Respiratory-related evoked potentials in chronic obstructive pulmonary disease and healthy aging.

Altered neural processing and increased respiratory sensations have been reported in chronic obstructive pulmonary disease (COPD) as larger respiratory-related evoked potentials (RREPs), but the effect of healthy-aging has not been considered adequately. We tested RREPs evoked by brief airway occlusions in 10 participants with moderate-to-severe COPD, 11 age-matched controls (AMC) and 14 young controls (YC), with similar airway occlusion pressure stimuli across groups. Mean age was 76 years for COPD and AMC groups, and 30 years for the YC group. Occlusion intensity and unpleasantness was rated using the modified Borg scale, and anxiety rated using the Hospital Anxiety and Depression Scale. There was no difference in RREP peak amplitudes across groups, except for the N1 peak, which was significantly greater in the YC group than the COPD and AMC groups (p = 0.011). The latencies of P1, P2 and P3 occurred later in COPD versus YC (p < 0.05). P3 latency occurred later in AMC than YC (p = 0.024). COPD and AMC groups had similar Borg ratings for occlusion intensity (3.0 (0.5, 3.5) [Median (IQR)] and 3.0 (3.0, 3.0), respectively; p = 0.476) and occlusion unpleasantness (1.3 (0.1, 3.4) and 1.0 (0.75, 2.0), respectively; p = 0.702). The COPD group had a higher anxiety score than AMC group (p = 0.013). A higher N1 amplitude suggests the YC group had higher cognitive processing of respiratory inputs than the COPD and AMC groups. Both COPD and AMC groups showed delayed neural responses to the airway occlusion, which may indicate impaired processing of respiratory sensory inputs in COPD and healthy aging.

Absence of inspiratory premotor potentials during quiet breathing in cervical spinal cord injury.

A premotor potential, or Bereitschaftspotential (BP), is a low-amplitude negativity in the electroencephalographic activity (EEG) of the sensorimotor cortex. It begins ~1 s prior to the onset of inspiration in the averaged EEG. Although normally absent during quiet breathing in healthy, younger people, inspiration-related BPs are present in people with respiratory disease and healthy, older people, indicating a cortical contribution to quiet breathing. People with tetraplegia have weak respiratory muscles and increased neural drive during quiet breathing, indicated by increased inspiratory muscle activity. Therefore, we hypothesized that BPs would be present during quiet breathing in people with tetraplegia. EEG was recorded in 17 people with chronic tetraplegia (14M, 3 female; 22-51 yr; C3-C7, American Spinal Injury Association Impairment Scale A-D; >1 yr postinjury). They had reduced lung function and respiratory muscle weakness [FEV1: 54 ± 19% predicted, FVC: 59 ± 22% predicted and MIP: 56 ± 24% predicted (mean ± SD)]. Participants performed quiet breathing and voluntary self-paced sniffs (positive control condition). A minimum of 250 EEG epochs during quiet breathing and 60 epochs during sniffs, time-locked to the onset of inspiration, were averaged to determine the presence of BPs at Cz, FCz, C3, and C4. Fifteen participants (88%) had a BP for the sniffs. Of these 15 participants, only one (7%) had a BP in quiet breathing, a rate similar to that reported during quiet breathing in young able-bodied participants (12%). The findings suggest that, as in young able-bodied people, a cortical contribution to quiet breathing is absent in people with tetraplegia despite higher neural drive.NEW & NOTEWORTHY People with tetraplegia have weak respiratory muscles, increased neural drive during quiet breathing, and a high incidence of sleep-disordered breathing. Using electroencephalographic recordings, we show that inspiratory premotor potentials are absent in people with chronic tetraplegia during quiet breathing. This suggests that cortical activity is not present during resting ventilation in people with tetraplegia who are awake and breathing independently.

Inspiratory pre-motor potentials during quiet breathing in ageing and chronic obstructive pulmonary disease.

KEY POINTS: A cortical contribution to breathing, as indicated by a Bereitschaftspotential (BP) in averaged electroencephalographic signals, occurs in healthy individuals when external inspiratory loads are applied. Chronic obstructive pulmonary disease (COPD) is a condition where changes in the lung, chest wall and respiratory muscles produce an internal inspiratory load. These changes also occur in normal ageing, although to a lesser extent. In the present study, we determined whether BPs are present during quiet breathing and breathing with an external inspiratory load in COPD compared to age-matched and young healthy controls. We demonstrated that increased age, rather than COPD, is associated with a cortical contribution to quiet breathing. A cortical contribution to inspiratory loading is associated with more severe dyspnoea (i.e. the sensation of breathlessness). We propose that cortical mechanisms may be engaged to defend ventilation in ageing with dyspnoea as a consequence. ABSTRACT: A cortical contribution to breathing is determined by the presence of a Bereitschaftspotential, a low amplitude negativity in the averaged electroencephalographic (EEG) signal, which begins ∼1 s before inspiration. It occurs in healthy individuals when external inspiratory loads to breathing are applied. In chronic obstructive pulmonary disease (COPD), changes in the lung, chest wall and respiratory muscles produce an internal inspiratory load. We hypothesized that there would be a cortical contribution to quiet breathing in COPD and that a cortical contribution to breathing with an inspiratory load would be linked to dyspnoea, a major symptom of COPD. EEG activity was analysed in 14 participants with COPD (aged 57-84 years), 16 healthy age-matched (57-87 years) and 15 young (18-26 years) controls during quiet breathing and inspiratory loading. The presence of Bereitschaftspotentials, from ensemble averages of EEG epochs at Cz and FCz, were assessed by blinded assessors. Dyspnoea was rated using the Borg scale. The incidence of a cortical contribution to quiet breathing was significantly greater in participants with COPD (6/14) compared to the young (0/15) (P = 0.004) but not the age-matched controls (6/16) (P = 0.765). A cortical contribution to inspiratory loading was associated with higher Borg ratings (P = 0.007), with no effect of group (P = 0.242). The data show that increased age, rather than COPD, is associated with a cortical contribution to quiet breathing. A cortical contribution to inspiratory loading is associated with more severe dyspnoea. We propose that cortical mechanisms may be engaged to defend ventilation with dyspnoea as a consequence.