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Biomedical subjects

M van der Heijden

Publications and source records attributed to M van der Heijden.

11 recordsLinked to original sources
PubMed2006

Effect of prior statin therapy on capillary permeability in the lungs after cardiac or vascular surgery.

Cholesterol-lowering statins can ameliorate severe forms of vascular hyperpermeability in experimental studies, and may thereby ameliorate acute lung injury and sepsis. It is unknown whether this also applies to humans. This study aimed to define whether or not prior statin therapy reduces mild post-operative increases in pulmonary capillary protein permeability associated with acute lung injury after cardiac or major vascular surgery. A prospective observational study was performed in an intensive care unit of a university hospital on 64 patients, 37 after elective cardiac and 27 after major vascular surgery, of whom 68 and 44%, respectively, had received prior statin therapy. A mobile probe system was used to measure the pulmonary leak index (PLI), i.e. the transvascular transport rate of gallium-67-radiolabelled transferrin. For all of the patients together, the mean PLI did not differ between the statin and control groups (22.9 versus 24.4 x 10(-3) min(-1)). The prevalence of an elevated PLI was 57% in the statin and 59% in the control group. Subgroup analysis did not reveal significant differences caused by statins in the PLI of these patients. Prior statin therapy neither has an adverse effect on mildly increased pulmonary capillary permeability in patients after cardiac or major vascular surgery nor does it ameliorate this increased capillary permeability.

Adult↗
PubMed1999

Masking with interaurally delayed stimuli: the use of "internal" delays in binaural detection.

Detectability of 500-Hz tones was measured in the presence of broadband masking noise using three types of binaural conditions. In the first, the masker was presented diotically and the tone was interaurally delayed. In the second, the masker was interaurally delayed and the 500-Hz tone was presented either in phase (S0) or out of phase (S pi). In the third, the masker consisted of the sum of two independent noises having interaural delays of equal magnitude and opposite sign. The signal was, once more, presented either in phase (S0) or out of phase (S pi). Comparisons among the data and quantitative analyses assuming the use of compensatory "internal delays" suggested that internal delays are operative and compensate accurately for external delays of up to approximately 750 microseconds. The analyses also indicated that larger internal delays (i.e., up to 2 to 3 ms) are probably also operative. However, performance using such large internal delays appears to be degraded in accord with the hypothesis that their application introduces "noise" in the internal representation of the stimuli.

Auditory Perception↗
PubMed1998

A randomized, placebo-controlled study of loop diuretics in patients with essential hypertension: the bumetanide and furosemide on lipid profile (BUFUL) clinical study report.

This study was conducted to determine whether loop diuretics are more effective than placebo in reducing blood pressure without raising serum lipid levels, and whether bumetanide is more effective than furosemide in this respect. In a double-blind, 24-week placebo-controlled crossover study, 27 patients with essential hypertension were treated in four periods of 6 weeks each, including placebo twice, furosemide 40 mg daily, and bumetanide 1 mg daily. Several metabolic parameters, including serum lipid levels, and blood pressure were assessed. Overall levels of total cholesterol, triglycerides, and low-density lipoprotein (LDL) cholesterol were 5%, 12.4%, and 4.8% higher, respectively, during loop diuretic therapy than during placebo treatment. Overall systolic and diastolic blood pressure measurements were 12 mmHg and 4 mmHg lower, respectively, during loop diuretic therapy than during placebo treatment. Any added effect of bumetanide on serum lipid levels and blood pressure compared with furosemide, however, could not be confirmed. Our results indicate that the loop diuretics bumetanide and furosemide are effective in reducing blood pressure, and influence serum lipid levels markedly less than do thiazide diuretics or chlorthalidone. In addition, these results indicate that differences in blood pressure reduction and serum lipid levels between the two compounds were small and nonsignificant.

Adult↗
PubMed1998

Binaural detection as a function of interaural correlation and bandwidth of masking noise: implications for estimates of spectral resolution.

Detection thresholds were measured for an antiphasic (S pi) 500-Hz tone masked by a binaural noise, as a function of the bandwidth of the noise. Several values of interaural correlation of the masking noise were used, ranging from -1 to +1. The bandwidth dependence of the thresholds showed a pattern consistent with a 100-Hz-wide critical band for most values of interaural correlation, even for those values which resulted in a considerable binaural release of masking. Only when the interaural correlation of the masking noise was very close to, or equal to, unity was the bandwidth dependence of the thresholds in accord with an approximately 300-Hz-wide "binaural" critical band measured in previous studies. Our analysis of the data calls into question the commonly stated notion that binaural processing is characterized by a wider critical band than is monaural processing.

Auditory Perception↗
PubMed1997

A new way to account for binaural detection as a function of interaural noise correlation.

The purpose of this communication is to describe a new method for predicting masking level differences (MLDs) as a function of the interaural correlation of the masking noise. The general idea is to decompose a binaural noise masker having an arbitrary value of interaural correlation into two parts: an No constituent and an N pi constituent. It is shown that the amount of masking produced by a noise having an arbitrary interaural correlation is equal to the addition of the masking effects produced by the No and N pi constituents that compose the masker. The new approach was used to generate predictions of MLDs for N rho S pi and N rho So conditions. Those predictions accounted for 98% of the variance in the classical data of Robinson and Jeffress [J. Acoust. Soc. Am. 35, 1947-1952 (1963)]. Finally, it is shown that the "additivity of masking" method is mathematically equivalent to assuming that binaural detection consists of a stage of errorless binaural processing preceded by a corrupted representation of the stimulus.

Auditory Perception↗
PubMed1997

Binaural detection with spectrally nonoverlapping signals and maskers: evidence for masking by aural distortion products.

Thresholds were measured for diotic tonal signals in the presence of interaurally delayed bands of Gaussian noise. When the signal frequency was 525 Hz., the spectrum of the noise was either below (highest frequency, 450 Hz) or above (lowest frequency, 600 Hz) the frequency of the signal. When the signal frequency was 450 Hz, the spectrum of the noise was always above the signal frequency (lowest frequency, 600 Hz). Signals had a 250-ms duration and were temporally centered within the 300-ms long bursts of noise. The spectrum level of the noise was 60 dB. Thresholds obtained in all three conditions varied essentially sinusoidally with the interaural delay of the noise. For signals below the spectrum of the noise, the periodicities within the data were close to, but not identical with, the periodicities of the signals. This outcome is discussed in terms of masking produced by aural distortion products stemming from interactions within the bands of noise [cf. van der Heijden and Kohlrausch, J. Acoust. Soc. Am. 98, 3125-3134 (1995)]. For signals above the spectrum of the noise, the periodicities in the data suggested that masking was produced by components within the band of noise. Patterns within the data are also discussed in terms of limitations concerning the magnitude of external delays that can be matched by internal delays that are incorporated in modern models of binaural processing.

Auditory Perception↗
PubMed1995

The role of envelope fluctuations in spectral masking.

Two experiments are reported in this study. In the first experiment the masking effect of five different types of narrow-band maskers was compared. The masker was either a tone, a narrow-band Gaussian noise, or a multiplication noise obtained by multiplying a sinusoid with a low-pass Gaussian noise. The noise maskers had a bandwidth of either 20 or 100 Hz. In all cases the masker had a center frequency of 1.3 kHz and a duration of 500 ms. Five-point growth-of-masking functions were measured using a 2-kHz tonal target with a duration of 400 ms, temporally centered in the masker. Six subjects participated in the experiment. Although considerable intersubject differences were observed, the data of all subjects showed several common trends. First, the tonal maskers produced more masking than the noise maskers. Second, Gaussian noise maskers produced more masking than multiplication noise maskers of the same bandwidth. Finally, 100-Hz-wide noise maskers produced more masking than 20-Hz-wide maskers of the same type. Differences in masked thresholds between the various masker types generally increased with masker level, and exceeded 25 dB in some conditions. The results are discussed in terms of masker envelope fluctuations. In the second experiment the masking effect was investigated for a bandpass noise at 1.3 kHz, with regular zero crossings, but with the envelope characteristics of a 100-Hz-wide Gaussian noise. Five-point growth-of-masking functions were measured using a tonal target of 2 kHz.(ABSTRACT TRUNCATED AT 250 WORDS)

Auditory Perception↗
PubMed1995

Comparison of auditory filter shapes obtained with notched-noise and noise-tone maskers.

The notched-noise method has been widely used to estimate the shape of the auditory filter. Results obtained using this method may be influenced by combination bands produced by the interaction of components within the upper band of noise in the notched-noise masker. To assess the possible effect of such combination bands, results were compared for two types of masker: A notched noise, as used in previous experiments; and a masker in which the upper band of noise was replaced by a sinusoid with a frequency corresponding to the lower edge frequency of that band. This is referred to as the noise-tone masker. The signal frequency was 2 kHz, and measurements were obtained for two different spectrum levels of the noise masker, 30 and 45 dB. Auditory filter shapes derived using the two maskers were similar on their low-frequency sides, as expected. The low-frequency sides were less steep at the higher masker level. The high-frequency sides of the auditory filters derived using the noise-tone masker were sometimes slightly steeper than those obtained using the notched-noise masker, but the effect was generally small. Changes with level on the high-frequency sides were not consistent across subjects. An analysis of the notched-noise data taking into account the effects of the combination bands suggests that the maximal spectrum level of the combination bands, in the region just below the lower spectral edge of the primary noise band, is about 20 to 30 dB below the spectrum level of the primary band.(ABSTRACT TRUNCATED AT 250 WORDS)

Auditory Perception↗
PubMed1994

Using an excitation-pattern model to predict auditory masking.

This paper evaluates the extent to which auditory masking can be reliably predicted from excitation patterns. For this purpose a quantitative model proposed by Glasberg and Moore [Hear. Res. 47, 103-138 (1990)] was used to calculate excitation patterns evoked by stationary sounds. Model simulations were performed for a number of masking experiments, reported in the literature, by calculating excitation patterns for the masker-alone as well as for the masker-plus-target conditions. As a threshold criterion, a difference between the two patterns of 1 dB at any frequency was imposed. For narrow-band-noise masking patterns, the method yields a fairly precise prediction of experimental data. For other conditions, however, systematic deviations between model predictions and data are observed. For instance, the model does not reproduce the typical tip-tail shape of psychophysical tuning curves. Furthermore, the nonlinearities in level dependence are not correctly described, and the model fails to reproduce a realistic two-tone masking curve.

Acoustic Stimulation↗