Rationale: Inspiratory muscle endurance as expressed by the tension-time index of the diaphragm [TTI=(Pdi/\nPdimax) Ã?â?? (Ti/Ttot)] in normal subjects and cardiorespiratory disorders requires the use of esophageal and gastric\nballoons. A noninvasive technique can be used in which the ratio of tidal volume to vital capacity Vt/FVC is substituted\nfor Pdi/Pdimax, with the resulting relationship [(Ti/Ttot) Ã?â?? (Vt/FVC)] called the breathing intolerance index (BIT). The\nresponse to medical management of BIT in patients with cardiomyopathy with chronic heartfailure has not been\nassessed before and after medical management.\nObjectives: To compare control of ventilation and BIT in patients with stable dilated cardiomyopathy at rest and\nexercise, and to analyze BIT, oxygen uptake and carbon dioxide elimination at baseline and approximately one year\nafter initiating medical management.\nMethods: Control of ventilation and BIT were assessed in 24 patients (mean age 55.5 years; 17 males) at rest\nand at peak exercise during bicycle ergometry, at baseline and approximately 14 months later.\nResults: Median peak VO2 was 12.9 mL/kg/min and 14.3 mL/kg/min at baseline and followup, respectively\n(p<0.036, adjusted for age, gender and BMI). It increased 4.3 times from rest to peak exercise at baseline and 4.7\ntimes at followup (NS). Peak Vââ?¬â?¢O2 increased by 10.5% between baseline and followup (p=0.036 after adjusting for\nage, sex and BMI). BIT did not change significantly. Peak Vââ?¬â?¢O2/BIT increased significantly from baseline to follow-up\n(p=0.008, adjusted for age, sex and BMI). No patients died or experienced acute heart failure during the study.\nConclusions: Peak Vââ?¬â?¢O2 in relation to non-invasively measured peak tension-time index of the respiratory\nmuscles (BIT) increases significantly after one year of medical management, indicating increased efficient oxygen\nutilization as cardiac function improves. BIT is useful for noninvasively assessing inspiratory muscle endurance and\nrelating oxygen uptake to ventilation in patients with dilated cardiomyopathy and chronic congestive heart failure
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