Abstract
<jats:p>Determining the dynamics of morphostructural changes in the diaphragm under conditions of pneumoperitoneum is critically important for establishing the pathogenetic mechanisms of postoperative respiratory dysfunction, since detailing the transitions from functional maladaptation to irreversible structural destruction of muscle tissue allows for the substantiation of safe parameters for laparoscopic interventions and the development of effective strategies to minimize intraoperative damage to the respiratory muscles. The aim of the study is to establish the dynamics of structural organization violations in the lumbar part of the diaphragm under conditions of pneumoperitoneum by identifying morphological changes in myocytes and performing a correlation analysis of morphometric indicators at time intervals of 1, 3, and 5 hours of experimental exposure. The study was performed on 40 adult male rats weighing 210.0±15.0 g, aged 5-6 months, which were divided into 4 groups: control and three experimental. Animals of the last three experimental groups were simulated pneumoperitoneum. The simulation was carried out by insufflation of CO2 into the abdominal cavity (pressure 10 mm Hg, flow 0.1 l/min). Morphological analysis included light microscopy (Masson's, Heidenhain's, and H&E staining) and electron microscopy. Morphometric parameters included muscle fiber diameter, relative volume of damage, and the nucleo-sarcoplasmic ratio. Statistical analysis of the results was carried out using the “STATISTICA 10.0” software. The significance of the difference between the groups was determined using the non-parametric Wilcoxon and Mann-Whitney tests. To establish correlations, Spearman's non-parametric method of correlation analysis was used. The study revealed that prolonged pneumoperitoneum provokes deep structural changes in the lumbar part of the diaphragm, which progress from reactive hyperhydration to pronounced destruction of myofibrils. In the early stages of the experiment, the microscopic picture is characterized by the development of acute interstitial and intracellular edema, accompanied by the expansion of the sarcoplasm with relative stability of the nuclear apparatus. With an increase in the duration of intra-abdominal hypertension (3-5 hours), signs of metabolic depletion and gradual alteration of myocytes are recorded in the structure of the diaphragm. Submicroscopic changes indicate a progressive accumulation of metabolic products in the sarcoplasm, which causes a change in the nuclear-sarcoplasmic balance and creates conditions for the development of intracellular hypoxia. The most pronounced structural disorders are observed after 5 hours of exposure, when a significant increase in the proportion of damaged myofibers is recorded in the tissue. Morphologically, this is manifested by foci of myofibril lysis, fiber fragmentation, and disruption of sarcolemma integrity. It has been established that the progression of hypertension leads to a linear accumulation of microstructural damage. The results obtained confirm that postoperative diaphragmatic dysfunction is caused not only by tissue stretching but also by progressive structural destruction, which indicates the need for strict optimization of intra-abdominal pressure parameters to minimize alterative processes.</jats:p>