High end tidal CO2 association with blood pressure response to sodium loading in older adults

Objective To test the hypothesis that blood pressure of older adults with high resting end tidal CO 2 (PETCO 2 ) is sensitive to high dietary intake of sodium chloride. Design and methods Forty-four Caucasian men and women, aged 41-79 years (mean ± SEM 55.5 ± 1.4), restricted their dietary intake of sodium chloride for 11 days and ingested sodium chloride capsules (an additional 190 mmol sodium/day) during the last seven of those days. On days 1, 4 and 11, resting PETCO 2 and blood pressure were monitored for 25 min in the laboratory, followed by ambulatory blood pressure monitoring in the natural environment for 24 h. Overnight urine samples were obtained at days 4 and 11 to estimate excretion of sodium and of an endogenous digitalis-like factor (EDLF) that is sensitive to changes in plasma volume. Results Individual resting PETCO 2 remained stable within and between laboratory monitoring sessions and was correlated with urinary excretion of the endogenous digitalis-like factor, both before and after the period of high sodium intake. The high-sodium diet was associated with increased urinary sodium excretion and body weight in all quartiles of PETCO 2 . The high-sodium diet produced significant increases in resting and in 24 h systolic blood pressures in the upper two quartiles of the PETCO 2 distribution, and significant increases in resting and in 24 h diastolic blood pressures in the highest PETCO 2 quartile only. Conclusion These findings indicate that blood pressure sensitivity to sodium loading is differentially associated with high resting PETCO 2 in older adults. A high PETCO 2 may be an index of a dynamic steady state that influences sodium transport mechanisms.