Changes in the perception of inspiratory resistive loads during partial curarization.

Abstract

SUMMARY1. The ability of normal subjects to estimate the magnitude of resistive loads and to detect resistive loads was determined using standard psychophysical techniques. The experiments were repeated during maintained partial neuromuscular blockade with D-tubocurarine.2. During curarization the ability to detect the presence of a small inspiratory resistive load was not significantly impaired. This finding is consistent with the view that changes in the usual breath-by-breath relation between pressure and flow mediate detection.3. The size of resistive loads was over-estimated during partial curarization. Subjects thus placed more reliance on sensing the increased motor command required during curarization than on alternative peripheral signals related to pressure, flow or resistance.4. The exponent for the power function relating the perceived magnitude of a resistive load to its actual size (Stevens, 1957) was reduced during partial neuromuscular blockade.5. These results suggest that detection of resistive loads depends upon sensing apparent information arising from an unexpected pressure-flow disturbance but that estimation of the size of an added load depends, in part, on sensing the outgoing motor command.

Unaltered respiratory-related evoked potentials after acute diaphragm dysfunction in humans

“…Inspiratory strength training does not alter load detection but reduces the perceived magnitude of both resistive and elastic loads [4]. Conversely, globally weakening inspiratory muscle exacerbates the sense of inspiratory efforts [5,6]. This is similar to that occurring in upper limb muscles where the development of fatigue increases the perceived heaviness of a lifted object [7], and illustrates the role of respiratory muscle afferents in the genesis of respiratory sensations.…”

“…This result is in line with various types of data relating respiratory muscle function and respiratory sensations. Indeed, global inspiratory muscle dysfunction or fatigue, as induced by partial curarisation [6] and exhaustion following repeated maximal static inspiratory efforts [5] lead to the overestimation of inspiratory loads. Conversely, respiratory sensations seem preserved in situations where inspiratory muscle groups are altered separately.…”

Chronic lung diseases and the perception of breathlessness: a clinical perspective

“…In subsequent experiments, these and other workers showed that breathing frequency and inspiratory duration [20], the presence or absence of respiratory muscle weakness [21] or fatigue [22] ventilatory drive [23] and length tension relationships [24] were also variables which affect respiratory sensation. The findings of these experiments are significant because they indicate that respiratory sensation and thus by extrapolation breathlessness is determined by many factors associated with the act of breathing.…”

An Official American Thoracic Society Statement: Update on the Mechanisms, Assessment, and Management of Dyspnea

“…With weakened respiratory muscles, the requirement for motor command is increased, and the perception of inspiratory force, effort, and work can be substantially magnified (54,60,61,63), even in the absence of an increase in ventilation. It is likely that simultaneous information from muscle afferents focuses and calibrates sensation from corollary discharge (42,64).…”

“…Perception of breathing effort or work can be produced in the laboratory by external resistive or elastic loads (e.g., 37, 54-57), by volitional hyperpnea (e.g., 54, 58, 59), or by weakening the respiratory muscles via changes in operating length, fatigue, or partial neuromuscular blockade (60)(61)(62). With weakened respiratory muscles, the requirement for motor command is increased, and the perception of inspiratory force, effort, and work can be substantially magnified (54,60,61,63), even in the absence of an increase in ventilation.…”