Applications of segmented regression models for biomedical studies

Reference values of body composition parameters for Vietnamese men and women

BACKGROUND

Body composition parameters are linked to cardio-metabolic risk. However, high-quality reference values of body composition are scarce, particularly in Asian population. The aim of study was to construct sex- and age-specific normative reference values of body composition for the Vietnamese population.

METHODS

This study was designed as a cross-sectional investigation that involved 2700 women and 1459 men aged between 20 and 90 (average 48, SD 15) who were participants in the population-based Vietnam Osteoporosis Study. Whole-body composition parameters (e.g., fat mass and lean mass) and site-specific (head, arms, trunk, and legs) parameters were measured by dual-energy X-ray absorptiometry (Hologic Horizon). Reference curves for each parameter and anatomical site were constructed using the Generalized Additive Model for Location Scale and Shape modeling technique.

RESULTS

Overall, 8% of women and 11% of men were classified as obese (body mass index ≥ 27.5 kg/m²). Most fat mass was deposited at the trunk (~50%), followed by the leg (~33%). Women had ~10% more body fat (relative to body weight) than men. However, whole-body lean mass was higher in men than women, with the average difference being ~13 kg. Moreover, men had more bone mineral content than women (2110 vs. 1600 g). We also provided a comparison of age-related changes in body composition parameters between Vietnamese and US Whites.

CONCLUSION

These data provide gender- and age-specific reference values of body composition parameters for Vietnamese population. These normative values provide health professionals and the public with a resource for interpretation of body composition data.

Activated CD11b+ CD15+ granulocytes increase in the blood of patients with uveal melanoma

PURPOSE

To determine whether activated CD11b(+) CD15(+) granulocytes increase in the blood of patients with uveal melanoma.

METHODS

Peripheral blood mononuclear cells (PBMCs) were isolated by density gradient centrifugation from the blood of patients with primary choroidal/ciliochoroidal uveal melanomas (six women, four men; age range, 46-91 years) and healthy control donors (14 women, 10 men; age range, 50-81 years). The expression of CD15 and CD68 on CD11b(+) myeloid cells within PBMCs and primary uveal melanomas was evaluated by flow cytometry. CD3zeta chain expression by CD3epsilon(+) T cells in PBMCs and within primary uveal melanomas was measured as an indirect indication of T-cell function.

RESULTS

The percentage of CD11b(+) cells in PBMCs of patients with uveal melanoma increased 1.8-fold in comparison to healthy donors and comprised three subsets: CD68 negative CD15(+) granulocytes, which increased 4.1-fold; CD68(-) CD15(-) cells, which increased threefold; and CD68(+) CD15(low) cells, which were unchanged. A significant (2.7-fold) reduction in CD3zeta chain expression on CD3epsilon(+) T cells, a marker of T-cell dysfunction, was observed in PBMCs of patients with uveal melanoma in comparison with healthy control subjects and correlated significantly with the percentage of CD11b(+) cells in PBMCs. CD3zeta chain expression on T cells within primary tumors was equivalent to CD3zeta expression in PBMCs of the same patient in four of five patients analyzed.

CONCLUSIONS

Activated CD11b(+) CD15(+) granulocytes expand in the blood of patients with uveal melanoma and may contribute to immune evasion by ocular tumors by inhibiting T-cell function via decreasing CD3zeta chain expression.

A simplified method for measuring critical pressures during sleep in the clinical setting

Upper airway critical pressure measurements correlate with the degree of upper airway obstruction during sleep and may have a role in the diagnosis and treatment of obstructive sleep apnea. Nevertheless, the utility of the critical pressure has not yet been realized in the clinical setting because significant technical expertise is still required for the acquisition and analysis of pressure-flow data. Using segmented regression, we developed and validated a simplified approach to analyze the pressure-flow relationship and to determine the effects of protocol-related factors in 44 subjects with sleep apnea. When compared with expert visual analysis, segmented regression method was found to accurately determine the critical pressure (-0.98 +/- 2.47 cm H(2)O vs. -1.07 +/- 2.47 cm H(2)O, respectively; p = 0.46). Furthermore, it was found that two series of measurements acquired at varying nasal pressure levels with two or more breaths per level were sufficient to determine the critical pressure with a minimum of variability. Therefore, this analytic approach has the potential for standardizing and simplifying the ascertainment of the critical pressure for studies examining the effect of therapeutic devices and agents on upper airway collapsibility during sleep.