Respiratory Control

A 65-year-old patient with a long history of smoking undergoes pulmonary function testing. The results show a significantly decreased FEV 1 ​ and a forced vital capacity (FVC) that is near normal, resulting in an FEV1/FVC ratio of 42%. Based on the provided materials, which of the following best describes the pathophysiological state and the characteristic finding on a flow-volume curve?

• Obstructive disease; the effort-independent portion of the expiratory curve is depressed inward.
• Obstructive disease; the total lung capacity (TLC) and residual volume (RV) are significantly decreased.
• Restrictive disease; the peak expiratory flow (PEF) is increased due to high elastic recoil.
• Restrictive disease; the flow-volume curve is shifted to the right with reduced lung volumes.

During a deep inspiration to total lung capacity (TLC), airway resistance is significantly lower than at residual volume (RV). Which mechanical principle primarily accounts for this reduction in resistance?

• The transmural pressure gradient across the airway wall becomes more negative.
• Increased sympathetic discharge causes bronchodilation at higher volumes.
• Radial traction by the elastic recoil of alveolar septa pulls the airways open.
• Laminar flow is converted to turbulent flow as the velocity of air increases.

A clinician is reviewing the cellular mechanisms of Hypoxic Pulmonary Vasoconstriction (HPV). According to the 'redox-based regulation of KV channel' hypothesis, what is the sequence of events triggered by alveolar hypoxia in pulmonary artery smooth muscle cells (PASMCs)?

• Increased H2O2 ​production → Activation of soluble guanylate cyclase → Tonic vasorelaxation.
• Activation of KV channels → Hyperpolarization → Release of Ca2+ from the sarcoplasmic reticulum.
• Inhibition of NADPH oxidase → Decreased superoxide production → Membrane hyperpolarization.
• Inhibition of KV channels → Membrane depolarization → Ca2+ influx via L-type channels.

In the human respiratory tree, where is the major site of airways resistance located during normal, quiet breathing?

• Medium-sized bronchi.
• Trachea.
• Upper airways including the nose and pharynx.
• Terminal bronchioles (smaller than 2 mm).

Which of the following best describes the physiological significance and mechanism of the Haldane effect?

• Oxygenation of hemoglobin in the lungs promotes the binding of CO2 to amino groups.
• High 2,3−DPG levels shift the oxyhemoglobin dissociation curve to the left.
• Deoxygenated hemoglobin has a higher affinity for CO2, facilitating its transport from tissues to the lungs.
• Increased CO2 ​and H+ concentration in tissues causes hemoglobin to release oxygen more readily.