The presence of emphysema does not affect the systemic bioactivity of inhaled fluticasone in severe chronic obstructive pulmonary disease

Do airway clearance mechanisms influence the local and systemic effects of inhaled corticosteroids?

The role of airway clearance in inhaled drug therapy is complex. Disease-induced bronchoconstriction results in a central drug-deposition pattern where mucociliary clearance is most efficient. When drug-induced bronchodilation is achieved, deposition and uptake becomes more peripheral, and because there is less mucociliary clearance in the periphery, this will lead to an unintentional increase in lung exposure and enhance the risk of systemic side effects. In addition, mucociliary clearance is pathologically reduced in both asthma and chronic obstructive pulmonary disease. Among inhaled corticosteroids, rate of dissolution and lung uptake differs considerably. For the slowly dissolving, lipophilic steroids, the contribution of mucociliary clearance to these findings appears significant, and variability in lung and systemic exposure resulting from variable mucociliary function appears to be amplified. In addition, dose optimisation of non-stable asthma becomes more complex. The present review highlights the impact of mucociliary clearance on inhaled corticosteroid disposition and identifies critical areas where more research is needed.

Inspiratory muscle load and capacity in chronic heart failure

BACKGROUND

Although breathlessness is common in chronic heart failure (CHF), the role of inspiratory muscle dysfunction remains unclear. We hypothesised that inspiratory muscle endurance, expressed as a function of endurance time (Tlim) adjusted for inspiratory muscle load and inspiratory muscle capacity, would be reduced in CHF.

METHODS

Endurance was measured in 10 healthy controls and 10 patients with CHF using threshold loading at 40% maximal oesophageal pressure (Poes(max)). Oesophageal pressure-time product (PTPoes per cycle) and Poes(max) were used as indices of inspiratory muscle load and capacity, respectively.

RESULTS

Although Poes(max) was slightly less in the CHF group (-117.7 (23.6) v -100.0 (18.3) cm H(2)O; 95% CI -37.5 to 2.2 cm H(2)O, p = 0.1), Tlim was greatly reduced (1800 v 306 (190) s; 95% CI 1368 to 1620 s, p<0.0001) and the observed PTPoes per cycle/Poes(max) was increased (0.13 (0.05) v 0.21 (0.04); 95% CI -0.11 to -0.03, p = 0.001). Most of this increased inspiratory muscle load was due to a maladaptive breathing pattern, with a reduction in expiratory time (3.0 (5.8) v 1.1 (0.3) s; 95% CI 0.3 to 3.5 s, p = 0.03) accompanied by an increased inspiratory time relative to total respiratory cycle (Ti/Ttot) (0.43 (0.14) v 0.62 (0.07); 95% CI -0.3 to -0.1, p = 0.001). However, log Tlim, which incorporates the higher inspiratory muscle load to capacity ratio caused by this altered breathing pattern, was >/=85% predicted in seven of 10 patients.

CONCLUSIONS

Although a marked reduction in endurance time was observed in CHF, much of this reduction was explained by the increased inspiratory muscle load to capacity ratio, suggesting that the major contributor to task failure was a maladaptive breathing pattern rather than impaired inspiratory muscle endurance.