Evaluating the effectiveness of interventions: exploration of two statistical methods.

Repeated measures designs are often used to evaluate the effectiveness of interventions. In these designs, the outcomes are measured on several occasions before and after implementation of the intervention. Two statistical methods, the repeated measures analysis of variance (RM-ANOVA) and hierarchical linear models (HLM), can be used to analyze the data. The authors provide an overview of the statistical models underlying RM-ANOVA and HLM and discuss the strengths and limitations of each. They propose that the 2 methods are complementary in determining the effectiveness of interventions.     

Stimulation of β-adrenoceptors inhibits store-operated channel currents via a cAMP-dependent protein kinase mechanism in rabbit portal vein myocytes

Previously we have described the properties of store-operated channel currents (SOCs) in freshly dispersed rabbit portal vein smooth muscle cells. In addition to Ca²⁺ store depletion these SOCs could also be activated by α-adrenoceptor stimulation and diacylglycerol (DAG) via a protein kinase C (PKC)-dependent mechanism. In the present study we have investigated the effect of β-adrenoceptor stimulation on SOCs in rabbit portal vein myocytes. With whole-cell recording the selective β-adrenoceptor agonist isoprenaline reduced the current evoked by cyclopiazonic acid (CPA, sarcoplasmic/endoplasmic reticulum ATPase inhibitor) by over 85%. With cell-attached patch recording, bath application of isoprenaline produced a pronounced inhibition of SOC activity evoked by either CPA or the acetoxymethyl ester form of BAPTA (BAPTA-AM). SOC activity evoked by CPA, the DAG analogue, 1-oleoyl-acetyl- sn -glycerol (OAG) or the phorbol ester, phorbol-12,13-dibutyrate (PDBu) was also markedly inhibited by the adenylate cyclase activator, forskolin, and the cell-permeable non-hydrolysable analogue of cyclic adenosine monophosphate (cAMP), 8-Br-cAMP. With inside-out patches, bath application of PDBu evoked channel currents with similar properties to SOCs which were inhibited by over 90% by a catalytic subunit of protein kinase A (PKA) and by 8-Br-cAMP. Moreover bath application of PKA inhibitors, H-89, KT5720 and an inhibitory peptide to quiescent cell-attached or inside-out patches, activated channel currents with similar properties to SOCs. These data suggest that in rabbit portal vein myocytes, stimulation of β-adrenoceptors inhibits SOC activity via a cAMP-dependent protein kinase signal transduction cascade. In addition it is concluded that constitutive PKA activity has a profound inhibitory effect on SOC activity in this vascular preparation.     

Hyperventilation increases muscle protein synthesis in critically ill trauma patients

BACKGROUND: Critically ill trauma patients are often in negative nitrogen balance and demonstrate advanced muscle protein wasting, which is in part due to a decrease in muscle protein synthesis. Previous studies have been performed on the relationship between pH and protein metabolism. Some evidence suggests that alkalosis might enhance protein synthesis. The purpose of the present study is to determine whether protein synthesis is increased in trauma patients who have a respiratory alkalosis from hyperventilation. METHODS: Trauma patients in the intensive care unit (n = 8) who were treated with hyperventilation for elevated intracranial pressures were enrolled. Muscle protein synthesis rates were determined in vivo using the flooding method with l-[(2)H(5)]phenylalanine. Measurements were performed twice on each patient within a 36-h period, first during hyperventilation and then after hyperventilation was discontinued. Hemoglobin oxygen saturation was maintained above 95% for all measurements. RESULTS: Protein synthesis in muscle was 1.38 +/- 0.11%/day during hyperventilation (pH 7.50 +/- 0.02, pCO(2) 27.3 +/- 1.0 mm Hg) and 0.93 +/- 0.15%/day after respiratory parameters were normalized (pH 7.39 +/- 0.01, pCO(2) 39.4 +/- 1.5 mm Hg). The synthesis rate was significantly higher (P < 0.01, paired t test), 0.46 +/- 0.13%/day (32.6%), at the time of hyperventilation. CONCLUSION: Muscle protein synthesis is elevated during hyperventilation in critically ill patients with traumatic brain injury. We believe this preliminary study provides data that warrant confirmation in larger clinical studies. It suggests that this ventilatory therapeutic strategy may have a role in mitigating the negative nitrogen balance and muscle protein wasting that can impair the recovery of these patients.