Water and electrolyte metabolism in congestive heart failure

Quantification of regional myocardial mean intracellular water lifetime: A nonhuman primate study in myocardial stress

Heart failure with preserved ejection fraction (HFpEF) is typically associated with early metabolic remodeling. Noninvasive imaging biomarkers that reflect these changes will be crucial in determining responses to early drug interventions in these patients. Mean intracellular water lifetime (τ_i ) has been shown to be partially inversely related to Na, K-ATPase transporter activity and may thus provide insight into the metabolic status in HFpEF patients. Here, we aim to perform regional quantification of τ_i using dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) in the nonhuman primate (NHP) heart and evaluate its region-specific variations under conditions of myocardial stress in the context of perturbed myocardial function. Cardiac stress was induced in seven naïve cynomolgus macaques using a dobutamine stepwise infusion protocol. All animals underwent 3 T cardiac dual-bolus DCE and tagging MRI experiments. The shutter-speed model was employed to quantify regional τ_i from the DCE-MR images. Additionally, τ_i values were correlated with myocardial strains. During cardiac stress, there was a significant decrease in global τ_i (192.9 ± 76.3 ms vs 321.6 ± 70 ms at rest, P < 0.05) in the left ventricle, together with an increase in global peak circumferential strain (-15.4% ± 2.7% vs -10.1% ± 2.9% at rest, P < 0.05). Specifically, slice-level analysis further revealed that a greater significant decrease in mean τ_i was observed in the apical region (Δτ_I = 182.4 ms) compared with the basal (Δτ_i = 113.2 ms) and midventricular regions (Δτ_i = 108.4 ms). Regional analysis revealed that there was a greater significant decrease in mean τ_i in the anterior (Δτ_i = 243.9 ms) and antero-lateral (Δτ_i = 177.2 ms) regions. In the inferior and infero-septal regions, although a decrease in τ_i was observed, it was not significant. Whole heart regional quantification of τ_i is feasible using DCE-MRI. τ_i is sensitive to regional changes in metabolic state during cardiac stress, and its value correlates with strain.

Variability in pK'1 of human plasma

(1) Results were presented of an investigation of the relationship between ionic strength and PK'1 (negative logarithmic form of the apparent overall first dissociation constant of carbonic acid in plasma) in separated human plasma at constant PCO2. (2) Ionic strength was varied by adding dry NaCl to diluted aliquots of plasma from six healthy people and dry NaCl plus dry NaHCO3 to diluted aliquots of plasma from six other healthy people. pK'1 was determined from simultaneous measurements of pH and PCO2, and measurements of TCO2. Values for solubility factor for CO2 (s) were corrected for differences in plasma water and in Na concentration. All plasmas were equilibrated at 37 degrees C in a tonometer with a constant gas mixture (5% CO2, 12% O2, 83% N2). Precision of pK'1 determinations averaged 0.003. pK'1 was also determined on fresh undiluted healthy plasma, similarly tonometered. (3) We report (a) considerable variability in pK'1 of fresh undiluted healthy plasma (from 6.0197 to 6.1217); and also in extrapolated values for pK'1 at a notional zero ionic strength (6.179 to 6.325); (b) that variation in plasma ionic strength alters pK'1; (c) that change in plasma bicarbonate [HCO3]p can also change pK'1; (d) that change in pK'1, changes measured pH. (4) Implications are discussed.