Expiratory muscle fatigue in normal subjects

1991 ◽  
Vol 70 (6) ◽  
pp. 2632-2639 ◽  
Author(s):  
S. Suzuki ◽  
J. Suzuki ◽  
T. Okubo
Keyword(s):  
Muscle Fatigue ◽  
Low Frequency ◽  
Normal Subjects ◽  
Work Load ◽  
Emg Activity ◽  
Transdiaphragmatic Pressure ◽  
Expiratory Muscle ◽  
Inspiratory Muscles ◽  
Loaded Breathing ◽  
Low Frequency Power

We examined expiratory muscle fatigue during expiratory resistive loading in 11 normal subjects. Subjects breathed against expiratory resistances at their own breathing frequency and tidal volume until exhaustion or for 60 min. Respiratory muscle strength was assessed from both the maximum static expiratory and inspiratory mouth pressures (PEmax and PImax). At the lowest resistance, PEmax and PImax measured after completion of the expiratory loaded breathing were not different from control values. With higher resistance, both PEmax and PImax were decreased (P less than 0.05), and the decrease lasted for greater than or equal to 60 min. The electromyogram high-to-low frequency power ratio for the rectus abdominis muscle decreased progressively during loading (P less than 0.01), but the integrated EMG activity did not change during recovery. Transdiaphragmatic pressure during loading was increased 3.6-fold compared with control (P less than 0.05). These findings suggest that expiratory resistive loaded breathing induces muscle fatigue in both expiratory and inspiratory muscles. Fatigue of the expiratory muscles can be attributed directly to the high work load and that of the inspiratory muscles may be related to increased work due to shortened inspiratory time.

Effects of fenoterol on inspiratory effort sensation and fatigue during inspiratory threshold loading

1996 ◽  
Vol 80 (3) ◽  
pp. 727-733 ◽  
Author(s):  
J. Suzuki ◽  
S. Suzuki ◽  
T. Okubo
Keyword(s):  
Low Frequency ◽  
Normal Subjects ◽  
Motor Command ◽  
Inspiratory Effort ◽  
Double Blind ◽  
Endurance Time ◽  
Transdiaphragmatic Pressure ◽  
Mouth Pressure ◽  
Residual Capacity ◽  
Low Frequency Power

We studied the effects of a single dose of fenoterol on the relationship between inspiratory effort sensation (IES) and inspiratory muscle fatigue induced by inspiratory threshold loading in healthy subjects. The magnitude of the threshold was 60% of maximal static inspiratory mouth pressure (PI,mmax) at functional residual capacity, and the duty cycle was 0.5. Subjects continued the threshold loaded breathing until the target mouth pressure could no longer be maintained (endurance time). The intensity of the IES was scored with a modified Borg scale. Either fenoterol (5 mg) or a placebo was given orally 2 h before loading in a randomized double-blind crossover protocol. The endurance time with fenoterol (34.4 +/- 8.6 min) was longer than that with the placebo (22.2 +/- 7.1 min; P < 0.05). The ratio of high- to low-frequency power of the diaphragmatic electromyogram (EMGdi) decreased during loading; the decrease was less with fenoterol (P < 0.05). The EMGdi also decreased with loading; the decrease was greater on fenoterol treatment (P < 0.01). The PI,mmax and maximal transdiaphragmatic pressure (Pdi) were similarly decreased after loading on either treatment. The intensity of the IES rose with time during loading in both groups but was lower with fenoterol than with the placebo (P < 0.05). The ratio of Pdi to integrated activity of the EMGdi increased with fenoterol (P < 0.05). Fenoterol treatment increased both superimposed Pdi twitch and Pdi twitch of relaxed diaphragm and decreased the value of (1-superimposed Pdi twitch/Pdi twitch of relaxed diaphragm). Thus we conclude that in normal subjects fenoterol reduces diaphragmatic fatigue and decreases the motor command to the diaphragm, resulting in a decrease in IES during inspiratory threshold loading and a prolongation of endurance.

Effect of inspiratory muscle fatigue on perception of effort during loaded breathing

1987 ◽  
Vol 62 (1) ◽  
pp. 300-307 ◽  
Author(s):  
G. S. Supinski ◽  
S. J. Clary ◽  
H. Bark ◽  
S. G. Kelsen
Keyword(s):  
Muscle Fatigue ◽  
Duty Cycle ◽  
Normal Subjects ◽  
Progressive Increase ◽  
Inspiratory Muscle ◽  
Sense Of Effort ◽  
Inspiratory Muscles ◽  
Pressure Time ◽  
Loaded Breathing ◽  
Inspiratory Muscle Fatigue

The present study examined the relationship between the intensity of the sense of effort during inspiratory threshold loading and the severity of inspiratory muscle fatigue. Studies were performed on normal subjects in whom the magnitude of airway pressure developed (Pm) and the duty cycle of breathing (TI/TT) were constrained to achieve a pressure-time integral (i.e., Pm/Pmax X TI/TT) 24% of maximum. In separate trials, the same pressure-time index (24%) was achieved using two widely different patterns of pressure magnitude and duty cycle to allow the effects of changes in the pattern of inspiratory muscle contraction on sensation and fatigue to be assessed. The intensity of the sense of effort was assessed using a category (Borg) scale. The severity of inspiratory muscle fatigue was assessed both from changes in the centroid frequency of the diaphragm electromyogram and from changes in the maximum static inspiratory pressure. Loaded breathing produced inspiratory muscle fatigue and a progressive increase in the sense of effort over time in all subjects. The rate at which the inspiratory muscles fatigued was the same with the two patterns of loading. In contrast, the rate of growth in the intensity of the sense of effort varied significantly as a function of the pattern of loaded breathing. The sense of effort increased at a faster rate with the high pressure-short duty cycle pattern of contraction as compared with the low pressure-long duty cycle pattern. As a result, the intensity of the sense of effort was not uniquely related to the severity of inspiratory muscle fatigue.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Changes in electromyographic activity, mechanical power, and relaxation rates following inspiratory ribcage muscle fatigue

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Antonio Sarmento ◽  
Guilherme Fregonezi ◽  
Maria Lira ◽  
Layana Marques ◽  
Francesca Pennati ◽  
...  
Keyword(s):  
Muscle Fatigue ◽  
Low Frequency ◽  
Mechanical Power ◽  
Electromyographic Activity ◽  
Median Frequency ◽  
Relaxation Rates ◽  
Shortening Velocity ◽  
Inspiratory Muscles ◽  
Underlying Mechanisms

AbstractMuscle fatigue is a complex phenomenon enclosing various mechanisms. Despite technological advances, these mechanisms are still not fully understood in vivo. Here, simultaneous measurements of pressure, volume, and ribcage inspiratory muscle activity were performed non-invasively during fatigue (inspiratory threshold valve set at 70% of maximal inspiratory pressure) and recovery to verify if inspiratory ribcage muscle fatigue (1) leads to slowing of contraction and relaxation properties of ribcage muscles and (2) alters median frequency and high-to-low frequency ratio (H/L). During the fatigue protocol, sternocleidomastoid showed the fastest decrease in median frequency and slowest decrease in H/L. Fatigue was also characterized by a reduction in the relative power of the high-frequency and increase of the low-frequency. During recovery, changes in mechanical power were due to changes in shortening velocity with long-lasting reduction in pressure generation, and slowing of relaxation [i.e., tau (τ), half-relaxation time (½RT), and maximum relaxation rate (MRR)] was observed with no significant changes in contractile properties. Recovery of median frequency was faster than H/L, and relaxation rates correlated with shortening velocity and mechanical power of inspiratory ribcage muscles; however, with different time courses. Time constant of the inspiratory ribcage muscles during fatigue and recovery is not uniform (i.e., different inspiratory muscles may have different underlying mechanisms of fatigue), and MRR, ½RT, and τ are not only useful predictors of inspiratory ribcage muscle recovery but may also share common underlying mechanisms with shortening velocity.

Relation between QT interval variability and muscle sympathetic nerve activity in normal subjects

2015 ◽  
Vol 309 (7) ◽  
pp. H1218-H1224 ◽  
Author(s):  
Fatima El-Hamad ◽  
Elisabeth Lambert ◽  
Derek Abbott ◽  
Mathias Baumert
Keyword(s):  
Supine Position ◽  
Sympathetic Nerve ◽  
Qt Interval ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Low Frequency ◽  
Normal Subjects ◽  
Nerve Activity ◽  
Head Up Tilt ◽  
Low Frequency Power

Beat-to-beat variability of the QT interval (QTV) is sought to provide an indirect noninvasive measure of sympathetic nerve activity, but a formal quantification of this relationship has not been provided. In this study we used power contribution analysis to study the relationship between QTV and muscle sympathetic nerve activity (MSNA). ECG and MSNA were recorded in 10 healthy subjects in the supine position and after 40° head-up tilt. Power spectrum analysis was performed using a linear autoregressive model with two external inputs: heart period (RR interval) variability (RRV) and MSNA. Total and low-frequency power of QTV was decomposed into contributions by RRV, MSNA, and sources independent of RRV and MSNA. Results show that the percentage of MSNA power contribution to QT is very small and does not change with tilt. RRV power contribution to QT power is notable and decreases with tilt, while the greatest percentage of QTV is independent of RRV and MSNA in the supine position and after 40° head-up tilt. In conclusion, beat-to-beat QTV in normal subjects does not appear to be significantly affected by the rhythmic modulations in MSNA following low to moderate orthostatic stimulation. Therefore, MSNA oscillations may not represent a useful surrogate for cardiac sympathetic nerve activity at moderate levels of activation, or, alternatively, sympathetic influences on QTV are complex and not quantifiable with linear shift-invariant autoregressive models.

Near-maximal voluntary hyperpnea and ventilatory muscle function

1984 ◽  
Vol 57 (6) ◽  
pp. 1742-1748 ◽  
Author(s):  
T. R. Bai ◽  
B. J. Rabinovitch ◽  
R. L. Pardy
Keyword(s):  
Muscle Function ◽  
Low Frequency ◽  
Normal Subjects ◽  
Pressure Time ◽  
Before And After ◽  
Expiratory Muscles ◽  
Four Levels ◽  
Frequency Relationship ◽  
Low Frequency Power ◽  
Relationship Of

Because of its potential relevance to heavy exercise we studied the ventilatory muscle function of five normal subjects before, during, and after shortterm near-maximal voluntary normocapnic hyperpnea. Measurements of pleural and abdominal pressures and diaphragm electromyogram (EMG) during hyperpnea and of maximum respiratory pressures before and after hyperpnea were made at four levels of ventilation: 76, 79, and 86% maximal voluntary ventilation (MVV) and at MVV. Measurements of pleural and abdominal pressures and diaphragm electromyogram (EMG) during hyperpnea and of maximum respiratory pressures before and after hyperpnea were made. The pressure-stimulation frequency relationship of the diaphragm obtained by unilateral transcutaneous phrenic nerve stimulation was studied in two subjects before and after hyperpnea. Decreases in maximal inspiratory (PImax) and transdiaphragmatic (Pdimax) strength were recorded posthyperpnea at 76 and 79% MVV. Decreases in the pressure-frequency curves of the diaphragm and the ratio of high-to-low frequency power of the diaphragm EMG occurred in association with decreases in Pdimax. Analysis of the pressure-time product (P X dt) for the inspiratory and expiratory muscles individually indicated the increasing contribution of expiratory muscle force to the attainment of higher levels of ventilation. Demonstrable ventilatory muscle fatigue may limit endurance at high levels of ventilation.

Increase in electromyogram low-frequency power in nonfatigued contracting skeletal muscle

1986 ◽  
Vol 61 (3) ◽  
pp. 1012-1017 ◽  
Author(s):  
A. R. Bazzy ◽  
J. B. Korten ◽  
G. G. Haddad
Keyword(s):  
Spectral Density ◽  
Power Spectral Density ◽  
Biceps Brachii ◽  
Low Frequency ◽  
Biceps Brachii Muscle ◽  
Power Spectral ◽  
Loaded Breathing ◽  
Low Frequency Power ◽  
The Relationship ◽  
Frequency Power

We studied the relationship between changing elbow joint angle and the power spectral density of the biceps brachii muscle electromyogram (EMG) during submaximal isometric contractions. For this purpose, we recorded the EMG of the biceps brachii muscle with surface electrodes in 13 subjects. Each subject held a 2.8-kg weight and contracted the biceps isometrically for 30 s at one of two lengths. The length of the muscle was changed by flexing the forearm toward the upper arm to form an angle of 135 degrees (L1) or 45 degrees (L2). We found that the mean centroid frequency (fc) of the EMG power spectral density was 26% lower at L1 than at L2 (P less than 0.01). For each subject there was no significant change in fc during the isometric contraction at either angle. In addition, in nine subjects who sustained fatiguing contractions of the biceps with a 6-kg load, fc decreased by 15% (P less than 0.025). These data suggest that a change in the length at which a muscle contracts isometrically can alter or induce indirectly an alteration in the frequency content of its EMG. This finding may have important implications for the assessment of respiratory muscle EMG especially during loaded breathing.

Dissociation between diaphragmatic and rib cage muscle fatigue

1988 ◽  
Vol 64 (3) ◽  
pp. 959-965 ◽  
Author(s):  
J. W. Fitting ◽  
T. D. Bradley ◽  
P. A. Easton ◽  
M. J. Lincoln ◽  
M. D. Goldman ◽  
...  
Keyword(s):  
Muscle Fatigue ◽  
Normal Subjects ◽  
Breathing Patterns ◽  
Recruitment Pattern ◽  
Rib Cage ◽  
Inspiratory Muscles ◽  
Resistive Breathing ◽  
Emg Power Spectrum ◽  
The Mean ◽  
Substantial Degree

To assess rib cage muscle fatigue and its relationship to diaphragmatic fatigue, we recorded the electromyogram (EMG) of the parasternal intercostals (PS), sternocleidomastoid (SM), and platysma with fine wire electrodes and the EMG of the diaphragm (DI) with an esophageal electrode. Six normal subjects were studied during inspiratory resistive breathing. Two different breathing patterns were imposed: mainly diaphragmatic or mainly rib cage breathing. The development of fatigue was assessed by analysis of the high-to-low (H/L) ratio of the EMG. To determine the appropriate frequency bands for the PS and SM, we established their EMG power spectrum by Fourier analysis. The mean and SD for the centroid frequency was 312 ± 16 Hz for PS and 244 ± 48 Hz for SM. When breathing with the diaphragmatic patterns, all subjects showed a fall in H/L of the DI and none had a fall in H/L of the PS or SM. During rib cage emphasis, four out of five subjects showed a fall in H/L of the PS and five out of six showed a fall in H/L of the SM. Four subjects showed no fall in H/L of the DI; the other two subjects were unable to inhibit diaphragm activity to a substantial degree and did show a fall in H/L of the DI. Activity of the platysma was minimal or absent during diaphragmatic emphasis but was usually strong during rib cage breathing. We conclude that fatigue of either the diaphragm or the parasternal and sternocleidomastoid can occur independently according to the recruitment pattern of inspiratory muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of human diaphragm fatigue

1982 ◽  
Vol 53 (5) ◽  
pp. 1196-1206 ◽  
Author(s):  
F. Bellemare ◽  
A. Grassino
Keyword(s):  
Frequency Band ◽  
Time Course ◽  
Low Frequency ◽  
Normal Subjects ◽  
Rate Of Change ◽  
Center Frequency ◽  
Cycle Duration ◽  
Transdiaphragmatic Pressure ◽  
Inspiratory Resistance ◽  
Rate Of Decay

The time course of the frequency content of the electromyogram (EMG) was studied in the diaphragm of five normal subjects breathing through high inspiratory resistance. The ratio between the power content of a high-frequency band (150– Hz) (H) and a low-frequency band (20http://hwmaint.jap.physiology.org/cgi/content/abstract/53/4/99240 Hz) (L) was calculated for each breath and expressed as a fraction of the initial breath. The rate of decay (when existent) was exponential and was quantified by measuring the time constant of decay of H/L (TF). Runs were held sustaining the ratio of inspiratory time to total breath cycle duration (TI/Ttot) from 0.2 to 1 and transdiaphragmatic pressure (Pdi) of 0.1http://hwmaint.jap.physiology.org/cgi/content/abstract/53/4/992 0.8 of Pdimax. It was found that TF was monotonically related to Pdi X TI/Ttot, following a hyperbolic relationship. TF was compared with velocity of conduction of the myopotentials and with center frequency of the EMG power spectrum and found to follow similar trends showing, however, different absolute rate of change. The values of TF were found to be directly related to the time a given pattern could be sustained (Tlim). It is concluded that EMG changes and Tlim are related and are expressions of the metabolic changes induced by the contraction pattern.

Respiratory response to abdominal and rib cage muscle paralysis in dogs

1993 ◽  
Vol 74 (5) ◽  
pp. 2309-2317 ◽  
Author(s):  
J. F. Brichant ◽  
M. Gorini ◽  
A. De Troyer
Keyword(s):  
Tidal Volume ◽  
Abdominal Cavity ◽  
Emg Activity ◽  
Abdominal Muscles ◽  
Respiratory Response ◽  
Muscle Paralysis ◽  
Transdiaphragmatic Pressure ◽  
Rib Cage ◽  
Inspiratory Muscles ◽  
Arterial Blood

To assess the respiratory response to abdominal and rib cage muscle paralysis, we measured tidal volume, esophageal and gastric pressures, arterial blood gases, and the electromyogram (EMG) of the diaphragm during progressive epidural anesthesia (lidocaine 2%) in 35 supine anesthetized dogs. The EMG activity of the diaphragm was measured with fine-wire electrodes; the abdominal cavity was thus left intact. Paralysis of the abdominal muscles alone did not produce any alterations. In contrast, when all rib cage muscles were also paralyzed, there were substantial increases in the peak height and the rate of rise of diaphragmatic EMG activity that were associated with a decrease in tidal volume and an increase in arterial PCO2 (PaCO2); swings in transdiaphragmatic pressure, however, were unchanged. The increased diaphragmatic activation due to rib cage muscle paralysis persisted after bilateral cervical vagotomy and was well explained by the increased PaCO2. These observations indicate that in the dog 1) the rib cage muscles contribute significantly to tidal volume, and their paralysis causes, through the increased hypercapnic drive, a compensatory increase in diaphragmatic activation; and 2) the rib cage inspiratory muscles enhance the diaphragm's ability to generate pressure during breathing.

scholarly journals Accuracy of noninvasive estimates of respiratory muscle effort during spontaneous breathing in restrictive diseases

2003 ◽  
Vol 95 (4) ◽  
pp. 1542-1549 ◽  
Author(s):  
Francisco García-Río ◽  
José M. Pino ◽  
Angeles Ruiz ◽  
Salvador Díaz ◽  
Concepción Prados ◽  
...  
Keyword(s):  
Spontaneous Breathing ◽  
Respiratory Muscle ◽  
Usual Interstitial Pneumonia ◽  
Neuromuscular Diseases ◽  
Normal Subjects ◽  
Esophageal Pressure ◽  
Chronic Obstructive ◽  
Obstructive Pulmonary Disease ◽  
Transdiaphragmatic Pressure ◽  
Inspiratory Muscles

Mean inspiratory pressure (Pi), estimated from the occlusion pressure at the mouth and the inspiratory time, is useful as a noninvasive estimate of respiratory muscle effort during spontaneous breathing in normal subjects and patients with chronic obstructive pulmonary disease. The aim of this study was to compare the Pi with respect to mean esophageal pressure (Pes) in patients with restrictive disorders. Eleven healthy volunteers, 12 patients with chest wall disease, 14 patients with usual interstitial pneumonia, and 17 patients with neuromuscular diseases were studied. Pi, Pes, and mean transdiaphragmatic pressure were simultaneously measured. Tension-time indexes of diaphragm (TTdi) and inspiratory muscles (TTmu) were also determined. In neuromuscular patients, significant correlations were found between Pi and Pes, Pi and transdiaphragmatic pressure, and TTmu and TTdi. A moderate agreement between Pi and Pes and between TTmu and TTdi was found. No significant correlation between these parameters was found in the other patient groups. These findings suggest that Pi is a good surrogate for the invasive measurement of respiratory muscle effort during spontaneous breathing in neuromuscular patients.

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