The threshold for detecting a rise in airflow resistance during tidal breathing is lower in older patients with COPD than in healthy people of similar age

Introduction: To investigate whether or not the threshold for subjectively detecting an increase in the resistance to airflow (LDT) during tidal breathing at rest rises in older age in patients with COPD, as it does in healthy people and asthmatics in remission.

Material and methods: We conducted an open cross-sectional study of 31 older patients (age 55-89) with COPD and 60 healthy volunteers (age 55-86). Inspiratory and expiratory resistive load detection thresholds (ILDT and ELDT respectively) and spirometry were measured.

Results: The mean (SD) ILDT was 5.93 (7.02) kPa.s/L in COPD patients, compared to 11.11 (8.47) in healthy people (P < 0.001) in the same age range. There was no significant correlation between ILDT and age in the COPD group (r = -0.182, P = 0.326), though significant correlation with age was found in healthy people (r = 0.591, P < 0.001). ILDT and ELDT in COPD patients correlated significantly with the FEV1/FVC ratio (r = 0.367, P = 0.048 and r = 0.481, P = 0.007 respectively) but not with other spirometry indices, height, weight, BMI, oxygen saturation or smoking pack-years.

Conclusion: LDT during tidal breathing appears to be sensitized, and thereby lower, in older COPD patients, possibly due to altered central regulation of the threshold or as a consequence of the effect lung compliance, recoil and volume changes have on afferent input from mechano-receptors in COPD. Older COPD patients with good cognition are therefore likely to be as aware of changing airways resistance as younger patients and take appropriate therapeutic action.