Osmolality, NaCl dietary intake, and regulation of ventilation by CO2
Anderson, J.W.; Jennings, D.B.
American Journal of Physiology 255(1 Pt 2): R105-R112
1988
ISSN/ISBN: 0002-9513 PMID: 3134823 Document Number: 305522
The ventilatory response to carbon dioxide (VR) was examined in 6 dogs during the second week of sequential dietary periods of low sodium chloride (less than 5 mEq NaCl daily), high NaCl (about 120 mEq NaCl daily) and then repeated low NaCl. Water intake was maintained constant at 77 ml/kg daily. PCO2 of arterial blood (PaCO2) and the PaCO2 threshold of the VR increased between the high-NaCl and the second low-NaCl period; the PaCO2 threshold did not change between the first low-NaCl and the high-NaCl period. Arterial [H+] ([H+]a) threshold of the VR increased between the first low-NaCl period and the high-NaCl period, but did not change further in the second low-NaCl period. Variations in [H+]a threshold of the VR between dogs on high- and low-NaCl diets were correlated with plasma osmolality, and this accounted for a positive linear relation between [H+]a and plasma osmolality. During the high-NaCl period, the arterial strong ion difference, [SID]a = ([Na+]) + [K+] - ([lactate -] + [Cl-]), decreased, forcing [H+]a to increase. During high-NaCl diet, PaCO2 decreased relative to plasma osmolality, counterbalancing the decrease in [SID]a and maintaining the relation between [H+]a and plasma osmolality. The compensatory mechanism for the decrease in PaCO2 during high NaCl was a shift in the relation between PaCO2 threshold of the VR and plasma osmolality to a lower PaCO2 threshold.