Differences in Respiratory Muscle Responses to Hyperpnea or Loaded Breathing in COPD

Introduction We aimed to compare acute mechanical and metabolic responses of the diaphragm and rib cage inspiratory muscles during two different types of respiratory loading in patients with COPD. Methods In 16 patients (age:65±13, 56% male, FEV1:60±6%pred, Pimax:82±5%pred) assessments of respiratory muscle electromyography (EMG), esophageal (Pes) and gastric (Pga) pressures, breathing pattern, and noninvasive assessments of systemic (VO2, cardiac output, oxygen delivery and extraction) and respiratory muscle hemodynamic and oxygenation responses (blood flow index [BFI], oxygen delivery index, deoxyhemoglobin concentration [HHb] and tissues oxygen saturation [StiO2]), were performed during hyperpnea and loaded breathing. Results During hyperpnea, breathing frequency, minute ventilation, esophageal and diaphragm pressure-time product (PTP)/min, cardiac output and VO2 were higher than during loaded breathing (P0.05). SCA-BFI and oxygen delivery index were lower, and SCA-HHb was higher during loaded breathing compared to hyperpnea. Furthermore, SCA and intercostal muscle StiO2 were lower during loaded breathing compared to hyperpnea (P