Acute Cardiopulmonary and Muscle Oxygenation Responses to Normocapnic Hyperpnea Exercise in COPD

This study aimed to investigate cardiorespiratory responses and intercostal muscle oxygenation during normocapnic hyperpnea exercise in chronic obstructive pulmonary disease (COPD).

Twenty-two patients with COPD performed a cardiopulmonary cycling exercise test to assess peak oxygen consumption (V˙O2peak) and minute ventilation (V˙Epeak). They also performed a normocapnic hyperpnea exercise alone, at 50%-60% of V˙Epeak to exhaustion, using a respiratory device (Spirotiger) connected to a gas analyzer to monitor V˙O2, V˙E, and end-tidal CO2 partial pressure. Cardiac output, and intercostal and vastus lateralis muscle oxygenation were continuously measured during exercise using finger photoplethysmography and near-infrared spectroscopy, respectively. Arterial blood gases (arterial PCO2) and inspiratory capacity were obtained at rest and at the end of hyperpnea exercise.

The hyperpnea exercise lasted 576 ± 277 s at a V˙E of 34.5 ± 12.1 L·min-1 (58% ± 6% of V˙Epeak), a respiratory rate of 22 ± 4 breaths per minute, and a tidal volume of 1.43 ± 0.43 L. From rest to the end of hyperpnea exercise, V˙O2 increased by 0.35 ± 0.16 L·min-1 (P < 0.001), whereas end-tidal CO2 partial pressure and arterial PCO2 decreased by ~2 mm Hg (P = 0.031) and ~5 mm Hg (P = 0.002, n = 13), respectively. Moreover, inspiratory capacity fell from 2.44 ± 0.84 L at rest to 1.96 ± 0.59 L (P = 0.002). During the same period, heart rate and cardiac output increased from 69 ± 12 bpm and 4.94 ± 1.15 L·min-1 at rest to 87 ± 17 bpm (P = 0.002) and 5.92 ± 1.58 L·min-1 (P = 0.007), respectively. During hyperpnea exercise, intercostal deoxyhemoglobin and total hemoglobin increased by 14.26% ± 13.72% (P = 0.001) and 8.69% ± 12.49% (P = 0.003) compared with their resting value. However, during the same period, vastus lateralis oxygenation remained stable (P > 0.05).

In patients with COPD, normocapnic hyperpnea exercise provided a potent cardiorespiratory physiological stimulus, including dynamic hyperinflation, and increased intercostal deoxyhemoglobin consistent with enhanced requirement for muscle O2 extraction.