in a group subjected to denervation and ganglionic blockade (n = 6), did we observe sustained oscillations in this frequency range. Since the oscillations were not seen after combined afferent (mechanoreceptor denervation) and efferent (ganglionic) blockade, central oscillators as a source of the oscillations can be ruled out. A simple model of a circulating pressoric factor may explain the fluctuations, provided that there is a time delay between the stimulus and the release or action of the factor. The findings suggest that a circulating factor accounts for the 0.01-Hz oscillations, which is dependent on intact pathways from the cardiac receptors or baroreceptors to the central nervous system. This hypothesis is put forward since cardiopulmonary and baroreceptor denervation blocked the oscillations seen after ganglionic blockade.

Animals↗
PubMed1997

Linear and nonlinear properties of heart rate control in infants at risk.

The aim of this study was to test whether the heart rate (HR) control in infants at risk differs in comparison with healthy infants. Twelve former preterm infants suffering from bronchopulmonary dysplasia and 18 control infants, matched for their postconceptional age, were examined polygraphically during quiet and active sleep. HR, low-frequency (LF) power, high-frequency (HF) power, total power, and the ratio of LF to HF power (LF/HF) of the instantaneous HR spectra were calculated for linear analysis. The largest Lyapunov exponent (LLE) of the R-R interval time series was calculated to determine a nonlinear property of HR. Infants at risk had significantly lower LF power (median: 0.51 x 10(-3) vs. 1.16 x 10(-3) Hz2) and lower LF/HF (median: 1.05 vs. 1.94) during quiet sleep. LLE was positive, revealing low-dimensional chaotic behavior of HR control, and did not differ between both groups (median: quiet sleep, 0.05 bit/s vs. 0.06 bit/s; active sleep, 0.16 bit/s vs. 0.15 bit/s). Sleep state-related changes in spectral parameters and LLE were similar in both groups. In infants at risk, the lower LF/HF during quiet sleep can be interpreted in terms of changes in the rhythmic components of the sympathovagal balance of the autonomic system, which is an expression of linear properties of HR control. Conversely, the lack of differences in LLE between both groups indicates similar nonlinear properties of the control system.

Bronchopulmonary Dysplasia↗
PubMed1997

Spectrum analysis of cardiovascular time series.

The demand for noninvasive assessment of cardiovascular control parameters has promoted the use of spectrum analysis. These techniques have been applied on a broad basis; however, because of the abstract mathematical approach, spectrum analysis in physiology is still not fully accepted by some circles in the scientific community. Thus it is the goal of the following review to focus on the rationale for applying spectrum analysis in different fields of circulation research, which range from determining arterial baroreceptor reflex sensitivity to the early detection of heart allograft rejection. Within this scope, major findings regarding the physiological and pathophysiological regulation of the cardiovascular system are discussed. In addition, inherent limitations of these methods are made clear. Toward the end of this survey, a perspective is provided for the general readership.

Animals↗
PubMed1997

Flow versus pressure in the control of renin release in conscious dogs.

In Goldblatt hypertension, renal artery stenosis reduces renal arterial pressure (RAP) and renal blood flow (RBF) and thereby increases plasma renin activity (PRA) levels. Although it is clear that reduction in RAP stimulates renin, the decrease in RBF may contribute to higher PRA as well. However, it has hitherto never been possible to dissociate a decrease in RBF from a concomitant decrease in RAP. To overcome this restriction, we used two protocols. 1) RAP was reduced in a single step to 70 +/- 0.2 mmHg (N = 8). RBF followed the sudden fall in RAP within 15 s but subsequently took on initial levels. In contrast, renal venous PRA increased from 0.95 +/- 0.22 to 5.6 +/- 1.4 ng angiotensin I.ml-1.h-1 (P < 0.05) and remained at higher values even after RBF had regained control conditions. 2) Resonance between RAP and RBF was induced by superimposing slow sinusoidal RAP waves with a period length of 450 s (N = 9), leading to a phase shift of roughly 180 degrees (time delay, 241 +/- 12 s), i.e., RBF was maximal at minimal RAP. Under these conditions, renin release was only dependent on decrements in RAP (delay of only 27 +/- 8 s). In conclusion, RBF played no major role in renin release.

Animals↗
PubMed1997

Identification of a renin threshold and its relationship to salt intake in a patient with pure autonomic failure.

Animal studies have demonstrated a threshold below which renin release increases proportionally to a decrease in renal perfusion pressure. Demonstration of a similar mechanism in humans, however, has proved difficult, as any attempt to lower blood pressure below the putative renin threshold results in renin release mediated by reflex activation of the sympathetic nervous system. In this study, we report on our observations in a 71-year-old woman who presented with a 20-year history of faintness and syncope and was diagnosed as having pure autonomic failure. Graded head-up tilting resulted in a stepwise reduction in mean arterial blood pressure to a minimum of 54 mm Hg, with no signs of increased sympathetic activity. A fall in blood pressure below 80 mm Hg resulted in a distinct rise in plasma renin activity, and a similar threshold pressure was observed under both a 50- and a 100-mmol/d sodium chloride diet. Below the threshold, response to changes in perfusion pressure was proportionally greater under the 50-mmol/d diet than under a 100- or 200-mmol/d diet. These observations demonstrate that a pressure threshold for renin release at 10 to 15 mm Hg below ambient blood pressure, as described previously in animal studies, is also present in humans. The significance of this pressure-dependent mechanism of renin release for the long-term regulation of blood pressure and water and mineral balance in humans remains to be determined.

Aged↗
PubMed1996

Blood-pressure variability is buffered by nitric oxide.

The baroreflex constitutes the only hitherto known buffer of rapid blood pressure oscillations. In order to investigate the influence of nitric oxide (NO) and the sinoaortic and cardiopulmonary baroreflex pathways on the dynamic properties of blood pressure control, we determined the power spectra of 24-h blood pressure time series of conscious dogs. This was done in the intact state (n = 6), during blockade of NO synthesis via the false substrate NG-nitro-L-arginine ((L-NNA), 16.5 +/- 2 mg/kg body weight i.v., n = 5) and in animals devoid of baroreceptor reflexes (n = 5). After L-NNA, blood pressure (BP) increased by roughly 20 mmHg to 137 +/- 6 mmHg (P < 0.01), heart rate decreased from 97 +/- 6 to 68 +/- 3 beats/min (P < 0.01). The power of blood pressure variations within the frequency range 0.1-0.5 Hz was tripled by L-NNA (P < 0.05). By comparison total sinoaortic and cardiopulmonary denervation increased power of slower oscillations ( < 0.1 Hz) by a factor of 4.7 (P < 0.05). Thus, NO and the baroreceptor reflex both play an important role as physiological blood pressure buffers, NO for rapid (0.1-0.5 Hz) and the baroreflex for slower fluctuations ( < 0.1 Hz).

Animals↗
PubMed1996

Development of heart rate power spectra reveals neonatal peculiarities of cardiorespiratory control.

Postnatal adaptation should be associated with changes in cardiac rhythmic behavior. To examine the development of heart rate variability, instantaneous heart rate (IHR) and the corresponding breathing signals of 16 healthy infants were analyzed. This was pursued by use of fast Fourier transformation beginning with the 1st day until the 6th mo of life. Power in the low-frequency range (LF, 0.02-0.2 Hz) and high-frequency range (HF, 0.2-1.5 Hz), total power (TP), the quotient LF/HF, and the frequency of the peak in LF and HF (LFF and HFF, respectively) were derived from the IHR spectrum. The peak frequency in HF (RF) was detected in the respiratory spectrum. Power and frequency of IHR rhythms undergo a marked development. TP, LF, and HF are lowest from the end of the 1st mo until the 2nd mo. LF predominates over HF, with LF/HF reaching its peak during 1- to 2-mo period. HF, recording respiratory related rhythms is negatively correlated with the breathing rate (BR). HFF and RF both show an increasing tendency during the 1st mo followed by a decrease down to the 6th mo. However, HFF is lower than RF if BR is high, mainly during the first 2 mo. The distinct changes in BR and its important influence on the IHR spectrum underscore the importance of monitoring respiration as a further measure in the diagnosis of infants. LFF is on average between 0.075 and 0.095 Hz, exhibiting an irregular course with minimum at the 10th, 21st-28th, and 90th day being apparent. The developmental pattern of LFF may by interpreted in terms of the maturation of the nervous system involved in the generation of circulatory rhythms.

Aging↗
PubMed1996

Modulation of cardiovascular control mechanisms and their interaction.

It is generally held that the role of a specific control element can only be understood within its physiological environment. The reviewed studies make it clear that there is a potent interplay between locally produced substances such as adenosine, nitric oxide, prostaglandins, and various others all interacting with the central level of control. This can occur at central sites (e.g., nitric oxide in the brain) or in the periphery (e.g., neural influence on autoregulation). The interactions are more or less pronounced during specific physiological challenges. Furthermore, several of these interactions are altered under pathological circumstances, and in some cases, the interactions seem to maintain or even augment the severity of disease. When more than three parameters participate in an interaction, the resulting regulation may become extremely complex. If these parameters are nonlinearly coupled with each other, the only way to shed light onto the nature of control network is by treating it as a black box. With the use of spectral analysis or nonlinear methods, it is possible to disentangle the fundamental nature of the system in terms of the complexity and stability. Therefore, modern developments in cardiovascular physiology utilizing these techniques, some of which are derived from the "chaos theory," are reviewed.

Animals↗
PubMed1996

Chaos in blood pressure control.

A number of control mechanisms are comprised within blood pressure regulation, ranging from events on the cellular level up to circulating hormones. Despite their vast number, blood pressure fluctuations occur preferably within a certain range (under physiological conditions). A specific class of dynamic systems has been extensively studied over the past several years: nonlinear coupled systems, which often reveal a characteristic form of motion termed "chaos". The system is restricted to a certain range in phase space, but the motion is never periodic. The attractor the system moves on has a non-integer dimension. What all chaotic systems have in common is their sensitive dependence on initial conditions. The question arises as to whether blood pressure regulation can be explained by such models. Many efforts have been made to characterise heart rate variability and EEG dynamics by parameters of chaos theory (e.g., fractal dimensions and Lyapunov exponents). These method were successfully applied to dynamics observed in single organs, but very few studies have dealt with blood pressure dynamics. This mini-review first gives an overview on the history of blood pressure dynamics and the methods suitable to characterise the dynamics by means of tools derived from the field of nonlinear dynamics. Then applications to systemic blood pressure are discussed. After a short survey on heart rate variability, which is indirectly reflected in blood pressure variability, some dynamic aspects of resistance vessels are given. Intriguingly, systemic blood pressure reveals a change in fractal dimensions and Lyapunov exponents, when the major short-term control mechanism--the arterial baroreflex--is disrupted. Indeed it seems that cardiovascular time series can be described by tools from nonlinear dynamics [66]. These methods allow a novel description of some important aspects of biological systems. Both the linear and the nonlinear tools complement each other and can be useful in characterising the stability and complexity of blood pressure control.

Animals↗
PubMed1996

Linear and non-linear properties of heart rate in postnatal maturation.

OBJECTIVE: An investigation was made of how postnatal maturation of cardiac control can be described by linear and non-linear methods of time series analysis. METHODS: Sixteen healthy and term newborns were studied during their first 6 months of life. Power spectrum analysis including total power (TP), low frequency power (LF), high frequency power (HF) and LF/HF ratio were performed on the instantaneous heart rate (IHR) time series and mean heart rate (HR) was derived. The largest Lyapunov exponent (LLE) was calculated using a modified Wolf algorithm and checked by means of the surrogate-data test. RESULTS: There is an age dependency for the parameters LLE, HR, TP, HF, LF, LF/HF for active and LLE, HR, TP, HF, LF/HF for quiet sleep. HR is characterised by a steep increase between the 5th and 7th day. HF demonstrates a distinct development with high values around the first week and 90-180th day and low values around the 10-60th day. TP, LF and LF/HF show significantly higher values in active sleep in comparison to quiet sleep. For all ages and sleep stages, positive LLE were found, indicating sensitivity to initial conditions, a hall-mark of chaos. For the period between the 7 and 90th days of life, the LLE for active sleep took on larger values compared with the LLE of quiet sleep. CONCLUSIONS: This study shows that by linear as well as non-linear analysis one can reveal the complexity of the IHR development in humans and may gain insight into the system controlling the heart during the period considered. The positive LLE indicate that there is a non-linear component in the heart rate control. There is no "straight line" development for the parameters analysed within the first 6 months. This may result from manifold influences on the autonomic system, due to structural and functional maturation in this period of life.

Heart↗
PubMed1995

On the origin of low-frequency blood pressure variability in the conscious dog.

1. Baroreceptor denervation increases blood pressure variability below 0.1 Hz. This study was undertaken to determine to what extent these fluctuations originate from the central nervous system or from cardiovascular sources. 2. Blood pressure was recorded at a rate of 10 Hz for approximately 3.5 h in conscious, resting dogs. Power density spectra were calculated from all 2(17) points of each recording session and integrated between 0.0002 and 0.1 Hz. 3. Blockade of the afferent limb of the baroreceptor reflex by surgical denervation of sinoaortic and cardiopulmonary afferents (Den; n = 6) significantly increased integrated power more than sixfold compared with a control group (n = 11). 4. Impairment of the efferent limb in non-deafferented dogs by either alpha 1-adrenergic blockade with prazosin (Praz; n = 7) or ganglionic blockade with hexamethonium (Hex; n = 6) failed to raise variability. 5. Both prazosin (n = 6) and hexamethonium (n = 3) reduced the increased variability in denervated dogs. 6. In non-deafferented dogs receiving hexamethonium, elevation of mean blood pressure to the hypertensive level of the Den group, by a continuous infusion of noradrenaline (n = 4), did not change the variability. 7. It is concluded that in the absence of changes in posture, most of the increased blood pressure variability after baroreceptor denervation is derived from the central nervous system. 8. Direct comparison of power spectra of the Den (total variability) and Hex groups (variability derived from the cardiovascular system only) suggests that the central nervous system is also the prevalent source of low-frequency blood pressure variability in intact animals.

Animals↗
PubMed1995

Modulation of erythropoietin formation by changes in blood volume in conscious dogs.

1. A possible influence of the filling of the circulatory system on the plasma concentration of erythropoietin, which is the major regulator of erythrocyte formation, was investigated in conscious dogs. 2. Over an experimental period of 5 h, the animals were subjected to either haemorrhage (hypovolaemia), blood volume expansion (hypervolaemia), or exchange transfusion of blood with dextran (isovolaemic anaemia). 3. A reduction of blood volume by 20% induced by haemorrhage increased plasma erythropoietin levels approximately 1.5-fold in the absence of significant changes in haematocrit. 4. An expansion of blood volume by 12% induced by an intravenous infusion of dextran did not change plasma erythropoietin levels, although the haematocrit decreased by 0.04. 5. A reduction of the haematocrit by 0.12 in the absence of changes in blood volume induced by an isovolaemic exchange transfusion (dextran vs. blood) increased plasma erythropoietin levels approximately 3-fold. 6. Total renal oxygen supply did not change in any of the three experimental protocols. 7. These data indicate that in dogs the erythropoietin production rate is modulated by changes in blood volume, and suggest a possible role of erythropoietin in the regulation of blood volume.

Anemia↗
PubMed1995

Does low frequency power of arterial blood pressure reflect sympathetic tone?

We tested whether power spectral analysis of arterial blood pressure (ABP) is a feasible tool to detect differences in peripheral sympathetic nerve activity in normotensive and hypertensive rats with differing basal sympathetic tones. Nine Wistar Kyoto rats (WKY), 10 Sprague-Dawley rats (SD), 10 spontaneously hypertensive rats (SHR) and 9 hypertensive transgenic rats harbouring the mouse Ren-2 gene (TGR) were chronically instrumented with femoral artery catheters and nerve electrodes around the sympathetic major splanchnic nerve. Two days after surgery ABP and splanchnic nerve activity (SpNA) were recorded in the conscious state during basal conditions as well as during alpha 1-adrenergic receptor blockade. Power spectra and squared coherence in the low (LF, 0.02-0.20 Hz), mid (MF, 0.20-0.80 Hz) and high (HF, respiration peak +/- 0.3 Hz) frequency bands were calculated for ABP and SpNA. Mean blood pressure in SHR (133 +/- 8 mmHg) and TGR (142 +/- 8 mmHg) was significantly higher (P < 0.05) than in WKY (115 +/- 3 mmHg) and SD (95 +/- 4 mmHg). SpNA in SHR was higher than in WKY (23.4 +/- 6.4 microV vs. 11.6 +/- 0.8 microV, P < 0.05) while SpNA in TGR was lower than in SD (20.1 +/- 3.9 microV vs. 28.8 +/- 4.2 microV, P < 0.05). LF and MF components of ABP variability were not significantly higher in those rats with high sympathetic tones. However, alpha 1-adrenergic receptor blockade reduced LF and MF components of ABP and SpNA in all strains except SHR. LF and MF coherence was not greater in rats with high sympathetic tones than in those with low sympathetic tones. The reduction of LF and MF components of ABP variability by alpha 1-adrenergic receptor blockade indicates an important contribution of peripheral sympathetic nerve activity to LF and MF blood pressure variability on an acute basis. However, the lack of higher LF and MF power in the ABP spectra of those rats with high SpNA together with the finding that LF and MF coherence was not higher in those rats with high SpNA led to the conclusion that LF and MF spectral components of ABP do not appear to be suitable markers for the prevailing sympathetic nerve activity.

Adrenergic alpha-1 Receptor Antagonists↗