Question 1

Stimulation to increase ventilation does not occur until the PaO₂ falls below what level?

Accepted Answer

Stimulation to increase ventilation typically does not occur until the partial pressure of oxygen (PaO2) falls below 60 mm Hg. This threshold triggers the body's response to increase breathing to enhance oxygen uptake.

Question 2

Why does it take about 24 hours for a full ventilatory response to develop to acute hypoxemia?

Accepted Answer

Initial cerebrospinal fluid (CSF) alkalemia, which occurs as a result of the initial hyperventilation induced by hypoxemia, temporarily blunts the hypoxic ventilatory response. This is because the resultant increase in blood pH (alkalemia) reduces the sensitivity of the central chemoreceptors to CO2, thereby temporarily limiting the ventilatory response to hypoxemia. Over time, as the CSF pH adjusts, the full ventilatory response to hypoxemia can develop.

Question 3

Adjustment of respiratory muscle contractions to accommodate varying loads is regulated by which of the following?

Accepted Answer

The answer of Adjustment of respiratory muscle contractions to accommodate...

Question 4

Which receptors are primarily responsible for the initial increase in ventilation that occurs at the beginning of exercise?

Accepted Answer

Proprioceptors, located in muscles, tendons, and joints, are primarily responsible for the initial increase in ventilation at the beginning of exercise. They sense the movement and position of the body, sending signals to the respiratory centers to adjust breathing rate in response to physical activity.

Question 5

Which of the following is indirectly responsible for minute-to-minute control of breathing?

Accepted Answer

CO₂ levels indirectly control breathing by affecting the pH of the blood. Increased CO₂ leads to increased hydrogen ion concentration, lowering pH, which is detected by central chemoreceptors that stimulate the respiratory center to adjust breathing rate.

Question 6

What group of nerve cells senses and responds to changes in the chemical composition of its fluid environment?

Accepted Answer

Chemoreceptors are specialized nerve cells that sense and respond to changes in the chemical composition of their fluid environment. They are responsible for detecting changes in the pH, oxygen and carbon dioxide levels, and the concentration of various chemicals in the body, such as glucose and electrolytes.

Question 7

In the face of chronically elevated levels of CO₂, what happens to the response mediated by the central chemoreceptors?

Accepted Answer

Chronically elevated levels of CO2 lead to adaptation of the central chemoreceptors, resulting in a decrease in their sensitivity to changes in CO2. As a result, the response mediated by the central chemoreceptors is muted or decreased.

Question 8

Coexisting arterial hypoxemia, acidemia, and high PaCO₂ (i.e., asphyxia) will have what affect on the peripheral chemoreceptors?

Accepted Answer

Coexisting arterial hypoxemia, acidemia, and high PaCO2 (asphyxia) all stimulate peripheral chemoreceptors. This results in a maximal increased drive to breathe to attempt to correct the imbalance.

Question 9

Both anemia and carbon monoxide (CO) poisoning can cause severe hypoxia, yet neither condition results in a major stimulation of breathing. Why is this so?

Accepted Answer

The peripheral chemoreceptors, which are primarily responsible for detecting changes in blood oxygen levels, respond to low partial pressure of oxygen (hypoxemia) rather than low oxygen content. Both anemia and CO poisoning reduce the oxygen-carrying capacity of the blood without necessarily causing a significant drop in the partial pressure of oxygen. Therefore, they do not majorly stimulate an increase in breathing through the peripheral chemoreceptors.

Question 10

How should oxygen therapy be administered to chronically hypercapnic patients?

Accepted Answer

Chronically hypercapnic patients have adapted to elevated levels of carbon dioxide in their blood, and giving them excessive oxygen can suppress their respiratory drive and lead to worsening hypoventilation. However, withholding oxygen is not appropriate if the patient is hypoxemic. Therefore, the goal should be to provide enough oxygen to maintain adequate oxygenation without causing respiratory depression. The specific target oxygen saturation should be determined by the underlying respiratory condition and comorbidities.

Question 11

What is the response of a patient with chronic hypercapnia to a sudden acute rise in carbon dioxide?

Accepted Answer

Patients with chronic hypercapnia have chronically elevated levels of carbon dioxide in their blood, which can lead to a blunted respiratory drive. However, an acute rise in carbon dioxide levels can still trigger an increase in respiratory drive, as the body attempts to compensate for the sudden change. This response is known as the hypercapnic ventilatory response.

Question 12

What has the primary responsibility for sensing and responding to changes in blood levels of CO₂?

Accepted Answer

Central chemoreceptors, located in the medulla oblongata, primarily sense changes in CO2 levels in the blood by detecting changes in the pH of cerebrospinal fluid, which reflects CO2 concentration.

Question 13

In what manner would oxygen therapy induce worsening $\dot { V }$ / $\dot { Q }$ mismatch and thus a further elevation in CO₂ in a chronically hypercapnic patient?

Accepted Answer

Oxygen therapy can worsen $\dot { V }$ / $\dot { Q }$ mismatch in chronically hypercapnic patients by improving blood flow to poorly ventilated alveoli, which can paradoxically decrease overall oxygenation by increasing perfusion to areas of the lung that are not adequately ventilated.

Question 14

Which respond more rapidly to high levels of CO₂?

Accepted Answer

Carotid chemoreceptors respond more rapidly to changes in CO₂ levels than aortic chemoreceptors or central chemoreceptors. Ventral respiratory centers are involved in controlling breathing rate and depth in response to changes in CO2 levels, but not CO₂ levels.

Question 15

Which of the following centers respond more strongly to high levels of CO₂?

Accepted Answer

Central chemoreceptors, located in the medulla oblongata, are primarily responsible for detecting changes in CO2 levels in the blood and cerebrospinal fluid, responding more strongly to high levels of CO2.

Question 16

What happens in chronic hypercapnia? I.The central chemoreceptive response to CO₂ is decreased. II.The cerebrospinal fluid pH is restored to normal. III.Responsiveness to increased CO₂ is decreased.

Accepted Answer

In chronic hypercapnia, the body adapts to the consistently high levels of CO2. This adaptation includes a decreased central chemoreceptive response to CO2, allowing the body to tolerate higher levels of CO2 without triggering increased respiration as aggressively as it would in an acute setting. Additionally, the cerebrospinal fluid (CSF) pH is restored towards normal due to renal compensation, which adjusts the bicarbonate levels in the blood, indirectly affecting the CSF pH. Lastly, the overall responsiveness to increased CO2 is decreased, as the body's systems adjust to the chronic high levels of CO2, making the respiratory drive less sensitive to CO2 levels.

Question 17

When given high concentrations of oxygen, a patient with chronic hypercapnia may develop a more serious respiratory acidosis. Which of the following might be contributing to the patient's increased PCO₂? I.worsening ventilation-perfusion ( $\dot { V }$ / $\dot { Q }$ ) balance II.desensitization of the carotid bodies III.removal of the hypoxic stimulus

Accepted Answer

I and III are correct. Worsening ventilation-perfusion balance and removal of the hypoxic stimulus can both lead to increased PCO2.

Question 18

In the face of hyperoxia, what is the response of the peripheral chemoreceptors to hypercapnia?

Accepted Answer

High arterial PO₂ (hyperoxia) decreases the peripheral chemoreceptors' PCO₂ sensitivity to almost zero.

Question 19

Where are the peripheral chemoreceptors located?
I.in the arch of the aorta
II.in the bifurcations of carotid arteries
III.on the ventrolateral surfaces of the medulla

Accepted Answer

Peripheral chemoreceptors are located in the carotid bodies at the bifurcations of the carotid arteries and in the aortic bodies in the arch of the aorta. They are not located on the ventrolateral surfaces of the medulla; those are the locations of central chemoreceptors.

Question 20

Which of the following causes hypoxic stimulation of the carotid bodies? I.large decrease in arterial PO₂ II.large decrease in oxygen content III.CO₂ poisoning

Accepted Answer

The carotid bodies are primarily sensitive to changes in arterial PO2. A large decrease in arterial PO2 directly stimulates the carotid bodies, whereas changes in oxygen content or CO2 poisoning do not directly stimulate them because they do not affect the partial pressure of oxygen.

Quiz 14: Regulation of Breathing

Stimulation to increase ventilation does not occur until the PaO2 falls below what level?

Why does it take about 24 hours for a full ventilatory response to develop to acute hypoxemia?

Adjustment of respiratory muscle contractions to accommodate varying loads is regulated by which of the following?

Which receptors are primarily responsible for the initial increase in ventilation that occurs at the beginning of exercise?

Which of the following is indirectly responsible for minute-to-minute control of breathing?

What group of nerve cells senses and responds to changes in the chemical composition of its fluid environment?

In the face of chronically elevated levels of CO2, what happens to the response mediated by the central chemoreceptors?

Coexisting arterial hypoxemia, acidemia, and high PaCO2 (i.e., asphyxia) will have what affect on the peripheral chemoreceptors?

Both anemia and carbon monoxide (CO) poisoning can cause severe hypoxia, yet neither condition results in a major stimulation of breathing. Why is this so?

How should oxygen therapy be administered to chronically hypercapnic patients?

What is the response of a patient with chronic hypercapnia to a sudden acute rise in carbon dioxide?

What has the primary responsibility for sensing and responding to changes in blood levels of CO2?

In what manner would oxygen therapy induce worsening V˙\dot { V }V˙ / Q˙\dot { Q }Q˙​ mismatch and thus a further elevation in CO2 in a chronically hypercapnic patient?

Which respond more rapidly to high levels of CO2?

Which of the following centers respond more strongly to high levels of CO2?

What happens in chronic hypercapnia? I.The central chemoreceptive response to CO2 is decreased. II.The cerebrospinal fluid pH is restored to normal. III.Responsiveness to increased CO2 is decreased.