title: Activation of human inspiratory muscles in an upside-down posture.
abstract: During quiet breathing, activation of obligatory inspiratory muscles differs in timing and magnitude. To test the hypothesis that this coordinated activation can be modified, we determined the effect of the upside-down posture compared with standing and lying supine. Subjects (n=14) breathed through a pneumotachometer with calibrated inductance bands around the chest wall and abdomen. Surface electromyographic activity (EMG) was recorded from the scalene muscles. Crural diaphragmatic EMG and oesophageal and gastric pressures were measured in a subset of six subjects. Quiet breathing and standard lung function manoeuvres were performed. The upside-down posture reduced end-expiratory lung volume. During quiet breathing, for the same inspiratory airflow and tidal volume, ribcage contribution decreased, abdominal contribution increased and transdiaphragmatic pressure swing doubled in the upside-down posture compared to standing (p<0.05). Despite this, crural diaphragm EMG was unchanged, whereas scalene muscle EMG was reduced by ∼half (p<0.05). Thus, the mechanical effect of an upside-down posture differentially affects inspiratory muscle activation.
authors.affiliation: Neuroscience Research Australia, Australia; University of New South Wales, Australia.
authors.forename: Anna L
authors.initials: AL
authors.lastname: Hudson
authors.affiliation: UMR MD2, Aix Marseille University & IRBA, Marseille, France; University of Toulon, La Garde, France.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Joulia
authors.affiliation: Neuroscience Research Australia, Australia; University of New South Wales, Australia.
authors.forename: Annie A
authors.initials: AA
authors.lastname: Butler
authors.affiliation: Neuroscience Research Australia, Australia; University of New South Wales, Australia.
authors.forename: Richard C
authors.initials: RC
authors.lastname: Fitzpatrick
authors.affiliation: Neuroscience Research Australia, Australia; University of New South Wales, Australia.
authors.forename: Simon C
authors.initials: SC
authors.lastname: Gandevia
authors.affiliation: Neuroscience Research Australia, Australia; University of New South Wales, Australia. Electronic address: j.butler@neura.edu.au.
authors.forename: Jane E
authors.initials: JE
authors.lastname: Butler
mesh_terms: D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D011187:Posture / Q000502:physiology*; D011312:Pressure; D012119:Respiration; D012132:Respiratory Muscles / Q000502:physiology*; D055815:Young Adult
keywords: Breathing; Diaphragm; Inspiratory drive; Posture; Scalene