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In vivo effects of acute changes in osmolality and sodium concentration on myocardial contractility
Abstract:
Effects of acute changes in osmolality and sodium concentration (Na) on myocardial contractility (MC) were examined in anesthetized dogs. Using a carotid to left anterior descending bypass, 4 cc of NaCl and/or dextrose of varying osmolality as injected and the percentage of change in MC measured. At Na = O mEq/L, a positive inotropic response occurred, which varied inversely as osmolality increased from 300 (MC = 100 +/- 23%) to 700 mOsm/L (MC = 39 +/- 10%, p less than 0.01). Similar ranges of positive responses of lesser magnitude were noted at Na = 75 mEq/L. At Na = 150, 190, or 350 mEq/L, similar increments in osmolality caused an increasingly negative inotropic response. An inverse relationship between Na and MC was noted with osmolality held constant. Injections of the nonionic contrast agent, P297, in 5% dextrose or 0.9% NaCl, resulted in 28 +/- 3% or -17 +/- 4% (p less than 0.01) change in MC, respectively. Sodium concentration and osmolality have independent effects on MC. Hyperosmolality/hypernatremia causes a negative inotropic response while hyponatremia causes a positive one.
Insights
Altering sodium concentration and osmolality significantly impacts heart muscle function. Low sodium levels boost myocardial contractility, while high levels and osmolality decrease it.
Area of Science:
- Cardiovascular Physiology
- Medical Diagnostics
Background:
- Myocardial contractility (MC) is crucial for cardiac function.
- Understanding factors affecting MC is vital for clinical practice.
Purpose of the Study:
- To investigate the independent effects of acute changes in osmolality and sodium concentration (Na) on myocardial contractility (MC).
Main Methods:
- Anesthetized dogs underwent carotid to left anterior descending bypass.
- Injections of NaCl and/or dextrose with varying osmolality were administered.
- Percentage change in MC was measured.
Main Results:
- Hyponatremia (Na = 0 mEq/L) induced a positive inotropic response, inversely related to increasing osmolality.
- Hypernatremia (Na = 150-350 mEq/L) resulted in a negative inotropic response with increasing osmolality.
- Nonionic contrast agent P297 demonstrated osmolality-dependent effects on MC.
Conclusions:
- Sodium concentration and osmolality exert independent effects on myocardial contractility.
- Hyperosmolality/hypernatremia negatively impacts MC, while hyponatremia positively affects it.