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      Alterações do pH, da P O2 e da P CO2 arteriais e da concentração de lactato sangüíneo de cavalos da raça Árabe durante exercício em esteira de alta velocidade Translated title: Changes in arterial pH, P O2, P CO2 and blood lactate concentration in Arabian horses during exercise on a high-speed treadmill

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          Abstract

          Avaliaram-se as alterações do pH, da P O2 e da P CO2 do sangue arterial e da concentração de lactato sangüíneo de 11 cavalos adultos da raça Árabe, submetidos a exercício progressivo em esteira de alta velocidade. Antes do exercício, no intervalo dos 15 segundos finais de cada mudança de velocidade e aos 1, 3 e 5 minutos após o término do exercício foram coletadas amostras de sangue arterial e venoso para a mensuração dos gases sangüíneos e da concentração de lactato. O exercício resultou em diminuição do pH, da pressão parcial de O2 (P O2) e da pressão parcial de CO2 (P CO2). A concentração de lactato sangüíneo elevou-se exponencialmente a partir da velocidade de 8,0m/s até os momentos após término do exercício.

          Translated abstract

          Changes in arterial blood pH, P O2 and P CO2, and blood lactate concentration in Arabian horses during exercise on a high-speed treadmill were investigated. Eleven horses were submitted to a conditioning period as well as to the incremental exercise test. The arterial and venous blood samples were obtained to evaluate the blood gas values and lactate concentration, prior to the beginning of the exercise, on the last 15 final seconds between every change of speed and at the 1, 3 and 5 minutes after the exercise. A decrease in pH, partial pressure of oxygen (P O2), and partial pressure of carbon dioxide (P CO2) and the blood lactate levels exponentially increase beyond the speed of 8m/s, during the incremental exercise test.

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          Multivariate Statistical Methods

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            Exercise-induced hypercapnia in the horse.

            The effects of exercise intensity and duration on blood gases in thoroughbred horses were studied to characterize the apparent exercise-induced failure in pulmonary gas exchange that occurs in these animals. In response to 2 min of exercise, arterial CO2 tension (PaCO2) decreased in mild and moderate exercise, returned to normocapnic levels in moderate to heavy exercise, and rose 5-10 Torr above resting values during very heavy exercise when CO2 production (VCO2) exceeded 20 times the resting value, and mixed venous CO2 tension approximated 140 Torr. Exercise-induced hypoxemia occurred at the onset of heavy exercise and was associated with the absence of a hyperventilatory response and an alveolar-arterial PO2 difference that increased four to six times above rest with very heavy exercise. PaCO2 was related to VCO2 but not fb, as changes in breathing frequency (fb) of 8-20 breaths/min at comparable VCO2 did not affect PaCO2. Prolonging very heavy exercise from 2 to 4 min caused a severe metabolic acidosis (arterial pH less than 7.15) and hypoxemia was maintained; however, CO2 was no longer retained, as PaCO2 gradually fell to below resting levels, due to an increased tidal volume at constant fb. We conclude that a truly compensatory hyperventilation to very heavy exercise in the horse is not achieved because of the excessive volumes and flow rates required by their extraordinarily high VCO2 and VO2. On the other hand, the frank CO2 retention during short-term high-intensity exercise occurs even though the horse is not apparently mechanically obligated to tolerate it.
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              Mechanism of exercise-induced hypoxemia in horses.

              Arterial hypoxemia has been reported in horses during heavy exercise, but its mechanism has not been determined. With the use of the multiple inert gas elimination technique, we studied five horses, each on two separate occasions, to determine the physiological basis of the hypoxemia that developed during horizontal treadmill exercise at speeds of 4, 10, 12, and 13-14 m/s. Mean, blood temperature-corrected, arterial PO2 fell from 89.4 Torr at rest to 80.7 and 72.1 Torr at 12 and 13-14 m/s, respectively, whereas corresponding PaCO2 values were 40.3, 40.3, and 39.2 Torr. Alveolar-arterial PO2 differences (AaDO2) thus increased from 11.4 Torr at rest to 24.9 and 30.7 Torr at 12 and 13-14 m/s. In 8 of the 10 studies there was no change in ventilation-perfusion (VA/Q) relationships with exercise (despite bronchoscopic evidence of airway bleeding in 3) and total shunt was always less than 1% of the cardiac output. Below 10 m/s, the AaDO2 was due only to VA/Q mismatch, but at higher speeds, diffusion limitation of O2 uptake was increasingly evident, accounting for 76% of the AaDO2 at 13-14 m/s. Most of the exercise-induced hypoxemia is thus the result of diffusion limitation with a smaller contribution from VA/Q inequality and essentially none from shunting.
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                Author and article information

                Journal
                abmvz
                Arquivo Brasileiro de Medicina Veterinária e Zootecnia
                Arq. Bras. Med. Vet. Zootec.
                Universidade Federal de Minas Gerais, Escola de Veterinária (Belo Horizonte, MG, Brazil )
                0102-0935
                1678-4162
                June 2006
                : 58
                : 3
                : 320-326
                Affiliations
                [01] Botucatu SP orgnameUNESP orgdiv1Faculdade de Medicina Veterinária e Zootecnia
                Article
                S0102-09352006000300006 S0102-0935(06)05800306
                b64c9781-73db-4260-b402-2c6367165356

                This work is licensed under a Creative Commons Attribution 4.0 International License.

                History
                : 22 November 2005
                : 14 July 2004
                Page count
                Figures: 0, Tables: 0, Equations: 0, References: 21, Pages: 7
                Product

                SciELO Brazil

                Self URI: Texto completo somente em PDF (PT)
                Categories
                Medicina Veterinária

                exercício,eqüino,esteira,hemogasometria,lactato,equine,exercise physiology,treadmill,blood gases,lactate

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