Diaphragm strength in chronic heart failure

Reduced respiratory muscle strength has been reported in chronic heart fail ure (CHF) in several studies. The data supporting this conclusion come almo st exclusively from static inspiratory and expiratory mouth pressure maneuv ers (MIP, MEP), which many subjects find difficult to perform. We therefore performed a study using measurements that are less dependent on patient ap titude and also provide specific data on diaphragm strength. In 20 male pat ients and 15 control subjects we measured MIP and MEP as well as esophageal and transdiaphragmatic pressure during maximal sniffs (Sn Pes, Sn Pdi) and cervical magnetic phrenic nerve stimulation (Tw Pdi). In a subgroup the re sponse to paired phrenic nerve stimulation (pTw Pdi) at interpulse interval s from 10 to 200 ms (5 to 100 Hz) was also determined. As expected, MIP was significantly reduced in the CHF group (CHF, 69.5 cm H2O; control, 96.7 cm H2O; p = 0.01), but differences were much less marked for Sn Pes (CHF, 95. 2 cm H2O; control, 104.8 cm H2O; p = 0.20) and MEP (CHF, 109.1 cm H2O; cont rol, 135.7 cm H2O; p = 0.09). Diaphragm strength was significantly reduced (Sn Pdi: CHF, 123.8 cm H2O; control 143.5 cm H2O; p = 0.04. Tw Pdi: CHF, 21 .4 cm H2O; control, 28.5 cm H2O; p = 0.0005). Paired phrenic nerve stimulat ion suggested a trend to increased twitch summation at 5 to 28 Hz in CHF, a lthough this did not reach significance. We conclude that mild reduction in diaphragm strength occurs in CHF, possibly because of an increased proport ion of slow fibers, but overall strength of the respiratory muscles remains well preserved.