Assessing perceptual sensitivity of respiratory load using constant airway resistance

Introduction: Breathlessness or dyspnoea is a complex subjective sensation that is an important feature of cardio-respiratory disease which is difficult to quantify. An objective measure would be useful as it would allow patients symptoms and response to therapy to be summarized and compared.

Objectives: This study aims to investigate whether a new approach could be used to quantify resistive load detection in participants with healthy lungs or obstructive lung disease with breathlessness.

Methods: Sixteen participants (five with chest disease, MRC dyspnoea score 4) were variously tested using three respiratory loading protocols, and applying a resistance between 0.2 to 1.5 kPa.L.sec-1 .

Results: In a healthy group (n=11) a sigmoidal relationship between load detection and applied load was observed with the 50% detection rate being 0.5 kPa.L.sec-1 and a minimal load detection between 0.2 and 0.3 kPa.L.sec-1 whereas in the group with chest disease (n=5) a threshold response was seen instead and a load below 0.75 kPa.L.sec-1 was undetectable.

Conclusions: In health there is a graded response to extrathoracic resistive respiratory loading, with the perceptual sensitivity independent of the method of load delivery. In lung disease the perceptual sensitivity is lost and load detection is reported (all or nothing) only above a threshold (0.75 kPa.L.sec-1). This approach provides a simple method for quantifying resistive load detection.