Airway resistance in chronic heart failure measured by impulse oscillometry

Abstract

Background: Patients with chronic heart failure (CHF) complain of breathlessness and fatigue on exertion, have reduced peak oxygen consumption (pVO2), and an increased ventilatory response to exercise (VE/VCO2 slope). These limitations correlate with abnormalities of spirometry (forced expiratory volume in 1 second [FEV1] and forced ventilatory capacity [FVC]). Increased airway resistance by increasing the work of breathing might contribute to exercise intolerance in CHF. Methods: Impulse oscillometry (IOS) measures airway resistance and lung compliance independently of respiratory muscle strength and patient compliance. Sound waves of varying frequencies are sent into the lungs and the amplitude and phase shift of the reflected waves give a measure of airway resistance (R) and reactance (X). Twenty-three CHF patients and 18 controls underwent peak exercise testing with metabolic gas analysis and had airway resistance assessment using the Jaeger (Würtzberg, Germany) IOS system. Results: Patients had a lower pVO2 (18.7 (4.0) v 39.2 (8.3) mL·kg·min; P <.0001), elevated VE/VCO2 slope (41.6 (8.1) v 27.4 (2.9)), and lower FEV1 (2.4 (0.4) v 3.2 (0.7) L/min; P =.0001) and FVC (3.3 (0.7) v 4.1 (1.1) L; P <.005) than controls. R and X correlated with spirometric abnormalities and were different between patients and controls (R at 5 Hz 0.44 (0.16) v 0.30 (0.15) kPa (L/s); P <.005 and X at 5 Hz −0.16 (0.08) v −0.09 (0.08) kPa (L/s); P <.05). R at 5 Hz correlated with pVO2 (0.46; P =.0025) and VE/VCO2 slope (0.43; P <.05). Conclusion: CHF patients have elevated airway resistance and reduced reactance measured with IOS compared with control subjects.