Diaphragm VO2, diaphragm EMG, pressure-time product and calculated ventilation in newborn lambs during hypercapnic hyperpnoea.

We examined the relationship between diaphragmatic EMG (EMGdi) and pressure-time index (Pt'), and diaphragmatic oxygen consumption (VO2di) in 6 newborn lambs quietly breathing air and during 3 levels of hypercapnic hyperpnoea (PaCO2 was equal to 48, 53, or 60 Torr). We also determined minute ventilation (VI), whole body oxygen consumption (VO2), diaphragmatic oxygen consumption (VO2di), and respiratory muscle oxygen consumption (VO2resp). VO2 did not change significantly throughout the experiment. While breathing air VO2di was 0.46 +/- 0.03 ml.min-1, VO2resp was 1.40 +/- 0.22 ml.min-1, and VI was 1.98 +/- 0.11 L.min-1. These values increased significantly during hyperpnoea and reached 3.88 +/- 0.45 ml.min-1, 7.22 +/- 1.12 ml.min-1, and 6.99 +/- 1.03 L.min-1, respectively. EMGdi, and Pt' also increased significantly during hyperpnoea. A strong linear relationship was found between the normalized values of EMGdi and Pt' (r = 0.90), between VO2di and EMGdi (r = 0.88), and between VO2di and Pt' (r = 0.88). The relationship between both EMGdi and VI and PaCO2 was logarithmic. We found that (i) both EMGdi and Pt' correlate well with VO2di, and (ii) VI, VO2di, and EMGdi increased significantly when PaCO2 was greater than 48 Torr.