Respiratory muscle power output in patients with chronic heart failure andpatients with chronic pulmonary obstructive disease

Background: The maximal pressure generated by inspiratory muscles (PIMax) i s an index of their strength which is diminished in both chronic obstructiv e pulmonary disease (COPD) and chronic heart failure (CHF). Although inspir atory muscle power output (IMPO), which includes both strength and velocity of shortening, has been shown to be reduced in COPD, there is no informati on regarding IMPO in CHF. Aim: To measure IMPO in patients with CHF and COP D. Patients and methods: we studied 9 CHF patients with functional capacity II and III and 9 patients were severe COPD. Eight normal subjects of simil ar ages were included as controls. Power output was measured using the incr emental threshold loading test. Results: Maximal IMPO was significantly red uced in both groups of patients. Power output developed with each increasin g load was also diminished, basically as a consequence of a reduction in Vi nsp. The degree of dyspnea at the end of the test was greater in COPD than in CHF patients and normal subjects. For a given level of power, dyspnea wa s also greater in patients than in normals subjects. There was no decrease in SpO(2) during the test. Conclusions: IMPO is equally reduced in COPD and CHF patients. Power output is better related to dyspnea than PIMax, probab ly because of the inclusion of shortening velocity (Rev Med Chile 2001; 129 : 51-59).