O2 Uptake in hyperthyroidism during constant work rate and incremental exercise |
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Authors: | I. Ben-Dov K. E. Sietsema K. Wasserman |
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Affiliation: | (1) Division of Respiratory and Critical Care, Physiology and Medicine, Department of Medicine, Harbor-UCLA Medical Center, 1000 W. Carson St., 90 509 Torrance, CA, USA |
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Abstract: | Summary To investigate the effect of hyperthyroidism on the pattern and time course of O2 uptake (O2) following the transition from rest to exercise, six patients and six healthy subjects performed cycle exercise at an average work rate (WR) of 18 and 20 W respectively. Cardiorespiratory variables were measured breath-by-breath. The patients also performed a progressively increasing WR test (1-min increments) to the limit of tolerance. Two patients repeated the studies when euthyroid. Resting and exercise steady-state (SS)O2 (ml·kg–1·min–1) were higher in the patients than control (5.8, SD 0.9 vs 4.0, SD 0.3 and 12.1, SD 1.5 vs 10.2, SD 1.0 respectively). The increase inO2 during the first 20 s exercise (phase I) was lower in the patients (mean 89 ml·min–, SD 30) compared to the control (265 ml·min–1, SD 90), while the difference in half time of the subsequent (phase 11) increase to the SSO2 (patient 26 s, SD 8; controls 17 s, SD 8) were not significant (P = 0.06). The OZ cost per WR increment (O2/WR) in ml·min–1·–1, measured during the incremental period (mean 10.9; range 8.3–12.2), was always within two standard deviations of the normal value (10.3, SD 1). In the two patients who repeated the tests, both the increment ofO2 from rest to SS during constant WR exercise and the O2/WRs during the progressive exercise were higher in the hyperthyroid state than during the euthyroid state. While both resting and exerciseO2 are increased in the hyperthyroid patients, the O2 cost of a given increment of WR is within the normal range. However, a small reduction in theO2 requirement to perform exercise following treatment of the hyperthyroid state suggests a subtle change O2 cost of muscle work in this disease. |
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Keywords: | Work efficiency O2 Uptake kinetics Pulmonary gas exchange Hypermetabolic state |
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