Minimal redistribution of pulmonary blood flow with exercise in racehorses

Bernard, Susan L.; Glenny, Robb W.; Erickson, Howard H.; Fedde, M. R.; Polissar, Nayak L.; Basaraba, Randall J.; Hlastala, Michael P.

doi:10.1152/jappl.1996.81.3.1062

Cited by 72 publications

(65 citation statements)

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“…Using fluorescent microspheres , the pulmonary blood flow redistribution with exercise in Thoroughbred racehorses was previously found to be consistent with the location of exercise-induced pulmonary haemorrhagic (EIPH) lesions that are found in the caudodorsal lung regions (O'Callaghan et al 1987). The location, size and regional mismatching factors that were observed in R 1 demonstrated that most pulmonary perfusion redistribution occurs in the dorsal region of the lung in exercised healthy horses therefore confirming the findings of Bernard et al (1996). In a more recent experiment, this phenomenon was found to be associated with a change in fractal dimension, which suggests that mediators act on the pulmonary vasculature in exercising horses (Sinclair et al 2000).…”

Section: Discussionsupporting

confidence: 65%

Exercise‐induced pulmonary perfusion redistribution in heaves

Harmegnies

Duvivier

Vandenput

et al. 2002

Equine Veterinary Journal

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SummaryThis study aimed to compare exercise-induced pulmonary perfusion redistribution in healthy vs. 'heavey' horses using scintigraphy, a minimally invasive technique. Six healthy (A) and 5 'heavey' horses in remission (B I ) and during clinical signs of disease (B II ) were investigated. Dimensions of the exercising pulmonary perfusion (Q E ) images were expressed in percent of the resting perfusion (Q R ) images. Computed Q E to Q R ratios (Q E /Q R ) images enabled the definition of the region more perfused at exercise than at rest (R 1 ).In all groups, exercise induced a major enlargement of the Q image but a larger increase of the lung height was found in 'heavey' horses. Compared to A, 'heavey' horses showed a larger R 1 region with a significantly higher Q E /Q R . Location of R 1 pointed out the dorsal lung region as a major site of pulmonary perfusion redistribution for all groups.This work demonstrated (1) the feasibility of using scintigraphy for studying exercise-induced pulmonary perfusion redistribution; (2) perfusion redistribution to the dorsal lung with exercise and (3) an intensified redistribution in 'heavey' horses, either clinically affected or not.

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Section: Discussionsupporting

confidence: 65%

Exercise‐induced pulmonary perfusion redistribution in heaves

Harmegnies

Duvivier

Vandenput

et al. 2002

Equine Veterinary Journal

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“…However, phasic changes in stroke volume, if these were to occur, would be most likely to covary with V T , which was accounted for in our model (via changes in intrathoracic pressure) rather than with the variability in heart rate occurring at the frequency of respiration (i.e., RSA). In addition, evidence suggests that preferential redistribution of flow, which could result in improved efficiency, does not occur with changes in cardiac output (4,18). Nonetheless, it is conceivable that phasic changes in stroke volume could account for the variance in ventilatory equivalents explained by RSA in our study.…”

Section: Discussionmentioning

confidence: 60%

Respiratory sinus arrhythmia is associated with efficiency of pulmonary gas exchange in healthy humans

Giardino

Glenny

Borson

et al. 2003

American Journal of Physiology-Heart and Circulatory Physiology

113

103

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. Respiratory sinus arrhythmia is associated with efficiency of pulmonary gas exchange in healthy humans. Am J Physiol Heart Circ Physiol 284: H1585-H1591, 2003. First published January 23, 2003 10.1152/ajpheart.00893.2002.-Respiratory sinus arrhythmia (RSA) may be associated with improved efficiency of pulmonary gas exchange by matching ventilation to perfusion within each respiratory cycle. Respiration rate, tidal volume, minute ventilation (V E), exhaled carbon dioxide (V CO2), oxygen consumption (V O2), and heart rate were measured in 10 healthy human volunteers during paced breathing to test the hypothesis that RSA contributes to pulmonary gas exchange efficiency. Cross-spectral analysis of heart rate and respiration was computed to calculate RSA and the coherence and phase between these variables. Pulmonary gas exchange efficiency was measured as the average ventilatory equivalent of CO2 (V E/V CO2) and O2 (V E/V O2). Across subjects and paced breathing periods, RSA was significantly associated with CO2 (partial r ϭ Ϫ0.53, P ϭ 0.002) and O2 (partial r ϭ Ϫ0.49, P ϭ 0.005) exchange efficiency after controlling for the effects of age, respiration rate, tidal volume, and average heart rate. Phase between heart rate and respiration was significantly associated with CO 2 exchange efficiency (partial r ϭ 0.40, P ϭ 0.03). These results are consistent with previous studies and further support the theory that RSA may improve the efficiency of pulmonary gas exchange.heart rate variability; phase; ventilatory equivalent RESPIRATORY SINUS ARRHYTHMIA (RSA), the increase and decrease in heart rate within each respiratory cycle, occurs mainly as a result of fluctuations of parasympathetic output to the heart, although sympathetic outflow also may influence variability (26). During inspiration, impulses originating in stretch receptors in the lungs travel via the vagi to inhibit the cardioinhibitory area in the medulla. The tonic vagal discharge that keeps the heart rate slow decreases, and the heart rate rises. The degree to which this modulation occurs is a function of the level of tonic vagal discharge and blood pressure (9, 21). Thus measures of RSA are frequently used as an index of vagal tone (e.g., 2,12,19,20).Certain features of respiratory mechanics also affect the amplitude of RSA independent of changes in vagal tone. For example, changes in respiration rate and, to a lesser extent, tidal volume (V T ) can affect the magnitude of RSA in the absence of any change in tonic vagal activity (8,11,15,23). This slowing of respiration rate and increase in V T are believed to allow more time for the action of acetylcholine on muscarinic receptors at the sinoatrial node during exhalation (7, 25a). Other influences on the genesis and magnitude of RSA include feedback from arterial baroreceptors, a central rhythm generator in the brain stem, and intracardiac reflexes (3).Although a great deal of research has been published concerning the physiological mechanisms mediating RSA, the question of what function, if any, RSA serv...

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“…Our selection of 15-m-diameter microspheres for the present study was influenced by previous reports examining the distribution of pulmonary blood flow in resting and exercising horses with this technique (2,6,21). However, in these reports, intrapulmonary arteriovenous shunting of 15-m-diameter microspheres was not examined.…”

Section: Discussionmentioning

confidence: 99%

“…However, in these reports, intrapulmonary arteriovenous shunting of 15-m-diameter microspheres was not examined. Although, in these experiments, cardiac (2,6,21) and other tissues may have been removed at necropsy, investigators did not report on the absence/presence of intravenously injected microspheres in the heart and/or other tissues.…”

Section: Discussionmentioning

confidence: 99%

Intrapulmonary arteriovenous shunts of >15 μm in diameter probably do not contribute to arterial hypoxemia in maximally exercising Thoroughbred horses

Manohar

Goetz²

2005

Journal of Applied Physiology

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Manohar, Murli, and Thomas E. Goetz. Intrapulmonary arteriovenous shunts of Ͼ15 m in diameter probably do not contribute to arterial hypoxemia in maximally exercising Thoroughbred horses. J Appl Physiol 99: 224 -229, 2005. First published March 17, 2005 doi:10.1152/japplphysiol.01230.2004.-The present study examined whether Thoroughbred horses performing strenuous exercise exhibit intrapulmonary arteriovenous shunting that may contribute to the observed arterial hypoxemia. Experiments were carried out on seven healthy, exercise-trained Thoroughbreds at rest, maximal exercise (galloping at 14 m/s on a 3.5% uphill grade for 120 s), and submaximal exertion (8 m/s on a 3.5% uphill grade for 150 s). Along with blood gas/hemodynamic parameters, intrapulmonary arteriovenous shunting was studied by injecting 15-m-diameter microspheres, labeled with different stable isotopes, into the right atrium while simultaneous blood samples were being withdrawn at a constant rate from the pulmonary artery and the aorta. Arterial hypoxemia was observed only during maximal exercise. Also, despite significant pulmonary arterial hypertension during submaximal and maximal exertion, 15-m microspheres did not traverse the pulmonary microcirculation to appear in the aortic blood. Thus our findings did not support a role for intrapulmonary arteriovenous shunts of Ͼ15 m in diameter in the exercise-induced arterial hypoxemia in racehorses. Interestingly, our observation that, in going from 30 to 120 s of maximal exertion, arterial O2 tension had remained unchanged despite significant reductions in mixed venous blood O 2 tension, hemoglobin-O2 saturation, and O2 content also discounts the importance of intrapulmonary arteriovenous shunts in causing arterial hypoxemia. This is because, assuming that a constant fraction of total pulmonary blood flow bypasses the gas-exchange areas of the equine lungs via intrapulmonary arteriovenous shunts during 30 -120 s of maximal exertion, the observed significant reductions in mixed venous blood oxygenation should cause a significant reduction in arterial O2 tension, which was not the case in our horses. Thus it is suggested that intrapulmonary arteriovenous shunting probably does not contribute to the exercise-induced arterial hypoxemia in racehorses.blood gas tensions during exertion; arterial desaturation during exercise; pulmonary microcirculation; microspheres IT IS WELL KNOWN THAT STRENUOUSLY EXERCISING racehorses experience significant arterial hypoxemia and desaturation of hemoglobin, and it is reported that these changes in arterial oxygenation limit athletic performance (1,3,8,(13)(14)(15)(16)24). A significant arterial hypercapnia is also observed in strenuously exercising Thoroughbred horses despite significantly increased alveolar ventilation. Although the inadequate alveolar hyperventilation during maximal exertion contributes to the observed reduction in arterial O 2 tension, this mechanism does not account for the entire decrease in arterial O 2 tension. Multiple inert-gas elimination studi...

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Minimal redistribution of pulmonary blood flow with exercise in racehorses

Cited by 72 publications

References 0 publications

Exercise‐induced pulmonary perfusion redistribution in heaves

Exercise‐induced pulmonary perfusion redistribution in heaves

Respiratory sinus arrhythmia is associated with efficiency of pulmonary gas exchange in healthy humans

Intrapulmonary arteriovenous shunts of >15 μm in diameter probably do not contribute to arterial hypoxemia in maximally exercising Thoroughbred horses

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