Effort sensation, chemoresponsiveness, and breathing pattern during inspiratory resistive loading.
Although inspiratory resistive loading (IRL) reduces the ventilatory response to CO2 (VE/PCO2) and increases the sensation of inspiratory effort (IES), there are few data about the converse situation: whether CO2 responsiveness influences sustained load compensation and whether awareness of respiratory effort modifies this behavior. We studied 12 normal men during CO2 rebreathing while free breathing and with a 10-cmH2O.l-1.s IRL and compared these data with 5 min of resting breathing with and without the IRL. Breathing pattern, end-tidal PCO2, IES, and mouth occlusion pressure (P0.1) were recorded. Free-breathing VE/PCO2 was inversely related to an index of effort perception (IES/VE; r = -0.63, P less than 0.05), and the reduction in VE/PCO2 produced by IRL was related to the initial free-breathing VE/PCO2 (r = 0.87, P less than 0.01). IRL produced variable increases in inspiratory duration (TI), IES, and P0.1 at rest, and the change in tidal volume correlated with both VE/PCO2 (r = 0.63, P less than 0.05) and IES/VE (r = -0.69, P less than 0.05), this latter index also predicting the changes in TI with loading (r = -0.83, P less than 0.01). These data suggest that in normal subjects perception of inspiratory effort can modify free-breathing CO2 responsiveness and is as important as CO2 sensitivity in determining the response to short-term resistive loading. Individuals with good perception choose a small-tidal volume and short-TI breathing pattern during loading, possibly to minimize the discomfort of breathing.
Clague
J E
JE
Regional Thoracic Unit, Fazakerley Hospital, Liverpool, United Kingdom.
Carter
J
J
Pearson
M G
MG
Calverley
P M
PM
D000328:Adult; D002245:Carbon Dioxide / Q000494:pharmacology; D002628:Chemoreceptor Cells / Q000502:physiology*; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology; D008297:Male; D005082:Physical Exertion / Q000502:physiology*; D012119:Respiration / Q000502:physiology*; D012129:Respiratory Function Tests; D015656:Respiratory Mechanics / Q000502:physiology
D002245:Carbon Dioxide