A6 Respiratory Problems

Topic

Ventilatory mechanics follow a normal pattern defined by a set of standard parameters: the resistance the airways offer to airflow, the extent to which the lung expands in response to a pressure change—its lung compliance—and the force the respiratory muscles can generate. When actual ventilatory mechanics deviate from these normal parameters, a respiratory problem arises, which can originate in three distinct ways.

The first pathway is increased airway resistance: when the airways offer more resistance to airflow than the normal parameter dictates, air flows with greater difficulty during exhalation, and this alteration constitutes an obstructive pattern.

The second pathway is reduced lung compliance: when the lung expands less than the normal parameter dictates in response to the same pressure change, the volume of air entering with each breath decreases, and this alteration constitutes a restrictive pattern.

The third pathway is respiratory muscle weakness: regarding these muscles, when the diaphragm or intercostal muscles generate less force than the normal parameter dictates, the volume of air moved with each breath is reduced—even if airway function and lung compliance are normal—because the muscular pump itself fails to expand the chest sufficiently.

The model distinguishes between these three pathways—increased airway resistance, reduced lung compliance, and respiratory muscle weakness—because each causes ventilatory mechanics to deviate from normal parameters through a different mechanism; it quantifies the severity of the respiratory problem based on how far each affected parameter diverges from its normal value: the greater the divergence, the greater the severity. Quantifying the severity of each pathway helps guide the strategy for retraining ventilatory mechanics: a strategy aimed at reducing airway resistance does not correct reduced lung compliance, and neither approach directly strengthens the diaphragm or intercostal muscles when they are the cause of the respiratory problem.

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