In vivo contractile properties of fatigued diaphragm

1987 ◽  
Vol 63 (2) ◽  
pp. 471-478 ◽  
Author(s):  
J. Road ◽  
R. Vahi ◽  
P. del Rio ◽  
A. Grassino
Keyword(s):  
Spontaneous Breathing ◽  
Central Fatigue ◽  
Contractile Properties ◽  
Peripheral Fatigue ◽  
Electromyographic Activity ◽  
Force Frequency ◽  
Shortening Velocity ◽  
Velocity Of Shortening ◽  
The Right

The effects of fatigue on diaphragmatic contractility in vivo are unknown. In this study we used sonomicrometry to examine the velocity of shortening and lengthening and the amount of shortening in the fresh and fatigued canine hemidiaphragm (8 dogs) including the force generated. Fatigue was produced by epiphrenic stimulation of the left phrenic nerve; the right hemidiaphragm acted as the control. We found that 1) hemidiaphragmatic fatigue caused an increase in frequency with reduced tidal volume; 2) fatigue resulted in a near complete cessation of tidal shortening during spontaneous breathing; 3) there was an initial decrease in central activation (electromyogram) to the fatigued hemidiaphragm, an indication of central fatigue; 4) force-frequency curves showed a considerable and prolonged loss of the amount of shortening, velocity, and force generated by the fatigued hemidiaphragm during supramaximal stimulation, an indication of peripheral fatigue; and 5) during spontaneous breathing in the fatigued hemidiaphragm, tidal shortening remained reduced for up to 3 h, whereas in the right right hemidiaphragm tidal shortening and electromyographic activity did not change. We conclude that fatigue of a hemidiaphragm alters the spontaneous breathing pattern and produces profound modifications in its contractile properties without altering contralateral hemidiaphragmatic performance.

Contractile properties of intercostal muscles and their functional significance

1985 ◽  
Vol 59 (2) ◽  
pp. 528-535 ◽  
Author(s):  
G. A. Farkas ◽  
M. Decramer ◽  
D. F. Rochester ◽  
A. De Troyer
Keyword(s):  
Length Change ◽  
Contractile Properties ◽  
Functional Coupling ◽  
Force Frequency ◽  
Active Length ◽  
Residual Capacity ◽  
Measured Length ◽  
The Right

To have some insight into the functional coupling between the parasternal intercostals (PS) and the diaphragm (DPM), we have examined the isometric contractile properties of bundles from canine PS and DPM muscles. Bundles of external (EXT) and internal (INT) interosseous intercostals were studied for comparison. In addition we have related sonometrically measured length of the intercostals in vivo at supine functional residual capacity (FRC) to in vitro optimal force-producing length (Lo). We found that 1) intercostal twitch speed is significantly faster than DPM, thus displacing their relative force-frequency curve to the right of that of the DPM; 2) the ascending limb of the active length-tension curve of all intercostals lies below the DPM curve; i.e., at 85% Lo, PS force is 46% of maximal force (Po), whereas DPM force is still 87% Po; 3) for any given length change beyond Lo, all intercostals generate greater passive tension than the DPM; 4) Po is greater for the intercostals than the DPM; and 5) at supine FRC, both EXT and INT in dogs are nearly operating at Lo, whereas the PS are operating at a length greater than Lo. We conclude that 1) PS produce less force than DPM during breathing efforts involving low- (10–20 Hz) stimulation frequencies, but they generate more force than DPM when high- (greater than 50 Hz) stimulation frequencies are required; and 2) the pressure-generating ability of the PS is better preserved than that of the DPM with increases in lung volume.

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.

Histochemical and physiological characteristics of the rat diaphragm

1985 ◽  
Vol 58 (4) ◽  
pp. 1085-1091 ◽  
Author(s):  
J. M. Metzger ◽  
K. B. Scheidt ◽  
R. H. Fitts
Keyword(s):  
Fiber Type ◽  
Contractile Properties ◽  
Effect Of Temperature ◽  
Type I ◽  
Force Frequency ◽  
Rat Diaphragm ◽  
Shortening Velocity ◽  
Type Distribution ◽  
Adult Rat ◽  
Fiber Type Distribution

The histochemical and contractile characteristics of the adult rat diaphragm were determined. Based on enzyme histochemistry, the rat diaphragm contained 40% type I, 27% type IIa, and 34% type IIb fibers. There were significantly more type I fibers in the ventral costal (VEN) compared with the crural (CRU) region of the muscle and a slightly higher percentage of type I's on the thoracic relative to the abdominal surface. The contractile properties and the effect of temperature (Q10) were similar in the VEN and CRU regions. Increasing temperature produced higher isometric peak tetanic tension, whereas twitch tension, contraction, and one-half relaxation time all decreased. The maximal shortening velocity increased linearly from 22 and 30 degrees C, then plateaued before decreasing between 35 and 37 degrees C. The VEN and CRU force-velocity curves became less concave as temperature increased from 22 to 35 degrees C. Furthermore, the force-frequency relation of both regions was shifted to the right as temperature increased. The isometric and isotonic contractile properties and fiber type distribution are similar in the VEN and CRU regions of the diaphragm. The rat diaphragm is clearly heterogeneous in fiber type distribution and functionally lies intermediate between slow- and fast-twitch limb skeletal muscles.

In vivo length and shortening of canine diaphragm with body postural change

1986 ◽  
Vol 60 (2) ◽  
pp. 661-669 ◽  
Author(s):  
S. L. Newman ◽  
J. D. Road ◽  
A. Grassino
Keyword(s):  
Supine Position ◽  
Spontaneous Breathing ◽  
Postural Change ◽  
Neural Drive ◽  
Optimal Length ◽  
Velocity Of Shortening ◽  
Integrated Electromyogram ◽  
Lateral Decubitus ◽  
Prone Posture

Using sonomicrometry, we measured the in vivo tidal shortening and velocity of shortening of the costal and crural segments of the diaphragm in the anesthetized dog in the supine, upright, tailup, prone, and lateral decubitus postures. When compared with the supine position, end-expiratory diaphragmatic length varied by less than 11% in all postures, except the upright. During spontaneous breathing, the tidal shortening and the velocity of shortening of the crural segment exceeded that of the costal segment in all postures except the upright and was maximal for both segments in the prone posture. We noted the phasic integrated electromyogram to increase as the end-expiratory length of the diaphragm shortened below and to decrease as the diaphragm lengthened above its optimal length. This study shows that the costal and crural segments have a different quantitative behavior with body posture and both segments show a compensation in neural drive to changes in resting length.

scholarly journals Altered in vivo left ventricular torsion and principal strains in hypothyroid rats

2010 ◽  
Vol 299 (5) ◽  
pp. H1577-H1587 ◽  
Author(s):  
Yong Chen ◽  
Aleefia Somji ◽  
Xin Yu ◽  
Julian E. Stelzer
Keyword(s):  
Mechanical Performance ◽  
Ventricular Myocardium ◽  
Left Ventricular ◽  
Contractile Properties ◽  
Shortening Velocity ◽  
Left Ventricular Torsion ◽  
Ventricular Torsion ◽  
Bridge Performance ◽  
Contractile Performance

The twisting and untwisting motions of the left ventricle (LV) lead to efficient ejection of blood during systole and filling of the ventricle during diastole. Global LV mechanical performance is dependent on the contractile properties of cardiac myocytes; however, it is not known how changes in contractile protein expression affect the pattern and timing of LV rotation. At the myofilament level, contractile performance is largely dependent on the isoforms of myosin heavy chain (MHC) that are expressed. Therefore, in this study, we used MRI to examine the in vivo mechanical consequences of altered MHC isoform expression by comparing the contractile properties of hypothyroid rats, which expressed only the slow β-MHC isoform, and euthyroid rats, which predominantly expressed the fast α-MHC isoform. Unloaded shortening velocity ( Vo) and apparent rate constants of force development ( ktr) were measured in the skinned ventricular myocardium isolated from euthyroid and hypothyroid hearts. Increased expression of β-MHC reduced LV torsion and fiber strain and delayed the development of peak torsion and strain during systole. Depressed in vivo mechanical performance in hypothyroid rats was related to slowed cross-bridge performance, as indicated by significantly slower Vo and ktr, compared with euthyroid rats. Dobutamine infusion in hypothyroid hearts produced smaller increases in torsion and strain and aberrant transmural torsion patterns, suggesting that the myocardial response to β-adrenergic stress is compromised. Thus, increased expression of β-MHC alters the pattern and decreases the magnitude of LV rotation, contributing to reduced mechanical performance during systole, especially in conditions of increased workload.

scholarly journals Effects of salbutamol on rat diaphragm contractility

1996 ◽  
Vol 81 (3) ◽  
pp. 1103-1110 ◽  
Author(s):  
H. F. Van der Heijden ◽  
R. H. Van Balkom ◽  
H. T. Folgering ◽  
C. L. Van Herwaarden ◽  
P. N. Dekhuijzen
Keyword(s):  
Time Course ◽  
Subcutaneous Administration ◽  
Contractile Properties ◽  
Force Generation ◽  
Force Frequency ◽  
Rat Diaphragm ◽  
Tetanic Force ◽  
Low Concentrations

The aim of this study was to investigate 1) the effects and time course of single doses of salbutamol on isometric contractile properties of isolated rat diaphragm strips and 2) whether these effects were caused by a direct effect on the muscle. Two experiments were performed. In one, salbutamol was administered subcutaneously in doses of 12.5, 25, 50, or 100 micrograms/kg (25 and 50 micrograms/kg sc resulted in serum concentrations of approximately 9 and approximately 15 micrograms/l, respectively, 0.5 h after injection) and in vitro contractile properties were determined 0.5, 1, 2, or 4 h after administration; in the other, salbutamol was added to the tissue bath in a concentration of < or = 2, approximately 10, approximately 20, and approximately 80 micrograms/l. Twice force, maximal tetanic force, and twitch force-to-tetanic force ratio all increased in a dose-dependent way in both experiments. The increases in force generation were slightly higher after subcutaneous administration. Force-frequency curves were shifted upward in both experiments. No significant effects of time of salbutamol administration were found, but the increase in force generation was most pronounced within 2 h after subcutaneous administration. In conclusion, in vitro force generation can be improved by low concentrations of salbutamol. The slightly higher increases in force generation after subcutaneous administration suggest that in vivo salbutamol may have additional positive inotropic actions on diaphragm contractility besides a direct beta 2-adrenergic effect on the muscle itself.

Diaphragm contractile dysfunction in MyoD gene-inactivated mice

2002 ◽  
Vol 283 (3) ◽  
pp. R583-R590 ◽  
Author(s):  
Jessica L. Staib ◽  
Steven J. Swoap ◽  
Scott K. Powers
Keyword(s):  
Power Output ◽  
Peak Power ◽  
Contractile Properties ◽  
Peak Power Output ◽  
Force Frequency ◽  
Shortening Velocity ◽  
Frequency Relationship ◽  
Myod Gene

MyoD is one of four myogenic regulatory factors found exclusively in skeletal muscle. In an effort to better understand the role that MyoD plays in determining muscle contractile properties, we examined the effects of MyoD deletion on both diaphragmatic contractile properties and myosin heavy chain (MHC) phenotype. Regions of the costal diaphragm from wild-type and MyoD knockout [ MyoD (−/−)] adult male BALB/c mice ( n = 8/group) were removed, and in vitro diaphragmatic contractile properties were measured. Diaphragmatic contractile measurements revealed that MyoD (−/−) animals exhibited a significant ( P < 0.05) downward shift in the force-frequency relationship, a decrement in maximal specific tension (Po; −33%), a decline in maximal shortening velocity (Vmax; −37%), and concomitant decrease in peak power output (−47%). Determination of MHC isoforms in the diaphragm via gel electrophoresis revealed that MyoD elimination resulted in a fast-to-slow shift ( P < 0.05) in the MHC phenotype toward MHC types IIA and IIX in MyoD (−/−) animals. These data indicate that MyoD deletion results in a decrease in diaphragmatic submaximal force generation and Po, along with decrements in both Vmax and peak power output. Hence, MyoD plays an important role in determining diaphragmatic contractile properties.

Free-wall shortening and relaxation during ejection in the canine right ventricle

1980 ◽  
Vol 239 (5) ◽  
pp. H601-H613 ◽  
Author(s):  
H. Pouleur ◽  
J. Lefevre ◽  
H. Van Mechelen ◽  
A. A. Charlier
Keyword(s):  
Pulmonary Blood Flow ◽  
Segment Length ◽  
Free Wall ◽  
Shortening Velocity ◽  
Mean Velocity ◽  
Velocity Of Shortening ◽  
Average Slope ◽  
Length Data ◽  
The Right ◽  
Pressure Fall

Relations between shortening, velocity of shortening, and relaxation of inflow and outflow segments of the right ventricular (RV) free wall (FW) were examined during ejection in 12 open-chest dogs after pharmacologic blockade by recording RV pressures, RVFW dimensions (piezoelectric crystals), and pulmonary blood flow. At heart rates of 113 +/0 8 (SD) beats/min, investigated segments remained isometric or even lengthened before the end of ejection. Tension-length data in the outflow tract converged at the time of peak systolic tension toward a common linear relation (average slope 65 +/- 10 cmH2O/mm, average intercept 5.9 +/- 0.9 mm), but markedly deviated from this line at the end of ejection. Consistent relations between peak tension and mean velocity of shortening were only observed during the first part of ejection. In addition the rate of segmental isometric relaxation, estimated from RV pressure fall was load dependent (e.g., +60% increase in relaxation rate when RVFW end-diastolic segment length increased from 12.9 +/- 0.8 to 13.5 +/- 0.8 mm). We conclude that under normal conditions, the tension-velocity-length relations of the RVFW are comparable to those of the left ventricle during the first part of ejection only. We also conclude that RV relaxation is load dependent and that a significant part of RV ejection occurs during RVFW relaxation.

Respiratory muscle length measured by sonomicrometry

1984 ◽  
Vol 56 (3) ◽  
pp. 753-764 ◽  
Author(s):  
S. Newman ◽  
J. Road ◽  
F. Bellemare ◽  
J. P. Clozel ◽  
C. M. Lavigne ◽  
...  
Keyword(s):  
Spontaneous Breathing ◽  
Muscle Length ◽  
Length Change ◽  
Lung Inflation ◽  
Velocity Of Shortening ◽  
Anesthetized Dogs ◽  
Supramaximal Stimulation ◽  
Irreversible Injury ◽  
Anatomical Part

The use of sonomicrometry to study the mechanical properties of the diaphragm in vivo is presented. This method consists of the implantation of piezoelectric transducers between muscle fibers to measure the fibers' changes in length. Ultrasonic bursts are produced by one transducer upon electrical excitation and sensed by a second transducer placed 1–2 cm away. The time elapsed between the generation of the ultrasound burst and its detection is used to calculate the intertransducer distance. Excitation and sampling are done at 1.5 kHz and the output is a DC signal proportional to the length change between the transducers. Neither irreversible injury to the diaphragm nor regional differences within an anatomical part or segment were noted. Measurements were stable within the physiological range of temperature. We measured costal and crural length and velocity of contraction in anesthetized dogs during spontaneous breathing, occluded inspirations, passive lung inflation, and supramaximal phrenic nerve stimulation. We found that shortening during spontaneous breathing was 11 and 6% for crural and costal, respectively. The crural leads the costal in velocity of shortening. Supramaximal stimulation results in a velocity of shortening of 5 resting lengths X s-1. During an occluded inspiration crural shortens as much as in the nonoccluded breath, whereas costal shortens less. During passive lung inflation there is a nearly linear relationship between lung volume and diaphragm length; however, the relationships of chest wall dimensions with diaphragm length are nonlinear and cannot be described by any simple function. Some of the implications of these data on the present understanding of diaphragmatic mechanics are discussed.

scholarly journals β-Alanine supplementation enhances human skeletal muscle relaxation speed but not force production capacity

2015 ◽  
Vol 118 (5) ◽  
pp. 604-612 ◽  
Author(s):  
Ricci Hannah ◽  
Rebecca Louise Stannard ◽  
Claire Minshull ◽  
Guilherme Giannini Artioli ◽  
Roger Charles Harris ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Exercise Performance ◽  
Muscle Relaxation ◽  
Femoral Nerve ◽  
Knee Extensor ◽  
Calcium Sensitivity ◽  
Contractile Properties ◽  
Force Frequency ◽  
Electromechanical Delay

β-Alanine (BA) supplementation improves human exercise performance. One possible explanation for this is an enhancement of muscle contractile properties, occurring via elevated intramuscular carnosine resulting in improved calcium sensitivity and handling. This study investigated the effect of BA supplementation on in vivo contractile properties and voluntary neuromuscular performance. Twenty-three men completed two experimental sessions, pre- and post-28 days supplementation with 6.4 g/day of BA ( n = 12) or placebo (PLA; n = 11). During each session, force was recorded during a series of knee extensor contractions: resting and potentiated twitches and octet (8 pulses, 300 Hz) contractions elicited via femoral nerve stimulation; tetanic contractions (1 s, 1–100 Hz) via superficial muscle stimulation; and maximum and explosive voluntary contractions. BA supplementation had no effect on the force-frequency relationship, or the force responses (force at 25 and 50 ms from onset, peak force) of resting or potentiated twitches, and octet contractions ( P > 0.05). Resting and potentiated twitch electromechanical delay and time-to-peak tension were unaffected by BA supplementation ( P > 0.05), although half-relaxation time declined by 7–12% ( P < 0.05). Maximum and explosive voluntary forces were unchanged after BA supplementation. BA supplementation had no effect on evoked force responses, implying that altered calcium sensitivity and/or release are not the mechanisms by which BA supplementation influences exercise performance. The reduced half-relaxation time with BA supplementation might, however, be explained by enhanced reuptake of calcium, which has implications for the efficiency of muscle contraction following BA supplementation.

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