Gj. Kahaly et al., INEFFECTIVE CARDIORESPIRATORY FUNCTION IN HYPERTHYROIDISM, The Journal of clinical endocrinology and metabolism, 83(11), 1998, pp. 4075-4078
Dyspnea on exertion is a common complaint in hyperthyroidism, and this
thyroid dysfunction has been implicated as a primary cause of impaire
d effort tolerance. Using spirometry and spiroergometry, 42 patients w
ith untreated hyperthyroidism were examined, and the condition was con
trolled 7 days later under propranolol monotherapy, as well as after 6
months in euthyroidism. While hyperthyroid, reduced forced vital capa
city and tidal volume at the anaerobic threshold (AT) were observed in
comparison to euthyroidism. Decreased oxygen (O-2) pulse at AT (7 +/-
0.4 vs. 9.1 +/- 0.4 mL/beat, P = 0.0012) and at maximal exercise was
noted in hyperthyroidism and was enhanced under propranolol (8.9 +/- 0
.4 mL/beat, P = 0.0001). During exercise, the increment of minute vent
ilation (16.1 +/- 0.7 us. 20.2 +/- 1.0 L/min, P = 0.0015), O-2 uptake
(9 +/- 0.5 vs. 11.4 +/- 0.5 mL/min/kg, P = 0.0022), O-2 pulse (4.0 +/-
0.3 vs. 5.6 +/- 0.3 mL/beat, P = 0.0001), and heart rate (53 +/- 2 us
. 65 +/- 3 beat/min, P = 0.0004) was markedly lower in hyper- us. euth
yroidism. Work rate at AT and at maximum was reduced in hyper- us. eut
hyroidism (107.4 +/- 3 vs. 141.1 +/- 4 watt, P = 0.0001). Negative cor
relations between free T3 and O-2 pulse at AT (r = -0.59, P = 0.0005),
delta O-2 uptake (r = -0.54, P = 0.0007), delta minute ventilation (r
= -0.48, P = 0.0007), and maximal work rate (r = -0.62, P = 0.0001) w
ere noted. In hyperthyroidism, analysis of respiratory gas exchange sh
owed low efficiency of cardiopulmonary function, respiratory muscle we
akness, and impaired exercise capacity, which were reversible in euthy
roidism.