PubMed · 8949114
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B Garrett, R Strettle. Progress report.. https://pubmed.ncbi.nlm.nih.gov/8949114/
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Current evidence suggests that patients with obstructive sleep apnea (OSA) may have greater pharyngeal critical pressure (Pcrit), which reflects the increase in upper airway collapsibility. The contribution of Pcrit to the severity of OSA and to the efficacious continuous positive pressure (nCPAPeff) therapy has never been extensively described and no data are available about the interaction of Pcrit, age, and anthropometric variables. To determine the relationship between Pcrit, severity of the disease, nCPAPeff, and anthropometric variables we measured Pcrit in a group of 106 patients with OSA. Pharyngeal critical pressure was derived from the relationship between maximal inspiratory flow and nasal pressure, Pcrit representing the extrapolated pressure at zero flow. Upper airway resistance (Rus) was determined as the reciprocal of the slope (DeltaPn/DeltaVImax cm H2O/L/s) in the regression equation. In a subgroup of 68 patients, during the diagnostic night, we measured as indices of respiratory effort, the maximal inspiratory esophageal pressure (Pes) at the end of apnea (Pesmax), the overall increase from the minimum to the maximum (DeltaPes), and the rate of increase of Pes during apnea (RPes). As a group, the mean Pcrit was 2.09 +/- 0.1 cm H2O (range, 0 to 4.5) and the mean Rus was 11.1 +/- 0.5 cm H2O/L/s. Although men have greater Pcrit, pharyngeal collapsibility was influenced neither by neck size nor by body mass index (BMI). Although there was a significant relationship between Pcrit and apnea plus hypopnea index (AHI) (r = 0.23, p = 0.02), neck circumference was the stronger predictor of apnea frequency, with Pcrit contributing only to the 3% of the variance. In the group of patients as a whole, a model including AHI, BMI, Rus, and Pcrit explained the 36% of the variance in nCPAPeff, with a greater contribution of AHI, Pcrit accounting for only 3% of the variation. In patients for whom the measure of respiratory effort was obtained, 42% of the variance in nCPAPeff was explained by RPes (33%) and BMI. From these results we conclude that Pcrit alone does not yield a diagnostically accurate estimation of OSA severity and nCPAPeff. Although individual collapsibility may predispose to pharyngeal collapse, upper airway occlusion may require the combination of several factors, including obesity, upper airway structure, and abnormalities in muscle control.
Three apolipoprotein B restriction fragment length polymorphism (RFLPs) (XbaI, MspI, and EcoRI) and the signal peptide insertion-deletion polymorphism were investigated using the polymerase chain reaction in 140 individuals from 5 Brazilian Indian tribes. All studied markers were polymorphic in this ethnic group. The insertion allele 5' beta SP*29 at the signal peptide previously observed in Mexican Americans was detected in about 8% of the chromosomes of 2 tribes (Gavião and Zoró), therefore confirming the Amerindian origin of this allele. Negative linkage disequilibrium was observed between alleles at the signal peptide and the EcoRI polymorphism in all tribes. In 3 populations (Gavião, Suruí, and Zoró) a negative disequilibrium was also detected between the insertion-deletion signal peptide markers and the XbaI polymorphism. In the whole sample of Amerindians 14 of the 24 (58%) possible 4-marker extended haplotypes were identified, but only haplotype 2 (5' beta SP*24/*X+/*M+/*E+) and haplotype 5 (5' beta SP*27/*X-/*M+/*E+) were shared by all tribes. No associations between plasma lipid levels or body mass index and these polymorphisms were observed in this sample.
Growth charts, which conventionally record only cross-sectional (distance) information, can be extended to monitor growth rate over time (velocity). To adjust for regression to the mean the velocity should be conditional on the previous measurement. By working on the SDS scale rather than the measurement scale, the only extra information required for velocity is the correlation structure of the SDS at different ages. The design and validation of such combined charts is an important part of their development.