Is Peripheral Oxygen Saturation a Reliable Predictor of Upper Airways Air-Flow Limitation?

BACKGROUND: Dyspnea secondary to acute upper airways airflow limitation (UAAFL) represents a clinical emergency that can be difficult to recognize without a suitable history; even when etiology is known, parameters to assess the severity are unclear and often improperly used. OBJECTIVES: The aim of this study was to assess the role of peripheral oxygen saturation (SpO2) as a predictor of severity of upper airway obstruction. METHODS: The authors propose an experimental model of upper airway obstruction by a progressive increase of UAAFL. Ten healthy volunteers randomly underwent ventilation for 6 min with different degrees of UAAFL. SpO2, heart rate, respiratory rate (RR), tidal volume, accessory respiratory muscle activation, and subjective dyspnea indexes were measured. RESULTS: In this model, SpO2 was not reliable as the untimely gravity index of UAAFL. Respiratory rate, visual analogue scale (VAS), and Borg dyspnea scale were statistically correlated with UAAFL (p < 0.0001 for RR and p < 0.05 for VAS and Borg scale). No significant changes were observed on heart rate (p > 0.05) and tidal volume (p > 0.05); a RR ≤ 7 breaths/min; VAS and Borg scale showed statistically significant parameters changes (p < 0.05). CONCLUSIONS: RR, VAS, and Borg dyspnea scales are sensitive parameters to detect and stage, easily and quickly, the gravity of an upper airways impairment, and should be used in emergency settings for an early diagnosis of a UAAFL. SpO2 is a poorer predictor of the degree of upper airways flow limitation.

Phospholipase C-η2 is activated by elevated intracellular Ca(2+) levels.

Phospholipase C-η2 (PLCη2) is a novel enzyme whose activity in a cellular context is largely uncharacterised. In this study the activity of PLCη2 was examined via [(3)H]inositol phosphate release in COS7 cells expressing the enzyme. PLCη2 activity increased approximately 5-fold in response to monensin, a Na(+)/H(+) antiporter. This was significantly inhibited by CGP-37157 which implies that the effect of monensin was due, at least in part, to mitochondrial Na(+)/Ca(2+)-exchange. Direct activation of PLCη2 by <1µM Ca(2+) was confirmed in permeabilised transfected cells. The roles of the PH and C2 domains in controlling PLCη2 activity via membrane association were also investigated. A PH domain-lacking mutant exhibited no detectable activity in response to monensin or Ca(2+) due to an inability to associate with the cell membrane. Within the C2 domain, mutation of D920 to alanine at the predicted Ca(2+)-binding site dramatically reduced enzyme activity highlighting an important regulatory role for this domain. Mutation of D861 to asparagine also influenced activity, most likely due to altered lipid selectivity. Of the C2 mutations investigated, none altered sensitivity to Ca(2+). This suggests that the C2 domain is not responsible for Ca(2+) activation. Collectively, this work highlights an important new component of the Ca(2+) signalling toolkit and given its sensitivity to Ca(2+), this enzyme is likely to facilitate the amplification of intracellular Ca(2+) transients and/or crosstalk between Ca(2+)-storing compartments in vivo.