Final answer:
In obstructive lung diseases, the Forced Expiratory Volume in 1 second (FEV1) represents a decreased flow rate, indicating increased resistance in the lung airways, which leads to slower exhalation of air.
Step-by-step explanation:
The respiratory value that represents a decreased flow rate during obstructive lung disease is the Forced Expiratory Volume in 1 second (FEV1). During obstructive lung diseases such as asthma and emphysema, there is increased resistance in the lung airways, making it hard for the patient to get the air out of their lungs. This results in a slower flow rate and thus a lower FEV1. Additionally, the FEV1/FVC (Forced Vital Capacity) ratio is an important diagnostic tool, where a lower ratio indicates obstructive lung disease. Conversely, in restrictive lung diseases, such as lung fibrosis, the FVC is reduced, but the FEV1/FVC ratio is usually higher because airways are not obstructed, allowing air to be expelled faster.
In obstructive lung disease, the decreased flow rate can be represented by a decreased Forced Expiratory Volume in 1 second (FEV1). FEV1 measures the amount of air that can be forcibly exhaled in one second after taking a deep breath. In obstructive lung disease, the airway obstruction results in slow exhalation, leading to a decreased flow rate.
On the other hand, Forced Vital Capacity (FVC), Peak Expiratory Flow Rate (PEFR), and Total Lung Capacity (TLC) are not directly related to the flow rate and may or may not be affected in obstructive lung diseases.