著者

Hajime OHMURA James H. JONES

出版者

日本ウマ科学会

雑誌

Journal of Equine Science (ISSN:13403516)

巻号頁・発行日

vol.28, no.3, pp.99-103, 2017 (Released:2017-09-20)

参考文献数

25

被引用文献数

15

---

We investigated changes in heart rate (HR) and HR variability as a function of age in newborn foals to old Thoroughbred horses. Experiments were performed on a total of 83 healthy and clinically normal Thoroughbred horses. Resting HR decreased with age from birth. The relationship between age and HR fit the equation Y=48.2X-0.129(R2=0.705); the relationship between age and HR for horses 0–7 years old fit the equation Y=44.1X-0.179(R2=0.882). Seven-day-old horses had the highest HR values (106 ± 10.3 beat/min). The low frequency (LF) and high frequency (HF) powers increased with age in newborn to old horses. These changes in HR and HR variability appear to result from the effects of ageing. Three- to seven-year-old race horses had the lowest HR values (32.9 ± 3.5 beat/min) and the highest LF and HF powers except for the HF powers in the oldest horses. Race training may have contributed to these changes. Horses of ages greater than 25 years old had the highest HF powers and the lowest LF/HF ratios. In individual horses, 8 of the 15 horses over 25 years old had LF/HF ratios of less than 1.0; their HR variability appears to be unique, and they may have a different autonomic balance than horses of younger age.

著者

Hajime Ohmura Atsushi Hiraga James H. Jones

出版者

一般社団法人日本体力医学会

雑誌

The Journal of Physical Fitness and Sports Medicine (ISSN:21868131)

巻号頁・発行日

vol.2, no.2, pp.163-168, 2013-05-25 (Released:2013-06-21)

参考文献数

48

被引用文献数

3

---

Thoroughbred racehorses have been selectively bred for racing for centuries. The excellent exercise capacity of Thoroughbreds is thought to depend largely on their extraordinarily high cardiopulmonary function. Their high aerobic capacity (VO2max) might be amplified by the exercise-induced hypoxemia that they experience even during submaximal exercise. In humans and horses, accumulated O2 deficit (AOD) has been the primary approach used to assess net anaerobic capacity during exercise. The exercise-induced hypoxemia Thoroughbreds experience allows an alternative approach to measuring net anaerobic energy utilization using plasma lactate accumulation rate (PLAR). Horses increase their aerobic capacity when breathing hyperoxic gas that eliminates exercise-induced hypoxemia, and PLAR decreases stoichiometrically. Relating the decrease in PLAR to the increase in VO2max yields a quantitative index of how much net aerobic power a horse is utilizing. Comparison in horses of the net anaerobic power estimated by the two methods, AOD and PLAR, shows systematic bias and suggests PLAR may be more accurate.

著者

Hajime OHMURA Kazutaka MUKAI Akira MATSUI Toshiyuki TAKAHASHI James H. JONES

出版者

Japanese Society of Equine Science

雑誌

Journal of Equine Science (ISSN:13403516)

巻号頁・発行日

vol.31, no.4, pp.67-73, 2020 (Released:2020-12-18)

参考文献数

23

被引用文献数

4

---

Supramaximal exercise while inspiring different O2 gases may induce different responses in cardiopulmonary function at the same relative and/or absolute exercise intensity. The purpose of this study was to compare the effects of supramaximal exercise in hypoxia, normoxia and hyperoxia on cardiopulmonary function in Thoroughbred horses. Using a crossover design, five well-trained horses were made to run up a 6% grade on a treadmill at supramaximal speeds sustainable for approximately 110 sec (approximately 115% VO2max) while breathing normoxic gas (NO, 21% O2) or hypoxic gas (LO, 15.3% O2) in random order. Horses also ran at the same speed, incline and run time as in NO while breathing hyperoxic gas (HONO, 28.8% O2) and as in LO while breathing normoxic gas (NOLO). Runs were on different days, and cardiopulmonary variables were analyzed with repeated-measures ANOVA and the Holm-Šidák method for pairwise comparisons. Supramaximal speeds differed significantly between NO and LO (14.0 ± 0.5 [SD] m/sec vs. 12.6 ± 0.5 m/sec), but run times to exhaustion did not (112 ± 17 sec vs. 103 ± 14 sec). The VO2max in NO was higher than that in LO (165 ± 11 vs. 120 ± 15 ml (min× kg)), as was the arterial oxygen tension (66 ± 5 vs. 45 ± 2 Torr). Oxygen consumption was increased in HONO and NOLO compared with the values in NO and LO, respectively. Supramaximal exercise in hypoxia induces more severe hypoxemia and decreases VO2max compared with normoxia at the same relative intensity. Conversely, supramaximal exercise in hyperoxia alleviates hypoxemia and increases VO2 compared with normoxia at the same absolute intensity.

著者

Eric K. BIRKS Hajime OHMURA James H. JONES

出版者

Japanese Society of Equine Science

雑誌

Journal of Equine Science (ISSN:13403516)

巻号頁・発行日

vol.30, no.4, pp.87-92, 2019 (Released:2019-12-18)

参考文献数

26

被引用文献数

2

---

Measurements of gas exchange while breathing gases of different O2 concentrations are useful in respiratory and exercise physiology. High bias flows required in flow-through indirect calorimetry systems for large animals like exercising horses necessitate the use of inconveniently large reservoirs of mixed gases for making such measurements and can limit the amount of equilibration time that is adequate for steady-state measurements. We obviated the need to use a pre-mixed reservoir of gas in a semi-open flow-through indirect calorimeter by dynamically mixing gases and verified the theoretical accuracy and utility of making such measurements using the mass-balance N2-dilution method. We evaluated the accuracy of the technique at different inspired oxygen fractions by measuring exercising oxygen consumption (VO2) at two fully aerobic submaximal exercise intensities in Thoroughbred horses. Horses exercised at 24% and 50% maximum oxygen consumption (VO2 max) of each horse while breathing different O2 concentrations (19.5%, 21% and 25% O2). The N2-dilution technique was used to calculate VO2. Repeated-measures ANOVA was used to tested for differences in VO2 between different inspired O2 concentrations. The specific VO2 of the horses trotting at 24%VO2max and cantering at 50%VO2max were not significantly different among the three different inspired oxygen fractions. These findings demonstrate that reliable measurements of VO2 can be obtained at various inspired oxygen fractions using dynamic gas mixing and the N2-dilution technique to calibrate semi-open-circuit gas flow systems.