Lung Mechanics and Oxygen Consumption During Spontaneous Ventilation and Severe Heart Failure

Abstract

The effects of acute heart failure on lung mechanics and oxygen consumption (VO2) during normocarbic spontaneous ventilation were studied in 21 anesthetized pigs. Heart failure severe enough to double oxygen extraction (O2ex) was induced with intravenous esmolol boluses and infusion. Compared to normal, the inspiratory elastic work of breathing (Wel) increased from 335 +/- 371 (mean +/- SD) to 559 +/- 48 mm Hg.ml (p less than 0.003) during heart failure, lung compliance (CL) fell from 121 +/- 144 to 22 +/- 15 ml/mm Hg (p less than 0.05), and respiratory power climbed from 140 +/- 200 to 245 +/- 214 mm Hg.ml.min-1 (p less than 0.002). These mechanical changes were accompanied by a decrease in both VO2 (221 +/- 61 to 191 +/- 50 mlO2/min, p less than 0.05) and oxygen delivery (DO2) (680 +/- 240 to 260 +/- 90 mlO2/min, p less than 0.004). The VO2/DO2 ratio doubled (p less than 0.0002), confirming increased O2ex. In conclusion, severe acute heart failure decreased CL, and increased Wel and respiratory power significantly. The depressed cardiac output limits both DO2, and to some extent, VO2. However, a greater proportion of the delivered O2 is consumed, supplying indirect evidence which suggests that the respiratory muscles' VO2 increases as a consequence of increased power expenditure.