Occupational Medicine Prof. Francesco S. Violante

1. Occupational MedicineProf. Francesco S. Violante Noise, Ionizing and Non-ionizing Radiations,

2. Noise • Sound = a series of pressure variances (oscillations) propagating through an elastic medium (a solid, a liquid or a gas) and perceived by the human ear as sound sensation • Noise = an undesired and annoying sound that, due to its physical characteristics, is potentially able to cause a temporary or permanent physical or psychic damage to the human organism (Giaccai, 1995 mod.)‏

3. Physical Characteristics • Λ= Wavelength: horizontal distance between two subsequent crests or troughs • A= Amplitude of the wave: maximum wave range • T = Period: time required for one oscillation

4. Physical Characteristics • Frequency = Number of oscillations per second. It is measured in Hz (the human ear can detect frequencies between 16 and 16000 HZ)‏ • Acoustic intensity = sound energy radiated by the source (acoustic power, W) per unit area perpendicular to the direction of propagation (W/m2)‏ • Timbre = refers to sound quality and is determined by the wave shape

5. Unit of measurement • Noise intensity is usually measured in Decibels (dB). The Decibel is the logarithm of the ratio between a reference sound intensity and the intensity which is being measured minimum pressure variance value detectable by the human ear for a pure tone of 1000 HZ • Range: from 0 dB,which corresponds to the hearing threshold level, to 120 dB, which corresponds to the pain threshold level

6. Perception • Sound is transmitted through air (external ear middle ear) and bone conduction (middle ear  inner ear) • The auditory apparatus (inner ear, organ of Corti) transforms sound (mechanical energy carried by sound waves) into action potentials that reach the cortical acoustic areas through the acoustic nerve, determining the sound sensation

7. Perception • External ear: gathers sound waves and transmits them to the middle ear • Middle ear: transmits and amplifies the sound energy from the eardrum to the oval window through the ossicular chain and the contraction of the stapedius and tensor tympani muscles • Inner ear: transduction of mechanical energy (acoustic waves) into an electric signal (action potentials of the acoustic nerve)‏

8. Anatomy of the Ear

9. Organ of Corti

10. Perception • The discrimination of sound frequency takes place at the level of the organ of Corti thanks to a tonotopic localization of receptors (high frequencies near the staples, low frequencies at the cochlea)‏ • The discrimination of sound intensity depends on the number of impulses reaching the cortex

11. Perception • Sounds with intensity levels >70-75 dB induce a reflex contraction of the stapedius and tensor tympani muscles, which attenuates by 20 dB the acoustic energy reaching the inner ear (low-pitched tones)‏ • This mechanism is not effective in case of: • chronic exposures (due to adaptation and muscular fatigue)‏ • Impulsive noises (reaching the inner ear before the reflex occurrs)‏

12. Clock ticking 20 dB Whispering 30 dB Conversation 60-70 dB Motor vehicles on a highway 100 dB Rock concert, circular saw 110 dB Taking off airplane 120 dB Intensity of noise: examples

13. Occupational Exposure • Industrial sectors with noise rates frequently ≥ 85 dBA: • Engineering sector • Building sector • Wood sector • Textile sector • Paper mills • Food industry

14. Distribution of 9.368.000 Production Workers who had Noise Exposure Levels of 80 dB or greater (USA)

15. Percentage trend of noise-induced hypoacusias and deafness with respect to the total number of occupational diseases (diseases “tabled” in D.P.R 336; year of manifestation: 1985-1999)‏ Source: INAIL data processed by ISPESL

16. Percentage trend of hearing loss cases compensated by INAIL, by occupation (“tabled” occupational diseases only) Source: INAIL

17. Prevalence of Hearing Loss > 45 Dbhl for the General Population in Great Britain (Davis, 1988)‏

18. Percentage trend of hearing loss cases compensated by INAIL, by age (”tabled” occupational diseases only) Source: INAIL

19. Noise effects • Auditory effects • Temporary Threshold Shift (TTS)‏ • Hypoacusia due to chronic acoustic trauma • Hypoacusia due to acute acoustic trauma (injury)‏ • Extraauditory effects

20. Auditory effects • Temporary Threshold Shift (TTS) = elevation of the auditory threshold as compared to rest • TTS2 or physiological auditory fatigue is measured 2 minutes after the end of exposure and has a duration of 16 hours • TTS16 or pathologic auditory fatigue is masured 2 minutes after end of exposure and has a duration of more than 16 hours

21. Auditory effects • Physiological auditory fatigue (TTS2) • It varies among subjects but remains constant in the same subject • It increases proportionally with sound pressure, for stimuli over 70 dB • It begins with stimulating frequency and then extends to other frequencies according to increase in intensity • Recovery is proportional to the logarithm of time (most of the recovery takes place within the first hours)‏ • It does not usually exceed 30 dB

22. Auditory effects Hypoacusia due to chronic acoustic trauma • If noise exposure persists (daily occupational exposure≥ 85 dBA or attention value) the temporary damage to auditory cells (TTS) progressively tends to become permanent Permanent Threshold Shift (PTS)or hypoacusia due to chronic acoustic trauma or noise-induced hypoacusia

23. Example of audiometric tracing of noise-induced hypoacusia

24. Auditory effects • The damage affects the organ of Corti (external ciliated cells)‏ • It is a bilateral neurosensorial (or perceptive) hypoacusia, almost always symmetrical, progressively irreversible and evolutive, as a result of persistent exposure to noise • It mainly concerns high frequencies ranging from 3000 to 6000 Hz with an initial peak at 4000 Hz

25. Hypoacusia due to chronic acoustic trauma Onset is progressive (and nearly always insidious), and develops in four phases: • Initial phase: at the end of the work-shift, the worker complains of tinnitus (buzzing, ringing) ,“full ear” feeling, headache, giddiness, daze, asthenia, etc. • Audiometric phase: symptomatology is absent (a slight intermittent tinnitus at most) and the damage is revealed only by an audiometric test (deficit at 4000 Hz)‏

26. Hypoacusia due to chronic acoustic trauma • Onset phase: appearance of auditory deficits (hypoacusia) for high-pitched tones (4000 and 6000 Hz), combined with difficulty conversating, especially in noisy environments, and need to turn up the volume of radio or TV • Illness phase:appearance of auditory deficits (hypoacusia) for speech frequencies (500 and 2000 Hz), which can affect social life; permanent and/or nocturnal tinnitus (with insomnia) and appearance of the “recruitment” phenomenon (distorted and annoying perception of noises of relatively high intensity) are also possible

27. Hypoacusia due to chronic acoustic trauma Diagnosis • Pathological and working anamnesis • Risk assessment for exposure to noise • Tonal audiometry (with determination of air and bone conduction) performed in silent cabin in conditions of acoustic rest, preceded by otoscopic examination • Vocal audiometry • Tympanometry and reflectometry • Evoked auditory potentials

28. Hypoacusia due to chronic acoustic trauma Synergic effects with noise • Vibrations • High temperatures • Organic solvents (derived from benzene)‏ • Carbon sulphide • Carbon Oxide • Cyanides • Methylmercury • Pesticides

29. Epidemiological studies Risk factors associated with hearing loss: - Old age - Previous ear surgery - Decline of cognitive function - Diabetes mellitus - Hypercholesterolemia - Use of analgesics - Smoking (E. Toppilla et al., Individual Risk Factors in the Development of Noise-Induced HearingLoss. Noise Health. 2000; 2(8): 59-70)‏

30. Extra-auditory effects • They seem to be attributable to the connections between the acoustic pathways and CNS areas different from the auditory cortex • E.g. the reticular zone, which is connected via descending pathways to the mechanisms that control voluntary motility, spinal reflexes, with the hypothalamus (and the neurovegetative system)‏

31. Extraauditory effects • They seem to be attributable to the connections between acoustic pathways and CNS areas, different from the auditory cortex, related to the neurovegetative system • Sleep disorders • Reduced attention and concentration • Anxiety and irritation • Reduction in working efficiency • Increase in cardiac frequency and arterial pressure • Increase in gastric secretion

32. Ionizing and Non-ionizing Radiations

33. Ionizing Radiations • Ionizing radiations are electromagnetic particles and waves whose energy is sufficient to directly or indirectly ionize the atoms they pass through, so as to modify matter properties • It is believed that any exposure to ionizing radiations provokes “biological effects”, which are generally harmful; type, appearance and severity of such effects can differ widely

34. Ionizing Radiations • Electromagnetic Radiations • X rays • Gamma rays • Corpuscular Radiations • Alpha particle • Beta particle • Neutrons • Nrotons

35. Ionizing Radiations Alpha rays • Particles carrying a double positive charge, composed of two helium nuclei (2 neutrons and 2 protons)‏ • Source: radioactive atomic nuclei with a high atomic number • Penetrating power: extremely weak, skin basal layer (100-fold weaker than beta rays) Radius in tissues: few µ • Ionizing power: very high (1000-fold higher than that of beta particles)‏ • Dangerousness: dangerous only if emitted inside the human body

36. Ionizing Radiations Beta rays • Particles made of electrons (beta-) and positrons (beta+) emitted by a decaying nucleus. Some high-speed beta particles interact with matter, emitting x rays (natural x rays)‏ • Source: radioactive atomic nuclei, accelerators • Penetrating Power: weak, 1 cm below skin surface (100-fold stronger than alpha rays, but 100-fold weaker than gamma rays) Radius in tissues:: fewmm

37. Ionizing Radiations • Ionizing power: minimal • Dangerousness: always harmful with internal sources; harmful for structures at less than 1 cm from the skin

38. Ionizing Radiations Neutrons • The neutron is, together with the proton, one of the two components of atomic nuclei; neutrons have no electric charge and lose energy through interaction with the atomic nuclei of the materials they pass through • Source: nuclear reactors and accelerators, nuclear explosions • Dangerousness: high. The source is always external and emissions cease only when the source is switched off

39. Ionizing Radiations Gamma rays • Source: radioactive atomic nuclei, nuclear explosions • Penetrating power: strong (100-fold stronger than that of beta rays). A few centimeters of lead reduce the intensity of these rays by a factor of 2 • Ionizing power: they produce secondary electrons that ionize air • Dangerousness: always dangerous, even when emitted by external sources

40. Ionizing Radiations X rays • Electromagnetic radiations similar to gamma rays, but with a lower frequency • Source: artificial production (x-rays tube), collision between electrons and matter • Penetrating power: high • Ionizing power: high • Dangerousness: high, but lower than that of gamma rays

41. Ionizing Radiations

42. Ionizing Radiations Natural background • Radioactivity is a natural phenomenon, we are constantly exposed to natural radiations • External sources cosmic radiations, radioactive substances contained in the soil and in building materials • Internal sources radioactive substances which are inhaled or ingested and the radioactive constituents of our body, especially potassium 40

43. Ionizing Radiations • Absorbed dose (D) • Indicates the quantity of energy imparted by radiation and absorbed by tissues and results from the interaction of radiation with matter • D = dE / dm = ratio of energy imparted to a given volume to the mass contained in that volume; the higher the absorbed dose, the more severe the effect of a radiation • The unit of measurement (SI) is the Gray (Gy)‏

44. Ionizing Radiations In order to compare the effects of different types of IR, a numeric coefficient or QF is used(it depends on the LET# and is linearly proportional to the RBE* of each type of IR)‏ # number of ionizations produced per unit path length in the biological medium * ratio of the dose of a “standard” radiation (produced by a 250-kv x-ray source), expressed as D250, to the dose of the analysed radiation (Dr) that is necessary to obtain the same biological effect (= D250/Dr)‏

45. Ionizing Radiations Doseequivalent (H)‏ • The product of absorbed dose in tissue (D) and the quality factor (QF) is defined as dose equivalent (H=QFD). • The unit of measurement (SI) is the Sievert (Sv)‏ • Since the QF for x and  rays is 1, Sv and Gy for x and  rays are equivalent We often refer to dose or absorbed dose equivalent per unit time, that is intensity or absorbed dose rate (Gy· s-1), or dose equivalent rate (Sv· s-1)‏

46. BIOLOGICAL EFFECTS OF IONIZING RADIATIONS IONIZING LIVING RADIATIONS MATTER  ELEMENTARY PHYSICAL PHENOMENA  IONIZATIONS  FREE RADICALS  DIRECT AND INDIRECT ACTIONS  BIOLOGICAL EFFECTS

47. BIOLOGICAL EFFECTS OF IONIZING RADIATIONS • It is believed that, to inactivate cells, IR damage some essential macromolecules (biological target) as DNA, proteins, sugars and complex lipids • The effect of IR on the biological target can occur either by direct or indirect action

48. BIOLOGICAL EFFECTS OF IONIZING RADIATIONS > ionizing ability> damage Direct action • Target molecules are directly damaged by rupture of molecular links • The target is a structure, which is: • Sensitive to IR • Essential in the biological system Direct action • Cellular macromolecules get damaged by free radicals, resulting from water radiolysis

49. BIOLOGICAL EFFECTS OF IONIZING RADIATIONS Ionizing radiations damages • DETERMINISTIC DAMAGES: • Somatic effects: appearing in the irradiated individual • STOCHASTIC DAMAGES: • Somatic effects • Genetic effects:occurring in the offspring of the irradiated individual

50. DETERMINISTIC DAMAGE (graded or non-stochastic damage)‏ • This damage is exclusively somatic • There is a threshold level • The severity of damage depends on the dose • The latent period is usually short (late onset in some cases)‏ • Dose-effect relationship is represented by a sigmoid curve • Damage can be: • direct (early):mainly affecting parenchymal cells • indirect (late): affecting vascular and connective tissue structure • generalized • localized