Biomedical subjects

N H Holstein-Rathlou

Publications and source records attributed to N H Holstein-Rathlou.

102 records · Page 6Linked to original sources

PubMed1985

The predictive value of bronchial histamine challenge in the diagnosis of bronchial asthma.

A prospective survey aiming to study the predictive value of bronchial histamine challenge was performed on 151 patients with a forced expiratory volume1 (FEV1) above 60% of predicted. According to variations in peak expiratory flow rate (PEFR) and medical history the patients were classified as asthmatics (n = 97) or non-asthmatics (n = 54). The diagnostic properties of the challenge were calculated using the statement of Baye. Considering PC20 values below 4.00 mg/ml as positive, the predictive value of a positive test was about 0.80 and the predictive value of a negative about 0.76. When PC20 was below 0.125 mg/ml the predictive value of a positive test was 1.00, but an increase in PC20 in the range from 4.00 to 16 mg/ml did not increase the predictive value of a negative test. In this study the prevalence of asthma was about 0.6. We therefore conclude that bronchial histamine challenge is a valuable test for detection and exclusion of bronchial asthma, when the prevalence of the disease is high. In populations with a lower frequency of bronchial asthma the diagnostic value of a positive bronchial challenge will be negligible.

Adolescent↗

PubMed1985

Differences in tubuloglomerular feedback--oscillatory activity between spontaneously hypertensive and Wistar-Kyoto rats.

In 12 to 18-week-old Wistar-Kyoto rats, regular oscillations in the proximal intratubular pressure occurred spontaneously. The median frequency was 29.7 mHz (range 20-46.7 mHz). In spontaneously hypertensive rats, spontaneous oscillations also occurred, but these were highly irregular. In both strains, oscillations could be elicited by free flow microperfusion with artificial tubular fluid. When furosemide was added to the artificial tubular fluid in a concentration of 0.1 mmol/l, the oscillations were abolished in both strains of rats. It is concluded that, in both strains of rats, the oscillatory phenomena depend upon tubuloglomerular feedback activity, and that the differences in the oscillatory patterns between the two strain of rats represent a difference in the parameter setting of the tubuloglomerular feedback system.

Animals↗

PubMed1985

Effects of acute volume loading on kidney function in patients with essential hypertension, as estimated by the lithium clearance method.

This study investigated the mechanism underlying the exaggerated natriuresis seen in patients with essential hypertension. The study used the lithium clearance method, which permits accurate determination of both proximal and distal sodium reabsorption in man. One litre of isotonic sodium chloride, intravenously (i.v.), produced a significant increase in sodium excretion in patients with essential hypertension, both during and after the infusion. This increase in sodium excretion was accompanied by a significant increase in the clearance of lithium, indicating an increased output of isotonic fluid from the proximal tubules. The calculated distal reabsorption of sodium increased during the natriuresis. In the normotensive controls, sodium excretion increased only after the infusion of 1 l isotonic saline. This was accompanied by a modest increase in absolute distal sodium reabsorption. However, when the amount of saline was increased to 2 l, similar changes to those seen in hypertensives given 1 l of saline occurred in normotensive subjects. Furthermore, chronic antihypertensive treatment abolished the phenomenon of exaggerated natriuresis. It is concluded that the exaggerated natriuresis represents the normal response to sodium loading being reset to a lower level. This resetting may be a secondary consequence of the high blood pressure, since lowering the pressure abolishes the phenomenon.

Adult↗

PubMed1982

Effects of halothane-nitrous oxide inhalation anesthesia and Inactin on overall renal and tubular function in Sprague-Dawley and Wistar rats.

Real function, plasma renin concentration (PRC) and prostaglandin (PG) excretion rate was studied in groups of Sprague-Dawley (SPRD) and Wistar (WIST) rats anesthetized with either Halothane-N2O or Inactin. Conscious rats were used as controls. A. In Halothane-N2O anesthesia inulin clearance (CIN) and absolute proximal reabsorption rate (APR) was moderately decreased (by about 20%), while renal plasma flow (RPF), urine flow and solute excretion remained unchanged as compared to conscious rats. There was a linear relationship between the reciprocal of the proximal occlusion time (OT) and CIN in Halothane anesthesia indicating that the proximal luminal diameter was constant and independent of CIN. B. Inactin anesthesia CIN was similarly reduced but APR was more depressed (by about 35%). RPF and solute excretion rate decreased only in SPRD rats, while urine flow was significantly reduced in both strains. 1/OT was invariant to changes in CIN indicating luminal diameter variations in proportion to CIN. Urinary PGE2-and PGF2 alpha excretion rates and PRC were moderately elevated in operated animals of both strains regardless of the anesthetics used. It is concluded that renal functional parameters in surgically prepared rats are more severely depressed by Inactin than by Halothane-N2O anesthesia. The gas anesthesia is equally well tolerated by both strains of rats.

Anesthesia, Inhalation↗

PubMed1981

Interaction between prostaglandins of the E-type with a urinary component from halothane anesthetized rats.

Prostaglandins of the E-type (PGE's) were found to react or combine with a urinary metabolite of Halothane yielding products which were left unrecovered during the purification procedure preceding specific radioimmunoassay of PGE2. The products were retained on sephadex LH-20 columns, and showed on thin layer silica gel plates (TLC) Rf values lower than those of the parent PGE-compounds. The product formation is supposed to involve the beta-hydroxyketone system of PGE, since PG's of the F and A type were unaffected. The product formation could be avoided by inducing anaesthesia with Hexobarbitone and maintaining the anaesthesia with Halothane-nitrous oxide or it could be reversed by adding barbiturates to urine samples obtained from animals anaesthetized with Halothane-nitrous oxide alone. The barbiturates effectively competed with PGE for the metabolite leaving PGE to behave normally on sephadex LH-20 and TLC, thus enabling us to evaluate correctly the PGE2 content by RIA.

Anesthetics↗

PubMed1981

Comparison of three measures of proximal tubular reabsorption: lithium clearance, occlusion time, and micropuncture.

Fractional lithium clearance (CLi/CIn), transit time-occlusion time (e-TT/OT), and late proximal tubular fluid-to-plasma inulin ratio [1/(TF/P)In] collected by micropuncture were determined successively in the same rat during Amytal anesthesia. The rats were examined during hydropenia, after partial aortic constriction, or during saline diuresis. There was a linear relationship (r = 0.80) between CLi/CIn and e-TT/OT. The 1/(TF/P)In ratio correlated closely with both CLi/CIn (r = 0.88) and e-TT/OT (r = 0.91) when intraluminal pressure was maintained at the free-flow level during fluid collection. If fluid collection was guided merely by the position of an oil droplet and the luminal diameter, the 1/(TF/P)In data were not correlated with either CLi/CIn or e-TT/OT. Over a wide range of proximal absolute and fractional reabsorption rates the technically simpler lithium clearance and TT/OT methods may provide data on proximal fractional reabsorption that are as accurate and reliable as data obtained by pressure-controlled micropuncture collection. Micropuncture carried out without pressure control provides highly inaccurate data and is clearly inferior to the other methods. These results are consistent with the possibility that lithium is reabsorbed exclusively by the proximal tubules, 17-20% being reabsorbed by the pars recta.

Absorption↗

PubMedDate not supplied

Nonlinear analysis of renal autoregulation under broadband forcing conditions.

Linear analysis of renal blood flow fluctuations, induced experimentally in rats by broad-band (pseudorandom) arterial blood pressure forcing at various power levels, has been unable to explain fully the dynamics of renal autoregulation at low frequencies. This observation has suggested the possibility of nonlinear mechanisms subserving renal autoregulation at frequencies below 0.2 Hz. This paper presents results of 3rd-order Volterra-Wiener analysis that appear to explain adequately the nonlinearities in the pressure-flow relation below 0.2 Hz in rats. The contribution of the 3rd-order kernel in describing the dynamic pressure-flow relation is found to be important. Furthermore, the dependence of 1st-order kernel waveforms on the power level of broadband pressure forcing indicates the presence of nonlinear feedback (of sigmoid type) based on previously reported analysis of a class of nonlinear feedback systems.

Animals↗

PubMedDate not supplied

Application of fast orthogonal search to linear and nonlinear stochastic systems.

Standard deterministic autoregressive moving average (ARMA) models consider prediction errors to be unexplainable noise sources. The accuracy of the estimated ARMA model parameters depends on producing minimum prediction errors. In this study, an accurate algorithm is developed for estimating linear and nonlinear stochastic ARMA model parameters by using a method known as fast orthogonal search, with an extended model containing prediction errors as part of the model estimation process. The extended algorithm uses fast orthogonal search in a two-step procedure in which deterministic terms in the nonlinear difference equation model are first identified and then reestimated, this time in a model containing the prediction errors. Since the extended algorithm uses an orthogonal procedure, together with automatic model order selection criteria, the significant model terms are estimated efficiently and accurately. The model order selection criteria developed for the extended algorithm are also crucial in obtaining accurate parameter estimates. Several simulated examples are presented to demonstrate the efficacy of the algorithm.

Algorithms↗

PubMedDate not supplied

Compact and accurate linear and nonlinear autoregressive moving average model parameter estimation using laguerre functions.

A linear and nonlinear autoregressive moving average (ARMA) identification algorithm is developed for modeling time series data. The algorithm uses Laguerre expansion of kernals (LEK) to estimate Volterra-Wiener kernals. However, instead of estimating linear and nonlinear system dynamics via moving average models, as is the case for the Volterra-Wiener analysis, we propose an ARMA model-based approach. The proposed algorithm is essentially the same as LEK, but this algorithm is extended to include past values of the output as well. Thus, all of the advantages associated with using the Laguerre function remain with our algorithm; but, by extending the algorithm to the linear and nonlinear ARMA model, a significant reduction in the number of Laguerre functions can be made, compared with the Volterra-Wiener approach. This translates into a more compact system representation and makes the physiological interpretation of higher order kernels easier. Furthermore, simulation results show better performance of the proposed approach in estimating the system dynamics than LEK in certain cases, and it remains effective in the presence of significant additive measurement noise.

Algorithms↗

PubMedDate not supplied

Approximate entropy and point correlation dimension of heart rate variability in healthy subjects.

The contribution of nonlinear dynamics to heart rate variability in healthy humans was examined using surrogate data analysis. Several measures of heart rate variability were used and compared. Heart rates were recorded for three hours and original data sets of 8192 R-R intervals created. For each original data set (n = 34), three surrogate data sets were made by shuffling the order of the R-R intervals while retaining their linear correlations. The difference in heart rate variability between the original and surrogate data sets reflects the amount of nonlinear structure in the original data set. Heart rate variability was analyzed by two different nonlinear methods, point correlation dimension and approximate entropy. Nonlinearity, though under 10 percent, could be detected with both types of heart rate variability measures. More importantly, not only were the correlations between these measures and the standard deviation of the R-R intervals weak, the correlation among the nonlinear measures themselves was also weak (generally less than 0.6). This suggests that in addition to standard linear measures of heart rate variability, the use of multiple nonlinear measures of heart rate variability might be useful in monitoring heart rate dynamics.

Adult↗

PubMedDate not supplied

Robust nonlinear autoregressive moving average model parameter estimation using stochastic recurrent artificial neural networks.

In this study, we introduce a new approach for estimating linear and nonlinear stochastic autoregressive moving average (ARMA) model parameters, given a corrupt signal, using artificial recurrent neural networks. This new approach is a two-step approach in which the parameters of the deterministic part of the stochastic ARMA model are first estimated via a three-layer artificial neural network (deterministic estimation step) and then reestimated using the prediction error as one of the inputs to the artificial neural networks in an iterative algorithm (stochastic estimation step). The prediction error is obtained by subtracting the corrupt signal of the estimated ARMA model obtained via the deterministic estimation step from the system output response. We present computer simulation examples to show the efficacy of the proposed stochastic recurrent neural network approach in obtaining accurate model predictions. Furthermore, we compare the performance of the new approach to that of the deterministic recurrent neural network approach. Using this simple two-step procedure, we obtain more robust model predictions than with the deterministic recurrent neural network approach despite the presence of significant amounts of either dynamic or measurement noise in the output signal. The comparison between the deterministic and stochastic recurrent neural network approaches is furthered by applying both approaches to experimentally obtained renal blood pressure and flow signals.

Algorithms↗

PubMedDate not supplied

Nonlinear analysis of renal autoregulation in rats using principal dynamic modes.

This article presents results of the use of a novel methodology employing principal dynamic modes (PDM) for modeling the nonlinear dynamics of renal autoregulation in rats. The analyzed experimental data are broadband (0-0.5 Hz) blood pressure-flow data generated by pseudorandom forcing and collected in normotensive and hypertensive rats for two levels of pressure forcing (as measured by the standard deviation of the pressure fluctuation). The PDMs are computed from first-order and second-order kernel estimates obtained from the data via the Laguerre expansion technique. The results demonstrate that two PDMs suffice for obtaining a satisfactory nonlinear dynamic model of renal autoregulation under these conditions, for both normotensive and hypertensive rats. Furthermore, the two PDMs appear to correspond to the two main autoregulatory mechanisms: the first to the myogenic and the second to the tubuloglomerular feedback (TGF) mechanism. This allows the study of the separate contributions of the two mechanisms to the autoregulatory response dynamics, as well as the effects of the level of pressure forcing and hypertension on the two distinct autoregulatory mechanisms. It is shown that the myogenic mechanism has a larger contribution and is affected only slightly, while the TGF mechanism is affected considerably by increasing pressure forcing or hypertension (the emergence of a second resonant peak and the decreased relative contribution to the response flow signal).

Animals↗