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Query: UMLS:C0020440 (hypercapnia)
 7,939 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The physiological role of carbonic anhydrase III in slow-twitch skeletal muscle was investigated using isolated mouse soleus (N = 30) contracting once every 1.7 min for 75 min in Krebs-Henseleit solution gassed with either 95% oxygen - 5% carbon dioxide (normocapnia) or 90% oxygen - 10% carbon dioxide (hypercapnia). Each contraction was 500 ms in duration at 50 Hz. When muscles contracted in normocapnic solution (pH 7.42), the developed tension decreased an average of 6.1 +/- 0.8% over 25 min. For the next 50 min, 15 muscles remained normocapnic, while the remainder contracted in hypercapnic solution (pH 7.20). Tension decreased significantly more with hypercapnia. For the last 25 min, both normocapnic and hypercapnic muscles were divided into three treatment groups (N = 5). One group continued in the same environment, while acetazolamide (final concentration of 10(-5) M) was added to the bath of the second and sodium cyanate (final concentration of 10(-5) M) was added to the bath of the third group. Acetazolamide had no effect on tension in either carbon dioxide environment. Sodium cyanate significantly decreased tension from the hypercapnic control but had no effect in normocapnia. Thus carbonic anhydrase III inhibition with sodium cyanate increased the effect of hypercapnia implying that carbonic anhydrase III assists in the regulation of free hydrogen ion concentration in slow-twitch skeletal muscle.
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PMID:Carbonic anhydrase III inhibition in normocapnic and hypercapnic contracting mouse soleus. 310 51

1. The physiological basis of inspiratory effort sensation remains uncertain. Previous studies have suggested that pleural pressure, rather than inspiratory muscle fatigue, is the principal determinant of inspiratory effort sensation. However, only a limited range of inspiratory flows and breathing patterns have been examined. We suspected that inspiratory effort sensation was related to the inspiratory muscle tension-time index developed whatever the breathing pattern or load, and that this might explain the additional rise in sensation seen with hypercapnia. 2. To investigate this we measured hypercapnic rebreathing responses in seven normal subjects (six males, age range 21-38 years) with and without an inspiratory resistive load of 10 cm H2O. Pleural and transdiaphragmatic pressures, mouth occlusion pressure and breathing pattern were measured. Diaphragmatic and ribcage tension-time indices were calculated from these data. Inspiratory effort sensation was recorded using a Borg scale at 30s intervals during each rebreathing run. 3. Breathing pattern and inspiratory pressure partitioning were unrelated to changes in inspiratory effort sensation during hypercapnia. Tension-time indices reached pre-fatiguing levels during both free breathing and inspiratory resistive loading. 4. Stepwise multiple regression analysis using pooled mechanical, chemical and breathing pattern variables showed that pleural pressure was more closely related to inspiratory effort sensation than was transdiaphragmatic pressure.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Physiological determinants of inspiratory effort sensation during CO2 rebreathing in normal subjects. 828 53