Evaluation of respiratory muscle function in patients with left ventricular failure

The decrease in strength of respiratory muscles, determined by measuring the maximal respiratory pressures in the mouth, has been evoked as a mechanism of dyspnoea in patients with left ventricular failure (LVF). Knowing the limitations of this technique in the evaluation of the "real" strength, we propose to apply in this group of patients the different techniques available to study the maximal respiratory pressures. We studied 20 male patients, with LVF (GI), classes II and III of New York Heart Association (NYHA), and we compared them with 19 male aged-matched controls without cardiopulmonary disease (GII). We assessed the maximal respiratory pressures at the mouth level, expiratory (PME) and inspiratory (PMI), the nasal Sniff (SNIF-N) and the esophageal Sniff (SNIF-E). We have obtained the following results: PME: GI - 138.7 ± 42.1 cmH₂O; GII - 152.5 ± 40.8.8 cmH₂O; p:NS; PMI: GI - 74.1 ± 22.2 cmH₂O; GII - 85.8 ± 16.6 cmH₂O; p<0.03; SNIF-N: GI - 95.6 ± 22.2 cmH₂O; GII - 96.6 ± 16.6 cmH₂O; p:NS; SNIF-E: GI - 96.2 ± 20.6 cmH₂O; GII - 97.5 ± 18.5 cmH₂O; p:NS. When comparing PMI with SNIF-N we found a statistical significant difference between the groups: GI - p<0.0002 e GII - p<0.009. There was no statistical difference between SNIF-N and SNIF-E. In conclusion, PMI underestimates the strength of inspiratory muscles. LVF patients in NYHA classes II and III did not present a decrease in the global strength of respiratory muscles, once there were no significant differences in PME and SNIF values, between patients and control group. Finally we did not detect differences between SNIFF-N and SNIFF-E pressures so we think that the assessment of SNIFF-N pressure can be used as a non-invasive method to evaluate the strength of inspiratory muscles.