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PubMed2003

Adrenergic contribution during acclimatization to high altitude: perspectives from Pikes Peak.

We have examined the sympathoadrenal responses to both acute and chronic high-altitude exposure at the summit of Pikes Peak, CO, in both men and women. A dissociation between the adrenal medullary response (acute) with that of the sympathetic nervous system (chronic) is observed. Both alpha- and beta-adrenergic contributions to key metabolic and physiologic adjustments to high-altitude exposure are evident.

Acclimatization↗
PubMed2006

Effects of altitude on effort tolerance in non-acclimatized patients with ischemic left ventricular dysfunction.

BACKGROUND: Few studies exist on the effects, in terms of work capacity and safety, of exposure to moderately high altitudes in patients with stable ischemic left ventricular dysfunction. Moreover no data are currently available on the cardiorespiratory response to walks in the mountains. AIM: The objective of this study is to evaluate the effects of altitude on effort tolerance during walks in the mountains and to determine whether exposure to altitude may be harmful to patients with ischemic left ventricular dysfunction. METHODS: Forty-five patients with stable chronic ischemic left ventricular dysfunction (ejection fraction=35+/-4%, and peak VO2>/=18/ml/kg per min in a preliminary effort test) were compared to 24 normal subjects. All subjects underwent a series of 6-min walking tests at three different altitudes: 500, 2000 and 2970 m above sea level. Cardiorespiratory response was assessed by a validated portable instrument. The resting arterial PO2 was measured at the three altitudes. RESULTS: No complications were observed during any tests in either the patients or the healthy controls. Overall, healthy subjects had higher values of 6-min walking test VO2 and walked longer distances in the test than did the patients with left ventricular dysfunction. The mean distances walked in the 6-min walking test were similar at 500 and at 2000 m in both the healthy controls and the patients; at 2970 m, however, the distances decreased in both groups, and more so in the patients (-11+/-3%) than in the controls (-5+/-2%) (P<0.01). VO2 during the 6-min walking test remained stable when the test was carried out at 500 and 2000 m (20.4+/-3.6 versus 19.9+/-4.1 ml/kg per min in patients, and 30.2+/-3.4 versus 29.8+/-4.2 ml/kg per min in the controls; P, NS), but decreased at 2970 m by 13.9+/-3% in patients (P<0.01) and by 6.6+/-2.1% in controls (P<0.01) (patients versus controls, P<0.01). Finally, a similar, significant decrease in arterial PO2 was observed in both groups only at 2970 m (-29%, P<0.01). CONCLUSION: Patients with stable ischemic left ventricular dysfunction had good tolerance while walking at high altitudes, but showed a moderate decrease in work capacity at 2970 m, which was greater than in normal subjects.

Acclimatization↗
PubMed1983

Thyroid hormone metabolism after acclimatization to warm or cold temperature under conditions of high or low energy intake.

The separate effects of ambient temperature and energy intake on the metabolism of thyroid hormones in the young pig have been investigated. Piglets were kept singly from 4 weeks of age at 10 or 35 degrees C on a high (H), or low (L) energy intake, such that H = 2L. At the tenth week of age blood samples were taken 16-21 h after the last meal for the determination of plasma concentrations of thyroxine (T4) and 3,5,3'-triiodothyronine (T3). At the end of the tenth week of age the fractional disappearance rate (K) of T4 was determined and finally the K value for T3 was estimated. Plasma concentrations of T4 and T3 were greater in animals on a high intake than in those on a low intake, (P less than 0.02), but the temperature at which the animals lived had no significant effect. The values of K for T4 and T3 were greater at 10 than at 35 degrees C (P less than 0.010 and P less than 0.05), and energy intake had no significant effect. Calculations of the catabolic rates in nmol/kg X h revealed that for T4 the rate was greater at 10 than at 35 degrees C (P less than 0.001) and on a high than on a low intake (P less than 0.01). Similar differences were found between the mean values of T3 with respect to both temperature and energy intake, but the variance was large and they did not reach statistical significance. It is concluded that the metabolism of thyroid hormones is influenced independently by both ambient temperature and energy intake.

Acclimatization↗