Structural and oxidative enzyme characteristics of the diaphragm
- 1 September 2002
- journal article
- Published by Wiley in Equine Veterinary Journal
- Vol. 34 (S34), 459-463
- https://doi.org/10.1111/j.2042-3306.2002.tb05466.x
Abstract
During exercise, the horse can achieve oxygen uptakes and ventilations in excess of 200 ml/kg/min and 1800 l/min, respectively. Whether the diaphragm has the capacity to contribute substantially to inspiratory effort in the exercising horse is not known. To investigate the potential for the horse diaphragm to generate tension, lung displacement and sustain ventilatory function, we measured diaphragm thickness, muscle length and oxidative enzyme activity (citrate synthase) within the ventral, medial and dorsal costal and crural diaphragm. In the diaphragms of 6 mature horses (5 Thoroughbreds, one Quarter Horse; body mass (mean +/- s.e.) 475 +/- 14 kg, age 4 +/- 1 years), the mass of the freshly-excised diaphragm was 4.54 +/- 0.19 kg of which 79% was the costal diaphragm, 17% the crural diaphragm and 4% the central tendon. The medial costal region (2.1 +/- 0.1 cm) was significantly thicker (P3.2 +/- 0.3 cm, P<0.05) than any costal diaphragm region. With respect to the costal diaphragm, excised muscle length was greatest (P<0.05) in the medial costal (17.2 +/- 1.0 cm) than either the ventral costal (<12.6 +/- 1.5 cm) or dorsal costal (<13.9 +/- 1.8 cm) regions and therefore the medial region would be expected to exhibit the greatest absolute length change on inspiration. Citrate synthase activity was high throughout the diaphragm (40.8 +/- 113 to 55.3 +/- 9.7 micromol/g/min), but was not significantly different among regions. These structural characteristics and the oxidative potential of the horse diaphragm are consistent with the diaphragm providing a significant and substantial contribution to the inspiratory effort during exercise in the horse. Consequently, clinical and physiological investigations of exercise performance should not ignore the potentially crucial importance of the diaphragm.Keywords
This publication has 27 references indexed in Scilit:
- The effect of exercise on diaphragmatic activation in horsesRespiration Physiology, 1996
- Composition and size of type I, IIA, IID/X, and IIB fibers and citrate synthase activity of rat muscleJournal of Applied Physiology, 1996
- Inferences on passive diaphragm mechanics from gross anatomyJournal of Applied Physiology, 1994
- Three-dimensional reconstruction of the in vivo human diaphragm shape at different lung volumesJournal of Applied Physiology, 1994
- Stride length and respiratory tidal volume in exercising thoroughbred horsesRespiration Physiology, 1993
- Respiratory muscle recruitment in awake ponies during exercise and CO2 inhalationRespiration Physiology, 1991
- Regional distribution of blood flow within the diaphragmJournal of Applied Physiology, 1991
- Biochemical characteristics of mammalian diaphragmsRespiration Physiology, 1988
- Vasodilator reserve in respiratory muscles during maximal exertion in poniesJournal of Applied Physiology, 1986
- Running and Breathing in MammalsScience, 1983