Effect of Group B Streptococcal Sepsis on Diaphragmatic Function in Young Piglets

Abstract

ABSTRACT: Recent studies indicate that diaphragmatic pressure generation (Pdi) is impaired by bacterial infection. However, group B streptococcus (GBS) had no effect on Pdi when infused into 4-wk-old piglets. As responsiveness to GBS is age-dependent, we therefore studied the acute effect of GBS infusion on Pdi, using a younger, 2-wk-old piglet model. Using trans-Pdi with phrenic nerve stimulation, we studied the effect of continuous GBS infusion in seven anesthetized, spontaneously breathing 2-wk-old piglets. Pdi was measured under baseline conditions (50% O₂/ 50% N₂) and at 1, 2, and 4 h of GBS infusion. GBS was infused at a rate which caused a doubling of the pulmonary artery pressure but which avoided hypotension or acidosis—both of which can decrease Pdi. In addition, the piglets were kept hyperoxic [PaO₂ > 13.3 kPa (100 torr)], and no piglet with hypercapnia [PaCO₂ > 8.7 kPa (65 torr)] was included, as hypoxia and hypercapnia can also cause respiratory muscle dysfunction. For the GBS group, diaphragmatic contractility declined significantly by 1 h at 30-, 50-, and 100-Hz stimulation frequency and, by 2 h, was significantly decreased at all frequencies. We conclude that 2-wk-old piglets, in contrast to 4-wk-old piglets, demonstrate a decline in Pdi during GBS infusion. These data demonstrate an age-related response to GBS in the piglet. This finding implies that a decline in Pdi during acute GBS infusion is not due to a secondary effect from shock (i.e. acidosis, hypercapnia, or hypoxemia) or due to the catabolic effects of a chronic infection, but is due to a direct effect of sepsis on diaphragmatic muscle function.

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