The Relative Contributions of Compression and Hypoxia to Development of Muscle Tissue Damage: An In Vitro Study

Abstract

Deep pressure ulcers develop in tissues subjected to sustained mechanical loading. Though it has been hypothesized that this damage mechanism results from local tissue ischemia, it has recently been shown with a cell model that sustained compression can cause cell deformation, leading to tissue breakdown. The present study focuses on the assessment of cell viability during compression and ischemia in an in vitro muscle model to determine their relative contributions to damage development. A model system was developed consisting of engineered skeletal muscle produced from the culture of murine muscle cells in a collagen gel. The tissue was subjected to 0, 20, or 40% compression under hypoxic or normoxic conditions. Experiments were performed on the stage of a microscope and cell viability was monitored using fluorescent markers for apoptotic and necrotic cell death. Hypoxia did not lead to significant cell death over a 22 h period. By contrast, compression led to immediate cell death that increased with time. No additional effect of hypoxia on cell death was observed. These data show that contrary to existing theories, compression can cause development of muscle damage and that hypoxia does not contribute to cell death development within 22 h in engineered muscle.

Everyday sitting behavior of full-time wheelchair users

“…However, tissue loading is the defining cause of pressure ulcers and distinguishes them from other insults such as vascular and ischemic ulcers [1][2]. The mechanisms by which tissue loading leads to tissue breakdown have not been established [3], but current theories suggest that a combination of cell damage from prolonged deformation, ischemia of soft tissues, and a disruption in the equilibrium of the lymphatic system are involved [4][5][6]. Long-standing research has clearly demonstrated that the damaging effects of pressure are related to both its magnitude and duration [1][2], which is consistent with the proposed mechanisms of damage.…”

Comparison between a weight compression and a magnet compression for experimental pressure ulcers in the rat. Histological studies and effects of anesthesia

“…However, the pressure on the tissue may have gradually increased due to thinning of the skin and subcutaneous connective tissue that was sandwiched between the magnet and implanted steel plate/ magnet. Other than these methods mentioned above, both cultured muscles (Gawlitta et al, 2007) and artifi cial skin (Bronneberg et al, 2007) have been studied in vitro.…”

Development of an in vitro model of myotube ischemia

“…24,25 In contrast to the two-dimensional model in this study, a three-dimensional model of simulated ischemia of myotubes has also been developed. 26,27 However, it may be difficult to test the tissue-protective effects of compounds in the latter model as the surface area of the myotubes exposed to the culture media and the compounds dissolved in the culture media are limited.…”

“…40 The two-dimensional model used in this study resulted in a larger proportion of cells undergoing ischemia-induced apoptosis, rather than necrosis as compared to a threedimensional model of myotube ischemia. 26,27 This may be due to the fact that in a three-dimensional model, cells on the outside of the construct form a dense layer, which acts as a barrier to diffusion. 40 As a result, adequate oxygen and nutrients are not delivered to the center of the construct where cells become more susceptible to necrosis.…”