Expiratory threshold loading impairs cardiovascular function in health and chronic heart failure during submaximal exercise

Miller, Jordan D.; Hemauer, Sarah J.; Smith, Curtis A.; Stickland, Michael K.; Dempsey, Jerome A.

doi:10.1152/japplphysiol.00862.2005

Cited by 33 publications

(25 citation statements)

References 31 publications

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“…It is known that pulmonary mechanics affect cardiac function (Miller et al 2006), but the majority of this work is done in healthy subjects at rest. The PAV could be useful in manipulating pulmonary pressure during various intensities of exercise and assessing the cardiac consequences.…”

Section: Future Directionsmentioning

confidence: 99%

A proportional assist ventilator to unload respiratory muscles experimentally during exercise in humans

Dominelli

Henderson

Sheel

2016

Experimental Physiology

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New Findings r What is the central question of this study?Can a modern proportional assist ventilator (PAV) function sufficiently well to unload the respiratory muscles during exercise? r What is the main finding and its importance?A PAV can be constructed with contemporary hardware and software and be used at all exercise intensities to unload the respiratory muscles by up to 70%. Previously, PAVs have allowed researchers to address many fundamental physiological problems in clinical and healthy populations, but those versions are no longer functional or available. We describe the creation of a PAV that permits researchers to use it as an experimental tool.Manipulation of the normally occurring work of breathing (WOB) during exercise can provide insights into whole-body regulatory mechanisms in clinical patients and healthy subjects. One method to reduce the WOB uses a proportional assist ventilator (PAV). Suitable commercially available units are not capable of being used during heavy exercise. This investigation was undertaken in order to create a PAV and assess the degree to which the WOB could be reduced during exercise. A PAV works by creating a positive mouth pressure (P m ) during inspiration, which consequently reduces the WOB. Spontaneous breathing patterns can be maintained, and the amplitude of P m is calculated using the equation of motion and predetermined proportionality constants. We generated positive P m using a breathing apparatus consisting of rigid tubing, solenoid valves to control the airflow direction and a proportional valve connected to compressed gas. Healthy male and female subjects were able to use the PAV successfully while performing cycling exercise over a range of intensities (50-100% of maximal workload) for different durations (from 30 s to 20 min) and different protocols (constant versus progressive workload). Inspiratory WOB was reduced up to 90%, while total WOB was reduced by 70%. The greatest reduction in WOB (50-75%) occurred during submaximal exercise, but at maximal ventilations (>180 l min −1 ) a 50% reduction was still possible. The calculated change in WOB and subsequent reduction in respiratory muscle oxygen consumption resulted in equivalent reductions in whole-body oxygen consumption. With adequate familiarization and practice, our PAV can consistently reduce the WOB across a range of exercise intensities.

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Section: Future Directionsmentioning

confidence: 99%

A proportional assist ventilator to unload respiratory muscles experimentally during exercise in humans

Dominelli

Henderson

Sheel

2016

Experimental Physiology

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“…However, it is possible that the excessively high-positive expiratory pressures produced during maximal exercise in athletes with EFL (251) could substantially limit cardiac function. Positive P ITP during expiration reduces ventricular transmural pressure, thereby decreasing the rate of ventricular filling during diastole and reducing stroke volume and cardiac output (367,494). In addition, active expiration against positive resistance impedes femoral venous return, even in the face of an active muscle pump (368).…”

Section: Mechanical Interactions During Exercisementioning

confidence: 99%

“…In addition, EFL and prolonged T E during heavy exercise often result in positive intrathoracic pressures that meet or exceed those at which dynamic compression of the airways occurs (251). This is important because positive intrathoracic pressures will reduce ventricular transmural pressure thereby decreasing the rate of ventricular filling during diastole, and reducing stroke volume and cardiac output (367,494). Active expiration against positive resistance impedes femoral venous return, even in the face of an active "muscle pump" (368,369).…”

Section: Locomotor Muscle Fatiguementioning

confidence: 99%

Ventilation and Respiratory Mechanics

Sheel

Romer

2012

Comprehensive Physiology

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During dynamic exercise, the healthy pulmonary system faces several major challenges, including decreases in mixed venous oxygen content and increases in mixed venous carbon dioxide. As such, the ventilatory demand is increased, while the rising cardiac output means that blood will have considerably less time in the pulmonary capillaries to accomplish gas exchange. Blood gas homeostasis must be accomplished by precise regulation of alveolar ventilation via medullary neural networks and sensory reflex mechanisms. It is equally important that cardiovascular and pulmonary system responses to exercise be precisely matched to the increase in metabolic requirements, and that the substantial gas transport needs of both respiratory and locomotor muscles be considered. Our article addresses each of these topics with emphasis on the healthy, young adult exercising in normoxia. We review recent evidence concerning how exercise hyperpnea influences sympathetic vasoconstrictor outflow and the effect this might have on the ability to perform muscular work. We also review sex-based differences in lung mechanics.

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“…Furthermore, expiratory flow limitation and prolonged expiratory time during heavy exercise often result in positive intrathoracic pressures that meet or exceed those at which dynamic compression of the airways occurs (54). Positive intrathoracic pressures will reduce ventricular transmural pressure, thereby decreasing the rate of ventricular filling during diastole, and reducing stroke volume and cardiac output (86,121). Active expiration against positive resistance impedes femoral venous return, even in the face of an active "muscle pump" (87,88).…”

Section: Mechanisms By Which Respiratory Muscle Fatigue Could Affect mentioning

confidence: 99%

Exercise-induced respiratory muscle fatigue: implications for performance

Romer

Polkey²

2008

Journal of Applied Physiology

261

212

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Romer LM, Polkey MI. Exercise-induced respiratory muscle fatigue: implications for performance. J Appl Physiol 104: 879 -888, 2008. First published December 20, 2007 doi:10.1152/japplphysiol.01157.2007.-It is commonly held that the respiratory system has ample capacity relative to the demand for maximal O 2 and CO2 transport in healthy humans exercising near sea level. However, this situation may not apply during heavy-intensity, sustained exercise where exercise may encroach on the capacity of the respiratory system. Nerve stimulation techniques have provided objective evidence that the diaphragm and abdominal muscles are susceptible to fatigue with heavy, sustained exercise. The fatigue appears to be due to elevated levels of respiratory muscle work combined with an increased competition for blood flow with limb locomotor muscles. When respiratory muscles are prefatigued using voluntary respiratory maneuvers, time to exhaustion during subsequent exercise is decreased. Partially unloading the respiratory muscles during heavy exercise using low-density gas mixtures or mechanical ventilation can prevent exercise-induced diaphragm fatigue and increase exercise time to exhaustion. Collectively, these findings suggest that respiratory muscle fatigue may be involved in limiting exercise tolerance or that other factors, including alterations in the sensation of dyspnea or mechanical load, may be important. The major consequence of respiratory muscle fatigue is an increased sympathetic vasoconstrictor outflow to working skeletal muscle through a respiratory muscle metaboreflex, thereby reducing limb blood flow and increasing the severity of exerciseinduced locomotor muscle fatigue. An increase in limb locomotor muscle fatigue may play a pivotal role in determining exercise tolerance through a direct effect on muscle force output and a feedback effect on effort perception, causing reduced motor output to the working limb muscles. respiratory muscles; exercise; diaphragm; abdominals; magnetic stimulation; metaboreflex THE PURPOSE OF THIS MINIREVIEW is to address the question of whether the respiratory demands of exercise contribute significantly toward exercise limitation, either directly through limitations of the respiratory muscle pump or indirectly through effects on limb blood flow and locomotor muscle fatigue. We describe the mechanical and metabolic costs of meeting the ventilatory requirements of exercise. We then ask whether the respiratory muscles fatigue with exercise, what factors contribute to any such fatigue, and what the implications of these factors are for exercise tolerance. Finally, we deal with the potential mechanisms by which respiratory muscle fatigue could compromise exercise tolerance and whether it is possible to overcome this potential respiratory limitation. Our review focuses on the healthy young adult exercising near sea level. However, we also consider special circumstances that determine the balance between metabolic demand and respiratory system capacity in the highly trained endurance ...

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Expiratory threshold loading impairs cardiovascular function in health and chronic heart failure during submaximal exercise

Cited by 33 publications

References 31 publications

A proportional assist ventilator to unload respiratory muscles experimentally during exercise in humans

A proportional assist ventilator to unload respiratory muscles experimentally during exercise in humans

Ventilation and Respiratory Mechanics

Exercise-induced respiratory muscle fatigue: implications for performance

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