Respiratory and cardiovascular adjustments during exercise of increasing intensity and during recovery in thoroughbred racehorses.
Abstract: A new design of flowmeter is described and used in a comprehensive study of the respiratory and cardiovascular adjustments that occur during a standardised exercise test in Thoroughbred horses. The flowmeter system and associated lightweight, fibreglass mask (total mass, 0.7 kg) have a maximum dead space of 500 ml and negligible resistance to airflow. They have no systematic effect on blood gases and, together with a rapidly responding mass spectrometer, enable an accurate computation of gas exchange to be performed together with breath-by-breath determination of other respiratory variables. At the highest level of exercise (12 ms-1 on a 3 degrees incline), the rate of oxygen uptake (VO2) and carbon dioxide production (VCO2) increased to 29.4 times and 36.8 times their resting values, respectively. Respiratory minute volume (VE) increased to 27.0 times its resting value, with respiratory frequency (fR) making the major contribution at the walk and trot. However, with increasing cantering speeds, fR changed little as it was locked in a 1:1 fashion to stride frequency, and tidal volume (VT) then made the major contribution to the increase in VE. The ratio of ventilatory dead space (VD) to VT in resting horses was lower than that previously reported in the literature and this could be the result of the different respiratory recording systems that were used. There was a close relationship between VT and stride length at increasing cantering speeds. Despite the fact that alveolar ventilation (VA) was well matched to VO2, there was a significant reduction in arterial PO2 (PaO2) when the horses cantered at 8 ms-1 and this eventually fell to 34% below the resting value. The present data tend to support the idea that VA/Vb (where Vb is cardiac output) inequalities are important in causing this hypoxaemia. However, the reduction in PaO2 was more than compensated for by an increase in haemoglobin concentration, [Hb], so the concentration of oxygen in the arterial blood (CaO2) was significantly above the resting value at all levels of exercise. Both lactate concentration and PaCO2 increased during exercise, causing substantial reductions in pH of both arterial and mixed venous blood. This would have inevitably shifted the oxygen equilibrium curve of the Hb to the right, desaturating the arterial blood and thus exacerbating the effect of the hypoxaemia, as would the almost 4 degrees C rise in blood temperature. The tight respiratory/locomotor linkage might prevent the acidosis and hyperthermia having the stimulatory effects on VE that they have in humans at high work loads.(ABSTRACT TRUNCATED AT 400 WORDS)
Publication Date: 1993-06-01 PubMed ID: 8340728DOI: 10.1242/jeb.179.1.159Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This study introduces a new flowmeter design for studying respiratory and cardiovascular changes in Thoroughbred horses during exercise and recovery. The flowmeter, paired with a lightweight fiberglass mask, allows for precise computation of gas exchange and observation of other respiratory variables. The primary findings note significant increases in oxygen uptake and carbon dioxide production during intense exercise, and a major reduction in arterial oxygen pressure compensated by increased hemoglobin concentration.
Methodology and Equipment
- The researchers designed a new type of flowmeter and combined it with a lightweight fiberglass mask to monitor respiratory variables in Thoroughbred horses during a standardized exercise test.
- This apparatus has a low resistance to airflow and minimal dead space enabling an accurate measurement of gas exchange.
- Alongside a rapidly responding mass spectrometer, the research equipment provided breath-by-breath determination of additional respiratory factors.
Main Findings
- The highest level of exercise led to an increase in the rate of oxygen uptake (VO2) and carbon dioxide production (VCO2)by 29.4 times and 36.8 times of the resting values respectively.
- Respiratory minute volume (VE) also increased, with respiratory frequency (fR) contributing significantly to this during walking and trotting. This fR essentially synchronized with stride frequency during faster cantering,
- The ratio of ventilatory dead space (VD) to tidal volume (VT) was lower than previously documented indicating that the recording systems might influence results.
- The study noticed a correlation between stride length and tidal volume at varied cantering speeds.
Cardiovascular Adjustments
- Despite the good match of alveolar ventilation (VA) to oxygen uptake (VO2), there was a considerable drop in arterial oxygen pressure (PaO2) when the horse sustained a canter at 8 ms-1. The researchers had expected an opposite result based on the effective VA/VO2 relation and believe that inequalities in the VA/cardiac output ratio might cause this unnatural hypoxemia.
- The reduced PaO2 was counteracted by an increase in hemoglobin concentration, maintaining the oxygen concentration in the arterial blood (CaO2) well above resting value during all exercise intensities.
Blood Chemistry Changes
- The research observed an increase in lactate concentration and arterial carbon dioxide pressure during exercise. These changes resulted in significant reductions in arterial and mixed venous blood pH which would eventually shift the oxygen equilibrium curve to the right, desaturating the arterial blood.
Conclusion
- The researchers hypothesized that the physical linkage between respiration and locomotion might obstruct the acidosis and the increase in temperature from having the usual stimulating effects on VE, as observed in humans undertaking high-intensity tasks.
Cite This Article
APA
Butler PJ, Woakes AJ, Smale K, Roberts CA, Hillidge CJ, Snow DH, Marlin DJ.
(1993).
Respiratory and cardiovascular adjustments during exercise of increasing intensity and during recovery in thoroughbred racehorses.
J Exp Biol, 179, 159-180.
https://doi.org/10.1242/jeb.179.1.159 Publication
Researcher Affiliations
- School of Biological Sciences, University of Birmingham, Edgbaston, UK.
MeSH Terms
- Animals
- Cardiac Output
- Cardiovascular Physiological Phenomena
- Female
- Heart Rate
- Horses / physiology
- Hydrogen-Ion Concentration
- Lactates / blood
- Lactic Acid
- Male
- Oxygen / blood
- Oxygen Consumption
- Physical Exertion / physiology
- Respiration / physiology
- Rheology / instrumentation
Citations
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