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Lactic acidosis and diaphragmatic function in vitro

J R Coast1, R A Shanely, J M Lawler

  • 1S. A. Rasmussen Exercise Physiology Laboratory, Department of Health, Physical Education, Exercise Science and Nutrition, Northern Arizona University, Flagstaff 86011-5095, USA.

American Journal of Respiratory and Critical Care Medicine
|November 1, 1995
PubMed
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Physiologic levels of lactic acid and hydrogen ions do not cause diaphragm fatigue during heavy exercise. Studies show diaphragm contractility is unaffected by acidosis, suggesting other factors contribute to fatigue.

Area of Science:

  • Physiology
  • Exercise Physiology
  • Skeletal Muscle Physiology

Background:

  • Diaphragm fatigue is a common occurrence during strenuous physical activity.
  • Acidosis is known to induce skeletal muscle fatigue, but the diaphragm's role as a non-producer of lactic acid and hydrogen ions is unique.

Purpose of the Study:

  • To investigate the hypothesis that hydrogen ion and lactic acid concentrations, similar to those found in arterial blood during maximal exercise, reduce the contractility of isolated rat diaphragms in vitro.
  • To determine the direct impact of acidosis on diaphragm muscle function.

Main Methods:

  • Isolated rat diaphragm strips were exposed to control solutions and varying concentrations of lactic acid buffered to different pH levels (7.4, 7.2, 7.1, and 6.8).
  • The force-frequency relationship of the diaphragm strips was measured before and after inducing acidosis and subsequent stress.

Related Experiment Videos

  • Muscle strips underwent repeated contractions to simulate exercise conditions.

    • Main Results:

    • Diaphragm strips exposed to pH 7.4, 7.2, and 7.1 showed no significant difference in contractility compared to control.
    • Significant decrements in force were observed only in the diaphragm strips exposed to pH 6.8 (L68 group).
    • Reduced force in the L68 group occurred at stimulation frequencies below 100 Hz.

    Conclusions:

    • Physiologic levels of exogenous hydrogen ions do not appear to be a primary cause of in vitro diaphragm fatigue.
    • Acidosis at levels below pH 6.8 may contribute to diaphragm fatigue, but higher pH levels typical of maximal exercise do not.
    • Further research is needed to identify the primary mechanisms of diaphragm fatigue during heavy exercise.