Airway response to induced muscular contraction in spontaneously breathing rabbits.
The airways are thought to dilate during exercise in humans but the time course and mechanisms of the response are not fully described. The aim of the study was to document changes in airway calibre during electrically induced muscular contractions (MC) in spontaneously breathing rabbits. Experiments were also performed after induced bronchoconstriction to assess the effect of change in breathing pattern on airway calibre during MC. Respiratory resistance (R(RS)) was measured in 12 rabbits using the forced oscillation technique at 20 Hz before, during and after 30s MC in control conditions and after methacholine induced bronchoconstriction (Mch). MC was associated with significant decrease in R(RS) both at control and Mch. The MC induced increase in V(E) occurred with significant albeit small change in mean tidal volume (V(T)) at Mch but not control. An augmented breath (AB) occurred in 29/35 MCs and was usually associated with an abrupt drop in R(RS). The decrease in R(RS) induced by AB was significantly larger at Mch compared with control. Passively inflating the lung after MC induced significantly larger decrease in R(RS) than AB during MC. The data indicate bronchodilation by MC in spontaneously breathing rabbits. The mechanisms appear to include AB dependent airway wall stretching as well as removal of cholinergic input to the airway smooth muscle.
Marchal
François
F
Laboratoire de Physiologie, Faculté de Médecine, Avenue de la Forêt de Haye, F-54505 Vandoeuvre les Nancy, France. f.marchal@chu-nancy.fr
Demoulin
Bruno
B
Schweitzer
Cyril
C
Leblanc
Anne Laure
AL
Bertin
Noëlle
N
D000222:Adaptation, Physiological / Q000187:drug effects; D000403:Airway Resistance / Q000187:drug effects / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D016085:Bronchoconstrictor Agents / Q000494:pharmacology; D004558:Electric Stimulation; D016210:Methacholine Chloride / Q000494:pharmacology; D023421:Models, Animal; D009119:Muscle Contraction / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000187:drug effects / Q000502:physiology*; D011817:Rabbits; D015656:Respiratory Mechanics / Q000187:drug effects / Q000502:physiology*
D016085:Bronchoconstrictor Agents; D016210:Methacholine Chloride