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Abstract 203Poster Session III, Monday, 5/3 (poster 103)
Analysis of mathematical models indicated that periodic body accelerations(PGz)of the whole body in the Gz plane (headwards-footwards)caused increased shear stress of vascular endothelium.( Med.Biol.Eng.Comput 1983;21:446) Others found that PGz was associated with hemodynamic changes in humans and animals.( J.Appl.Physiol.1966;21:1725) However, increased shear stress of vascular endothelium releases Nitric Oxide (NO), a potent vasodilator that might account for these prior observations.( Am. J.Physiol. 1991;261:H257) The purpose of this study was to ascertain whether NO was released by PGz.L-NAME, an enzymatic inhibitor of NO synthase produces dose responsive, pulmonary and systemic hypertension.PGz was achieved with a platform that moved in a sinusoidal,headwards-footwards direction at frequencies between 2 and 4 Hz with and amplitude of 0.5-1 cm; it produced Gz accelerations of ± 0.2 to 0.8G. Eight tracheostomized, anesthetized piglets 10-12 kg in weight, were paralyzed and placed on conventional mechanical ventilation with FiO2 100% and PEEP of 5 cm H2O. Baseline(BL)arterial blood gases(ABG),pulmonary(Ppa)and systemic (Psa) vascular pressures and thermodilution cardiac output (CO) were measured followed by an intravenous infusion of L-NAME (10mg/kg) over 15 min. After reaching a stable Psa, and Ppa (30min)PGz was started at 2-4 Hz with amplitude of 0.5-1cm The preceding variables were measured at 5, 15, 30 min after PGz was begun. While on PGz, a second dose of L-NAME (10mg/kg) was infused and measurements done after 15 and 30 mins. Data are [Mean (SD)]ANOVA(*p <0.05 BL vs.L-NAME and + L-NAME vs. Time)PVR and SVR= Calculated Pulmonary and Systemic Vascular Resistance (mmHg/L/min). (Table) L-NAME produced marked pulmonary and systemic hypertension and decreased CO. PGz decreased both Psa and Ppa. The pulmonary and systemic vascular hypertensive response were blunted after the 2nd dose of L-NAME during PGz. Since L-NAME has a dose response effect, these data indicate that PGz produced systemic and pulmonary vasodilatation. PGz mechanism of action most likely relates to increased vascular endothelial shear stress,causing endogenous nitric oxide release.
Adams, J., Bassuk, J., Zabaleta, I. et al. The Effects of Periodic Body Acceleration(PGz)Using Noninvasive Motion Ventilation (NIMV), on L-NAME Induced Pulmonary and Systemic Hypertension.
Pediatr Res45, 36 (1999). https://doi.org/10.1203/00006450-199904020-00219
