Exercise-induced hyperkalemia and concentration of Na,K-pumps in skeletal muscle in mitral stenosis: effect of balloon mitral valvotomy.
OBJECTIVE
The study aim was to examine the effects of balloon mitral valvotomy (BMV) on exercise-induced hyperkalemia, and on changes in the concentration of Na,K-pumps in skeletal muscle, as an exaggerated exercise-induced rise in potassium concentration ([K+]) may contribute to exertional fatigue and breathlessness.


METHODS
Eight subjects were evaluated with mitral stenosis (mean age 34 +/- 5.2 years) before, and at two weeks and four months after BMV. Subjects underwent incremental exercise to exhaustion for exercise-induced rise in [K+] and vastus lateralis biopsy for concentration of Na,K-pumps.


RESULTS
Mean (+/- SE) valve area increased from 0.89 +/- 0.03 cm2 before to 1.75 +/- 0.05 cm2 after BMV. There was a progressive increase in VO2,max (15.3 +/- 1.6, 17.2 +/- 1.4 and 19.9 +/- 1.9 l/kg/min) at baseline, early after and later after BMV, respectively (p < 0.01). The rise in [K+] with absolute workload fell progressively at early and late follow up post-BMV (p < 0.05), but was unchanged when plotted against percentage of VO2,max to match for relative workload. The concentration of Na,K-pumps was similar to baseline at early follow up (233 +/- 10 versus 228 +/- 15 pmol/g wet weight), but was significantly increased at late follow up after four months (265 +/- 17 pmol/g; p < 0.05). When the relationship between the concentration of Na,K-pumps and the exercise-induced rise in [K+] was studied, a negative correlation was found. However, correlation analysis for the effects of changes in Na,K-pumps on changes in exercise hyperkalemia after BMV was not significant.


CONCLUSIONS
The progressive reduction in exercise-induced rise in [K+] after BMV may contribute to the progressive improvement in exercise performance. The increased concentration of Na,K-pumps in skeletal muscle may assist in this improvement, and emphasizes the importance of peripheral adaptations in clinical improvement after BMV.
Barlow
C W
CW
University Laboratory of Physiology, University of Oxford, UK.
Long
J E
JE
Manga
P
P
Meyer
T E
TE
Paterson
D J
DJ
Robbins
P A
PA
D000328:Adult; D002404:Catheterization; D015444:Exercise / Q000502:physiology*; D017079:Exercise Tolerance; D005260:Female; D006801:Humans; D006947:Hyperkalemia / Q000209:etiology*; D008297:Male; D008946:Mitral Valve Stenosis / Q000503:physiopathology / Q000628:therapy*; D018482:Muscle, Skeletal / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D000254:Sodium-Potassium-Exchanging ATPase