Acute and severe trabecular bone loss in a rat model of critical illness myopathy

Prolonged mechanical ventilation for critically ill patients with respiratory distress can result in severe muscle wasting with preferential loss of myosin. Systemic inflammation triggered by lung mechanical injury likely contributes to this myopathy, although the exact mechanisms are unknown. In this study, we hypothesized that muscle wasting following mechanical ventilation is accompanied by bone loss. The objective was to determine the rate, nature, and extent of bone loss in the femora of rats ventilated up to 10 days and to relate the bone changes to muscle deterioration. We have developed a rat model of ventilator-induced muscle wasting and established its feasibility and clinical validity. This model involves pharmacologic paralysis, parenteral nutrition, and continuous mechanical ventilation. We assessed the hindlimb muscle and bone of rats ventilated for 0, 2, 5, 8, and 10 days. Routine histology, microCT, and biomechanical evaluations were performed. Hindlimb muscles developed changes consistent with myopathy, whereas the femurs demonstrated a progressive decline in trabecular bone volume, mineral density, and microarchitecture beginning Day 8 of mechanical ventilation. Biomechanical testing showed a reduction in flexural strength and stiffness on Day 10. The bone changes correlated with the loss of muscle mass and myosin. These results demonstrate that mechanical ventilation leads to progressive trabecular bone loss parallel to muscle deterioration. The results of our study suggest that mechanically ventilated patients may be at risk of compromised bone integrity and muscle weakness, predisposing to post-ventilator falls and fractures, thereby warranting interventions to prevent progressive bone and muscle decline.