A comparison of cardiopulmonary adaptations to exercise in pregnancy at sea level and altitude

OBJECTIVE

The purpose of this study was to compare maternal cardiopulmonary and fetal responses of lowlander pregnant women in the third trimester to exercise at sea level and at an altitude of 6000 feet.

STUDY DESIGN

Seven women at 33.86 +/- 1 weeks' gestation performed a symptom-limited maximal exercise test and a submaximal cardiac output exercise test at sea level at an altitude of 6000 feet. Cardiopulmonary and metabolic variables were measured and compared at sea level and altitude.

RESULTS

Maximal oxygen consumption and work levels were limited by short-term altitude exposure. Ventilatory variables were not significantly influenced by altitude exposure. During submaximal exercise no alteration in exercise efficiency or response was seen for most of the variables when altitude and sea level data were compared. Both cardiac output and stroke volume were elevated at altitude at rest but not during exercise, suggesting a lower reserve for both variables at altitude. Level of plasma glucose, lactate, norepinephrine, and epinephrine were not significantly influenced by altitude exposure. Fetal heart rate responses did not differ between the sea level and altitude conditions.

CONDITIONS

Lowlander pregnant women in the third trimester have some limitations to maximal aerobic capacity but not submaximal exercise on short-term altitude exposure. No ominous fetal responses have been observed during this study. The results suggest that pregnant women may engage in at least brief moderate exercise bouts at moderate altitude without adverse consequences.

Effect of aging on changes in plasma potassium during exercise

BACKGROUND

Exercising skeletal muscle releases large amounts of potassium into plasma. beta-adrenergic receptors enhance reuptake of potassium into muscle. Since beta-adrenergic responses decline with aging in many tissues, the elderly might be predisposed to hyperkalemia during exercise.

METHODS

Venous plasma potassium (K+) was measured during graded bicycle exercise (30 W initial workload with 3-minute 30 W increments) in 18 healthy young men (24.0 +/- 2.9 yrs; mean +/- SD), 18 healthy untrained elderly men (70.0 +/- 3.6 yrs), and 7 elderly master athletes (70.0 +/- 4.6 yrs). Subjects exercised to exhaustion.

RESULTS

Exercise times and maximal oxygen uptake were: young (N = 14; 19.6 +/- 4.4 min, 42.1 +/- 3.8 ml/kg/min), elderly (N = 13; 11.7 +/- 1.9 min, 26.6 +/- 8.0 ml/kg/min), elderly master athletes (N = 6; 16.8 +/- 2.4 min, 40.2 +/- 10.2 ml/kg/min). The rate of increase in K+ was greater in both elderly (89 +/- 59 mumol/l/min) and elderly master athletes (88 +/- 26) compared with healthy young men (60 +/- 30), p < .05. Despite this greater rate of increase, the elderly group did not achieve higher maximal K+ concentrations than the young because of the much shorter duration of exercise in the elderly group. For subjects performing a maximal exercise test, the maximal increase in K+ was similar in the elderly (1.15 +/- 0.91), but significantly greater in elderly master athletes (1.70 +/- 0.31), compared with healthy young men (1.31 +/- 0.45).

CONCLUSIONS

Changes in K+ during short-lasting exercise are similar in untrained healthy elderly men compared with healthy young men, but elderly master athletes have greater changes in K+ during exercise. The greater rate of increase in potassium in healthy and athletic subjects supports the hypothesis of an age-related impairment of the beta 2-adrenergic process that mediates potassium flux into skeletal muscle.

Pulmonary responses to exercise in pregnancy

The pulmonary responses of 88 pregnant women were compared to those of 39 nonpregnant control subjects during different exercise intensities. At rest the pregnant women had higher tidal volumes, oxygen consumption, carbon dioxide production, and respiratory exchange ratio. With increased work loads the pregnant volunteers have consistently lagged behind the nonpregnant control subjects for every parameter, which indicates a decrease in pulmonary reserve and inability to exercise anaerobically.

Hormonal responses to exercise in diabetic and nondiabetic pregnant patients

The hormonal responses to low-level exercise in pregnancy have been studied in 13 insulin-requiring diabetic patients and 42 control subjects. We found no significant changes in plasma glucose, epinephrine, glucagon, or FFA with this level of exercise in the study group and control subjects; but plasma norepinephrine showed a significant increase with exercise. This type of exercise appears to be safe and could serve as a model for exercise prescription for attaining improved glucose tolerance in pregnant diabetic women.

Fetal bradycardia induced by maternal exercise

Fetal bradycardia that occurred during maternal exercise (a symptom-limited VO2 max treadmill test) in the fetuses of three healthy pregnant women is described. The mechanism of this bradycardia is believed to be mediated by catecholamines. The fetal bradycardia seems to be transitory and appears to be compensated for by an increase in fetal heart rate after the cessation of exercise.