Low efficiency of oxygen utilization during exercise in hyperthyroidism

Body Weight Changes in Hyperthyroidism: Timing and Possible Explanations during a One Year Repeated Measurement Study

BACKGROUND

Weight gain during treatment of hyperthyroidism is a frequent and for many patients unwanted outcome. With this repeated measurement study, we explored the timing of weight changes during the first year of antithyroid drug (ATD) treatment and assessed the correlation between body weight changes and changes in thyroid hormones, resting energy expenditure (REE), physical activity level, and energy efficiency.

METHODS

Patients with new onset hyperthyroidism were investigated every second month during the first year of ATD treatment. At each investigation, the following were measured: body weight, thyroid hormone concentrations, physical activity level, and daily number of steps, REE, and exercise performance.

RESULTS

Two men and eleven women, all sedentary, mean age 49(SD: 9.3) years were included. Significant changes after 1 year occurred for body weight (68.9-74.1 kg), thyroid hormones (free T3 [fT3] 17.5 to 4.42 pmol/L), REE (1,630-1,484 kcal/24 h), and energy efficiency at lower (50 W) workloads (16.0-17.6%). In individual patients, only REE and fT3 correlated to changes in body weight. Physical activity level did not change during treatment.

CONCLUSION

In this study, treatment of hyperthyroidism was associated with marked increase in body weight in the patients. This increase correlated to a decrease in REE and only to a negligible extent to changes in energy efficiency and not at all to changes in physical activity level of daily living.

Elevated energy coupling and aerobic capacity improves exercise performance in endurance-trained elderly subjects

Increased maximal oxygen uptake (V(O(2)max)), mitochondrial capacity and energy coupling efficiency are reported after endurance training (ET) in adult subjects. Here we test whether leg exercise performance (power output of the legs, P(max), at V(O(2)max)) reflects these improvements with ET in the elderly. Fifteen male and female subjects were endurance trained for a 6 month programme, with 13 subjects (69.5 ± 1.2 years old, range 65-80 years old; n = 7 males; n = 6 females) completing the study. This training significantly improved P(max) (Δ17%; P = 0.003), V(O(2)max) (Δ5.4%; P = 0.021) and the increment in oxygen uptake (V(O(2))) above resting (ΔV(O(2)m-r) = V(O(2)max) - V(O(2)rest; Δ9%; P < 0.02). In addition, evidence of improved energy coupling came from elevated leg power output per unit V(O(2))at the aerobic capacity [Δ(P(max)/ΔV(O(2)m-r)); P = 0.02] and during submaximal exercise in the ramp test as measured by delta efficiency (ΔP(ex)/ΔV(O(2)); P = 0.04). No change was found in blood lactate, muscle glycolysis or fibre type. The rise in P(max) paralleled the improvement in muscle oxidative phosphorylation capacity (ATP(max)) in these subjects. In addition, the greater exercise energy coupling [Δ(P(max)/ΔV(O(2)m-r)) and delta efficiency] was accompanied by increased mitochondrial energy coupling as measured by elevated ATP production per unit mitochondrial content in these subjects. These results suggest that leg exercise performance benefits from elevations in energy coupling and oxidative phosphorylation capacity at both the whole-body and muscle levels that accompany endurance training in the elderly.

Exercise efficiency is reduced by mitochondrial uncoupling in the elderly

A reduction in exercise efficiency accompanies ageing in humans. Here we evaluated the impact of changes in the contractile-coupling and mitochondrial-coupling efficiencies on the reduction in exercise efficiency in the elderly. Nine adult (mean, 38.8 years old) and 40 elderly subjects (mean, 68.8 years old) performed a cycle ergometer test to measure O2 uptake and leg power output up to the aerobic limit ( ). Reduced leg power output per unit O2 uptake was reflected in a drop in delta efficiency (εD) from 0.27 ± 0.01 (mean ± SEM) in adults to 0.22 ± 0.01 in the elderly group. Similar declines with age were apparent for both the leg power output at and the ATP generation capacity (ATPmax) determined in vivo using (31)P magnetic resonance spectroscopy. These similar declines resulted in unchanged contractile-coupling efficiency values (εC) in the adult (0.50 ± 0.05) versus the elderly group (0.58 ± 0.04) and agreed with independent measures of muscle contractile-coupling efficiency in human quadriceps (0.5). The mitochondrial-coupling efficiency calculated from the ratio of delta to contractile-coupling efficiencies in the adults (εD/εC = 0.58 ± 0.08) corresponded to values for well-coupled mitochondria (0.6); however, εD/εC was significantly lower in the elderly subjects (0.44 ± 0.03). Conversion of ATPmax per mitochondrial volume (ATPmax/Vv[mt,f]) reported in these groups into thermodynamic units confirmed this drop in mitochondrial-coupling efficiency from 0.57 ± 0.08 in adults to 0.41 ± 0.03 in elderly subjects. Thus, two independent methods revealed that reduced mitochondrial-coupling efficiency was a key part of the drop in exercise efficiency in these elderly subjects and may be an important part of the loss of exercise performance with age.

Structured exercise program improves functional capacity and delays relapse in euthyroid patients with Graves' disease

PURPOSE

To evaluate short- and long-term effects of structured exercise program in euthyroid patients with Graves' disease.

METHODS

The study employed a retrospective case-control design. The exercise group (n = 62) underwent 3 weeks of structured exercise program consisting of daily walking, strengthening, and stretching exercises while the control group (n = 62) participated in leisure activities. Thyroid profile, aerobic capacity, and perceived fatigue were evaluated on in-patient admission and discharge. Time to discontinuation of anti-thyroid medication after discharge and time to relapse of symptoms were determined.

RESULTS

The exercise group increased estimated peak oxygen consumption (significant group-by-time ANOVA interaction, P < 0.001), decreased serum thyroxin (P = 0.038), increased serum thyrotropin (P = 0.071), and reported less fatigue (Fisher's exact test, p < 0.001) from admission to discharge. The anti-thyroid medication was withdrawn within 6 months of discharge in significantly greater proportion of subjects in the exercise than control group (84% vs. 18%). Conversely, the rate of relapse within 12 months of medication withdrawal was smaller in the exercise (29%) than control group (72%).

CONCLUSIONS

The results suggest that structured exercise program may normalize thyroid profile, improve aerobic capacity, and reduce fatigue on the short-term basis as well as reduce the need for anti-thyroid medication on the long-term basis.

Serum thyrotropin levels and blood pressure response to exercise in a population-based study

BACKGROUND

Studies on the relation between thyroid function and exercise blood pressure (EBP) are rare and not population-based, and have yielded inconsistent results. The aim of this study was to investigate whether serum thyrotropin (TSH) levels are related to increased EBP.

METHODS

Cross-sectional data from 1438 subjects (711 women) aged 25-83 years without histories of cardiovascular diseases from the 5-year follow-up of the population-based Study of Health in Pomerania (SHIP-1) were analyzed. Blood pressure was measured at the 100 W stage of a symptom-limited bicycle ergometry test. Increased EBP was defined as a value above the sex- and age-specific 80th percentile of participants with serum TSH levels within the reference range (0.25-2.12 mIU/L).

RESULTS

There was no association between serum TSH levels and EBP after adjusting for sex, age, waist circumference, diabetes mellitus, smoking status, and antihypertensive medication. The odds for increased systolic EBP (odds ratio 1.24, 95% confidence interval 0.88; 1.76) and diastolic EBP (odds ratios 0.98, 95% confidence interval 0.70; 1.39) as well as for exercise-induced increase of systolic and diastolic blood pressure were not significantly different between subjects with high and low serum TSH levels within the reference range. Similar findings were found for both subjects with TSH levels below and above the reference range, respectively.

CONCLUSIONS

We conclude that serum TSH levels are not associated with exercise-related blood pressure response.

The mechanical performance and histomorphological structure of the descending aorta in hyperthyroidism

Thyroid hormones decrease systemic vascular resistance by directly affecting vascular smooth muscle relaxation. There is limited literature about their effect on the mechanical performance of the aortic wall. Therefore, the authors determined the influence of hyperthyroidism on the mechanical properties and histomorphological structure of the descending thoracic aorta in rats. Severe hyperthyroidism was induced in 20 male Wistar rats by administering L-thyroxine (T(4)) in their drinking water for 8 weeks; age-matched normal euthyroid rats acted as controls. Animals were sacrificed, and the mechanical and histomorphometrical characteristics of the descending thoracic aorta were studied. The aortic wall of hyperthyroid rats was stiffer than that of euthyroid animals at the upper physiologic levels of stress or strain (p < 0.05) but less stiff at the lower physiologic and lower levels (p < 0.05). The aorta of hyperthyroid animals compared with that of euthyroid ones showed an increase of the internal and external diameters (p < 0.05), the media area (p < 0.05), the number of smooth muscle cell nuclei (p < 0.05), and the collagen density (p < 0.05) and a decrease in the elastin laminae thickness (p < 0.001) and elastin density (p < 0.001). In hyperthyroid rats, the aortic wall was stiffer at the upper physiologic and higher levels of stress and strain. These changes correlated with microstructural changes of the aortic wall. The coexistence of hyperthyroidism with disease states or clinical conditions that predispose to increased arterial pressure may be associated with increased arterial stiffness and have undesirable consequences on the mechanical performance of the thoracic aorta and hemodynamic homeostasis. These changes could lead to an increased risk for developing vascular complications.

Reduced oxygen uptake increase to work rate increment (DeltaVO2/DeltaWR) is predictable by VO2 response to constant work rate exercise in patients with chronic heart failure

Patients with reduced peak oxygen uptake (VO2) due to chronic heart failure (CHF) exhibit abnormal VO2 kinetics even during mild to moderate exercise. This is characterized by a reduced ratio of the VO2 increase to the work rate increment (DeltaVO2/DeltaWR) during ramp exercise, and by a slow increase in VO2 during constant work rate exercise. Because the slow kinetics alone is unlikely to explain the reduced DeltaVO2/DeltaWR on theoretical grounds, we can postulate that the linearity between work rate and VO2 may be impaired when exercise is imposed in a ramp fashion. The present study was designed to address this issue. In 21 CHF patients and 17 normal controls, we performed both symptom-limited exercise testing (15 W. min(-1) ramp) and a constant work rate exercise test (0 W followed by 50-W step). The VO2 step response was used to mathematically derive the hypothetical VO2 ramp response by time integration. Although peak VO2 and work rate were both significantly lower in patients, the attenuation in peak VO2 was more prominent ( p<0.05), which could be explained by a lower DeltaVO2/DeltaWR in patients compared with controls [8.1 (SD 1.0) and 9.8 (0.5) ml. min(-1). W(-1), p<0.01]. The hypothetical DeltaVO2/DeltaWR derived from the VO2 step response was also significantly lower in patients [8.7 (1.0) and 10.0 (0.7) ml. min(-1). W(-1), p<0.01]. The hypothetical and measured DeltaVO2/DeltaWR were highly correlated ( r=0.78, p<0.001). Thus, we can reasonably predict the VO2 ramp response from the VO2 response to a step increase in work rate, indicating that linearity between VO2 and work rate is held constant irrespective of loading patterns. Additional studies, such as those including evaluation of anaerobic bioenergetics, are needed to further elucidate the precise mechanism(s) of this phenomenon.

Slow component of [V]O(2) kinetics: the effect of training status, fibre type, UCP3 mRNA and citrate synthase activity

OBJECTIVE

In healthy individuals performing constant-load exercise at intensities above the lactate threshold a secondary rise in pulmonary oxygen uptake ([V]O(2)) occurs. [V]O(2) reaches a maximum and exhaustion rapidly prevails for a range of work rates lower than the maximal work rate achieved during a conventional rapid-incremental test. This phenomenon is called the slow component (SC) of [V]O(2) kinetics and represents an increase in [V]O(2) without an increase in work rate. Although still under debate, the magnitude of the SC is believed to be associated with the percentage of type II muscle fibres and their recruitment. In this study we investigated the relationship between the magnitude of the relative SC, citrate synthase activity, UCP2 and UCP3 mRNA levels and muscle fibre composition in both endurance-trained and recreationally active subjects.

METHOD

The magnitude of the relative SC was measured in 12 endurance-trained (Tr) and 15 recreationally active (RA) male subjects. The magnitude of the relative SC was determined as the difference between the end-exercise [V]O(2) and 3 min [V]O(2) divided by the difference between end-exercise [V]O(2) and baseline [V]O(2). UCP2 and UCP3 mRNA expression in the vastus lateralis was measured by RT-PCR with beta-actin mRNA used as an internal control. These values were also normalized against cytochrome-b mRNA to control for training induced changes in mitochondria when comparing the Tr and RA groups. Type I, IIa and IIx skeletal muscle fibre composition was determined using a routine myosin ATPase histochemical staining technique. Citrate synthase (CS) activity was measured using spectrophotometric detection.

RESULTS

The magnitude of the relative SC of the Tr group had the highest correlation with citrate synthase activity (r=-0.90, P<0.001) and that of the RA group with [V]O(2) peak (r=-0.68, P<0.01). For the Tr group other correlations with the magnitude of the relative SC included UCP3 mRNA levels (r=0.69, P<0.05) and the percentage of type I fibres (r=-0.58, P<0.05), while for the RA group they included UCP3 mRNA (r=0.58, P<0.05) and the percentage of type IIa muscle fibres (r=0.59, P<0.05). The Tr subjects had a lower relative SC (P=0.04) and a lower expression of UCP2 (P=0.04), and UCP3 mRNA (P=0.01) than the RA subjects. When the groups were combined the magnitude of the relative SC correlated with UCP3 mRNA (r=0.70, P<0.01), percentage of type IIa muscle fibres (r=0.60, P<0.01) and [V]O(2) peak (r=-0.73, P<0.01). Additionally UCP3 mRNA correlated with the percentage of type IIa muscle fibres (r=0.63, P<0.001).

CONCLUSION

Citrate synthase activity and [V]O(2) peak are indicators of aerobic fitness. The high negative correlations between the magnitude of the relative SC and citrate synthase activity and [V]O(2) peak, of the Tr and RA subjects, respectively, suggests that the magnitude of the relative SC is inversely correlated with aerobic fitness. Additionally the correlations between UCP3 mRNA and the magnitude of the relative SC for both groups individually and combined suggest that the uncoupling activity of the UCP3 protein may also influence the magnitude of the relative SC.

Effect of vitamin E on the response to ischemia-reperfusion of Langendorff heart preparations from hyperthyroid rats

Hyperthyroidism has been reported to decrease heart antioxidant capacity and increase its susceptibility to in vitro oxidative stress. This may affect the heart response to ischemia-reperfusion, a condition that increases free radical production. We compared the functional recovery from in vitro ischemia-reperfusion (Langendorff) of hearts from euthyroid (E), hyperthyroid (H, ten daily intraperitoneal injections of T3, 10 microg/100g body weight), vitamin E-treated (VE, ten daily intramuscular injections, 20 mg/100g body weight) and hyperthyroid vitamin E-treated (HVE) rats. We also determined lipid peroxidation, tissue antioxidant capacity and the tissue capability to face an oxidative stress in vitro. A significant tachycardia was displayed during reperfusion following 20 min ischemia by the hyperthyroid hearts, together with a low recovery of left ventricular developed pressure (LVDP) and left ventricular dP/dt(max). When H hearts were paced at 300 beats/min, the functional recovery (LVDP and dP/dt(max)) was close to 100% and significantly higher than in E paced hearts. At the end of the ischemia-reperfusion protocol, myocardium antioxidant capacity was significantly lower, whereas lipid peroxidation and the susceptibility to in vitro oxidative stress were higher in the T3 treated (H) than in euthyroid rats. The in vitro tachycardic response, the reduction in the antioxidant capacity and the increase in lipid peroxidation were prevented by treatment of hyperthyroid rats with vitamin E (HVE). These results suggest that the tachycardic response to reperfusion following chronic T3 pretreatment was associated with the reduced capability of the heart to face oxidative stresses in hyperthyroidism.

[Cardiopulmonary parameters in hyperthyroidism]

BACKGROUND

Hyperthyroid patients often suffer from impaired exercise capacity with dyspnoea. Two well established, non-invasive methods were used to evaluate the influence of hyperthyroidism on cardiopulmonary function.

PATIENTS AND METHODS

In 42 patients with hyperthyroidism we performed spirometry and cardiopulmonary exercise testing before and after 7 days of propranolol therapy as well as in euthyroidism.

RESULTS

In hyperthyroidism reduced vital capacity and 1-second capacity were observed (95.5 +/- 2.4% vs 102.6 +/- 1.5%; p = 0.0087; 89.4 +/- 2.3% vs 95.2 +/- 2.2%; p = 0.0179). No changes showed during beta-blockade. At the anaerobic threshold reduced tidal volume and enhanced respiratory frequency were noted (1119.8 +/- 48.9 ml vs 1289.3 +/- 62.7 ml; p = 0.0227; 28.3 +/- 0.8 vs 25.4 +/- 0.9; p = 0.0012). A significant tachycardia could be shown. Impaired response to exercise in pulse and respiratory frequency were observed. Work at the anaerobic threshold was impaired in hyperthyroidism (70 +/- 5 watts vs 86.9 +/- 5.7 watts; p = 0.016) and did not change during propranolol therapy. Oxygen pulse at the anaeorbic threshold was reduced in hyperthyroidism (7.7 +/- 0.4 ml O2/beat vs 9.1 +/- 0.4 ml O2/beat; p = 0.0012) and increased with propranolol (8.9 +/- 0.4 ml O2/beat; p = 0.0001).

CONCLUSION

In hyperthyroidism significant changes in cardiopulmonary function were noted at rest and exercise. High resting function and impaired response to exercise suggest a cardiopulmonary work with low efficiency. Propranolol leads to economization and lowers patients complaints.

Ineffective cardiorespiratory function in hyperthyroidism

Dyspnea on exertion is a common complaint in hyperthyroidism, and this thyroid dysfunction has been implicated as a primary cause of impaired effort tolerance. Using spirometry and spiroergometry, 42 patients with untreated hyperthyroidism were examined, and the condition was controlled 7 days later under propranolol monotherapy, as well as after 6 months in euthyroidism. While hyperthyroid, reduced forced vital capacity and tidal volume at the anaerobic threshold (AT) were observed in comparison to euthyroidism. Decreased oxygen (O2) 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 ventilation (16.1 +/- 0.7 vs. 20.2 +/- 1.0 L/min, P = 0.0015), O2 uptake (9 +/- 0.5 vs. 11.4 +/- 0.5 mL/min/kg, P = 0.0022), O2 pulse (4.0 +/- 0.3 vs. 5.6 +/- 0.3 mL/beat, P = 0.0001), and heart rate (53 +/- 2 vs. 65 +/- 3 beat/min, P = 0.0004) was markedly lower in hyper- vs. euthyroidism. Work rate at AT and at maximum was reduced in hyper- vs. euthyroidism (107.4 +/- 3 vs. 141.1 +/- 4 watt, P = 0.0001). Negative correlations between free T3 and O2 pulse at AT (r = -0.59, P = 0.0005), delta O2 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) were noted. In hyperthyroidism, analysis of respiratory gas exchange showed low efficiency of cardiopulmonary function, respiratory muscle weakness, and impaired exercise capacity, which were reversible in euthyroidism.

Reduced metabolic efficiency of skeletal muscle energetics in hyperthyroid patients evidenced quantitatively by in vivo phosphorus-31 magnetic resonance spectroscopy

Skeletal muscle energetics of seven hyperthyroid patients were investigated throughout a rest-exercise-recovery protocol using phosphorus-31 magnetic resonance spectroscopy (31P MRS) to quantitatively document in vivo the metabolic bases of impaired muscle performance in hyperthyroidism. The contributions of the main pathways of adenosine triphosphate (ATP) synthesis to energy production and proton efflux were measured and compared with results from normal muscle. At rest, a reduced concentration of phosphocreatine (PCr) was calculated for hyperthyroid patients when compared with controls, whereas pH and concentrations of inorganic phosphate (Pi) and phosphomonoesters (PME) were not different from controls. During exercise, the analysis of changes in pH and PCr concentration demonstrated that (1) at the onset of exercise, the magnitude of glycolysis activation is significantly larger for patients, resulting in a marked pH decrease; (2) the energy cost of exercise is higher for patients as compared with controls performing the same amount of work; and (3) both anaerobic and aerobic pathways are significantly more activated in the hyperthyroid group throughout the 3 minutes of exercise. During recovery, the rates of proton efflux and PCr resynthesis were similar in both groups, excluding any alteration in oxidative function and proton handling as a cause of initial glycolytic hyperactivation. The increased energy cost measured for patients during exercise evidences an increased need for energy, which is (1) probably linked to the existence of additional ATP-consuming mechanism(s), and (2) supported by hyperactivation of both aerobic and anaerobic pathways. These findings imply that, all things equal, a hyperthyroid muscle requires more energy to function than normal, and as a result is potentially more fatiguable.