Noise-induced hearing loss in an automobile sheet-metal pressing plant. A retrospective investigation covering 25 years.

Hearing damage suffered by male workers in an automobile sheet-metal pressing plant has been studied on five occasions during the period 1964-89. The hearing threshold data have been analysed in order to determine hearing loss due to noise in various age groups. The hearing thresholds were better on later occasions. In the youngest group of workers only 45% exhibited normal hearing in 1964, while in 1989 the corresponding figure was 88%. The same tendency towards improved hearing could also be seen in the age groups 30-39 and 40-49 years. In the oldest age group, 50-59 years, hearing handicap decreased from 58% in 1964 to 11% in 1989. With the aid of the average hearing loss, it has also been possible to estimate the equivalent noise level to which present-day workers have been exposed, as well as the reduction in level of exposure during the past 25 years. The effects of a long-term technical and medical occupational health care programme including noise-reduction measures and improved use of hearing protectors are discussed.

Models for studying the progression of hearing loss caused by noise.

A computer-controlled fixed-frequency Békésy audiometer has been used together with simplified mathematical models for hearing threshold measurements and analysis in 1,796 subjects from seven different noise environments with exposures varying from less than 80 dB(A) to greater than 95 dB(A). The methods of measurement and analysis have been used to determine hearing loss caused by noise for various age groups for men and women. It has also been possible to estimate the equivalent noise level to which workers are nowadays subjected under hearing protectors and the reduction in exposure level over the past 40 years. The results illustrate the effects of noise-reduction measures and the use of hearing protectors on the development of hearing loss suffered by workers in the actual Swedish industries.

The inhibition of granulocyte phagocytosis by various components of nasal drops.

The effect of two decongestive substances and two preservatives used in nasal drops on phagocytosis by human granulocytes was studied. The vasoactive substances oxymetazoline chloride and zylometazoline chloride incubated with human granulocytes during 20 min. gave a reduction of phagocytosis to almost zero when using concentrations found in commercially used nasal drops (500 mg/l respectively 1000 mg/l). However, a dilution of 1:100 was consistent with an almost normal phagocytic function. The preservatives benzalkonium chloride and thiomersal gave a dose related reduction of phagocytosis down to zero. A dilution of 1:100 of the benzalkonium chloride solution used commercially (200 mg/l) and a dilution of 1:10 of the thiomersal solution used commercially (24 mg/l) were needed to get an almost normal phagocytic function. These results together with previous studies indicate that the addition of preservatives in nasal drops should be questioned, excluded or replaced with other less harmful substances.

Histologic features of the temporomandibular joint disk and posterior disk attachment: comparison of symptom-free persons with normally positioned disks and patients with internal derangement.

To gain further knowledge about the differences between normal and pathologic anatomy of the temporomandibular joint disk, we examined histologically disks obtained at autopsy from 10 symptom-free persons and compared our findings with observations involving 17 surgically removed disks. The surgical patients had internal derangement and severe long-standing temporomandibular joint pain and dysfunction. The normal disks were biconcave, whereas the surgically removed disks were deformed and thicker than the normal disks. Chondrocytes (4 joints), a surface layer of proliferative connective tissue (4 joints), vessels (2 joints), and splitting (4 joints) were seen in the surgical specimens but not in the normal specimens. The surgical specimens also showed higher maximal density of fibroblasts and vessels. It was concluded that surgically removed temporomandibular joint disks demonstrated several histologic alterations that were not seen in normal disks. These characteristics may serve as the basis for development of a histologic grading of pathologic conditions of the temporomandibular joint disk and the posterior disk attachment.

Inhibitory effects of nasal drops components on granulocyte chemotaxis.

A possible toxic effect of components in nasal drops on chemotaxis by human granulocytes was studied. The vasoactive substances oxymetazoline chloride and xylometazoline chloride gave a successive reduction of chemotaxis down to zero for a concentration of 500 mg/l which is around that used in commercial preparations. The preservative benzalkonium chloride which is used in nasal drops in a concentration of 200 mg/l was deleterious for chemotaxis at a concentration of 0.8 mg/l. Thiomersal was deleterious for chemotaxis at a concentration of 1 mg/l which should be compared with a concentration of 24 mg/l used as preservative in nasal drops. Together with previous studies the present results indicate that the addition of preservatives in nasal drops should be questioned especially as they can be safely distributed without any risk of bacterial contaminations nowadays.

Computerized audiometry--a facility to prevent hearing damages caused by noise.

A computerized audiometer has been developed to perform pure-tone manual or fixed-frequency Békésy audiometry. A number of statistical evaluation programs are part of the integrated audiometer. It means that even small but statistically certain changes in hearing thresholds can be revealed at an early stage.

Aerodynamics and mucociliary function of upper airways.

The anatomical shape of the nasal cavities is of great importance for the air conditioning capacity of the upper respiratory tract. It means that the size of the anterior and posterior opening allows an adequate degree of turbulent air stream. A specific vascular system of the mucosa is responsible for temperature regulation of the inspired air. The humidification capacity is regulated actively by production of secretions and passively by condensation of water vapour on the mucosa during expiration and evaporation during the following inspiration due to temperature difference. The mucociliary activity of the nose is one of the most important defense mechanisms of the entire respiratory tract. The efficiency of the mucosal clearance is due to different internal and external influences. The effect of various environmental factors will be mentioned as well as expected consequences of the modern trend to use drugs for nasal application.

Acetylcysteine and its derivatives: functional and morphological effects on tracheal mucosa in vitro.

The effect of acetylcysteine and its derivatives on the mucociliary activity was investigated using a rabbit tracheal in vitro model system. High concentrations of N-acetyl-L-cysteine (Mucomyst), acetylcysteine, cysteine and glutathione significantly reduced the mucociliary activity. Application of Mucomyst (50 and 100 mg/ml) caused (within 1 h) marked changes in the ultrastructure of the ciliated epithelium of the rabbit trachea: compound cilia were commonly found and the epithelial cells showed signs of autolysis and were eventually shed. Although these lesions were obtained with higher concentrations than those generally present after inhalation or instillation, our results indicate the need of long-term in vivo studies of this drug.

Effects of erythromycin, aminoglycosides and doxycycline on mucociliary activity in vitro of rabbit trachea.

The effect of different antibiotics on the mucociliary activity of the upper respiratory tract of rabbit was tested in vitro. Erythromycin base had no effect, although erythromycin lactobionate had a minor inhibitory effect. Kanamycin and gentamicin had no inhibitory effect in high concentrations. Doxycycline had the highest mucociliary inhibitory effect; however, the toxic concentrations are more than 10 times the clinically relevant serum levels after oral administration.

Ototoxicity of netilmicin.

Ototoxicity and efficacy of netilmicin was evaluated in 76 consecutive patients with moderate to severe infections with Gram-negative rods and Staphylococcus aureus. Netilmicin alone was efficacious in 47 patients and in another 23 patients cure or improvement was seen with netilmicin combined with another antibiotic, usually penicillin. Therapeutic failure was seen in 4 cases, 2 of which were regarded as netilmicin failures. Vestibular function and hearing acuity was thoroughly examined by electronystagmography and audiometry. In spite of the extensive examination of the audiovestibular function it was possible to detect only one probable case of ototoxicity related to netilmicin, a reversible vestibular dysfunction. The importance of pre-therapeutic audiovestibular examination is stressed.

Effects of penicillins in vitro on mucociliary activity of rabbit trachea.

The effect of eight penicillins on the mucociliary activity of rabbit trachea was tested in vitro. Carbenicillin and ampicillin had a minor inhibitory effect. Penicillin G and V and pheneticillin were a little more ciliestatic. Propicillin, cloxacillin and dicloxacillin were most toxic. The mucociliary toxicity increased with increasing lipophilicity of the penicillins and correlated well with their known neurotoxic in vivo effects.

Hemifacial spasm: electrophysiological findings and the therapeutic effect of facial nerve block.

Twenty patients with cryptogenic hemifacial spasm have been examined electrophysiologically and treated with blockade of the facial nerve with phenol injections after localization of the nerve by electrical stimulation. The electrophysiological findings suggested a central origin of the spasms. The phenol injections abolished the spasms, but they recurred in most patients after 6 to 12 months. A few patients appeared to get permanent relief after one or more phenol injections. We used phenol blockade of the facial nerve as our first therapeutic treatment of choice in patients with distressing hemifacial spasm because it is a safe, simple, and repeatable procedure.

Effects of cystic fibrosis serum and cell culture medium on the mucociliary activity of the respiratory tract. An in vitro study in rabbits.

As previously reported a cystic fibrosis factor (CFF) is associated with the dyskinetic ciliary motion induced by serum and cell culture medium from patients with cystic fibrosis (CF). In this study a sensitive, standardization method, for the photoelectric recording of mucociliary activity was used to examine the effect of sera and media from cell cultures taken from patients with CF and healthy controls, on the mucociliary activity of rabbit trachea in vitro. No signs of decreased mucociliary activity were observed and electron microscopy showed normal ultrastructure and orientation of cilia.