Perception of intrinsic and extrinsic respiratory loads in children with life-threatening asthma.

There is a subpopulation of asthmatic patients with a history of life-threatening asthma (LTA) who have a reduced perception of respiratory loads. The aim of this study was to determine if these patients have a reduced perception of both intrinsic and extrinsic loads. Children with asthma were classified into life-threatening asthma and control asthmatic groups. Perception of extrinsic loads was assessed by magnitude estimation of inspiratory resistive loads. Magnitude estimation was measured with handgrip estimation of resistive load magnitude. Perception of intrinsic loads was by methacholine bronchoprovocation in doses sufficient to a drop to 40% below baseline of forced expired volume in 1 sec (FEV(1)). Chest tightness, breathlessness, and air hunger, as estimated by a Borg scale were, used to rate methacholine perception. Life-threatening asthma subjects had a lower slope than nonlife-threatening asthma subjects for magnitude estimation of resistive loads. Life-threatening asthma patients also had a lower maximum Borg score for all three symptoms. There was no significant difference in magnitude estimation of symptom type.These results suggest that life-threatening asthma subjects have poor perception of extrinsic and intrinsic loads. This suggests that there is a similarity between the sensations elicited by intrinsic and extrinsic loads, allowing for the identification of poor-perceiving patients with either method of assessment and who suffer from life-threatening asthma.