Effect of age and blood pressure on determination of normal fluid status in a general population using whole body and calf bioimpedance techniques.

Normal fluid status (dry weight) can be identified by hydration markers established in the healthy population. The general population average could be influenced by age with its accompanying physiological changes and/or illness. The aims of this study were (1) to evaluate the effect of age and systolic blood pressure (SBP) on these markers; (2) to compare mean values of hydration markers as assessed by different bioimpedance techniques. Subjects from the general population (n  =  212, males 105, 57.1% White, 31.6% Black, and 11.3% others) were studied. Body weight, height and SBP were measured. Whole body and calf bioimpedance (Hydra 4200) methods were utilized with subjects in the supine position. Calf normalized resistivity (CNR), fluid overload (FO), extracellular (ECV) and intracellular (ICV) volume measurements ECV/total body water (TBW) were calculated. Subjects were stratified by age; young (Group1): 18-35 years; middle (Group2): 36-60 years, senior (Group3): 61-80 years. Body mass index (BMI), CNR, and ECV/TBW differed significantly between age groups, and genders. ECV and FO increased with age in males. Decreased CNR (indicating relative increased fluid load) (p  <  0.001) and increased SBP (p  <  0.001) were associated with age in all three groups. CNR in Group1 was the same as in 36.0% of subjects in Group2 and 12.5% of subjects in Group3. In those subjects in Group2 and Group3, with CNR levels comparable to Group1 subjects, SBP was lower than in their peers in each respective age group. In conclusion average CNR in Group1 represents the range of healthy subjects. Since CNR is correlated with age, subjects in Group2 and Group3 are more likely to have fluid overload. Although about a third of subjects in Group2 and Group3 were in the range of Group1, the age and associated factors should be considered when CNR is used to identify fluid status in senior patients.