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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effect of acute hypercapnia on skeletal muscle contractility and relaxation rate was investigated. The contractile force of fresh and fatigued quadriceps femoris (QF) and adductor pollicis (AP) was studied in normal humans by use of electrical stimulation. Maximum relaxation rate from stimulated contractions was measured for both muscles. Acute hypercapnia led to a rapid substantial reduction of contraction force. The respiratory acidosis after 9% CO2 was breathed for 20 min [mean venous blood pH 7.26 and end-tidal PCO2 (PETCO2) 65.1 Torr] reduced 20- and 100-Hz stimulated contractions of QF to 72.8 +/- 4.4 and 80.0 +/- 5.1% of control values, respectively. After 8 and 9% CO2 were breathed for 12 min, AP forces at 20- and 50-Hz stimulation were also reduced. Twitch tension of AP was reduced by a mean of 25.5% when subjects breathed 9% CO2 for 12 min [mean arterialized venous blood pH (pHav) 7.25 and PETCO2 66 Torr]. Over the range of 5% (pHav 7.38 and PETCO2 47 Torr) to 9% CO2, there was a linear relationship between twitch tension loss and pHav, arterialized venous blood PCO2, and PETCO2. Acute respiratory acidosis (mean PETCO2 61 Torr) increased the severity of low-frequency fatigue after intermittent voluntary contractions of AP. At 20 min of recovery, twitch tension was 63.2 +/- 13.4 and 46.8 +/- 16.4% of control value after exercise breathing air and 8% CO2, respectively. Acute hypercapnia (mean PETCO2 65.1 and 60.5 Torr) did not alter the maximum relaxation rate from tetanic contractions of fresh QF and from twitch tensions of AP.
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PMID:Effect of acute hypercapnia on limb muscle contractility in humans. 226 73

Three elderly patients with established chronic obstructive airways disease were admitted with a short history of increasing dyspnoea and tiredness and (in two cases) a deterioration in mental state. Acute respiratory acidosis was diagnosed and mechanical ventilation instituted. Two hours after beginning mechanical ventilation the mean arterial pH had risen to 7.40, but all patients showed a dramatic fall in the serum phosphate concentration (lowest value 0.3 mmol/l (0.9 mg/100 ml] accompanied by a low urinary excretion of phosphate. No patient could tolerate withdrawal of mechanical ventilation until the serum and urinary concentrations of phosphate had returned to normal. Recovery from acute respiratory acidosis should be added to the list of conditions associated with severe hypophosphataemia.
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PMID:Severe hypophosphataemia during recovery from acute respiratory acidosis. 643 41