Effect of tension and timing of contraction on the blood flow of the diaphragm

An open-chest animal model was developed to study the diaphragmatic blood flow (Qdi) during bilateral electrophrenic stimulation. Two patterns of stimulation were used, continuous and intermittent, and both patterns were held at various transdiaphragmatic pressures (Pdi). The contractions were nearly isometric and held at an initial length of supine functional residual capacity (FRC). Qdi was measured in six dogs by catheterizing a branch of the diaphragmatic vein and by counting the blood drops with an infrared cell. During continuous contractions Qdi increased as a function of Pdi up to 70 +/- 12 ml . 100 g-1 . min-1 at 20% Pdimax. At higher levels Qdi decreased progressively and approached zero at 75% of Pdimax. A postcontraction hyperemia occurred at Pdi values greater than 20% Pdimax and increased as a function of Pdi. During intermittent contractions Qdi was a unique function of the diaphragmatic tension-time index (TTdi), a product of Pdi times the duty cycle (contraction time/total cycle time). Qdi increased progressively up to a TTdi of 25% Pdimax and decreased above that point toward zero at TTdi of 80% Pdimax. The postcontraction hyperemia appeared at a TTdi of about 15% of Pdimax and increased as a function of TTdi. It is concluded that Qdi is limited beyond a TTdi of about 20% Pdimax, as indicated by the increase in postcontraction hyperamia, and that Qdi is a function of both Pdi and the timing of contraction.

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Effects of contraction frequency and duty cycle on diaphragmatic blood flow

Journal of Applied Physiology ◽

10.1152/jappl.1985.58.1.265 ◽

1985 ◽

Vol 58 (1) ◽

pp. 265-273 ◽

Cited By ~ 29

Author(s):

B. Buchler ◽

S. Magder ◽

C. Roussos

Keyword(s):

Blood Flow ◽

Duty Cycle ◽

Contraction Time ◽

Phrenic Nerve Stimulation ◽

Contraction Frequency ◽

Time Index ◽

High Duty Cycle ◽

Duty Cycles ◽

Tension Time ◽

Microsphere Method

The effects of diaphragmatic contraction frequency (no. of intermittent tetanic contractions/min) at a given tension-time index and of duty cycle (contraction time/total cycle time) on diaphragmatic blood flow were measured in anesthetized mongrel dogs during bilateral supramaximal phrenic nerve stimulation. Diaphragmatic blood flow was measured by the radionuclide-labeled microsphere method. Contraction frequency was varied between 10 and 160/min at duty cycles of 0.25 and 0.75. Diaphragmatic blood flow increased with contraction frequency from 1.47 +/- 0.13 ml X min-1 X g-1 (mean +/- SE) at an average of 18/min to 2.65 +/- 0.16 ml X min-1 X g-1 at 74/min (P less than 0.01) with a duty cycle of 0.25 and from 1.32 +/- 0.19 ml X min-1 X g-1 at an average of 15/min to 1.96 +/- 0.15 ml X min-1 X g-1 at 80/min (P less than 0.02) with a duty cycle of 0.75. At higher contraction frequencies diaphragmatic blood flow did not increase further at both duty cycles. In addition, diaphragmatic blood flow was higher with a duty cycle of 0.25 than 0.75 at all contraction frequencies. We conclude that frequency of contraction is a major determinant of diaphragmatic blood flow and that high duty cycle impedes diaphragmatic blood flow.

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Diaphragmatic blood flow in the dog

Journal of Applied Physiology ◽

10.1152/jappl.1986.60.2.554 ◽

1986 ◽

Vol 60 (2) ◽

pp. 554-561 ◽

Cited By ~ 5

Author(s):

H. Bark ◽

S. M. Scharf

Keyword(s):

Blood Flow ◽

Duty Cycle ◽

Stimulus Frequency ◽

Phase Flow ◽

Transdiaphragmatic Pressure ◽

Relaxation Phase ◽

Duty Cycles ◽

Tension Time ◽

Phrenic Artery ◽

Electromagnetic Flow Probe

In anesthetized mongrel dogs we measured the blood flow in the left phrenic artery (Qdi), using an electromagnetic flow probe, before and during supramaximal phrenic nerve stimulation (pacing). This was done at constant respiratory rate (24/min) but at three different stimulation frequencies at a duty cycle of 0.4 (20, 50, and 100 Hz) and at three different duty cycles at a stimulation frequency of 50 Hz (duty cycle = 0.2, 0.4, and 0.8). Qdi was unchanged during diaphragm contraction until transdiaphragmatic pressure (Pdi) was greater than approximately 11 cmH2O, whereafter it began to decrease, reaching zero at Pdi approximately 20 cmH2O. Thus, when Pdi was greater than 21 cmH2O, all flow occurred during relaxation. Qdi averaged over the entire respiratory cycle (Qt) was less at duty cycle = 0.8 than under the other conditions. This was because of decreasing length of relaxation phase rather than a difference of relaxation phase flow (Qr), which was maximal during all conditions of phrenic stimulation. During pacing-induced fatigue, Qt actually rose slightly as Pdi fell. This was due to an increase in contraction phase flow while Qr remained constant. The relationship between Qt and tension-time index was not unique but varied according to the different combinations of duty cycle and stimulus frequency.

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Bioenergetics of contracting skeletal muscle after partial reduction of blood flow

Journal of Applied Physiology ◽

10.1152/jappl.1998.84.6.1882 ◽

1998 ◽

Vol 84 (6) ◽

pp. 1882-1888 ◽

Cited By ~ 28

Author(s):

Michael C. Hogan ◽

L. Bruce Gladden ◽

Bruno Grassi ◽

Creed M. Stary ◽

Michele Samaja

Keyword(s):

Blood Flow ◽

Steady State ◽

Force Production ◽

Normal Blood ◽

Normal Flow ◽

Contracting Muscle ◽

Time Index ◽

Atp Concentration ◽

Tension Time ◽

Normal Blood Flow

The purpose of this study was to examine the bioenergetics and regulation of O2 uptake (V˙o 2) and force production in contracting muscle when blood flow was moderately reduced during a steady-state contractile period. Canine gastrocnemius muscle ( n = 5) was isolated, and 3-min stimulation periods of isometric, tetanic contractions were elicited sequentially at rates of 0.25, 0.33, and 0.5 contractions/s (Hz) immediately followed by a reduction of blood flow [ischemic (I) condition] to 46 ± 3% of the value obtained at 0.5 Hz with normal blood flow. TheV˙o 2 of the contracting muscle was significantly ( P < 0.05) reduced during the I condition [6.5 ± 0.8 (SE) ml ⋅ 100 g−1 ⋅ min−1] compared with the same stimulation frequency with normal flow (11.2 ± 1.5 ml ⋅ 100 g−1 ⋅ min−1), as was the tension-time index (79 ± 12 vs. 123 ± 22 N ⋅ g−1 ⋅ min−1, respectively). The ratio ofV˙o 2 to tension-time index remained constant throughout all contraction periods. Muscle phosphocreatine concentration, ATP concentration, and lactate efflux were not significantly different during the I condition compared with the 0.5-Hz condition with normal blood flow. However, at comparable rates of V˙o 2 and tension-time index, muscle phosphocreatine concentration and ATP concentration were significantly less during the I condition compared with normal-flow conditions. These results demonstrate that, in this highly oxidative muscle, the normal balance of O2 supply to force output was maintained during moderate ischemia by downregulation of force production. In addition, 1) the minimal disruption in intracellular homeostasis after the initiation of ischemia was likely a result of steady-state metabolic conditions having already been activated, and 2) the difference in intracellular conditions at comparable rates ofV˙o 2 and tension-time index between the normal flow and I condition may have been due to altered intracellular O2 tension.

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Effects of intensive exercise training on myocardial performance and coronary blood flow

Journal of Applied Physiology ◽

10.1152/jappl.1980.49.3.444 ◽

1980 ◽

Vol 49 (3) ◽

pp. 444-449 ◽

Cited By ~ 31

Author(s):

R. J. Barnard ◽

H. W. Duncan ◽

K. M. Baldwin ◽

G. Grimditch ◽

G. D. Buckberg

Keyword(s):

Blood Flow ◽

Coronary Blood Flow ◽

Diastolic Pressure ◽

Systolic Pressure ◽

Work Capacity ◽

Left Ventricular ◽

Maximum Exercise ◽

Time Index ◽

Significant Difference ◽

Tension Time

Five instrumented and eight noninstrumented dogs were progressively trained for 12-18 wk on a motor-driven treadmill. Data were compared with 14 instrumented and 8 noninstrumented control dogs. Gastrocnemius malate dehydrogenase activity was significantly increased in the trained dogs (887 +/- 75 vs. 667 +/- 68 mumol . g-1 . min-1). The trained dogs also showed significant increases in maximum work capacity, cardiac output (7.1 +/- 0.5 vs. 9.1 +/- 0.7 1/min), stroke volume (25.9 +/- 2.0 vs. 32.0 +/- 2.0 ml/beat), and left ventricular (LV) positive dP/dtmax (9,242 +/- 405 vs. 11,125 +/- 550 Torr/s). Negative dP/dtmax was not significantly different. Peak LV systolic pressure increased with exercise, but there was no significant difference between the trained and control dogs. LV end-diastolic pressure did not change with exercise and was the same in both groups. Tension-time index was lower in the trained dogs at rest and submaximum exercise (9.7 km/h, 10%) but was not different at maximum exercise. Diastolic pressure-time index was significantly higher in the trained dogs at rest and during submaximum exercise but was not different at maximum exercise. LV coronary blood flow was significantly reduced at rest (84 +/- 4 vs. 67 +/- 6 mo . min-1 . 100 g-1) and during submaximum exercise (288 +/- 24 vs. 252 +/- 8 ml . min-1 . 100 g-1). During maximum exercise flow was not significantly different (401 +/- 22 vs. 432 +/- 11 ml . min-1 . 100 g-1) between the control and trained groups. The maximum potential for subendocardial flow was unchanged with training despite the development of mild hypertrophy.

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Is the blood flow response to a single contraction determined by work performed?

Journal of Applied Physiology ◽

10.1152/japplphysiol.00779.2003 ◽

2004 ◽

Vol 96 (6) ◽

pp. 2146-2152 ◽

Cited By ~ 30

Author(s):

Jason J. Hamann ◽

John B. Buckwalter ◽

Philip S. Clifford ◽

J. Kevin Shoemaker

Keyword(s):

Blood Flow ◽

Forearm Blood Flow ◽

Voluntary Contraction ◽

Single Muscle ◽

Peak Tension ◽

Blood Flow Response ◽

Time Index ◽

Flow Response ◽

Constant Tension ◽

Tension Time

Nine healthy volunteers performed a series of single handgrip isometric contractions to test the hypothesis that the blood flow response to a contraction is determined solely by the tension-time index (isometric analog of work). Contractions were performed in duplicate at 15, 30, and 60% of maximal voluntary contraction (MVC) at durations of 0.5, 1, and 2 s. Forearm blood flow (FBF) was measured beat by beat by using Doppler ultrasound. Peak FBF responded in a graded fashion to graded increases in peak tension with contraction time held constant (35, 56, and 90 ml/min for 15, 30, and 60% MVC for 1 s, respectively). When tension was kept constant, peak FBF responded in a graded fashion to graded increases in duration (77, 90, and 97 ml/min for 60% MVC for 0.5, 1, and 2 s). With a constant tension-time index, peak FBF responded in a graded fashion to graded increases in peak tension (48, 56, and 77 ml/min for 15% MVC/2 s, 30% MVC/1 s, and 60% MVC/0.5 s). Similar trends were also observed for total postcontraction hyperemia. Blood flow increased regardless of whether the change in tension-time index was accomplished by an increase in tension or duration of contraction. However, with a constant tension-time index, the change in blood flow was related to the peak tension developed. Our results suggest that the blood flow response to a single muscle contraction is not determined solely by the work performed (tension-time index) but also by the number of muscle fibers recruited.

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Effect of contraction frequency on the contractile and noncontractile phases of muscle venous blood flow

Journal of Applied Physiology ◽

10.1152/japplphysiol.00226.2003 ◽

2003 ◽

Vol 95 (3) ◽

pp. 1139-1144 ◽

Cited By ~ 15

Author(s):

Michael C. Hogan ◽

Bruno Grassi ◽

Michele Samaja ◽

Creed M. Stary ◽

L. B. Gladden

Keyword(s):

Blood Flow ◽

Metabolic Rate ◽

Duty Cycle ◽

Venous Blood ◽

Venous Blood Flow ◽

Contraction Frequency ◽

Time Integral ◽

Tension Time ◽

Percent Contribution ◽

Rhythmic Contractions

The purpose of this study was to test the hypothesis that increasing muscle contraction frequency, which alters the duty cycle and metabolic rate, would increase the contribution of the contractile phase to mean venous blood flow in isolated skeletal muscle during rhythmic contractions. Canine gastrocnemius muscle ( n = 5) was isolated, and 3-min stimulation periods of isometric, tetanic contractions were elicited sequentially at rates of 0.25, 0.33, and 0.5 contractions/s. The O2 uptake, tension-time integral, and mean venous blood flow increased significantly ( P < 0.05) with each contraction frequency. Venous blood flow during both the contractile (106 ± 6, 139 ± 8, and 145 ± 8 ml·100 g-1·min-1) and noncontractile phases (64 ± 3, 78 ± 4, and 91 ± 5 ml·100 g-1·min-1) increased with contraction frequency. Although developed force and duration of the contractile phase were never significantly different for a single contraction during the three contraction frequencies, the amount of blood expelled from the muscle during an individual contraction increased significantly with contraction frequency (0.24 ± 0.03, 0.32 ± 0.02, and 0.36 ± 0.03 ml·N-1·min-1, respectively). This increased blood expulsion per contraction, coupled with the decreased time in the noncontractile phase as contraction frequency increased, resulted in the contractile phase contribution to mean venous blood flow becoming significantly greater (21 ± 4, 30 ± 4, and 38 ± 6%) as contraction frequency increased. These results demonstrate that the percent contribution of the muscle contractile phase to mean venous blood flow becomes significantly greater as contraction frequency (and thereby duty cycle and metabolic rate) increases and that this is in part due to increased blood expulsion per contraction.

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Tension-time index, fatigue, and energetics in isolated rat diaphragm: a new experimental model

Journal of Applied Physiology ◽

10.1152/japplphysiol.00237.2003 ◽

2004 ◽

Vol 96 (1) ◽

pp. 89-95 ◽

Cited By ~ 7

Author(s):

Paul F. Klawitter ◽

Thomas L. Clanton

Keyword(s):

Duty Cycle ◽

Mechanical Load ◽

Contractile Function ◽

Creatine Phosphate ◽

Energy Utilization ◽

Fatigue Properties ◽

Muscle Energetics ◽

Contracting Muscle ◽

Time Index ◽

Tension Time

The tension-time index (TTI) has been used to estimate mechanical load, energy utilization, blood flow, and susceptibility to fatigue in contracting muscle. The TTI can be defined, for a rhythmically contracting muscle, as the product of average force development divided by maximum tetanic force times duty cycle [contraction time ÷ (contraction + relaxation time)]. In this study, the TTI concept was applied to isolated diaphragm via a method that allowed TTI to be clamped at a predetermined value. The hypothesis tested was that, at constant TTI, muscle energetics and the extent of fatigue would vary with stimulation frequency. Isolated diaphragm strips were stimulated at 25, 50, 75, or 100 Hz for 4 min, one per second. Duty cycle was continuously adjusted to maintain TTI at 0.07, which was near the highest TTI tolerated for 4 min, at 20-Hz stimulation. At the end of the fatigue run, muscles were either immediately frozen for determination ATP, creatine, and creatine phosphate concentrations ( n = 6) or stimulated for evaluation of low- and high-frequency fatigue ( n = 5). Results demonstrated no difference in the extent of fatigue or in the final ATP and creatine phosphate concentrations between groups. Large within-run increases in duty cycle were required at low stimulation frequencies, but only small increases were required at the highest frequencies. The results demonstrate that, at a constant TTI, similar fatigue properties predominate at all stimulation frequencies with no clear distinction between high- and low-frequency fatigue. The method of clamping TTI during fatigue may be useful for evaluating energetics and contractile function between treatment groups in isolated muscle when treatment influences baseline contractile characteristics.

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Relationship of changes in diaphragmatic muscle blood flow to muscle contractile activity

Journal of Applied Physiology ◽

10.1152/jappl.1987.62.1.291 ◽

1987 ◽

Vol 62 (1) ◽

pp. 291-299 ◽

Cited By ~ 12

Author(s):

H. Bark ◽

G. S. Supinski ◽

J. C. Lamanna ◽

S. G. Kelsen

Keyword(s):

Blood Flow ◽

Duty Cycle ◽

Contractile Activity ◽

Muscle Blood Flow ◽

Muscle Tension ◽

Mechanically Ventilated ◽

Diaphragmatic Muscle ◽

Tension Time ◽

Relationship Of ◽

Muscle Contractile

The effect of increases in diaphragmatic muscle contractile activity on diaphragm blood flow remains unclear. The present study examined the effect of electrically induced isometric diaphragmatic muscle contractions on diaphragmatic blood flow. Studies were performed on diaphragmatic muscle strips prepared in anesthetized mechanically ventilated dogs. Diaphragmatic contractile activity was quantitated as the tension-time index (TTI) (i.e., the product of tension magnitude and duration). Blood flow to the strip (Qdi) was measured from the volume of the phrenic venous effluent using a drop counter. The separate effects on Qdi of 30-s periods of continuous and rhythmic contractions were examined. Qdi increased with increases in TTI and peaked at a TTI of 20–30% of maximum after which Qdi fell progressively with further increases in TTI. At levels of TTI greater than 30%, the pattern of muscle contraction significantly affected blood flow. Qdi was significantly lower during activity and the postcontraction hyperemia significantly greater at a given TTI when contractions were continuous than when contractions were intermittent. Above a TTI of 30%, Qdi during contraction decreased linearly with increases in duty cycle and curvilinearly with increases in tension. We conclude that during isometric diaphragmatic contractions, diaphragmatic blood flow may become mechanically impeded, and the magnitude of the impediment in blood flow depends on the pattern of diaphragmatic contractions. With increases in contractile activity above a critical level, changes in duty cycle exert progressively greater effects on diaphragmatic blood flow than changes in muscle tension.

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