Heat in medicine

1. Heat in medicine Prof. Dr. Moustafa Moustafa Mohamed Ahmed Vice Dean Faculty of Allied Medical Scince Pharos University By ;dr ;mervat mostafa

2. By the end of the lecture, the students will Learn the basic concepts of heat, heat transfer, units of heat energy and latent heat

3. Heat • Heat is thermal energy transferred from system to another • Heat is measured in calories. • The amount of heat required to raise one gram of water 1° Celsius is one calorie. • When heat energy flows into a substance, the temperature of the substance usually rises.

4. No heat energy can be extracted.

5. Temperature Scales • Degree Centigrade Scale • The Celsius scale is determined by fixing the temperature span between the freezing and boiling points of water to be 100°C, and by defining the freezing point of water to be 0°C.

6. Fahrenheit scale • The Fahrenheit scale uses 180°F to span between the same two physical points, and uses 32°F as the freezing point of water. These two temperature scales are simply related to each other (as you should verify) by:

7. KELVIN is another unit of temperature that is used for many scientific calculations. It begins at absolute zero and therefore has no negative numbers.

8. Example Find the general relation between the Fahrenheit and Kelvin temperature scales and determine absolute zero in °F. Solution: We can find the general relation by substituting Equation (12.2) for TC into Equation (1) for TF. After substitution we find that

9. The amount of heat energy needed to raise the temperature of a substance ”Q” is proportional to the temperature change “DT” and the mass of the substance “m” Q= m c DT = C DT • where C is heat capacity = mc and c is the specific heat of the substance • Specific heat capacity is the amount of heat required to raise the temperature of one gram of that material 1° C.

10. Amount of Heat Gain Or Loss • The amount of heat energy needed to raise the temperature of a substance ”Q” is proportional to the temperature change “DT” and the mass of the substance “m” Q= m c DT = C DT • where C is heat capacity = mc and c is the specific heat of the substance • Specific heat capacity is the amount of heat required to raise the temperature of one gram of that material 1° C.

11. Unit of heat energy Calorie (Unit of heat energy) define as the amount of heat energy needed to raise the temperature of one gram of water one Celsius degree 1 Calorie = 4.18 Joule where Joule is the unit of energy in SI unit

12. Example • Ex: How much heat is needed to raise the temperature of 3 kg of copper by 20o (c=0.886 kJ/kg) • Solution: • Q =mc DT = 3.0 x 0.886 x 20 = 53.16 kJ

13. Calorimetry • The specific heat of an object can be measured by: • heating the object to some temperature, • placing it in water bath that of known mass and temperature, and • measuring the final temperature • If the system is isolated from the surrounding, then the heal leaving the object equals the heat entering the water and its container. • This procedure is called Calorimetry and the insulated water container is called Calorimeter.

14. Heat Loss = Heat Gain • Heat loss from the object • Qout = m c ( Tio –Tf) • M= mass of the object,, • c= specific heat of the object • Tio= initial temperature of the object • Tf= final temperature • Amount of heat gained by water and container • Qin = mwCw(Tf – Tiw) + mccc (Tf –Tiw))

15. Calculate specific heat for lead given: Mass of lead mpb = 0.6 kg Mass of water mw = 500 g Mass of calorimeter Mc = 200 g Initial temperature of lead Tio =100 Initial temperature of water Tiw = 17.3 Final temperature Tf =20 oC Specific heat capacitance of calorimeter Cc = 0.900 kJ/kg.ok Specific heat capacitance of water = 4.18 kJ/kg.ok Example

16. Latent Heat • When heat is added to ice at 0 oC the temperature of ice does not change. Instead the ice melts. • The heat needed to melt a substance of mass “m” is proportional to the mass of the substance m with no change in its temperature Qf = m Lf • Where Qf is the quantity of heat needed to melt the ice, m its mass and Lf the latent heat of fusion. • Also latent heat of vaporization is given by: Qv = m Iv • Where Iv is the latent heat of vaporization

17. Ex 1: How much heat do you need to heat 1.5 kg of ice at 1 atmospheric pressure from -20 until al the ice has been changed to vapor at 100 oC. Given: Specific heat of ice cice= 2.05 kJ/kg Latten fusion of ice Lf= 333.5 kJ/kg, Specic heat of water Cw = 4.18 kJ/kg, and Latten vaporization Lv = 2.26 MJ/kg Example

18. Questions • Define: heat, heat capacity, specific heat capacity and latent heat • If 500 gram of cupper at 200 oC is added to 500 gram of water at 20 oC what is the final temperature (Specific heat of cupper and water are Cw = c=0.386 kJ/kg and 4.18 and kJ/kg, respectively)

19. Heat Transfer • Heat always travels from a hot object to a cold object. • So how does heat travel from one object to another? • heat travel from one object to another through • CONDUCTION, • CONVECTION and • RADIATION.

20. Conductionis the main way for heat to transfer in solid materials. • All solid materials conduct heat, but some do a better job than others. Generally, metals are good conductors while porous materials are not. Good conductors of electricity are usually good conductors of heat.

21. Liquids and gases do not conduct heat very well, but they can transfer heat by convection. Look at the illustration above. Water carries heat from a hot engine through a pump and delivers it to a radiator, whose duty is to give up heat to the air. Remember, with convection, heat is transferred from one place to another by motionof the gas or liquid.

22. Convection During the daytime, cool air over water moves to replace the air rising up as the land warms the air over it. During the nighttime, the directions change -- the surface of the water is sometimes warmer and the land is cooler.

23. The easiest way to explain heat transfer by radiationis by the heat we feel from the sun. Even though the sun is 93 million miles away, we still feel its heat. It travels to earth through the vacuum of space (no air) by way of rays! If you hold your hand near a light bulb (but not too close!), much of the heat that you feel is from radiation.

24. Thermal expansion • Almost all substances expand when heated and contract when cooled. This is true of most liquids and solids as well as gases. • Thermometer: Fluid in a tube. The height of the fluid is a measure for the temperature. • Change of length (1 D), area (2 D) and volume (3 D) is related to temperature: Thermal Expansion

25. Part two

26. Linear Expansion • A solid rod of length L is found to expand by an amount that is directly proportional to the temperature increase and to its length according to

27. 2 D Area Expansion • Calculation gives us for area of any shape

28. 3 D Volume Expansion • Calculation gives us for volume of any shape

29. Heat and Life • The rates of the metabolic processes necessary for life, such as cell divisions and enzyme reactions, depend on temperature • For a given animal there is usually an optimum rate for the various metabolic processes. Warm-blooded animals (mammals and birds) have evolved methods for maintaining their internal body temperature at near constant levels. As a result, warm-blooded animals are able to function at an optimum level over a wide range of external temperature.

30. Energy Requirement of People • All living systems need energy to function. In animals, this energy is used to circulate blood, obtain oxygen, and repair cells, and so on. • The amount of energy consumed by a person during a given activity divided by the surface area of the person’s body is approximately the same for most people. • The energy consumed for various activities in Cal/m2. Hr. is known as metabolic rate.

31. Metabolic Rate for Selected Activities

32. Total energy consumption per hour • To obtain the total the total energy consumption per hour, we multiply the metabolic rate by the surface area of the person. • The following empirical formula yields a good estimate for the surface area. Area (m2) = 0.202 x W0.425 x H0.725 • Here W is the weight of the person in kilogram, and H is the height of the person in meters.

33. Example The surface area of a 70 kg man of height 1.55 m is about 1.7 m2. His metabolic rate at rest is therefore (40 Cal/m2. Hr) x 1.7 m2 = 68 Cal/hr, or about 70 cal/ hr. the metabolic rate at rest is called the basal metabolic rate.

34. Example • For a woman, the energy requirement increase somewhat during pregnancy due to the growth and metabolism of the fetus. As the following calculation indicates, the energy needed for the growth of fetus is actually rather small. Let us assume that the weight gain of the fetus during the 270 days of gestation is uniform. If at birth the fetus weight 3 kg, each day it gain 11 g. because 75% of tissue consists of water and inorganic minerals, only 2.75 g of the daily mass increase is due to organic materials, mainly protein. Therefore, the extra Calories per day required for the growth of the fetus is

35. Heat Transfer • Heat always travels from a hot object to a cold • object. • So how does heat travel from one object to • another? • heat travel from one object to another through • Conduction, • Convection • Radiation. • Evaporation.

36. Conduction • Conduction: heat transfer by direct contact with another medium. (hot or ice packs) • The total heat transferred depend on: • The area of contact • The temperature difference • The time of contact • The thermal conductivity of the materials

37. Hot baths, hot pack and hot paraffin when applied to the skin heat transfer to the body by conduction. • Conductive heat transfer leads to local surface heating, since the circulating blood effectively removes heat that penetrate deep in the tissue.

38. Convection • Convection means heat transfer by indirectly through secondary conductive medium. (air or liquid) • Example is the air circulation which is established by a room radiator. • The air near the radiator is heated by conduction making it less dense than the cooler air in the room. • Therefore, the warmer air rises and is replaced by the cooler air down-wards around the radiator.

39. Radiation • Radiation means heat transfer by or from its source to surrounding environment in form of waves or rays. (ultraviolet light) • Radiation is electromagnetic energy that travels through space with the speed of light (3x108 m/s). • The easiest way to explain heat transfer by radiation is by the heat we feel from the sun.

41. Thermotherapy • Treatments using heat • Increase the temperature of the body region to cause vasodilatation; • –Increases blood flow to area • Decreases pain and muscle spasms • Increasing flexibility to tissues • Comforting for most patients

42. Cryotherapy • Treatments using Cold • Decreases tissue temperature • Skin Color change from white to red • Decrease in total blood flow • Decrease in nerve conduction

43. Cryotherapy • Cryotherapy is the local or general use of low temperatures in medical therapy. Cryotherapy is used to treat a variety of benign and malignant lesions.The term "cryotherapy" comes from the Greek cryo meaning cold, and therapy meaning cure. Cryotherapy has been used as early as the seventeenth century. • Its goal is to decrease cellular metabolism, increase cellular survival, decrease inflammation, decrease pain and spasm, promote vasoconstriction, and when using extreme temperatures, to destroy cells by crystallizing the cytosol. The most prominent use of the term refers to the surgical treatment, specifically known as cryosurgery. Other therapies that use the term are cryogenic chamber therapy and ice pack therapy.

44. Cryosurgery Cryosurgery is the application of extreme cold to destroy abnormal or diseased tissue. Cryotherapy is used to treat a number of diseases and disorders, most especially skin conditions like warts, moles, skin tags and solar keratoses. Liquid nitrogen is usually used to freeze the tissues at the cellular level. The procedure is used often because of its efficacy and low rates of side effects. Medical Cryotherapy gun

45. Assignments Assignments : 1-2-3(the tpoics as in the lecture).