Heart rate and energy expenditure of pregnant and lactating women

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Abstract
Data on heart rate and oxygen consumption of 21 mature pregnant women, and of 16 of them postpartum, were examined for evidence of the suitability of heart rate as an index of energy expenditure during pregnancy. Energy expenditure, measured by indirect calorimetry, and heart rate were recorded with subjects at rest (lying, sitting, and standing) and working (on a treadmill and cycle ergometer) at three different levels. Energy expenditure (EE) and heart rate (HR) were highly correlated during the second half of gestation and postpartum. Both EE and HR were affected by pregnancy state, but the relationship between HR and EE was not changed. Slopes of regression of two linear components of EE/HR relationship were 0.01–0.02 for resting, and 0.05–0.06 for working measures. The slopes under resting and working conditions are significantly different from zero, and from each other. Prediction of EE from HR is unreliable in the range 80–120 beats/min where resting and working HRs overlap.