Sodium sensitivity in young adults with high resting end-tidal CO2

Background Previous research with normotensive adults aged over 40 years ('older') found that sensitivity of blood pressure of subjects with high resting end-tidal partial pressures of CO 2 to high sodium intake was greater than normal. Objective To test the hypothesis that the lesser sensitivity of blood pressure of young normotensive adults to high sodium intake is also a function of resting end-tidal partial pressure of CO 2 . Design Forty-eight Caucasian men and women (age 28.5 ± 1.4 years) had a lower than normal dietary intake of sodium chloride for 4 days, and then ingested sodium chloride capsules for 7 days (an additional 190 mmol/day sodium chloride). Resting end-tidal partial pressure of CO 2 and blood pressure, and 24 h ambulatory blood pressure, were measured before and after the high-sodium diet Overnight urine samples were collected before and after the high-sodium diet to determine dietary compliance, and to assess changes in urinary excretion of endogenous digitalis-like factors (a ouabain-like factor, and a marinobufagenin-like factor) that covary with plasma volume. Results Subjects with high end-tidal partial pressures of CO 2 had lower resting heart rates and lower urinary excretion of ouabain-like factor before sodium loading. Sodium loading decreased mean partial pressure of CO 2 (by 0.8 ± 0.2 mmHg) and increased only ambulatory systolic blood pressure (by 2.1 ± 0.8 mmHg) for the whole group. However, the changes in resting systolic (r=0.32, p<0.025) and diastolic (r=0.36, p<0.01) blood pressures and in 24 h systolic (r=0.28, p< 0.05) blood pressure after sodium loading were all positive functions of individual resting end-tidal partial pressures of CO 2 . Sodium loading increased urinary excretion of marinobufagenin-like factor (by 1.78 ± 0.88 nmol) and the magnitude of the individual increase was a function of end-tidal partial pressure of CO 2 . Conclusions The results indicate that a high resting partial pressure of CO 2 augments the effects of high sodium intake on plasma volume, levels of endogenous digitalis-like factors, and blood pressure in young normotensive humans.