Journal of Applied Physiology, Vol 65, Issue 4 1723-1728, Copyright © 1988 by American Physiological Society
Costal diaphragmatic O2 and lactate extraction in laryngeal hemiplegic ponies during exercise
M. Manohar, T. E. Goetz and D. Nganwa
Department of Veterinary Biosciences, College of Veterinary Medicine, University of Illinois, Urbana-Champaign 61801.
Diaphragmatic O2 and lactate extraction were examined in seven healthy
ponies during maximal exercise (ME) carried out without, as well as with,
inspiratory resistive breathing. Arterial and diaphragmatic venous blood
were sampled simultaneously at rest and at 30-s intervals during the 4 min
of ME. Experiments were carried out before and after left laryngeal
hemiplegia (LH) was produced. During ME, normal ponies exhibited
hypocapnia, hemoconcentration, and a decrease in arterial PO2 (PaO2) with
insignificant change in O2 saturation. In LH ponies, PaO2 and O2 saturation
decreased well below that in normal ponies, but because of higher
hemoglobin concentration, arterial O2 content exceeded that in normal
ponies. Because of their high PaCO2 during ME, acidosis was more pronounced
in LH animals despite similar lactate values. Diaphragmatic venous PO2 and
O2 saturation decreased with ME to 15.5 +/- 0.9 Torr and 18 +/- 0.5%,
respectively, at 120 s of exercise in normal ponies. In LH ponies,
corresponding values were significantly less: 12.4 +/- 1.3 Torr and 15.5
+/- 0.7% at 120 s and 9.8 +/- 1.4 Torr and 14.3 +/- 0.6% at 240 s of ME.
Mean phrenic O2 extraction plateaued at 81 and 83% in normal and LH
animals, respectively. Significant differences in lactate concentration
between arterial and phrenic-venous blood were not observed during ME. It
is concluded that PO2 and O2 saturation in the phrenic-venous blood of
normal ponies do not reach their lowest possible values even during ME.
Also, the healthy equine diaphragm, even with the added stress of
inspiratory resistive breathing, did not engage in net lactate production.
