Muscle shortening increases sensitivity of fatigue to severe hypoxia in canine diaphragm

1991 ◽  
Vol 71 (6) ◽  
pp. 2309-2316 ◽  
Author(s):  
B. T. Ameredes ◽  
M. W. Julian ◽  
T. L. Clanton
Keyword(s):  
Flow Characteristics ◽  
Muscle Length ◽  
Isometric Tension ◽  
Severe Hypoxia ◽  
Mean Power ◽  
Tension Development ◽  
Moderate Hypoxia ◽  
O2 Supply ◽  
Mean Power Output

The effects of inspired O2 on diaphragm tension development during fatigue were assessed using isovelocity (n = 6) and isometric (n = 6) muscle contractions performed during a series of exposures to moderate hypoxia [fraction of inspired O2 (FIO2) = 0.13], hyperoxia (FIO2 = 1), and severe hypoxia (FIO2 = 0.09). Muscle strips were created in situ from the canine diaphragm, attached to a linear ergometer, and electrically stimulated (30 Hz) to contract (contraction = 1.5 s/relaxation = 2 s) from optimal muscle length (Lo = 8.9 cm). Isovelocity contractions shortened to 0.70 Lo, resulting in a mean power output of 210 mW/cm2. Fatigue trials of 35 min duration were performed while inspired O2 was sequentially changed between the experimental mixtures and normoxia (FIO2 = 0.21) for 5-min periods. In this series, severe hypoxia consistently decreased isovelocity tension development by an average of 0.1 kg/cm2 (P less than 0.05), which was followed by a recovery of tension (P less than 0.05) on return to normoxia. These responses were not consistently observed in isometric trials. Neither isovelocity nor isometric tension development was influenced by moderate hypoxia or hyperoxia. These results demonstrate that the in situ diaphragm is relatively insensitive to rapid changes in O2 supply over a broad range and that the tension development of the shortening diaphragm appears to be more susceptible to severe hypoxia during fatigue. This may reflect a difference in either the metabolic or blood flow characteristics of shortening contractions of the diaphragm.

Increased fatigue of isovelocity vs. isometric contractions of canine diaphragm

1990 ◽  
Vol 69 (2) ◽  
pp. 740-746 ◽  
Author(s):  
B. T. Ameredes ◽  
T. L. Clanton
Keyword(s):  
Respiratory Muscle ◽  
Force Production ◽  
Muscle Length ◽  
Isometric Tension ◽  
Diaphragm Muscle ◽  
Mean Power ◽  
Mean Power Output ◽  
Initial Peak ◽  
Shortening Contractions

A comparison of fatigue as a loss of force with repeated contractions over time was performed in canine respiratory muscle by isometric (nonshortening) and isovelocity (shortening) contractions. In situ diaphragm muscle strips were attached to a linear ergometer and electrically stimulated (30 or 40 Hz) via the left phrenic nerve to produce either isometric (n = 12) or isovelocity (n = 12) contractions (1.5 s) from optimal muscle length (Lo = 8.8 cm). Similar velocities of shortening between isovelocity experiments [0.19 +/- 0.02 (SD) Lo/S] were produced by maximizing the mean power output (Wmax = 210 +/- 27 mW/cm2) that could be developed over 1.5 s when displacement was approximately 0.30 Lo. Initial peak isometric tension was 1.98 kg/cm2, whereas initial peak isovelocity tension was 1.84 kg/mc2 (P less than 0.01) or 93% of initial isometric tension. Fatigue trials of 5 min were conducted on muscles contracting at a constant duty cycle (0.43). At the end of the trials, peak isovelocity tension had fallen to 50% of initial isometric tension (P less than 0.01), whereas peak isometric tension had only fallen by 27%. These results indicate that muscle shortening during force production has a significant influence on diaphragm muscle fatigue. We conclude that the effects of shortening on fatigue must be considered in models of respiratory muscle function, because these muscles typically shorten during breathing.

Calcium effects on contractility and heat production in mammalian myocardium

1986 ◽  
Vol 251 (1) ◽  
pp. H127-H132 ◽  
Author(s):  
J. E. Ponce-Hornos ◽  
A. C. Taquini
Keyword(s):  
Papillary Muscle ◽  
Heat Production ◽  
Muscle Length ◽  
Heat Rate ◽  
Isometric Tension ◽  
Tension Development ◽  
Contractile System ◽  
Dimensionless Ratio ◽  
Calcium Effects ◽  
Mammalian Myocardium

The effects of changing external Ca concentration ([Ca]o) on contractile parameters and heat production were investigated in the interventricular rabbit septa and the dog papillary muscle. Double reciprocal plots of tension development as a function of [Ca]o yielded half-maximal activation values of 1.04 +/- 0.17 and 2.8 +/- 0.7 mM Ca for the septum and papillary muscle, respectively. Resting heat rate was similar in both preparations, 1.9 +/- 0.08 mW . g-1 for the septum and 1.7 +/- 0.07 mW . g-1 for the papillary muscle, and it was not altered by changes in [Ca]o. Active heat production (Ha) normalized per unit of force developed (19 +/- 1.3 microJ . mN-1 . g-1) for the septum and the dimensionless ratio Ha/(To . lo), (0.30 +/- 0.02) for the papillary muscle, where To is the isometric tension and lo, the muscle length, remained unaltered with changes in [Ca]o. Total heat production per beat normalized per unit of force developed (Ht/T) for the septum and the ratio Ht/(To . lo) for the papillary muscle decreased hyperbolically with [Ca]o. Therefore, as a result of the unaltered economy of the contractile system and the unchanged resting heat rate, muscle economy improves as [Ca]o approaches physiological levels. Further increase in [Ca]o, over the physiological levels, can only slightly improve muscle economy.

Acute Beetroot Juice Supplementation Does Not Improve Cycling Performance in Normoxia or Moderate Hypoxia

2015 ◽  
Vol 25 (4) ◽  
pp. 359-366 ◽  
Author(s):  
Kristin E. MacLeod ◽  
Sean F. Nugent ◽  
Susan I. Barr ◽  
Michael S. Koehle ◽  
Benjamin C. Sporer ◽  
...  
Keyword(s):  
Steady State ◽  
Power Output ◽  
Time Trial ◽  
Small Sample ◽  
Oxygen Cost ◽  
Beetroot Juice ◽  
Mean Power ◽  
Double Blind ◽  
Moderate Hypoxia ◽  
Mean Power Output

Beetroot juice (BR) has been shown to lower the oxygen cost of exercise in normoxia and may have similar effects in hypoxia. We investigated the effect of BR on steady-state exercise economy and 10-km time trial (TT) performance in normoxia and moderate hypoxia (simulated altitude: ~2500 m). Eleven trained male cyclists (VO2peak ≥ 60 ml·kg-1·min-1) completed four exercise trials. Two hours before exercise, subjects consumed 70 mL BR (~6 mmol nitrate) or placebo (nitrate-depleted BR) in a randomized, double-blind manner. Subjects then completed a 15-min self-selected cycling warm-up, a 15-min steady-state exercise bout at 50% maximum power output, and a 10-km time trial (TT) in either normoxia or hypoxia. Environmental conditions were randomized and single-blind. BR supplementation increased plasma nitrate concentration and fraction of exhaled nitric oxide relative to PL (p < .05 for both comparisons). Economy at 50% power output was similar in hypoxic and normoxic conditions (p > .05), but mean power output was greater in the normoxic TT relative to the hypoxic TT (p < .05). BR did not affect economy, steady-state SpO2, mean power output, or 10-km TT completion time relative to placebo in either normoxia or hypoxia (p > .05 in all comparisons). In conclusion, BR did not lower the oxygen cost of steady-state exercise or improve exercise performance in normoxia or hypoxia in a small sample of well-trained male cyclists.

Hypoxia-elicited contraction of aorta and coronary artery via removal of endothelium-derived nitric oxide

1992 ◽  
Vol 263 (5) ◽  
pp. H1339-H1347 ◽  
Author(s):  
M. Muramatsu ◽  
Y. Iwama ◽  
K. Shimizu ◽  
H. Asano ◽  
Y. Toki ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Coronary Artery ◽  
Spontaneously Hypertensive Rat ◽  
Isometric Tension ◽  
Severe Hypoxia ◽  
Initial Increase ◽  
No Production ◽  
Moderate Hypoxia ◽  
Spontaneously Hypertensive ◽  
Sustained Increase

To characterize endothelium-derived contracting factor 1 (EDCF1) released under hypoxia, vascular rings isolated from spontaneously hypertensive rat (SHR) aorta and canine coronary artery were suspended for isometric tension recording in an organ chamber filled with a Krebs-Henseleit buffer. In SHR aorta precontracted with norepinephrine (10(-7) M), severe hypoxia induced an initial increase in tension by 36.7 +/- 7.5% followed by a 56.9 +/- 5.7% relaxation; moderate hypoxia induced only a sustained increase in tension by 20.6 +/- 2.5%. Inhibition of nitric oxide (NO) production with N omega-nitro-L-arginine methyl ester (L-NAME) (10(-3) M) augmented norepinephrine-induced precontraction by 76.1 +/- 12.3% and totally eliminated the hypoxic contraction. In canine coronary arteries precontracted with KCl (30 mM) in the presence of indomethacin (10(-5) M), severe hypoxia caused a sustained increase in tension by 68.9 +/- 7.3%, which was also abolished with L-NAME. When L-NAME (10(-3) M) was given after the precontraction, both of these vessels developed sustained contractions under normoxia and moderate hypoxia. These results suggest that the vasocontraction currently considered to be induced by EDCF1 is not caused by a contracting factor but rather is a contracting phenomenon derived from continuous inhibition of basal NO synthesis during hypoxia.

Stiffness of active smooth muscle during forced elongation

1987 ◽  
Vol 253 (3) ◽  
pp. C484-C493 ◽  
Author(s):  
R. A. Meiss
Keyword(s):  
Smooth Muscle ◽  
Phase Angle ◽  
Muscle Length ◽  
Isometric Tension ◽  
Microcomputer System ◽  
Tension Development ◽  
Stretch Rate ◽  
Angle Data ◽  
Cross Bridges ◽  
System Phase

The stiffness of isometrically contracting mesotubarium superius and ovarian ligament smooth muscle from estrous female rabbits was measured continuously by using sinusoidal length perturbations (at 80 Hz, less than 15 microns peak to peak). Muscles were stimulated with alternating current fields, and all records were digitized using a microcomputer system. Phase-angle data were used to resolve computed stiffness into elastic and viscous components. Stiffness measurements were continued during long ramp-type stretches (up to 25% of muscle length) delivered as soon as force was maximal. To use the period of isometric tension development as a standard for comparison, the expected stiffness was computed during the long stretch. Stiffness was reduced in approximate proportion to the ramp stretch rate, and the reduction was confined largely to the elastic component. Cooling the muscle increased the stiffness deviation at a given stretch rate. It is proposed that the long stretch detaches cross bridges that can reattach to new sites as myofilaments shear past one another. At higher shearing speeds, less time is available for reattachment and stiffness is further reduced.

Force-velocity shifts with repetitive isometric and isotonic contractions of canine gastrocnemius in situ

1992 ◽  
Vol 73 (5) ◽  
pp. 2105-2111 ◽  
Author(s):  
B. T. Ameredes ◽  
W. F. Brechue ◽  
G. M. Andrew ◽  
W. N. Stainsby
Keyword(s):  
Muscle Length ◽  
Isometric Tension ◽  
Maximal Velocity ◽  
Velocity Of Shortening ◽  
Low Load ◽  
Before And After ◽  
Force Velocity ◽  
The Hill ◽  
Isotonic Contractions

The force-velocity (F-V) relationships of canine gastrocnemius-plantaris muscles at optimal muscle length in situ were studied before and after 10 min of repetitive isometric or isotonic tetanic contractions induced by electrical stimulation of the sciatic nerve (200-ms trains, 50 impulses/s, 1 contraction/s). F-V relationships and maximal velocity of shortening (Vmax) were determined by curve fitting with the Hill equation. Mean Vmax before fatigue was 3.8 +/- 0.2 (SE) average fiber lengths/s; mean maximal isometric tension (Po) was 508 +/- 15 g/g. With a significant decrease of force development during isometric contractions (-27 +/- 4%, P < 0.01, n = 5), Vmax was unchanged. However, with repetitive isotonic contractions at a low load (P/Po = 0.25, n = 5), a significant decrease in Vmax was observed (-21 +/- 2%, P < 0.01), whereas Po was unchanged. Isotonic contractions at an intermediate load (P/Po = 0.5, n = 4) resulted in significant decreases in both Vmax (-26 +/- 6%, P < 0.05) and Po (-12 +/- 2%, P < 0.01). These results show that repeated contractions of canine skeletal muscle produce specific changes in the F-V relationship that are dependent on the type of contractions being performed and indicate that decreases in other contractile properties, such as velocity development and shortening, can occur independently of changes in isometric tension.

scholarly journals Muscle designed for maximum short-term power output: quail flight muscle

2002 ◽  
Vol 205 (15) ◽  
pp. 2153-2160 ◽  
Author(s):  
Graham N. Askew ◽  
Richard L. Marsh
Keyword(s):  
Power Output ◽  
Muscle Length ◽  
Pectoralis Muscle ◽  
Mean Power ◽  
Muscle Properties ◽  
Strain Cycle ◽  
The Central Nervous System ◽  
Power Outputs ◽  
Mean Power Output ◽  
Short Flight

SUMMARYTake-off in birds at high speeds and steep angles of elevation requires a high burst power output. The mean power output of the pectoralis muscle of blue-breasted quail (Coturnix chinensis) during take-off is approximately 400 W kg-1 muscle, as determined using two independent methods. This burst power output is much higher than has been measured in any other cyclically contracting muscle. The power output of muscle is determined by the interactions between the physiological properties of the muscle, the stimulation regime imposed by the central nervous system and the details of the strain cycle, which are determined by the reciprocal interaction between the muscle properties and the environmental load. The physiological adaptations that enable a high power output to be achieved are those that allow the muscle to develop high stresses whilst shortening rapidly. These characteristics include a high myofibrillar density, rapid twitch contraction kinetics and a high maximum intrinsic velocity of shortening. In addition, several features of the strain cycle increase the power output of the quail pectoralis muscle. First, the muscle operates at a mean length shorter than the plateau of the length/force relationship. Second,the muscle length trajectory is asymmetrical, with 70 % of the cycle spent shortening. The asymmetrical cycle is expected to increase the power output substantially. Third, subtle deviations in the velocity profile improve power output compared with a simple asymmetrical cycle with constant lengthening and shortening rates. The high burst power outputs found in the flight muscles of quail and similar birds are limited to very brief efforts before fatigue occurs. This strong but short flight performance is well-suited to the rapid-response anti-predation strategy of these birds that involves a short flight coupled with a subsequent sustained escape by running. These considerations serve as a reminder that the maximum power-producing capacities of muscles need to be considered in the context of the in vivosituation within which the muscles operate.

Force–velocity relationships in hypertensive arterial smooth muscle

1985 ◽  
Vol 63 (6) ◽  
pp. 669-674 ◽  
Author(s):  
C. S. Packer ◽  
N. L. Stephens
Keyword(s):  
Smooth Muscle ◽  
Spontaneously Hypertensive Rat ◽  
Peripheral Resistance ◽  
Muscle Length ◽  
Maximum Velocity ◽  
Isometric Tension ◽  
Arterial Smooth Muscle ◽  
Tension Development ◽  
Force Velocity ◽  
Wistar Kyoto

Increased total peripheral resistance is the cardinal haemodynamic disorder in essential hypertension. This could be secondary to alterations in the mechanical properties of vascular smooth muscle. Adequate study has not been made of the force–velocity (F–V) relationship in hypertensive arterial smooth muscle. Increased shortening in arterial smooth muscle would result in greater narrowing of arteries. The objectives of this investigation were to see if there is (i) increased shortening or increased maximum change in muscle length (ΔLmax where L stands for muscle length), (ii) an increased maximum velocity of shortening (Vmax) measured in lo per second where lo is the optimal muscle length for tension development, and (iii) a difference in maximum isometric tension (Po) developed in spontaneously hypertensive rat (SHR; N = 6) compared with normotensive Wistar Kyoto rat (WKY; N = 5) caudal artery strips. An electromagnetic muscle lever was employed in recording force–velocity data. Analysis of these data revealed the following: (a) the SHR mean Po of 6.21 ± 1.01 N/cm2 was not different from the mean WKY Po of 6.97 ± 1.64 N/cm2 (p > 0.05); (b) the SHR preparations showed greater shortening for all loads imposed; (c) the SHR Vmax of 0.016 lo/s was greater than the WKY Vmax of 0.013 lo/s (p < 0.05). This study provides evidence that while hypertensive arterial smooth muscle is not able to produce more force than normotensive arterial smooth muscle, it is capable of faster and greater shortening. The latter could result in increased narrowing of hypertensive arteries and increased blood pressure.

Effects of load and tone on the mechanics of isolated human bronchial smooth muscle

1999 ◽  
Vol 86 (2) ◽  
pp. 488-495 ◽  
Author(s):  
François-Xavier Blanc ◽  
Sergio Salmeron ◽  
Catherine Coirault ◽  
Martin Bard ◽  
Elie Fadel ◽  
...  
Keyword(s):  
Smooth Muscles ◽  
Muscle Length ◽  
Isometric Tension ◽  
Shortening Velocity ◽  
Bronchial Smooth Muscle ◽  
Tension Development ◽  
Resting Tension ◽  
Muscle Shortening ◽  
Baseline Values ◽  
Cross Bridges

Isotonic and isometric properties of nine human bronchial smooth muscles were studied under various loading and tone conditions. Freshly dissected bronchial strips were electrically stimulated successively at baseline, after precontraction with 10−7 M methacholine (MCh), and after relaxation with 10−5 M albuterol (Alb). Resting tension, i.e., preload determining optimal initial length ( L o) at baseline, was held constant. Compared with baseline, MCh decreased muscle length to 93 ± 1% L o( P < 0.001) before any electrical stimulation, whereas Alb increased it to 111 ± 3% L o( P < 0.01). MCh significantly decreased maximum unloaded shortening velocity (0.045 ± 0.007 vs. 0.059 ± 0.007 L o/s), maximal extent of muscle shortening (8.4 ± 1.2 vs. 13.9 ± 2.4% L o), and peak isometric tension (6.1 ± 0.8 vs. 7.2 ± 1.0 mN/mm2). Alb restored all these contractile indexes to baseline values. These findings suggest that MCh reversibly increased the number of active actomyosin cross bridges under resting conditions, limiting further muscle shortening and active tension development. After the electrically induced contraction, muscles showed a transient phase of decrease in tension below preload. This decrease in tension was unaffected by afterload levels but was significantly increased by MCh and reduced by Alb. These findings suggest that the cross bridges activated before, but not during, the electrically elicited contraction may modulate the phase of decrease in tension below preload, reflecting the active part of resting tension.

Length-dependent activation of in situ canine skeletal muscle

1979 ◽  
Vol 237 (1) ◽  
pp. C38-C42 ◽  
Author(s):  
C. R. Lambert ◽  
L. B. Gladden ◽  
W. N. Stainsby
Keyword(s):  
Skeletal Muscle ◽  
Muscle Length ◽  
Muscle Group ◽  
Plantaris Muscle ◽  
Tension Development ◽  
Inotropic State ◽  
Isometric Twitch ◽  
Length Dependent Activation ◽  
Different Levels

This study was designed to assess the contribution of length-dependent activation to the peak isometric twitch tension developed and the maximal rate of tension development (dP/dt) of in situ canine skeletal muscle. Length-developed tension and length-dP/dt relationships were generated for the dog gastrocnemius-plantaris muscle group at three different levels of inotropic state as determined by stimulation frequency. These relationships were then normalized with respect to maximal developed tension and maximal dP/dt and the normalized curves were superimposed for comparison. At progressively shorter muscle lengths the augmentation of tension production by a given increment in inotropic state was greater as measured by either developed tension or dP/dt. Thus, a given change in muscle length produced a greater change in performance in less potentiated muscles. These findings are similar to those from studies of isolated cardiac muscle and illustrate the lack of independence between activational state and muscle length for in situ skeletal muscle.

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