Ventilation-perfusion relationships during exercise in Standardbred trotters with red cell hypervolaemia

Department of Large Animal Clinical Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden.
Equine Veterinary Journal (Impact Factor: 2.37). 08/1999; 30:107-13. DOI: 10.1111/j.2042-3306.1999.tb05199.x
Source: PubMed


In order to evaluate the pulmonary gas exchange during exercise in Standardbred trotters with red cell hypervolaemia (RCHV), 12 horses with RCHV were compared with 9 normovolaemic (NV) horses. VO2 and VCO2 were determined with an open bias flow system. Cardiovascular and haemodynamic data were recorded during exercise at 4 different speeds on a treadmill. Pulmonary gas exchange was assessed by conventional blood gas variables (arterial and mixed venous blood gas tensions), and the ventilation-perfusion distribution VA/Q was estimated by the multiple inert gas elimination technique. VA and AaDO2 were calculated. Dispersions of perfusion and ventilation distribution (SDQ, SDV) were determined. HR, RR, Qt, VO2, VA, log SDV, C(a-åv)O2 and lactate did not differ between groups. The degree of hypoxaemia was more pronounced in the RCHV than in the NV (PaO2 = 54 and 59 mmHg; AaDO2 = 41 and 34 mmHg in RCHV and NV, respectively, at highest workload). Further, pH was lower in the RCHV and PaCO2 and VCO2 was significantly higher in the RCHV during the course of exercise (pH = 7.24 and 7.29; PaCO2 = 56 and 51 mmHg; VCO2 = 156 and 135 ml/kg x min in RCHV and NV, respectively, at highest workload). The PaO2 predicted from the VA/Q distribution was higher than actually measured in blood during heavy exercise which may suggest a certain diffusion limitation over the alveolar-capillary membranes in both groups but there was no difference between the 2 groups. The more pronounced hypoxaemia observed in RCHV trotters was mainly caused by increased VA/Q mismatch expressed as a significantly increased log SDQ (0.78 and 0.45 in RCHV and NV, respectively, at highest workload).

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    Full-text · Article · Aug 1999 · Equine Veterinary Journal
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    ABSTRACT: Five Standardbred trotters with red cell hypervolaemia (RCHV) were compared before and after removal of approximately 22% (36 ml/kg bwt) of the total blood volume in order to evaluate the haemodynamic responses, haemorheological alterations and oxygen transport during exercise to fatigue. Data were recorded during submaximal exercise at 4 different speeds on a treadmill and then during continued running at the highest speed step until fatigue. Oxygen uptake (VO2), pulmonary artery pressure (PAP), systemic artery pressure (SAP), heart rate (HR), haematocrit and haemoglobin concentrations (Hb) were measured. Arteriovenous O2 content difference (C(a-v)O2), pulmonary vascular resistance (PVR) and total systemic resistance (TSR) were calculated. Whole blood and plasma viscosity and erythrocyte aggregation tendency were determined with a rotational viscometer. Endoscopy was performed after exercise. ANOVA was used for statistical analysis. Phlebotomy resulted in a decrease in haematocrit and Hb during the course of exercise. Blood and plasma viscosity were lower and erythrocyte aggregation tendency was higher after phlebotomy. Throughout exercise, including submaximal work and continued running to fatigue, PAP, SAP, PVR, TSR and C(a-v)O2 were lower after phlebotomy. HR was higher after phlebotomy during submaximal exercise. Oxygen delivery and VO2 were lower after phlebotomy in the period from submaximal exercise to fatigue. Run time to fatigue was shorter after phlebotomy. Four horses showed exercise-induced pulmonary haemorrhage (EIPH) before phlebotomy and the degree of bleeding was diminished but not abolished after phlebotomy. The reductions in PVR, TSR, PAP and SAP after phlebotomy were probably a result of reduced blood viscosity. In conclusion, although a 22% reduction in blood volume improved the haemodynamic and haemorheological parameters and the degree of EIPH, it was found that RCHV trotters have to rely on high oxygen delivery to the working muscles for maintenance of maximal performance.
    No preview · Article · Aug 2001 · Equine Veterinary Journal
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    ABSTRACT: It is not known if pulmonary function and gas exchange during exercise are altered after pyogranulomatous pneumonia caused by Rhodococcus equi infection in the foal. The aim was to evaluate whether pulmonary gas exchange during high intensity exercise was altered in mature Standardbreds with a history of R. equi pneumonia as foals. In 7 foals, R. equi pneumonia was confirmed and treated. At age 3 years, when these horses were subjected to professional training, an inclined treadmill exercise test including 4 speeds was performed. Samples were collected when a steady state in VO2 was obtained. Red cell volume, heart rate, respiratory rate, and systemic and pulmonary mean arterial pressures were measured and cardiac output calculated. Oxygen and carbon dioxide tensions in arterial and mixed venous blood were analysed. The alveolar ventilation and the alveolar-arterial oxygen tension difference were determined. Pulmonary gas exchange was assessed and the ventilation-perfusion distribution, VA/Q, was estimated by the multiple inert gas elimination technique. Ventilation-perfusion mismatch and shunt were determined and diffusion limitation calculated. The gas exchange in Standardbred trotters previously infected with R. equi and successfully treated was not compromised during intense treadmill exercise compared with reference values for healthy, fit Standardbreds. We conclude that adult Standardbreds trotters with diagnosed R. equi pneumonia as foals, can achieve an adequate gas exchange at a workload close to VO2peak.
    No preview · Article · Oct 2002 · Equine Veterinary Journal
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