Respiratory Physiology - Oxygen-Hemoglobin Dissociation Curve

RESPIRATORY PHYSIOLOGY- 6 Dr. Khaled Abdel-Sater, MD  O2 TRANSPORT BY BLOOD Forms of O2: A- Physical Solution: Nature: The molecules of O2 are dissolved in plasma. Volume: It about 3% (0.3 ml% in the arterial blood, 0.13 ml % in venous), tissues take 15 ml/min (3x5 liters). - This is l...

RESPIRATORY PHYSIOLOGY- 6 Dr. Khaled Abdel-Sater, MD  O2 TRANSPORT BY BLOOD Forms of O2: A- Physical Solution: Nature: The molecules of O2 are dissolved in plasma. Volume: It about 3% (0.3 ml% in the arterial blood, 0.13 ml % in venous), tissues take 15 ml/min (3x5 liters). - This is less than tissues need (about 250 ml/min) Importance: It determines O2 pressure, so it determines the direction & rate of diffusion of gas in chemical combination from or to blood. B- Chemical Combination with Hb = 97%. - Volume: 19.5 ml% in arterial &14 ml% in venous. - Importance: It is main O2 supply to the tissue. Tissues utilize physical O2 at first then chemical O2 after that. Dr Khaled Abdel-Sater  Some Definitions 1- O2 content : is the volume of O2 present in combination with Hb / 100 ml blood It depends on: Amount of Hb, amount of O2, O2 affinity & metabolic state of organs 2-O2 Capacity : is the maximum volume of O2 present in combination with Hb when the Hb is fully saturation in 100 ml blood. Hb is 15 gm% & each 1 gm can carry 1.33 ml O2 O2 capacity = 15 X 1.33 = 20 ml. (but only 97 % of Hb which carried O2, so it contain 19.5 ml). O2 content 3-O2 Saturation = -------------------- X 100 = 97 % O2 capacity Dr Khaled Abdel-Sater  O2 Dissociation (Saturation) Curve: Def., It is the relationship between O2 tension and O2 saturation in the blood. Dr Khaled Abdel-Sater  Physiological Significance of the Curve -The shape of the curve is S-shaped upper segment is horizontal and lower segment is vertical. Upper segment is horizontal these means that O2 tension can be reduced to about 60 mmHg while the O2 saturation is decreased to 90%, this means that Hb can be still saturated even at lower O2 tension as at high altitudes and in excessive lung diseases. Lower segment is vertical this means that slight decrease in O2 tension is accompanied by marked decrease in O2 saturation. Dr Khaled Abdel-Sater Dr Khaled Abdel-Sater  N.B: -P50 refers to partial pressure of O2 at 50% saturation of Hb with O2. An index of the position of the Hb-O2 dissociation curve is given by the P50 (average), the PO2 (25 mmHg). Dr Khaled Abdel-Sater Dr Khaled Abdel-Sater Factors that shift the curve: Dr Khaled Abdel-Sater Dr Khaled Abdel-Sater  Significance of the Shift: 1-The Boher’s Effect: Def., Increase of CO2 (or H+) leads to decrease affinity of Hb to O2 so it give its O2 easily to tissues and visa versa. Importance: As blood pass through the lung, CO2 diffuse from blood to alveoli this decrease the CO2 level and increase O2 loading to Hb. -Then blood reach tissues, the CO2 diffuse from tissues to blood this increase the CO2 level and increase O2 removal from Hb more O2 free and more O2 supply to tissues. 2- The Exercise: With muscular exercise, there are CO2, H+, 2,3-DPG & temperature these lead to increase O2 removal from Hb, more O2 free and more O2 supply to tissues. Dr Khaled Abdel-Sater 3- CO Poisoning:It causes shift of the curve to left. This because: a- CO affinity to Hb is 210 times that of O2 more binding of CO to Hb. b- No release of CO or O2 from Hb and more saturation. Dr Khaled Abdel-Sater