Heliox increases quadriceps muscle oxygen delivery during exercise in COPD patients with and without dynamic hyperinflation

Abstract

Some reports suggest that heliox breathing during exercise may improve peripheral muscle oxygen availability in patients with chronic obstructive pulmonary disease (COPD). Besides COPD patients who dynamically hyperinflate during exercise (hyperinflators), there are patients who do not hyperinflate (non-hyperinflators). As heliox breathing may differently affect cardiac output in hyperinflators (by increasing preload and decreasing afterload of both ventricles) and non-hyperinflators (by increasing venous return) during exercise, it was reasoned that heliox administration would improve peripheral muscle oxygen delivery possibly by different mechanisms in those two COPD categories. Chest wall volume and respiratory muscle activity were determined during constant-load exercise at 75% peak capacity to exhaustion, while breathing room air or normoxic heliox in 17 COPD patients: 9 hyperinflators (forced expiratory volume in 1 s = 39 ± 5% predicted), and 8 non-hyperinflators (forced expiratory volume in 1 s = 48 ± 5% predicted). Quadriceps muscle blood flow was measured by near-infrared spectroscopy using indocyanine green dye. Hyperinflators and non-hyperinflators demonstrated comparable improvements in endurance time during heliox (231 ± 23 and 257 ± 28 s, respectively). At exhaustion in room air, expiratory muscle activity (expressed by peak-expiratory gastric pressure) was lower in hyperinflators than in non-hyperinflators. In hyperinflators, heliox reduced end-expiratory chest wall volume and diaphragmatic activity, and increased arterial oxygen content (by 17.8 ± 2.5 ml/l), whereas, in non-hyperinflators, heliox reduced peak-expiratory gastric pressure and increased systemic vascular conductance (by 11.0 ± 2.8 ml·min(-1)·mmHg(-1)). Quadriceps muscle blood flow and oxygen delivery significantly improved during heliox compared with room air by a comparable magnitude (in hyperinflators by 6.1 ± 1.3 ml·min(-1)·100 g(-1) and 1.3 ± 0.3 ml O(2)·min(-1)·100 g(-1), and in non-hyperinflators by 7.2 ± 1.6 ml·min(-1)·100 g(-1) and 1.6 ± 0.3 ml O(2)·min(-1)·100 g(-1), respectively). Despite similar increase in locomotor muscle oxygen delivery with heliox in both groups, the mechanisms of such improvements were different: 1) in hyperinflators, heliox increased arterial oxygen content and quadriceps blood flow at similar cardiac output, whereas 2) in non-hyperinflators, heliox improved central hemodynamics and increased systemic vascular conductance and quadriceps blood flow at similar arterial oxygen content.

Acute respiratory muscle unloading by normoxic helium–O2 breathing reduces the O2 cost of cycling and perceived exertion in obese adolescents

“…Although in normal subjects, this phenomenon may not happen during submaximal exercise (Wetter et al 1999), it could occur in obese patient population characterized by a substantially higher work of breathing and increased metabolic demands. Some previous studies in COPD patients (Louvaris et al 2012;Vogiatzis et al 2011) also demonstrated a reduced expiratory muscle activity during He-O 2 breathing, with consequent improvements in cardiac output and "central" hemodynamics and further increases in peripheral muscle O 2 delivery.…”

“…Also the calibration of the pneumotachograph was carried out by utilizing the experimental gas mixture (AIR or He-O 2 ). The possibility of this technical limitation was not mentioned in the studies by Brice and Welch (1983), Chiappa et al (2009), Esposito and Ferretti (1997), Louvaris et al (2012), Murphy et al (1969), Powers et al (1986).…”

An Official American Thoracic Society/European Respiratory Society Statement: Update on Limb Muscle Dysfunction in Chronic Obstructive Pulmonary Disease

“…Recently, NIRS has been used in combination with the light-absorbing tracer indocyanine green dye to quantify regional blood flow in muscle and connective tissue during dynamic exercise in patients with COPD (352). Subsequent studies showed that respiratory muscle unloading improves locomotor muscle blood flow and oxygen delivery during exercise in patients with different patterns and degrees of dynamic hyperinflation (429,494). 31 P-NMR spectroscopy is a noninvasive method to evaluate high-energy compounds ATP, PCr, inorganic phosphate (Pi), and intracellular pH of single muscle groups during exercise and recovery (495).…”

Effects of Expiratory Positive Airway Pressure on Dynamic Hyperinflation During Exercise in Patients With COPDThe Authors Respond:

“…The authors selected in their recent study the lower resistance model, with a dead space above the mean reported in their previous study. 7 The potential clinical implications of this were not discussed in the paper. 2 Currently there are no studies that have evaluated the effect of a variable dead space and internal resistance of HMEs on patients during NIV.…”

“…In order to make this classification, they adopted the criterion of an inspiratory capacity decrease of greater than 4.5% of the baseline value, or greater than 150 mL. 7 Cordonie et al considered DH to constitute any drop in inspiratory capacity, compared with the baseline value. This discrepancy in definition undermines the comparability of the findings as well as the ability of this classification to identify patients who will benefit from DH treatments.…”