Author Question: What happens in chronic hypercapnia? 1. The central chemoreceptive response to CO2 is decreased. 2. ... (Read 52 times)

Redwolflake15 · **on:** Jul 16, 2018

What happens in chronic hypercapnia? 1. The central chemoreceptive response to CO2 is decreased. 2. The cerebrospinal fluid pH is restored to normal. 3. Responsiveness to increased CO2 is decreased.

a. 1 only
b. 1 and 2 only
c. 2 and 3 only
d. 1, 2, and 3

Question 2

In what manner would O2 therapy induce worsening mismatch and thus a further elevation in CO2 in a chronically hypercapnic patient?

a. By improving blood flow to poorly venti-lated alveoli
b. By decreasing blood flow to poorly venti-lated alveoli
c. Causing bronchoconstriction, which worsens gas flow to low areas
d. Causing bronchodilation, which improves gas flow to poorly ventilated alveoli

Ksanderson1296 · **Reply #1 on:** Jul 16, 2018

Answer to Question 1

ANS: D
If PaCO2 rises gradually over time, as might occur in severe COPD because of steadily deterio-rating lung mechanics, the kidneys compensate by increasing the plasma bicarbonate concentra-tion, keeping the arterial pH within normal limits. As plasma bicarbonate levels increase, these ions slowly diffuse across the blood-brain barrier, keeping cerebrospinal fluid pH in its normal range. The central chemoreceptors respond to hydrogen ion concentration, not the CO2 molecule; thus, they sense a normal pH environment, even though the PaCO2 is abnormally high.

Answer to Question 2

ANS: A
Oxygen breathing causes more blood flow to be directed to poorly ventilated alveoli, which takes blood flow away from well-ventilated alveoli. The key point is that when already un-der-ventilated alveoli receive additional blood flow, blood PCO2 rises further. These events can occur without a fall in overall minute ventilation.