Lectures on respiratory physiology Acid-Base Balance

Some definitions An acid is a molecule that releases hydrogen ions in solution A base is a molecule that can accept a hydrogen ion A buffer is a substance that can reversibly bind hydrogen ions

Titration curve for the bicarbonate buffer system

CO 2 + H 2 OH + + HCO 3 - [H 2 CO 3 ] [H + ] x [HCO 3 - ] AT EQUILIBRIUM, K = [H + ] x [HCO 3 - ] SOLUBILITY x PCO 2 = H 2 CO 3 CA Law of Mass Action

0.03 x PCO 2 [H + ] x [HCO 3 - ] K = WHICH, AFTER TAKING LOGS, BECOMES : pH = pK + Log ( ) [HCO 3 - ] 0.03 x PCO 2 - THE HENDERSON - HASSELBALCH EQUATION

Derivation of normal pH

Davenport Diagram

PLASMA [HCO 3 - ], meq/l pH pH = Log( ) [HCO 3 - ] 1.2 PCO 2 = NORMAL

PLASMA [HCO 3 - ], meq/l pH PCO 2 :

PLASMA [HCO 3 - ], meq/l pH pH = pK + Log( ) [HCO 3 - ] 0.03 x PCO BUFFER LINE N

ACID - BASE DISTURBANCES: * RESPIRATORY ALKALOSIS * RESPIRATORY ACIDOSIS * METABOLIC ACIDOSIS * METABOLIC ALKALOSIS

PLASMA [HCO 3 - ], meq/l pH RESPIRATORY ACIDOSIS: BUFFER LINE H + + HCO 3 - CO 2 + H 2 O N

PLASMA [HCO 3 - ], meq/l pH RESPIRATORY ACIDOSIS: BUFFER LINE H + + HCO 3 - CO 2 + H 2 O N

PLASMA [HCO 3 - ], meq/l pH RESPIRATORY ACIDOSIS: BUFFER LINE H + + HCO 3 - CO 2 + H 2 O N

PLASMA [HCO 3 - ], meq/l pH RESPIRATORY ALKALOSIS: BUFFER LINE H + + HCO 3 - CO 2 + H 2 O N

PLASMA [HCO 3 - ], meq/l pH RESPIRATORY ALKALOSIS: BUFFER LINE H + + HCO 3 - CO 2 + H 2 O N

PLASMA [HCO 3 - ], meq/l pH METABOLIC ACIDOSIS: BUFFER LINE H + + HCO 3 - CO 2 + H 2 O N

PLASMA [HCO 3 - ], meq/l pH METABOLIC ACIDOSIS: BUFFER LINE H + + HCO 3 - CO 2 + H 2 O N

PLASMA [HCO 3 - ], meq/l pH METABOLIC ALKALOSIS BUFFER LINE H + + HCO 3 - CO 2 + H 2 O

PLASMA [HCO 3 - ], meq/l pH METABOLIC ALKALOSIS BUFFER LINE H + + HCO 3 - CO 2 + H 2 O

PLASMA [HCO 3 - ], meq/l pH COMPENSATED RESPIRATORY ACIDOSIS BUFFER LINE COMPENSATED METABOLIC ALKALOSIS

Oxygen Delivery to Tissues

CAPILLARIES DIFFUSION HEART AND CIRCULATION TISSUE VENTILATION THE OXYGEN TRANSPORT SYSTEM LUNGS PERFUSION DIFFUSION

Fick equation for diffusion through a tissue sheet

Distribution of PO 2 between capillaries

Critical PO 2 for mitochondrial respiration

Classification of tissue hypoxia: * Anemic hypoxia * Hypoxic hypoxia * Circulatory hypoxia * Histotoxic hypoxia