Asthma is most prevalent in Caucasian individuals.

Correct answer: True

Ventilation-perfusion (V/Q) matching is essential for efficient gas exchange in the lungs. Factors such as gravity influence blood flow, causing more perfusion in the lower lung regions compared with the upper regions, while ventilation may not perfectly match. Blocked alveolar ducts, as seen in mucus plugs or obstructive conditions, prevent air from reaching alveoli, creating areas of low ventilation relative to perfusion. Diseases such as pneumonia, pulmonary embolism, or chronic obstructive pulmonary disease can further disrupt the balance, leading to hypoxemia. Therefore, these factors collectively demonstrate how ventilation-perfusion mismatch can occur.

A. It only affects respiration during inhalation: Atmospheric pressure influences both inhalation and exhalation by creating the pressure gradient necessary for airflow. Limiting its effect to inhalation is inaccurate because it is a constant force acting on the body and lungs throughout the respiratory cycle.

B. It is the force exerted by surrounding air and is typically 760 mmHg at sea level: Atmospheric pressure is the weight of the air in the environment pressing on all surfaces. At sea level, it averages 760 mmHg and provides the baseline pressure against which intrapulmonary and intrapleural pressures are measured, driving air movement during breathing.

C. It is always lower than intrapleural pressure: In reality, intrapleural pressure is normally slightly negative relative to atmospheric pressure to keep the lungs inflated. Atmospheric pressure is generally higher than intrapleural pressure, so this statement is incorrect.

D. It fluctuates during the breathing cycle: Atmospheric pressure remains essentially constant during normal breathing. It is the intrapulmonary pressure that fluctuates with inhalation and exhalation, creating the gradient necessary for airflow, not the atmospheric pressure itself.