Metabolic Rate for Medical Engineering PDF

Metabolic Rate Definition: It is the amount of energy (heat ) production per hour Measurement: Direct: In which the heat produced by the person during a specified time is actually measured by apparatus called calorimeter. Indirect: In which the heat is calculated as follow:...

Metabolic Rate Definition: It is the amount of energy (heat ) production per hour Measurement: Direct: In which the heat produced by the person during a specified time is actually measured by apparatus called calorimeter. Indirect: In which the heat is calculated as follow: ***If the amount of heat resulting from oxidation of a mixed food ( CHO + Fat + Proteins ) using 1 liter of O2 is 4.8 Kcal/ lit ***If normal resting and fasting individual consumes O2 at a rate of 250 ml / min ***Rate of O2 consumption / h = 250 × 60 = 15.6 L / h ***Metabolic rate = 15.6 × 4.8 = 75 Kcal / hr Factors affecting M.R: Exercise: most marked increase Eating: especially proteins. Exposure to cold: shivering Endocrinal: catecholamine & thyroxin Emotional state: anxiety (increase catecholamine & muscle tone) Starvation: decrease MR (decrease sympathetic and thyroxine) Specific Dynamic Action (S.D.A.) -It is the power of food to increase the metabolic rate. -Metabolic rate starts to increase 1 hour after taking food. Reaches its maximum in 3 – 4 hours. Decreases to basal level in 12 – 18 hours Causes: It is due to the metabolic processes of the absorbed food in the liver. S.D.A. depends on: -The type of food ingested: 30% of caloric value of proteins 6% of caloric value of CHO & 4%of caloric value of fats 1 -Quantity of food ingested: The more the amount of food the more the S.D.A. -The external temperature: S.D.A. is maximum at 33°C S.D.A. is absent at 3°C Basal Metabolic Rate B.M.R. is the energy production in unit time ( one hour ) (MR)under basal conditions which are: 1-Complete physical and mental rest. Comfortable - Not sleep- No emotion 2-In post-absorptive state 12 – 14 hours after the last meal 3-Comfortable external temperature: The person should not feel cold or hot, neither shivering nor sweating. Comfortable temperature is 20 – 25 for dressed persons and 28 – 31 when naked How B.M.R. is expressed? Amount of heat in calories given by the body per hour per square meter surface area under basal conditions: Complete physical Post-absorptive Comfortable and mental rest state external temperature O2 consumption / Liter / hour 4.8 = 40 cal / m2 / h B.M.R = in normal adult male Body surface area / m2 2  Factors affecting B.M.R. Physiological factors: Pathological factors: 1- Age 5- Climate Increase BMR decrease BMR 1- Hyperthyroidism 1- Hypothyroidism 2- Hyperpitutrism 2- Hypopitutrism 2- Sex 6- Race 3- Hyper function 3-Hypofunction of of adrenalmedulla suprarenal cortex 3- Physical 7- Sleep 4-Fever 4-hypothermia habits 5- Heart failure 5-Prolonged 6-blood diseases starvation and 4- Dietetic 8- Pregnancy malnutrition habits 7- Diabetes insipidus Effect of age on B.M.R. Newly born infants : 25 Kcal /h/m2 2 – 5 years : 60 Kcal /h/m2 Puberty : 55 Kcal /h/m2 20 years : 40 Kcal /h/m2 After 20 years : 1 cal. Decreases for every 10 years. Effect of sex on B.M.R. B.M.R. is lower in females than males due to: a-Lack of androgens. b-Presence of greater fat stores Effect of physical habits: Athletes have B.M.R. 10% higher than sedentary individuals due to a- Greater muscle bulk b- Lesser amount of fat Effect of dietetic habits: Prolonged ingestion of proteins increases the B.M.R. about 10% more than if a mixed diet or CHO only were ingested. 3 Effect of Climate: -B.M.R. is higher in persons living in cold countries. -B.M.R. is lower in persons living in hot countries. Effect of Race: Pure and dark races have lower B.M.R. than mixed races. Effect of pregnancy : It increases during pregnancy due to: -Increased thyroid activity -Additional metabolic activity of the fetus Sleep It decreases B.M.R. due to: -Decrease muscle tone -Decrease sympathetic activity 4