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Quiz #4 – next Friday
Pulmonary Aspects of Acid-Base Balance
Why is pH regulation important?
Normal between 7.35 – 7.45
pH 6.6 – 7.8 compatible with life
H reacts with negatively charged molecules such as proteins to alter function.
For example, Hb combines with less oxygen when H combines with Hb
Enzymes become altered if pH is out of balance
Drug effectiveness is altered with changes in pH
Myocardial contractility is altered with decreased pH (↑ H )
Lots of examples of altered pH inducing arrhythmias, seizures, and vascular
Compared with other ions, H is highly regulated. Na for example can vary 1,000,000
times more than H . Thus H is precisely controlled. The basic defenses against
changes in H involve the respiratory system (can react within a few minutes), kidney
(hours/days and the most powerful of the three) and buffers (keep them tied up until
Acidemia: blood pH below 7.35
Alkalemia: blood pH above 7.45
Acidosis: abnormal process leading to acidemia
Alkalosis: abnormal process leading to alkalemia Lung diseases will affect the pH, PaO , PaCO a2d therefo2e these are important parameters
used in the strategies for the treatment of lung diseases.
Cyanosis, which is the bluish color of the mucus membrane, occurs when the %
saturation of oxygen and hemoglobin drops to below 80% or PaO of 50 – 60 mm Hg. 2
By altering the alveolar ventilation, the body has great control over acid-base balance.
Increasing the alveolar ventilation will increase the pH
Hyperventilation decreases the PaCO and hypove2tilation increases the PaCO and 2
decreases the pH
Since the alveolar ventilation can change drastically, the pH can be changed
Changes in H in the arterial blood can have substantial impacts on the rates of ventilation.
Increases in H have a greater impact on increasing ventilation than decreases in H
have on decreasing ventilation.
The pH resulting from CO dissol2ing in blood and the dissociation of carbonic acid is given by
the Henderson-Hasselbach Equation
pH = pKA + log (HCO )/(CO 3 2
Since CO obe2s Henry’s Law, CO can be repl2ced by (.03 x PCO ) 2
pKA = 6.1 and is a constant related to the dissociation of carbonic acid.
HCO in3arterial blood = 24 mmol/liter
Dissolved CO = .02 mmol/mm Hg/liter
pH = 6.1 + log 24/(0.03 x 40 mm Hg) = 6.1 + log 24/1.2
pH = 6.1 + log 20 = 6.1 + 1.3 = 7.4
**As long as the ratio of (HCO ) to (3CO + .03) =220, the pH is 7.4.
HCO is regulated by kidneys and pCO by the lungs. Both can be lowered or increased, hence
any of the four disturbances will cause a characteristic acid-base change. The disturbances
are: Respiratory acidosis