Acute unloading of the work of breathing extends exercise duration in patients with heart failure

This study investigated whether maximal exercise performance can be improved by acutely decreasing the work of breathing in these patients.

Exertional dyspnea is a frequent limiting symptom in patients with heart failure. It may result from increased work of breathing.

Fifteen patients with heart failure and nine age-matched normal subjects underwent two maximal exercise tests. Subjects exercised twice in randomized, single-blind manner using room air (RA) and a 79% helium/21% oxygen mixture (He). Respiratory gas analysis, Borg scale recordings of perceived dyspnea and near infrared spectroscopy of an accessory respiratory muscle were obtained during exercise.

In normal subjects there was no significant difference in peak oxygen uptake (Vo2) ([mean +/- SD] RA 38 +/- 8 vs. He 35 +/- 7 ml/kg per min), exercise duration (RA 724 +/- 163 vs. He 762 +/- 123 s) or peak minute ventilation (RA 97 +/- 27 vs. He 97 +/- 28 liters/min, all p = NS). Only three of nine control subjects thought that exercise with the He mixture was subjectively easier. In contrast, patients with heart failure exercised an average of 146 s longer with the He mixture (RA 868 +/- 293 vs. He 1,014 +/- 338, p < 0.01). Peak Vo2 (RA 19 +/- 4 vs. He 18 +/- 5 ml/kg per min) and peak minute ventilation (RA 53 +/- 12 vs. He 53 +/- 15 liters/min) were unchanged (both p = NS). The respiratory quotient at peak exercise was lower with the He mixture (RA 1.05 +/- 0.08 vs. He 0.98 +/- 0.06, p < 0.05). Thirteen of the 15 patients thought that exercise with the He mixture was subjectively easier (p < 0.02 vs. control group).

In patients with heart failure, pulmonary factors, including respiratory muscle work and airflow turbulence, contribute to limiting exercise performance. Therapeutic interventions aimed at attenuating work of breathing may be beneficial.