Right heart pressures and blood-gas tensions in ponies during exercise and laryngeal hemiplegia.

Right atrial, right ventricular, and pulmonary artery pressures, along with change in pleural pressure, were determined with catheter-tipped micromanometers in two groups of ponies at rest, as well as during moderate (trot; heart rate = 180 beats . min-1) and severe (gallop; heart rate = 220 beats . min-1) exercise performed on a treadmill. Group A (n = 8) ponies served as controls, and group B ponies (n = 6) had laryngeal hemiplegia (LH) induced by sectioning the left recurrent laryngeal nerve 20-29 days before the study. It was observed that LH ponies could not gallop for more than 45-90 s. With both levels of exertion, pressures in the right atrium, right ventricle, and pulmonary artery increased very significantly in normal ponies. The change in pleural pressure of galloping ponies was 30.4 +/- 2.9 cmH2O, and the respiratory (and stride) frequency was 138 +/- 4 breaths . min-1. During severe exercise in normal ponies, the systolic, mean, and diastolic pressures in the pulmonary artery were 107 +/- 7, 63.5 +/- 4.2, and 46 +/- 4 mmHg, despite the fact that no alveolar hypoxia could be detected. In LH ponies pulmonary artery pressures rose to levels observed in normal ponies, but during galloping, the change in pleural pressure (delta Ppl) (92 +/- 6 cmH2O) was three times that in normal ponies, and there was no synchronization of respiratory (86 +/- 6 breaths . min-1) frequency to stride frequency (142 +/- 3 strides . min-1). Despite these respiratory adjustments (decreased frequency and increased delta Ppl), arterial PO2 decreased and arterial PCO2 increased in galloping LH ponies.(ABSTRACT TRUNCATED AT 250 WORDS)