The "cost" of silence

Changes in the organism of control desk operators caused by difficulties faced during productionally relevant speech information processing under conditions of intense occupational noise, represent the psychophysiological "cost" of noise masking. Its presence attests to difficulties in processing before deterioration of the quality of the latter while its quantitative characterisation correlates positively with the degree of the masking effect of noise and with the neuropsychic stress of this particular type of work. For this reason an attempt is made to demonstrate noise masking under laboratory conditions with it approximate quantitative evaluation at two signal/noise ratios- +15 and The statistically significant differences between the values of pulse rate, plethysmography and vocal exertion at the above ratios point to both its presence, and to the necessity to be considered when assessing the occupational burden and standardisation of noise intensity in productions associated with speech signals.

Investigation of noise exposure effect on heart rate variability parameters

This paper deals with the study of the effect of 135 min exposure to noise with intensity Leq 95 dB(A) in experimental conditions. Three experimental sessions: before, at the onset, and at the end of the noise exposure were conducted. The comparison of heart rate variability (HRV) parameters before and on the onset of the experiment showed tendency for significant decrease of the cardiointervals variability parameters: standard deviation (SD), sum of positive differences between successive cardiointervals (S), total wave energy in the cardiotachogram (S*Ns), mean difference between successive cardiointervals (V). Statistically significant increase of the mean value was found at HRV parameters related to the distribution of the cardiointervals: control adequacy parameter (IARP), equilibrium autonomic parameter (IVE), autonomous balance (IVB), homeostasis parameter (HI). At the end of the third experimental session HRV parameters were almost restored, but they did not achieve the initial values. An elevation of the sympathetic activity under noise exposure effect was found. In this aspect, the heart rate variability parameters were interpreted as a sensitive indicator for the quality of cardiac rhythm and they can be used for assessment of the functional status and the level of preserving of the adaptive reserves of the investigated persons.

Tinnitus, heart rate variability, and some biochemical indicators

Twenty-three tinnitus patients between the ages of 25 and 66 years (mean age, 47.6) were examined completely in the neurootological clinic of the Medical University, Sofia. Heart rate variability measurements were obtained to reveal the relationship between tinnitus and the autonomic equilibrium. Some biochemical indicators (serotonin and the colored sedimentary uric reaction of Kimbarovski [CSURK]) also were followed up. For 19 patients with transitional disturbances in the vertebrobasilar blood circulation, the sympathetic portion of the autonomic nervous system predominates, and heart rate variability is suppressed. The higher suppression of heart rate variability and higher values of the health risk in four occupationally exposed patients are attributable to the higher expressed level of stress connected with the adverse work conditions. Changes in the health risk, CSURK, and serotonin blood values in four tinnitus patients also are discussed.

Spectral coherence between blood pressure and inter-beat intervals in hypertension

Continuous registration of blood pressure (BP) was obtained in 31 normotensives and 76 hypertensives (divided into 3 stages of hypertension) by a method where the blood pressure in a human finger was measured non-invasively in a beat-by-beat fully calibrated manner. From this signal, the power density spectra of inter-beat intervals (IBI), systolic blood pressure (SBP) and diastolic blood pressure (DBP) were derived. Total spectral power (TP) and low/high spectral frequency ratios of all spectra were calculated. Cross-correlation analysis between IBI, SBP and DBP spectra showed that the level of amplitude and phase spectral coherence (SC) was strongly dependent of the stage of hypertension. SC was calculated by means of appropriate mathematical algorithms. Multiple step regression analysis pointed out that the observed phenomenon is highly significant for both--the amplitude and the phase SC (p < 0.01).

Relationship between heart rate variability and hypercholesterolaemia

A statistically significant correlation between chronic (tonic) distress (expressed by long-term depression of heart rate variability-HRV) and the increase of the serum lipid level was found in the experimental group (39 clinically healthy subjects with hypercholesterolaemia; 16 women and 23 men; mean age 42.4 +/- 2.45 years). A statistically significant relationship was found also between the experimental and control group (39 healthy normocholesterolaemic subjects; 18 women and 21 men; mean age 43.7 +/- 2.18 years) when comparing distress indicating HRV-based measurements. Significant predictors of HRV depression were: total cholesterol and low-density lipoprotein cholesterol. The effect of a 3-month special diet served to 17 subjects selected from the experimental group led to a decrease of serum lipids but did not influence substantially HRV parameters. It can be concluded that HRV parameters reflecting stress reaction correlate with atherogenic serum lipids; their separate follow-up (which is quicker, easier and cheaper) can be used for prediction of cardiovascular health risk and probably for disorders in serum lipid metabolism.

Changes in some psychophysiological parameters in speech information processing under masking noise effect

The aim of the present work was to study the influence of masking broad-band (white), impulse and interrupted noise with intensities LAeq 60 and 90 dB(A) on the execution of some psychophysiological tasks. The following parameters were studied: pulse frequency and variation, breathing frequency and variation, vascular tone etc. The psychological tasks model different parts of the operators' activity and include: conduction of mathematical calculations at datum speed; test related to the information processing; complex optional task supplied by Piorkovski's device. After statistical processing of results by Student-Fischer's t test and monofactor dispersion analysis it was established that the masking noise effect was more strongly expressed in the execution of psychophysiological tasks connected with the main memory. Of all tested physiological parameters the changes in the peripheral circulation, expressed in elevated vascular tone of peripheral blood vessels, were the most significant.

[The hygienic ergonomic protection of speech communication over time]

In the course of the experimental laboratory studies it was found out a significant impairment of the communication following a 2-hour processing of speech signals in conditions of masking noise. In order to diminish the auditory exhaustion in impeded communication the authors created physiologically grounded model of the working and resting regime in accordance to the experimental data, which require the including of two breaks in the first half of the working day, i.e. after a two hour exposition to masking noise. The minimal duration of the break at the end of the second hour (according to the experimental data) must be not less than 10 minutes in order to reach the initial or near to it speech communication. The time of the second break may coincide with the regulated lunch-time. The created working and resting regime was approbated in working conditions at DF "Kremikovtsi". It was found out that following the introduction of the physiological regime of work and rest, the auditory exhaustion decreased which was expressed in lowering of the rate of tone-intensity steps.

[The effect of different types of music on the perception of speech information]

Under experimental conditions, the masking effect of three types of music and of "white" masking noise was studied using a special speech-audiometric test (L. Tsaneva 1978, 1993). The signal-to-noise relation was found to be the most significant factor affecting spoken information perception, regardless of the type of music used as masking agent (level of correlation coefficients, jR = 0.89). The types of music used (modern, classical, playback) showed no appreciable differences in masking, remaining at the same time stronger masking factors compared to "white" noise. Conclusions were made as to hygienic-ergonomic aspects to be considered for intensity of musical programs in conforming with pertinent standards.

Clinical meaning of GGT activity in follow-up of patients with alcohol-related liver injury and cholestasis

The dynamics of GGT was investigated in three groups of patients after removing some primary causes of GGT increase. Group A included 34 patients with alcohol-related liver disease, group B included 16 patients with alcoholic liver injury and cholestasis, caused by concomitant alcoholic pancreatitis and group C included 17 patients with extrahepatic cholestasis, caused by choledocholithiasis. Follow-up assays of GGT were performed on the 7th, 14th and 30th days. Our results showed that the dynamics of GGT was more rapid after removing the cause for cholestasis than in stopping alcohol consumption in patients with chronic liver diseases. On the 14th day more than a 50% decrease in GGT activity was noted in 20% of the patients from groups A and B and in almost all cases from group C. On the 30th day, the reference range of GGT was not attained by any of the patients with liver disease nor in five patients from group C. No significant correlation was found between the severity of liver damage and the extent of GGT increase at the beginning and at the end of the follow-up period.

[Changes in the pulse variability of operators on a 12-hour work shift regimen]

Studies are carried out on 51 workers from the state works "D. Dimov"--Yambol on the changes of the pulse variability in the course of 12-hour day and night shift work and subjective evaluation of the psychosomatic complaints, in view of assessment the work load and strain. This investigation is performed because the workers have lodged a complaint against the introduction of 12-hour shift regime of work. It is done twice--during the day and during the night shift. No changes giving indication for considerable over pressure of the physiological systems and decrease of the working capacity have been established during the working process. The conclusion is that this type of working activity--12-hour shift schedule endangers neither the health status of the workers, nor the security and reliability of the system "man-machine-environment" therefore its introduction is not in contradiction to the physiologically well-grounded norms for the organization of the working process.

[The assessment of the general functional status and of the psychosomatic complaints of workers at hydroelectric power plants]

Evaluation of the general functional status and psychosomatic complaints of 61 workers from the hydroelectric power stations is made. The following methods are used: 1. Assessment of the general functional state, by means of computer analysis of the cardiac variability, analysing the changes in the values of the following indices: average value of the cardiac intervals (X), their standard deviation (SD), coefficient of variation (CV), amplitude of the mode (AMO), index of stress (IS), index of the vegetative balance (IVB), homeostatic index (HI). The last 3 indices serve for determination of the complex evaluation of chronic fatigue and work adaptation (ChFWA). 2. Evaluation of the psychosomatic complaints, by the use of a questionnaire for the subjective psychosomatic complaints. 3. Studying the systolic and diastolic blood pressure. The average values received in workers from HPS were compared with the average values of the population of the country and with the average values of a similar working activity of a group of operators from the thermal power station HPS. In conclusion it could be noted that concerning ChFWA the received values in workers from HPS are not more unfavourable generalized values from that measured in workers, occupied with similar type of work in other industrial branches of the country. However, they are with more unfavourable data in comparison with the workers from HPS. The subjective evaluation of the operators concerning their psychic and body health status is moderately worse, both in comparison with the values of the index for the country, and in comparison with those of the operators from HPS.