| Aim: To investigate the respiratory dysfunctions and their types induced by the restraint position of mice or rats,preliminarily elucidate the mechanism underlying the respiratory dysfunctions.Methods: The observation of the death time of mice in the different restraint positions was used for the establishment of the mouse or rat asphyxia model induced by the restraint position.The model of rats'restraint position was established;Rats were divided into control group(C group),restraint position 6h group(R6h group)and restraint position 12h(R12h group).The changes of acid-base metabolic balance were measured by blood gas analysis;the ultrastructural alterations of the lung and diaphragm and their histopathological changes were examined with electron microscopy and routinal histological method; iNOS protein expression in diaphragm was detected with immunohistochemistry technique and western blotting.Results: 1 The death time at the different restraint position of mice (1)Limbs and neck were fixed,in supine position: Mice still survived after 24h;(2)Forelimbs were crossed in front of the chest with the hindlimbs and neck fixed and in the supine position: Mice survived about 10min;(3)Forelimbs were crossed behind the chest with hindlimbs and neck fixed and in the supine position: Mice still survived after 24h;(4)Limbs and neck were fixed with thoracic movement limited and in the supine position: The death time of mice was distributed between 12h-60h with the mean time of 32.55±15.23h;(5)Forelimbs were suspended by standard heavy weight in addition to hindlimbs and neck fixed,thoracic movement limited and in the supine position: 1)When forelimbs were suspended by the standard heavy weight of 100g, 125g and 150g, respectively, the death time of mice of 8-10 week age was 24.47±5.77h, 21.8±3.07h and 8.16±3.44h (P<0.01 vs the former two groups), respectively. 2)When forelimbs were suspended by the standard heavy weight of 100g and 125g respectively,the death time of mice of 5-6 week age was 16.18±6.29h and 10.08±7.12h. When forelimbs were suspended by the standard heavy weight of 100g, the death time of mice of 5-6 week age was distributed between 12h-24h,accounted for 75.26%. 3) When forelimbs were suspended by the standard heavy weight of 125g,the death time of mice of 8-10 week age or 5-6 week age was 21.8±3.07h and 10.08±7.12h(P<0.01 vs the former),respectively. 2 The changes of acid-base metabolic balance by blood gas analysis (1)Changes of pH in arterial blood: pH in C group was 7.36±0.02,while pH in R6h, R12h groups was 7.16±0.04, 7.06±0.07, respectively, which of both significantly decreased(P<0.01 vs C group), pH in R12h group significantly decreased(P<0.05 vs R6h group). (2)Changes of PaCO2 in arterial blood: PaCO2 in C group was 50.67±3.98mmHg, PaCO2 in R6h,R12h groups was 71.50±11.41mmHg, 88.5±8.78 mmHg, respectively,which of both significantly increased(P<0.01 vs C group),PaCO2 in R12h significantly increased(P<0.05 vs R6h group).(3)Changes of PaO2 in arterial blood: PaO2 in C group was 93.67±8.91mmHg, PaO2 in R6h,R12h groups was 90.17±8.11 mmHg,78.20±4.07mmHg,respectively. PaO2 in R6h decreased(P>0.05 vs C group),PaO2 in R12h significantly decreased(P<0.05 vs R6h group).(4)Changes of HCO3- in arterial blood: HCO3- in C group was 28.27±1.58mmol/L,HCO3- in R6h,R12h groups was 25.68±2.28mmol/L, 25.76±2.17mmol/L,respectively,and significantly decreased(P<0.05 vs C group). There was no significant difference for HCO3- between R6h group and R12h group(P>0.05). 3 The morphological changes (1)Compared with C group,the histological changes of lungs in R6h and R12h groups were as followed,local alveolar space was narrow,interalveolar septum was widened with inflammatory cells infiltration;Under transmission electron microscopes,there were few lamellar bodys and microvillus in typeⅡalveolar cell,mitochondria was vacuolated,respiratory membrane was thickened.(2)Compared with C group,the histological changes of lungs in R6h and R12h groups were as followed,local diaphragmatic muscle fibers were distorted and broken,spatium intermusculare was widened;Under transmission electron microscopes,myofibrils were broken,spatium intermusculare was widened, myofilaments were arranged in disorder,with mitochondrial swollen,arranged in bead like.4 iNOS protein expression in diaphram There was little or no visible iNOS expression in diaphragm in C,R6h or R12h group.Conclusions: 1.The mouse or rat asphyxia model induced by the restraint position was established with the thoracic movement limited,hindlimbs and neck fixed,forelimbs suspended by standard heavy weight and in the supine position. 2.The restraint position led to respiratory dysfunction with both respiratory and metabolic acidosis,especially more severe respiratory acidosis, to which the injurise of lung and diaphragm contributed. 3.In this experimental condition,there is little or no visible iNOS expression in the diaphragm,which may be related to the inadequate stimulation of confinement or duration of restraint position.
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