Perceived inspiratory difficulty during inspiratory threshold and hyperinflationary loadings

Area of Science:

• Respiratory Physiology
• Pulmonary Mechanics
• Clinical Investigation

Background:

• Dynamic hyperinflation increases end-expiratory lung volume (EELV) and intrinsic positive end-expiratory pressure (PEEPi).
• PEEPi acts as an inspiratory threshold load (ITL), impacting respiratory muscle function.
• The perception of inspiratory difficulty is a crucial clinical symptom in respiratory diseases.

Purpose of the Study:

• To independently assess the effects of imposed ITL and altered operating lung volume on perceived inspiratory difficulty.
• To determine the relative contributions of ITL and lung volume changes to inspiratory discomfort.

Main Methods:

• Eight healthy subjects were studied under controlled conditions.
• Increases in EELV and ITL were induced using continuous positive airway pressure (CPAP), external ITL, and positive end-expiratory pressure (PEEP).
• Perceived inspiratory difficulty was measured and analyzed using multiple regression.

Main Results:

• Both increased EELV and increased ITL independently raised perceived inspiratory difficulty.
• Combined increases in EELV and ITL (during PEEP) resulted in greater difficulty than independent increases.
• The imposed ITL was a significant predictor of inspiratory difficulty, explaining 40% of variations; changes in end-inspiratory lung volume explained an additional 24%.

Conclusions:

• Both imposed ITL and EELV independently contribute to the perception of inspiratory difficulty.
• The imposed ITL is a stronger predictor of perceived inspiratory difficulty than operating lung volume changes.
• These findings enhance understanding of respiratory mechanics and symptom perception.