lectures on respiratory physiology acid-base balance
TRANSCRIPT
Lectures on respiratory physiologyLectures on respiratory physiology
Acid-Base BalanceAcid-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
CO2 + H2O H+ + HCO3-
[H2CO3][H+] x [HCO3
-]
AT EQUILIBRIUM,
K =
[H+] x [HCO3-]
SOLUBILITY x PCO2
=
H2CO3
CA
Law of Mass Action
0.03 x PCO2
[H+] x [HCO3-]K =
WHICH, AFTER TAKING LOGS, BECOMES:
pH = pK + Log( ) [HCO3-]
0.03 x PCO2
- THE HENDERSON - HASSELBALCH EQUATION
Derivation of normal pH
Davenport Diagram
6.8 7.0 7.2 7.4 7.6 7.8 8.00
10
20
30
40
50P
LA
SM
A
[HC
O3- ]
, m
eq/l
pH
pH = 6.1 + Log( ) [HCO3
-]1.2
PCO2 = 40
7.40
24NORMAL
6.8 7.0 7.2 7.4 7.6 7.8 8.00
10
20
30
40
50P
LA
SM
A
[HC
O3- ]
, m
eq/l
pH
PCO2:40
3020
10
6080100
6.8 7.0 7.2 7.4 7.6 7.8 8.00
10
20
30
40
50
PL
AS
MA
[H
CO
3- ],
meq
/l
pH
pH = pK + Log( ) [HCO3
-]0.03 x PCO2
4080
20
BUFFERLINE
N
ACID - BASE DISTURBANCES:
* RESPIRATORY ALKALOSIS
* RESPIRATORY ACIDOSIS
* METABOLIC ACIDOSIS
* METABOLIC ALKALOSIS
6.8 7.0 7.2 7.4 7.6 7.8 8.00
10
20
30
40
50P
LA
SM
A
[HC
O3- ]
, m
eq/l
pH
RESPIRATORY ACIDOSIS:
4080
20
BUFFERLINE
H+ + HCO3- CO2 + H2O
N
6.8 7.0 7.2 7.4 7.6 7.8 8.00
10
20
30
40
50P
LA
SM
A
[HC
O3- ]
, m
eq/l
pH
RESPIRATORY ACIDOSIS:
4080
20
BUFFERLINE
H+ + HCO3- CO2 + H2O
N
6.8 7.0 7.2 7.4 7.6 7.8 8.00
10
20
30
40
50P
LA
SM
A
[HC
O3- ]
, m
eq/l
pH
RESPIRATORY ACIDOSIS:
40
80
20
BUFFERLINE
H+ + HCO3- CO2 + H2O
N
6.8 7.0 7.2 7.4 7.6 7.8 8.00
10
20
30
40
50P
LA
SM
A
[HC
O3- ]
, m
eq/l
pH
RESPIRATORY ALKALOSIS:
4080
20
BUFFERLINE
H+ + HCO3- CO2 + H2O
N
6.8 7.0 7.2 7.4 7.6 7.8 8.00
10
20
30
40
50P
LA
SM
A
[HC
O3- ]
, m
eq/l
pH
RESPIRATORY ALKALOSIS:
4080
20
BUFFERLINE
H+ + HCO3- CO2 + H2O
N
6.8 7.0 7.2 7.4 7.6 7.8 8.00
10
20
30
40
50P
LA
SM
A
[HC
O3- ]
, m
eq/l
pH
METABOLIC ACIDOSIS:
4080
20
BUFFERLINE
H+ + HCO3- CO2 + H2O
N
6.8 7.0 7.2 7.4 7.6 7.8 8.00
10
20
30
40
50P
LA
SM
A
[HC
O3- ]
, m
eq/l
pH
METABOLIC ACIDOSIS:
4080
20
BUFFERLINE
H+ + HCO3- CO2 + H2O
N
6.8 7.0 7.2 7.4 7.6 7.8 8.00
10
20
30
40
50P
LA
SM
A
[HC
O3- ]
, m
eq/l
pH
METABOLIC ALKALOSIS
4080
20
BUFFERLINE
H+ + HCO3- CO2 + H2O
6.8 7.0 7.2 7.4 7.6 7.8 8.00
10
20
30
40
50P
LA
SM
A
[HC
O3- ]
, m
eq/l
pH
METABOLIC ALKALOSIS
4080
20
BUFFERLINE
H+ + HCO3- CO2 + H2O
6.8 7.0 7.2 7.4 7.6 7.8 8.00
10
20
30
40
50P
LA
SM
A
[HC
O3- ]
, m
eq/l
pH
COMPENSATED RESPIRATORY ACIDOSIS
4080
20
BUFFERLINE
COMPENSATED METABOLIC ALKALOSIS
Oxygen Delivery to Tissues
CAPILLARIES
CAPILLARIES
DIFFUSION
HEART ANDCIRCULATION
TISSUE
VENTILATION
THE OXYGEN TRANSPORT SYSTEM
LUNGS
PERFUSION
DIFFUSION
Fick equation for diffusion through a tissue sheet
Distribution of PO2 between capillaries
Critical PO2 for mitochondrial respiration
Classification of tissue hypoxia:
* Anemic hypoxia
* Hypoxic hypoxia
* Circulatory hypoxia
* Histotoxic hypoxia