Distribution of blood flow during exercise after blood volume expansion in swine

Norton, Kevin; Delp, Michael D.; Jones, Margaret; Duan, Chunbo; Dengel, Donald R.; Armstrong, R. B.

doi:10.1152/jappl.1990.69.5.1578

Cited by 7 publications

(5 citation statements)

References 19 publications

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“…The observation that coronary venous oxygen saturation levels are maintained in exercising swine is consistent with the unchanged arterial carbon dioxide tension and pH at submaximal levels of exercise (80 -90% of maximum) (149). It is possible that during exhaustive exercise lactate production by skeletal muscle (430,431) and the associated decrease in blood pH (247) also facilitate a decrease in coronary venous oxygen saturation in swine.…”

Section: Myocardial Oxygen Extractionsupporting

confidence: 55%

“…In contrast, when 15-m-diameter microspheres were used, higher ENDO/EPI ratios have generally been reported with values of 1.10 -1.31 during heavy exercise ( Fig. 11) (24,26,327,430,431,440,499,500), although several studies in swine reported values near 1.00 (76,77,147,236,342). Conversely, Symons and Stebbins (547) reported higher ENDO/EPI values in awake swine at rest (1.68) and during moderate exercise (1.53) than any other laboratories; an explanation for their findings is not readily found.…”

Section: Subendocardial/subepicardial Blood Flow Ratiomentioning

confidence: 96%

“…4. Relations between heart rate (HR) and left ventricular myocardial blood flow (LVMBF) at rest and during treadmill exercise in dogs (24 -26, 33, 34, 37, 41, 44, 132, 137, 140, 141, 144, 174, 212, 214, 289, 356, 427, 440, 444, 473, 524, 567-569, 588, 624), swine (76,77,139,146,147,236,345,430,431,499,500,539,540,547,603), and horses (17,378,379,448). Data from humans were obtained principally from young healthy male subjects performing upright bicycle exercise (162,258,275,302,303,316,420,426,469,593,614,615).…”

Section: Coronary Blood Flowmentioning

confidence: 99%

“…11. Relation between heart rate (HR) and left ventricular subendocardial to subepicardial blood flow ratio (LV endo/epi) at rest and during treadmill exercise in dogs (24,26,34,132,140,427,440), swine (76,77,147,236,327,342,430,431,499,500), and horses (17,378,448), measured with microspheres 15 m in diameter. No data on transmural distribution of left ventricular blood flow are available in humans.…”

Section: Influence Of Vasomotor Tone On the Transmural Distribution Omentioning

confidence: 99%

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Regulation of Coronary Blood Flow During Exercise

Duncker

Bache

2008

Physiological Reviews

783

684

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Exercise is the most important physiological stimulus for increased myocardial oxygen demand. The requirement of exercising muscle for increased blood flow necessitates an increase in cardiac output that results in increases in the three main determinants of myocardial oxygen demand: heart rate, myocardial contractility, and ventricular work. The approximately sixfold increase in oxygen demands of the left ventricle during heavy exercise is met principally by augmenting coronary blood flow (~5-fold), as hemoglobin concentration and oxygen extraction (which is already 70-80% at rest) increase only modestly in most species. In contrast, in the right ventricle, oxygen extraction is lower at rest and increases substantially during exercise, similar to skeletal muscle, suggesting fundamental differences in blood flow regulation between these two cardiac chambers. The increase in heart rate also increases the relative time spent in systole, thereby increasing the net extravascular compressive forces acting on the microvasculature within the wall of the left ventricle, in particular in its subendocardial layers. Hence, appropriate adjustment of coronary vascular resistance is critical for the cardiac response to exercise. Coronary resistance vessel tone results from the culmination of myriad vasodilator and vasoconstrictors influences, including neurohormones and endothelial and myocardial factors. Unraveling of the integrative mechanisms controlling coronary vasodilation in response to exercise has been difficult, in part due to the redundancies in coronary vasomotor control and differences between animal species. Exercise training is associated with adaptations in the coronary microvasculature including increased arteriolar densities and/or diameters, which provide a morphometric basis for the observed increase in peak coronary blood flow rates in exercise-trained animals. In larger animals trained by treadmill exercise, the formation of new capillaries maintains capillary density at a level commensurate with the degree of exercise-induced physiological myocardial hypertrophy. Nevertheless, training alters the distribution of coronary vascular resistance so that more capillaries are recruited, resulting in an increase in the permeability-surface area product without a change in capillary numerical density. Maintenance of alpha- and ss-adrenergic tone in the presence of lower circulating catecholamine levels appears to be due to increased receptor responsiveness to adrenergic stimulation. Exercise training also alters local control of coronary resistance vessels. Thus arterioles exhibit increased myogenic tone, likely due to a calcium-dependent protein kinase C signaling-mediated alteration in voltage-gated calcium channel activity in response to stretch. Conversely, training augments endothelium-dependent vasodilation throughout the coronary microcirculation. This enhanced responsiveness appears to result principally from an increased expression of nitric oxide (NO) synthase. Finally, physical conditioning decreases e...

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Section: Myocardial Oxygen Extractionsupporting

confidence: 55%

Section: Subendocardial/subepicardial Blood Flow Ratiomentioning

confidence: 96%

Section: Coronary Blood Flowmentioning

confidence: 99%

Section: Influence Of Vasomotor Tone On the Transmural Distribution Omentioning

confidence: 99%

See 2 more Smart Citations

Regulation of Coronary Blood Flow During Exercise

Duncker

Bache

2008

Physiological Reviews

783

684

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“…We aimed for a cardiac output at peak exercise in the range of 25 L/min (3,22), pulmonary venous pressure of Ͻ18 mmHg, and mean arterial pressure in the range of 100 to 120 mmHg (3). To achieve these values, we increased the fractional flow to the peripheral-muscle to 90% (1,22,36,37) by adjusting the systemic arterial resistances. We decreased the venous resistance draining the peripheral-muscular (Rv-mus) bed by 50% based on a study in isolated gastrocnemius muscle (27).…”

Section: Introductionmentioning

confidence: 99%

Periodicity, time constants of drainage, and the mechanical determinants of peak cardiac output during exercise

Magder

Famulari

Gariepy

2019

Journal of Applied Physiology

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To analyze mechanical adaptations that must occur in the cardiovascular system to reach the high cardiac outputs known to occur at peak aerobic performance, we adapted a computational model of the circulation by adding a second parallel venous compartment as proposed by August Krogh in 1912. One venous compartment has a large compliance and slow time constant of emptying; it is representative of the splanchnic circulation. The other has a low compliance and fast time constant of emptying and is representative of muscle beds. Fractional distribution between the two compartments is an important determinant of cardiac output. Parameters in the model were based on values from animal and human studies normalized to a 70 kg male. The baseline cardiac output was set at 5 L/min, and we aimed for 25 L/min at peak exercise with a fractional flow to the peripheral-muscle region of 90%. Finally, we added the equivalent of a muscle pump. Adjustments in circuit and cardiac parameters alone increased cardiac output to only 15.6 L/min because volume accumulated in the muscle compartment and limited a higher cardiac output. Addition of muscle contractions decompressed the muscle region and allowed cardiac output to increase to 23.4 L/min. The pulsatility of blood flow imposes important constraints on the adaptations of cardiac and circulatory functions because it fixes the times for filling and emptying. Flow is further limited by the limits of cardiac filling on each beat. Muscle contractions play a key role by decompressing volume that would otherwise accumulate in the muscle vasculature and by decreasing the time for stroke return to the right ventricle. NEW & NOTEWORTHY We used a computational model of the circulation and previous human and animal data to model mechanical changes in the heart and circulation that are needed to reach the known high cardiac output at peak aerobic exercise. Key points are that time constants of drainage of circulatory compartments put limits on peak flow in a pulsatile system. Muscle contractions increase the rate of return to the heart and by doing so prevent accumulation of volume in the muscle compartment and greatly increase circulatory capacity.

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Peripheral Circulation

Laughlin

Davis

Secher

et al. 2012

Comprehensive Physiology

219

234

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Blood flow (BF) increases with increasing exercise intensity in skeletal, respiratory, and cardiac muscle. In humans during maximal exercise intensities, 85% to 90% of total cardiac output is distributed to skeletal and cardiac muscle. During exercise BF increases modestly and heterogeneously to brain and decreases in gastrointestinal, reproductive, and renal tissues and shows little to no change in skin. If the duration of exercise is sufficient to increase body/core temperature, skin BF is also increased in humans. Because blood pressure changes little during exercise, changes in distribution of BF with incremental exercise result from changes in vascular conductance. These changes in distribution of BF throughout the body contribute to decreases in mixed venous oxygen content, serve to supply adequate oxygen to the active skeletal muscles, and support metabolism of other tissues while maintaining homeostasis. This review discusses the response of the peripheral circulation of humans to acute and chronic dynamic exercise and mechanisms responsible for these responses. This is accomplished in the context of leading the reader on a tour through the peripheral circulation during dynamic exercise. During this tour, we consider what is known about how each vascular bed controls BF during exercise and how these control mechanisms are modified by chronic physical activity/exercise training. The tour ends by comparing responses of the systemic circulation to those of the pulmonary circulation relative to the effects of exercise on the regional distribution of BF and mechanisms responsible for control of resistance/conductance in the systemic and pulmonary circulations.

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Distribution of blood flow during exercise after blood volume expansion in swine

Cited by 7 publications

References 19 publications

Regulation of Coronary Blood Flow During Exercise

Regulation of Coronary Blood Flow During Exercise

Periodicity, time constants of drainage, and the mechanical determinants of peak cardiac output during exercise

Peripheral Circulation

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