Which of the following would be expected to have the greatest effect on the breathing effort ?

Options

A. slight change in venous carbon dioxide
B. large decrease in artial oxygen
C. large increase in arterial carbon dioxide
D. no change in hydrogen ion concentration

Answer

To determine which factor would have the greatest effect on breathing effort, we can analyze the components involved in the respiratory process. Here’s a step-by-step breakdown of the reasoning:

### Step 1: Understand Breathing Mechanics
Breathing involves the expansion and contraction of the lungs, which is influenced by the pressure differences created by respiratory muscles. The primary muscles involved are the diaphragm and intercostal muscles.

**Hint:** Consider how the muscles of respiration affect lung volume and pressure.

### Step 2: Recognize the Role of Lung Volume
The inspiratory lung volume refers to the amount of air that can be inhaled. A larger inspiratory lung volume leads to greater pressure changes within the thoracic cavity, which is essential for effective inhalation.

**Hint:** Think about how lung volume changes impact the pressure gradient necessary for air movement.

### Step 3: Consider Elastic Recoil
Elastic recoil is the tendency of the lungs to return to their resting state after being stretched. This recoil creates a pressure that must be overcome during inhalation. If the elastic recoil is strong, it requires more effort to inhale.

**Hint:** Reflect on how the lungs' elastic properties influence the effort required to breathe.

### Step 4: Analyze Carbon Dioxide Levels
An increase in arterial carbon dioxide (CO2) levels indicates that the body is not effectively expelling CO2, leading to a condition known as hypercapnia. This condition stimulates the respiratory center in the brain, increasing the drive to breathe.

**Hint:** Consider how changes in gas levels, particularly CO2, can signal the need for increased breathing effort.

### Step 5: Conclusion
Among various factors affecting breathing effort, a large increase in arterial carbon dioxide levels would have the greatest effect. This is because elevated CO2 levels trigger a stronger respiratory drive, leading to increased breathing effort to restore normal gas exchange.

**Final Answer:** The correct option is a large increase in arterial carbon dioxide.