Characteristics of sympathetic reflexes evoked by electrical stimulation of phrenic nerve afferents

Offner, Bertram; Dembowsky, Klaus; Czachurski, J.

doi:10.1016/0165-1838(92)90132-z

Cited by 22 publications

(15 citation statements)

References 19 publications

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“…Second, the time course of changes in Q L and LVR are consistent with a buildup of muscle metabolites (12). Third, the diaphragm has an abundance of type IV metaboreceptors (2), and in anesthetized rats, fatiguing the diaphragm via phrenic nerve stimulation caused a twofold, time-dependent increase in type IV afferent discharge (14).…”

Section: Discussionmentioning

confidence: 90%

“…On the basis of these findings, we predict that diaphragm fatigue will elicit sympathetically mediated vasoconstriction in resting limb muscle and perhaps also in other vascular beds, such as the coronary and renal circulation, which have been shown in anesthetized animals to increase their sympathetic nerve activity in response to electrical or pharmacological stimulation of phrenic nerve afferents (9,14,26).…”

Section: Discussionmentioning

confidence: 99%

“…First, an increase in firing rate of chemosensitive type IV afferent fibers in the diaphragm was observed in the anesthetized rat commensurate with the development of diaphragm fatigue secondary to phrenic nerve electrical stimulation (7). Second, electrical stimulation of phrenic afferent fibers evoked sympathoexcitatory responses in anesthetized animals (14,26) and chemical stimulation resulted in vasoconstriction in selected vascular beds (9). Third, in humans, we have demonstrated that an increase in muscle sympathetic nerve activity (MSNA) in the resting limb occurs over time in response to repeated diaphragm contractions, as induced by voluntary inspiratory efforts against resistance with a prolonged duty cycle taken to the point of task failure (24).…”

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confidence: 99%

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Threshold effects of respiratory muscle work on limb vascular resistance

Sheel

Derchak

Pegelow

et al. 2002

American Journal of Physiology-Heart and Circulatory Physiology

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. Threshold effects of respiratory muscle work onlimb vascular resistance. Am J Physiol Heart Circ Physiol 282: H1732-H1738, 2002; 10.1152/ajpheart.00798.2001.-The purpose of this study was to determine whether the human diaphragm, like limb muscle, has a threshold of force output at which a metaboreflex is activated causing systemic vasoconstriction. We used Doppler ultrasound techniques to quantify leg blood flow (Q L) and utilized the changes in mouth twitch pressure (⌬P MT) in response to bilateral phrenic nerve stimulation to quantify the onset of diaphragm fatigue. Six healthy male subjects performed four randomly assigned trials of identical duration (8 Ϯ 2 min) and breathing pattern [20 breaths/min and time spent on inspiration during the duty cycle (time spent on inspiration/total time of one breathing cycle) was 0.4] during which they inspired primarily with the diaphragm. For trials 1-3, inspiratory resistance and effort was gradually increased [30, 40, and 50% maximal inspiratory pressure (MIP)], diaphragm fatigue did not occur, and Q L, limb vascular resistance (LVR), and mean arterial pressure remained unchanged from control (P Ͼ 0.05). The fourth trial utilized the same breathing pattern with 60% MIP and caused diaphragm fatigue, as shown by a 30 Ϯ 12% reduction in P MT with bilateral phrenic nerve stimulation. During the fatigue trial, Q L and LVR were unchanged from baseline at minute 1, but LVR rose 36% and Q L fell 25% at minute 2 and by 52% and 30%, respectively, during the final minutes of the trial. Both LVR and Q L returned to control within 30 s of recovery. In summary, voluntary increases in inspiratory muscle effort, in the absence of fatigue, had no effect on LVR and Q L, whereas fatiguing the diaphragm elicited time-dependent increases in LVR and decreases in Q L. We attribute the limb vasoconstriction to a metaboreflex originating in the diaphragm, which reaches its threshold for activation during fatiguing contractions. diaphragm fatigue; leg blood flow; metaboreflex threshold; Doppler ultrasound; bilateral phrenic nerve stimulation IT IS WELL ESTABLISHED THAT thinly myelinated group III and unmyelinated IV afferent nerve fibers innervate limb skeletal muscle. These afferents are stimulated by metabolic byproducts (23), mechanical deformation (29), temperature (18), and vascular distension during muscular contraction (4). Stimulation of these afferents during muscular contraction elicits a powerful pressor response where sympathetic vasoconstrictor outflow is augmented to both resting and exercising skeletal muscle. A threshold exists for activation of this metaboreflex as numerous human studies have demonstrated a link between the metabolic events occurring within a contracting muscle (forearm) and the cardiovascular adjustments to handgrip exercise (3, 21). The current concept is that inadequate blood flow (or O 2 delivery) to the contracting muscle leads to an increase in the concentration of metabolites and the stimulation of chemosensitive afferents (type IV). The resulting ...

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Section: Discussionmentioning

confidence: 90%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Threshold effects of respiratory muscle work on limb vascular resistance

Sheel

Derchak

Pegelow

et al. 2002

American Journal of Physiology-Heart and Circulatory Physiology

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“…The diaphragm has an abundance of type IV metaboreceptors, and fatiguing the diaphragm via phrenic nerve stimulation caused an increase in type IV afferent discharge in anesthetized rats (15). Furthermore, when metaboreceptors in the diaphragm were stimulated electrically, pharmacologically, or with local lactic acid infusions, efferent sympathetic nerve activity increased and vascular conductance decreased in selected vascular beds (16,28,29). As shown in Figs.…”

Section: Effect Of Respiratory Muscle Fatigue On Msna and Bp Responsementioning

confidence: 91%

Inspiratory muscle fatigue increases sympathetic vasomotor outflow and blood pressure during submaximal exercise

Katayama¹,

Iwamoto

Ishida³

et al. 2012

American Journal of Physiology-Regulatory, Integrative and Comp

111

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Katayama K, Iwamoto E, Ishida K, Koike T, Saito M. Inspiratory muscle fatigue increases sympathetic vasomotor outflow and blood pressure during submaximal exercise. Am J Physiol Regul Integr Comp Physiol 302: R1167-R1175, 2012. First published March 28, 2012 doi:10.1152/ajpregu.00006.2012.-The purpose of this study was to elucidate the influence of inspiratory muscle fatigue on muscle sympathetic nerve activity (MSNA) and blood pressure (BP) response during submaximal exercise. We hypothesized that inspiratory muscle fatigue would elicit increases in sympathetic vasoconstrictor outflow and BP during dynamic leg exercise. The subjects carried out four submaximal exercise tests: two were maximal inspiratory pressure (PImax) tests and two were MSNA tests. In the PI max tests, the subjects performed two 10-min exercises at 40% peak oxygen uptake using a cycle ergometer in a semirecumbent position [spontaneous breathing for 5 min and with or without inspiratory resistive breathing for 5 min (breathing frequency: 60 breaths/min, inspiratory and expiratory times were each set at 0.5 s)]. Before and immediately after exercise, PImax was estimated. In MSNA tests, the subjects performed two 15-min exercises (spontaneous breathing for 5 min, with or without inspiratory resistive breathing for 5 min, and spontaneous breathing for 5 min). MSNA was recorded via microneurography of the right median nerve at the elbow. PImax decreased following exercise with resistive breathing, whereas no change was found without resistance. The time-dependent increase in MSNA burst frequency (BF) appeared during exercise with inspiratory resistive breathing, accompanied by an augmentation of diastolic BP (DBP) (with resistance: MSNA, BF ϩ83.4%; DBP, ϩ23.8%; without resistance: MSNA BF, ϩ19.2%; DBP, Ϫ0.4%, from spontaneous breathing during exercise). These results suggest that inspiratory muscle fatigue induces increases in muscle sympathetic vasomotor outflow and BP during dynamic leg exercise at mild intensity. respiratory muscle; sympathetic outflow; metaboreflex; dynamic leg exercise

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“…Diaphragm fatigue caused a timedependent increase in multiunit activity in small-diameter phrenic afferents in anesthetized cats (15,49) and in single-unit activity in group IV afferents in anesthetized rats (45). Furthermore, when metaboreceptors in the diaphragm or expiratory muscles were stimulated electrically, pharmacologically, or with local lactic acid infusions, efferent sympathetic nerve activity increased and vascular conductance decreased in several vascular beds, including those in limb muscle (48,96,102).…”

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

256

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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Characteristics of sympathetic reflexes evoked by electrical stimulation of phrenic nerve afferents

Cited by 22 publications

References 19 publications

Threshold effects of respiratory muscle work on limb vascular resistance

Threshold effects of respiratory muscle work on limb vascular resistance

Inspiratory muscle fatigue increases sympathetic vasomotor outflow and blood pressure during submaximal exercise

Exercise-induced respiratory muscle fatigue: implications for performance

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