Key result
Mechanical ventilation with 10 cm H2O PEEP in intact rats caused a significant fall in CO, SV and CBV (42, 48 and 17%) and an increase in SNA, HR and TPR (90, 13 and 83%) versus spontaneous breathing.
Why the study?
Does mechanical ventilation with PEEP alter sympathetic nerve activity and central hemodynamics in chloralose anaesthetized rats?
Does mechanical ventilation with PEEP alter sympathetic nerve activity and central hemodynamics in chloralose anaesthetized rats?
The excitation of the sympathetic nervous system during mechanical ventilation with PEEP is likely mediated by both unloading of arterial baroreceptors and cardiac receptors with vagal afferents.
Sympathetic excitation with PEEP in rats likely involves baroreceptor and vagal mechanisms; leaves open translation to clinical ventilation.
The aim of this study was to examine the effects of mechanical ventilation with increasing levels of positive end-expiratory pressure (PEEP) on sympathetic nerve activity (SNA), cardiac output (CO), stroke volume (SV), heart rate (HR), central blood volume (CBV), total peripheral resistance (TPR), mean arterial pressure (MAP), pulse pressure (PP) and right and left atrial transmural pressure in chloralose anaesthetized rats before and after vagotomy. Changing ventilatory pattern from spontaneous breathing (SB) to artificial ventilation with 10 cm H2O PEEP in intact animals caused a significant fall in CO, SV and CBV (42, 48 and 17%, respectively) and an increase in SNA, HR and TPR (90, 13 and 83%, respectively). The MAP increased slightly but significantly from 103 +/- 4 to 107 +/- 4 mmHg while PP decreased from 48 +/- 2 to 37 +/- 3, from spontaneous breathing (SB) to 10 cm H2O PEEP. Transmural left atrial pressure decreased significantly from 4.5 +/- 0.3 to 3.0 +/- 0.4 mmHg. After vagotomy, MAP and CO were significantly lower at 10 cm H2O PEEP and PP and SV were significantly lower at all levels of positive end-expiratory pressure than the corresponding prevagotomy values. In spite of a greater fall in MAP and PP during PEEP after vagotomy, the absolute and relative increase of SNA was significantly lower compared to corresponding prevagotomy values. We conclude that reflex cardiovascular adjustments elicited by ventilation with PEEP are not solely due to unloading of arterial baroreceptors as has been claimed by others. Unloading of cardiac receptors with tonically active inhibitory afferents in the vagi is probably also of great importance for the excitation of the sympathetic nervous system during mechanical ventilation with PEEP.
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Selldén et al. (1986) studied this question. Mechanical ventilation with 10 cm H2O PEEP vs. Spontaneous breathing was evaluated on Sympathetic nerve activity and central haemodynamics. Mechanical ventilation with 10 cm H2O PEEP in intact rats caused a significant fall in CO, SV and CBV (42, 48 and 17%) and an increase in SNA, HR and TPR (90, 13 and 83%) versus spontaneous breathing.
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