Background: Breathlessness is a common problem in chronic heart failure (CHF) patients, and respiratory muscle strength has been proposed to play an important role in causing breathlessness in these patients.
Objectives: The aim of this study was to investigate the relation between respiratory muscle strength and the severity of CHF, and the influence of respiratory muscle strength on abnormal ventilation during exercise in CHF patients.
Patients and methods: In this case series study, we assessed clinically stable CHF outpatients (N = 66, age: 57.7 ± 14.6 years). The peak oxygen consumption (peak VO2), the slope relating minute ventilation to carbon dioxide production (VE/VCO2 slope), and the slope relating tidal volume to respiratory rate (TV/RR slope) were measured during cardiopulmonary exercise testing. Respiratory muscle strength was assessed by measuring the maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP).
Results: The MIP and MEP decreased significantly as the New York Heart Association functional class increased (MIP, P = 0.021; MEP, P < 0.01). The MIP correlated with the TV/RR slope (r = 0.57, P < 0.001) and the VE/VCO2 slope (r = -0.44, P < 0.001), and the MEP also correlated with the TV/RR slope (r = 0.53, P < 0.001) and the VE/VCO2 slope (r = -0.25, P < 0.040). Stepwise multiple regression analysis revealed that age and MIP were statistically significant predictors of the TV/RR and VE/VCO2 slopes (both P < 0.05).
Conclusions: Respiratory muscle strength is related to the severity of CHF, and associated with rapid and shallow ventilation or excessive ventilation during exercise.
Keywords: Exercise Test; Heart Failure; Respiratory Muscle.