Respiratory Mechanisms in Acid-Base Homeostasis

The lungs control our blood pH. The lungs form the respiratory component and affect the PCO2 of blood. Ventilatory adjustments to pH change take several minutes to control any deviation, and frequently overcompensates. Thus, respiratory mechanisms are rapid compared to renal mechanisms in correcting blood pH.


EXAMPLES OF QUESTIONS AND ANSWERS

1. Explain how the lungs are involved in regulating blood pH.

1. The lungs flush acid out of the body by exhaling carbon dioxide (CO2)
2. Within physical limits, the body can raise and lower the rate of breathing to alter the amount of CO2 that is breathed out (expired).
3. This can affect blood pH within seconds to minutes

2. How does the lung regulate blood pH?

1. The lungs excrete or retain CO2, depending on blood pH
2. Under alkaline blood pH (alkalosis), the lungs will retain CO2 by slowing down breathing rate (hypoventilation), which will retain more CO2 in blood and increase blood PCO2, which in turn will help to reduce pH towards normal
3. Under acidic blood pH (acidosis), the lungs will rapidly excrete CO2 by increasing breathing rate (hyperventilation), which will expel CO2 faster and decrease blood PCO2, thus increasing pH towards normal

3. How is it possible for patients with lung problems to regulate blood pH?

1. Assisted respiration is used in patients with lung problems, including damaged lungs or paralysed breathing muscles.
2. Assisted respiration is of two types - non invasive and invasive
3. Non invasive assisted respiration uses a respirator - a mask is applied over the mouth and the patient breathes through the mask. 
4. In babies and young children suffering from severe viral infections and where breathing is affected and laboured, a nebulizer is used to help them breathe. They only need to use the nebuliser for a few minutes until breathing becomes normal and the babies/children are not struggling to breathe.
5. In patients with paralysis of the breathing muscles (Duchenne muscular dystrophy and the like), they are often confined to wheelchairs and a breathing machine attached to the back of the wheelchair to help them breathe out (as they can breathe in but not breathe out unassisted)
6. In invasive assisted respiration, the patient lies in bed and is hooked up to a blood and lung machine and remains as such till the patient is able to breathe normally or otherwise. This is seen in patients in ICU (intensive care unit), NICU (neonatal intensive care unit) and CCU (coronary care unit).