Which of the following is the correct statement for respiration in human ?

Options

A. Cigarette smoking may lead to inflammation of bronchi
B. Neural signals from pneumotaxic centre in pons region of brain can increase the duration of inspiration
C. Workers in paper making industries may suffer from lung fibrosis
D. About 90% of carbon dioxide `(CO_2)` is carried by hemoglobin as carbamino hemoglobin

Answer

To determine the correct statement regarding respiration in humans, let's analyze each option provided in the question step by step.

### Step-by-Step Solution:

1. **Cigarette Smoking and Bronchi Inflammation:**
- Cigarette smoking is known to cause inflammation of the bronchi. This inflammation can lead to structural changes in the bronchioles, including enlargement. The smoke irritates the respiratory tract, leading to increased mucus production and swelling of the airways.
- **Conclusion:** This statement is correct.

2. **Neural Signals from Pneumotaxic Center:**
- The pneumotaxic center, located in the pons region of the brain, plays a role in regulating the rhythm of breathing. It primarily helps to limit the duration of inspiration, thus preventing over-inflation of the lungs.
- **Conclusion:** The statement that neural signals from the pneumotaxic center can increase the duration of inspiration is incorrect; it actually decreases it.

3. **Workers in Paper Making Industry and Lung Fibrosis:**
- Lung fibrosis is typically associated with exposure to certain types of dust, such as silica dust in industries like stone breaking or grinding. Paper making does not usually lead to lung fibrosis.
- **Conclusion:** This statement is incorrect.

4. **Carbon Dioxide Transport:**
- About 70% of carbon dioxide is transported in the form of bicarbonate ions, while only about 23% is carried by hemoglobin as carbaminohemoglobin. Therefore, the claim that 90% of CO2 is carried by hemoglobin is incorrect.
- **Conclusion:** This statement is incorrect.

### Final Answer:
The only correct statement regarding respiration in humans is that **cigarette smoking may lead to inflammation of bronchi.**