Enhanced accumulation of biologically active compounds in lichens with potential functional food applications.

Lichens have great potential as food, functional food additives or flavourings. The presence of specific substances with multiple biological activities is one of the characteristics of lichens. However, research on lichens as a food source or functional food additive is limited. The present study simulated, for the first time, the potential bioaccessibility of active compounds from 6 lichen species in simulated gastric and intestinal conditions. An in vitro digestion showed that the lichen substances had different bioaccessibility and stability during digestion. It was found that the application of some metabolic modulators significantly altered the accumulation of metabolites in most species. In addition, the study demonstrated the antimicrobial activity of the tested extracts as well as of 14 isolated lichen metabolites. These multi-directional studies demonstrate the potential of lichens in terms of their use as antimicrobial functional food additives.

Distortion product otoacoustic emission (DPOAE) in tinnitus patients.

The aim of this study was to determine the effect of tinnitus (experiment I) and the combined effect of tinnitus and sensorineural hearing loss (experiment II) on the distortion product otoacoustic emission (DPOAE) for two age groups of tinnitus patients. Tinnitus patients with normal earing, along with normal-hearing control subjects, participated in experiment I. They were divided into two age groups, below 50 and above 50 years. Experiment I showed that the DPOAE levels in the tinnitus patients were lower than those in the normal-hearing (nontinnitus) subjects. The differences depended on the frequency and the age of the patients, suggesting the confounding influence of presbyacusis. The second group of tinnitus patients with increasing and notch-like hearing loss participated in experiment II. They were also divided into two age groups, below 50 and above 50 years. The data from experiment II showed that DPOAE activity well reflects the increasing and notch-like hearing loss functions up to about 40 dB HL. The effect of age on the DPOAE level was clearly noted only for the tinnitus patients with clinically normal-hearing thresholds and was ambiguous for the tinnitus patients with hearing loss.

Relationships of intensity discrimination to sensation and loudness levels: dependence on sound frequency.

The main purpose of the experiments described in this article was to establish the frequency dependence of auditory intensity jnd's (just noticeable differences) for pure tones as functions of loudness level (LL). For this purpose, two sets of experiments were performed. In the first, the jnd's were measured as functions of sensation level (SL) at sound frequencies of 0.125, 0.5, 1, 2, 4, 6, and 8 kHz. The SLs were set at 10, 20, 40, 60, and 80 dB in a random order. In the second, LLs corresponding to the set of the SL at 1 kHz were obtained, and the relationship of the jnd's to LL was determined. We investigated to what extent the constant loudness-constant jnd relationship found previously intrafrequency can be applied interfrequency. The detection experiments were performed with a continuous-pedestal paradigm and an adaptive two-alternative, forced-choice (2AFC) procedure that converges on 75% of correct responses. We found that the jnd's in dB plotted versus SL decreased roughly according to power functions, the rate of decrease depending on sound frequency. The jnd's increased with sound frequency at low SLs but became practically constant at high SLs. According to the second experiment, the jnd's followed approximately the same function of LL at all sound frequencies, except for a multiplicative constant, irrespective of the slope of the loudness level function. Thus, the constant loudness-constant jnd relationship appears to apply interfrequency except for a multiplicative constant that, with the continuous-pedestal paradigm, grew monotonically with the frequency.

Perception of amplitude and frequency modulated signals (mixed modulation).

This article discusses the detection of mixed modulation, i.e., simultaneous amplitude and frequency modulation (MM). The investigations have incorporated both a sine wave modulating signal and an irregular modulating signal, a very narrow noise band, of a specified center frequency. The results revealed that for a sinusoidal low-frequency modulating signal, amplitude and frequency changes that were separately subthreshold could be detected by listeners in mixed modulation. This indicates summation of sensations caused by simultaneous AM and FM modulation. This effect was not observed in the case of the irregular modulating signal. A hypothesis is advanced that the perception of modulated signals is governed by two mechanisms, viz., temporal and spectral. The operation of the two mechanisms depends mainly on the modulating frequency. The type of modulation does not play any significant role in this case.

Will hyperthermia conquer the elusive hypoxic cell? Implications of heat effects on tumor and normal-tissue microcirculation.

In tumor radiobiology, the hypoxic cell has become especially important because of recent evidence of acute hypoxic regions within experimental tumors. The impact of hyperthermia on the development of acute hypoxia is discussed. Two experiments for studying hyperthermia and hypoxia in tumors are presented. Knowledge of the microenvironment of tumor cells will be necessary to understand and improve tumor control.