Abstract: Objective To observe effects of restraint position on the changes of diaphragmatic mechanical characteristic in rats, and try to explore the role of nitric oxide（NO）. Methods Rat model of restraint position was established. Rats were divided into control group, restraint position 12 h and 24 h groups. The markers of respiratory functions in vivo and the biomechanical markers of diaphragmatic characteristic ex vivo were evaluated. Serum NO levels were measured with spectrophotometry. The expressions of nNOS and iNOS mRNA in diaphragm were detected using RT-PCR. Results Compared with control group, respiratory rate, tidal volume and minute ventilation were significantly decreased in the restraint position 12 h and 24 h groups. Pt of diaphragm significantly decreased and force-generating capacity reduced at low frequency stimulation in 12 h group. Force-generating capacity over the full range reduced at low and high frequency stimulation in 24 h group. Pt of diaphragm in control and restraint position groups increased after L-NNA pre-incubation. Force-frequency relationship after L-NNA pre-incubation reduced in 24 h group. NO level in serum increased significantly in the restraint position groups. Diaphragmatic nNOS mRNA expression was upregulated significantly in the restraint position groups. Conclusion Restraint position induces the decreasement of diaphragmatic contractility and the decreasement is mediated by NO from diaphragm or circulation blood.

Key words: forensic pathology, biomechanics, nitric oxide, position, diaphragm, rats