Breathlessness in Patients with Chronic Airflow Limitation: Mechanical Unloading of Inspiratory Muscles
Opiates and Anxiolytics: Opiates effectively relieve breathlessness in many patients with CAL Postulated mechanisms include reduced motor command output or altered central perception of inspiratory difficulty at a given ventilation. However, serious adverse effects, particularly respiratory depression, preclude their routine use except in the palliative treatment of the terminally breathless patient.
Benzodiazepines have the potential to relieve breathlessness by their anxiolytic action and/or by reducing respiratory motor output. However, several controlled studies of various benzodiazepines have failed to demonstrate any consistent improvement over placebo. Asthma medications inhalers Click Here Moreover, the active drugs tended to be poorly tolerated. Limitations of these studies include small sample sizes and uncertainty as to whether the patients with CAL studied suffered from morbid anxiety in addition to breathing difficulty. However, given the prevalence of severe anxiety in breathless patients with CAL, it is reasonable to recommend a trial of anxiolytic therapy on an individual basis with careful monitoring of the symptomatic response.
Currently, in the experimental setting, the efficacy of new methods of inspiratory muscle unloading is being evaluated in the management of breathlessness in CAL. In this respect, low-level continuous positive airway pressure (CPAP) administered acutely has been shown to ameliorate breathlessness and significantly improve exercise capacity in some patients with severe disease. Continuous positive airway pressure works by counterbalancing the effects of DH on the inspiratory muscles. Since the salutary effects of CPAP are achieved at a low level, ie, 4 to 5 cm H2O, its principal mechanical effect is thought to be that of negating the inspiratory threshold load with some reduction of the elastic work of breathing. Therefore, CPAP enhances neuroventilatory coupling and restores a more harmonious balance between perceived inspiratory effort (Pes/Pimax) and the anticipated mechanical consequence (change in respired volume) (Fig 3).
Figure 3 Left (A), Intensity of breathlessness (Borg scale) against time during CPAP-assisted exercise and bracketing unassisted control periods (Cl, C2) in a 71-year-old man (FEVi=30 percent predicted, RV=290 percent predicted) (From O’Donnell DE, Sanii R, Younes M. Am Rev Respir Dis 1988; 138:1510-14, by permission). Right, (B), Low-level CPAP improves the relationship between tidal Pes/Pimax and instantaneous changes in volume during exercise in CAL; autoPEEP=auto or intrinsic positive end-expiratory pressure.
Category: Respiratory Symptoms
Tags: breathlessness, chronic airflow limitation, copd, dynamic compression, dynamic hyperinflation, exercise