Anna Hudson – Abstract

Age-related adaptions in the neural control of the human diaphragm muscle

Hudson AL[1, 2], Nguyen DAT[1, 2], Lewis RHC[1, 2, 3], Gandevia SC[1, 2, 3] and Butler JE[1, 2]
1. NeuRA, Sydney, Australia
2. University of New South Wales, Sydney, Australia
3. Prince of Wales Hospital, Sydney, Australia

There are changes in the skeletal, pulmonary and respiratory neuromuscular systems with healthy ageing. A study using a gastro-oesophageal catheter to record EMG reported higher diaphragm EMG during eupnoea in healthy subjects > 50 years, but these measures may be affected by the normalisation process used (1). The definitive method to assess neural drive is the single motor unit technique. Here, to assess age-related changes in neural drive to the diaphragm during eupnoea, EMG was recorded from the costal diaphragm using a monopolar needle electrode in participants from three age groups (n ≥ 7 each): older (65-80 years); middle-aged (43-55 years) and young (23-26 years). In each group, 154, 174, and 110 single motor units, respectively, were discriminated. A mixed effects linear model showed no significant differences between age groups for onset (group range 9.5-10.2 Hz) or peak (14.1-15.0 Hz) discharge frequencies during eupnoea. However, there was delayed onset (by ~10% of inspiratory time; p=0.02) and earlier offset (by ~20% of inspiratory time; p=0.04) of single motor unit activity in the older group. The respiratory parameters during the recordings were similar across groups. The area of motor unit potentials was ~40% larger in the middle-aged and older groups (p<0.02). Therefore, although we found no age-related difference in firing frequencies during eupnoea, there were differences in the timing of motor unit activity in the older group. Changes in motor unit morphology indicate axonal sprouting and re-innervation of diaphragm muscle fibres is associated with ageing, even in middle-aged participants.

  1. Jolley CJ, Luo Y-M, Steier J, Reilly C, Seymour J, Lunt A, Ward K, Rafferty GF, Polkey MI & Moxham J. (2009). Neural respiratory drive in healthy subjects and in COPD. European Respiratory Journal 33, 289-297.