The document discusses the various effects and mechanisms of action of lasers on biological tissues. There are five main effects: 1) Thermal effects such as coagulation and vaporization, which can be used for cutting tissues. 2) Mechanical effects from high intensity lasers causing shock waves. 3) Photoablative effects allowing precise ablation without heat. 4) Photodynamic effects using light-activated drugs to kill cancer cells. 5) Photochemical and photobiological effects that can reduce pain and inflammation or enhance healing. Lasers have a variety of medical applications based on their different tissue interactions.

1. Action of laser on tissues Presented by- Dr. Md Nazrul Islam. Assistant Registrar, Orthopedic and traumatology Department, Shaheed Suhrawardy Hospital, Dhaka. “ Laser in Orthopedic Surgery ” (Part-2)

2. Laser “ Red light aids in the production of ATP in cells, which increases cellular health and energy. The radiation (energy) in normal cells stimulates adjacent cells to divide in the normal process of regeneration and healing. Laser light stimulates abnormal tissue to activate normal inter-cellular radiation, thus stimulating the normal healing process to start again. The photons produced by laser light normalize tissue by activating enzymes within cells. Once activated, enzymes within a cell trigger a chemical reaction in which more enzymes are activated in a domino-type effect. Low Level Laser Therapy has no effect on normal tissue. Photons will only be absorbed by cells that need them.” Holistic Bird Newsletter, www.holisticbird.com/hbn01/decjan/pages/laser.htm

3. Absorption of laser in Tissue: The IR( Infra red) region of the spectra, water molecules are dominant absorbers. • In the UV (Ultraviolet) and visible spectra, absorption by macromolecules like melanin and hemoglobin is more pronounced.

4. Electromagnetic Spectrum: Wavelength: It is the distance between repeating units of a propagating wave of a given frequency. Frequency: It is the number of occurrences of a repeating event per unit time.

5. Basic steps of laser action on biologic tissues:

6. Laser-tissue interactions

7. Basic effects of laser on tissues

8. Laser-tissue interactions

9. Mechanism of action of laser:

10. Basic effects of laser on tissues: . 1. Thermal effects . 2. Mechanical effects. 3. The photoablative effect. 4. The photodynamic effect. 5. Photochemical and Photobiological effects .

11. Thermal action of a laser beam can be described as one of three types, depending on the degree and the duration of tissue heating: A. Hyperthermia: B. Coagulation: C. Volatilisation: 1 . Thermal effects of lasers:

12. Phenomena of thermal effects of laser :

13. 1. Coagulation/ cauterizing of tissues, 2. Tissue vaporization for incising or excising. Recently, thermal power of laser have been widely used by surgeons to a. Cut into tissues ( carbon dioxide laser scalpel), b . Stop internal hemorrhage (Neodymium: YAG and argon laser photocoagulation) and- c. Treat tumors. Application of Thermal effects of lasers:

14. Video clip on cutting (Thermal) effect of laser:

15. Thermal effects of a laser beam. Laser osteotomy with the CO2-laser

16. Thermal effects of a laser beam.

17. 2. Mechanical effects Nd:YAG lasers, a very high intensity of luminous flux over a small area (between 1010 and 1012 W/cm2) ionizes atoms and creates a plasma. At the boundary of the ionized region, there is a very high pressure gradient which causes the propagation of a shock wave. It is the expansion of this shock wave which causes the destructive effect. Application of mechanical effects: a. General Surgery : coetaneous angiomas. b. Eye: principally in ophthalmology c. Urology: Endoscopic removal of kidney stone.

18. Mechanical effects of laser :

19. 3. The photoablative effect of laser: This effect is defined by as a pure ablation of material without thermal lesions at the margins, such as one would get with a scalpel. It occurs because of the principle of dissociation. The molecular bonds are broken and the tissue component are vaporized, without generation of any heat at the edges.

20. Uses of Photoablative effects of laser: 1. Orthopedic Surgery: 2. This procedure is for patients presenting with refraction problems. a. Myopia b. Hypermetropia, c. keratitis d. keratinisation, e. keratoplasty . The photoablative effect offers no practical advantage for making incisions or for ablating vascular tissues because they will bleed in the same way as with a scalpel. It can only be used on tissues which will not bleed.

21. Video clip on photoablative effect of laser :

22. The photoablative effect of laser :

23. Photoablative effect of Laser:

24. Application of photoablative effects

25. Application of photoablative effects

26. 4. The photodynamic effect Photodynamic therapy (PDT) is based on photoactive drugs that produce excited singlet-state oxygen molecules from local (ground-state) oxygen molecules under illumination with visible light.1 The singlet oxygen produces reactive oxygen species, primarily free radicals such as ·OH. These free radicals attack DNA and other vital biomolecules in the cell, leading to cell death.. Due to the limited tissue penetration of visible light, PDT has mostly been utilized for skin cancers. Applications : Cancer Psoriasis Macular degeneration

27. The photodynamic effect of laser: Photodynamic therapy works by the patient receiving a photosensitizing agent or photosensitizer which is a drug that exposes cancerous cells to the laser light which kills these cells. The photosensitizer has the ability to differentiate between good body cells & cancerous cells, and will not diffuse in the good cells, leaving to expose only cancerous cells.

28. The photodynamic effect of laser:

29. 5. Photochemical and Photobiological effects of Laser:

30. Photochemical and Photobiological effects of Laser: Photobiology is the scientific study of the interactions of light (technically, non-ionizing radiation) and living organisms. This field includes the study of photosynthesis, photomorphogenesis, visual processing, circadian rhythms, bioluminescence, and ultraviolet radiation effects

31. Application of Photochemical and Photobiological effects of Laser: To subside inflammation and Pain. To enhance wound, ulcer/ Bedsore healing. Bone tissue/ nerve regeneration / growth. Laser photosynthesis of previtamin D3. Laser Hair Removal/ Growth . Cosmetic/ LIPO-LASER Fat Dissolving Laser . Treatment of impotance. Cessation of smoking.

32. To subside inflammation and Pain.

33. To subside inflammation and Pain.

34. To subside inflammation and Pain .

35. To subside inflammation and Pain .

36. Healing skin ulcer, wound Bedsore.

37. Hard and soft tissues (Bone/ Muscular /nerve tissue) regeneration / growth.

38. Laser photosynthesis of vitamin D .

39. Hard and soft tissues (Bone/ Muscular /nerve tissue) regeneration / growth.

40. Hard and soft tissues (Bone/ Muscular /nerve tissue) regeneration / growth.

41. Bye. See you next day with “ Laser in Orthopedic Surgery” (Part-3) Laser on Soft Tissue