Journal
JOURNAL OF APPLIED PHYSIOLOGY
Volume 96, Issue 6, Pages 2187-2193Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/japplphysiol.00998.2003
Keywords
exercise recovery; locomotory-respiratory coupling; blood acid-base; equid
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Funding
- NHLBI NIH HHS [HL-50306, HL-69739] Funding Source: Medline
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Despite enormous rates of minute ventilation ((V)over dot E) in the galloping Thoroughbred (TB) horse, the energetic demands of exercise conspire to raise arterial PCO2 (i.e., induce hypercapnia). If locomotory-respiratory coupling (LRC) is an obligatory facilitator of high (V)over dot E in the horse such as those found during galloping (Bramble and Carrier. Science 219: 251-256, 1983), (V)over dot E should drop precipitously when LRC ceases at the gallop-trot transition, thus exacerbating the hypercapnia. TB horses (n=5) were run to volitional fatigue on a motor-driven treadmill (1 m/s increments; 14-15 m/s) to study the dynamic control of breath-by-breath (V)over dot E, O-2 uptake, and CO2 output at the transition from maximal exercise to active recovery (i.e., trotting at 3 m/s for 800 m). At the transition from the gallop to the trot, (V)over dot E did not drop instantaneously. Rather, V. E remained at the peak exercising levels (1,391+/-88 l/min) for similar to13 s via the combination of an increased tidal volume (12.6+/-1.2 liters at gallop; 13.9+/-1.6 liters over 13 s of trotting recovery; P<0.05) and a reduced breathing frequency [113.8 +/- 5.2 breaths/min (at gallop); 97.7 +/- 5.9 breaths/min over 13 s of trotting recovery (P<0.05)]. Subsequently, V. E declined in a biphasic fashion with a slower mean response time (85.4+/-9.0 s) than that of the monoexponential decline of CO2 output (39.9+/-4.7 s; P<0.05), which rapidly reversed the postexercise arterial hypercapnia (arterial PCO2 at gallop: 52.8 +/- 3.2 Torr; at 2 min of recovery: 25.0 +/- 1.4 Torr; P<0.05). We conclude that LRC is not a prerequisite for achievement of (V)over dot E commensurate with maximal exercise or the pronounced hyperventilation during recovery.
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