Pulmonary capillary blood volume in hyperpnea-induced bronchospasm

Area of Science:

• Pulmonary Medicine
• Respiratory Physiology

Background:

• Exercise and hyperpnea can trigger airway narrowing in asthma, a condition known as hyperpnea-induced bronchospasm (HIB).
• Changes in lung parenchymal mechanics, including increased peripheral airway resistance, are observed in HIB.
• The pulmonary circulation supplies the peripheral airways and lung parenchyma, leading to the hypothesis that altered pulmonary blood flow may influence airway resistance and tissue mechanics during HIB.

Purpose of the Study:

• To investigate whether pulmonary capillary blood flow increases during hyperpnea-induced bronchospasm (HIB) in individuals with asthma.
• To determine if changes in pulmonary capillary blood volume (VC) are associated with the airway narrowing observed in HIB.

Main Methods:

• Pulmonary capillary blood volume (VC) was measured using the diffusing capacity of the lung for carbon monoxide (DLCO) technique.
• Measurements were taken before and after a hyperpnea challenge in 13 subjects with asthma and HIB, and 10 control subjects.
• Two test gases with varying oxygen concentrations were used to determine DLCO.

Main Results:

• Subjects with asthma experienced a significant decrease in FEV1 after hyperpnea compared to controls (p < 0.001).
• Despite the bronchospasm, there were no significant changes in DLCO or VC from baseline values in the asthma group.
• Control subjects did not show significant changes in FEV1, DLCO, or VC.

Conclusions:

• Pulmonary capillary blood volume (VC) does not change following hyperpnea in individuals with or without asthma.
• The findings do not support the hypothesis that increased pulmonary blood flow contributes to hyperpnea-induced bronchospasm (HIB).
• Airway narrowing in HIB is likely mediated by mechanisms other than alterations in pulmonary capillary blood volume.