Measurement of respiratory muscle strength.

Abstract

Why must the chest physician become familiar with assessment of the respiratory muscles? Firstly, because dyspnoea in patients in whom no pulmonary cause can be detected may be due to respiratory muscle weakness.t2 Even moderately severe muscle weakness may be difficult to detect clinically3 and, indeed, it is possible to have total paralysis of the diaphragm without life threatening consequences.4 Secondly, because patients with clearly documented generalised neuromuscular disease usually also have respiratory muscle weakness2 and, for selected cases, treatment in the form of non-invasive ventilation is indicated.5 Finally, there has recently been increased awareness that respiratory muscle weakness can be a com- pounding factor in other disease processes such as mal- nutrition6 and steroid therapy.7 For all of these reasons it is important for respiratory physicians to initiate and to be able to interpret simple tests ofrespiratory muscle function. For most patients the suspicion of clinically important respiratory muscle weakness may be confirmed or excluded by simple tests that can be performed in the general hospital setting without the purchase of expensive equipment, but in some patients complex tests in a specialised laboratory are necessary (fig In this editorial the current techniques to assess respiratory muscle strength are reviewed with Is unexplainied breathlessness cdue to respiratory mLscle weakness? Nori-ial VC with Ye EXCILudes cliniically important <20% fall when supinle inspiratory muscle weakness No Yes MIP >80(M), >70 (F) co NTo SNIP >70 (M), >60 (F) Yes No Further respiratory and peripheral mnuscle assessment requlired. No Results suggest respiratory muscle weakness is likely Yes | Review cl nicalIpiCtL re. Is diaphragm weakness isolated? No Establish diagnosis if uncertain, consider phrenic nerve conduction studies EMG, muscle biopsy, neurological opinion No treatment requlired if lungs otherwise norrmal. Consider hemidiaphragm studies Regular follow Lip, SNIP, VC, MEP and Qs MVC at each visitI 1 Symptoms of respiratory mLIscle pump failLure Repeat formal studies with sleep study. Consider ventilatory assistance