Optimal diaphragmatic blood perfusion

1992 ◽  
Vol 72 (1) ◽  
pp. 149-157 ◽  
Author(s):  
F. Hu ◽  
A. Comtois ◽  
A. E. Grassino
Keyword(s):  
Time Course ◽  
Blood Perfusion ◽  
Fatigue Threshold ◽  
Transdiaphragmatic Pressure ◽  
Relaxation Phase ◽  
Time Index ◽  
Duty Cycles ◽  
Parabolic Function ◽  
Tension Time ◽  
Phrenic Artery

The intrabreath time course of phrenic artery blood perfusion (Qpha) was studied in five anesthetized dogs. The diaphragm was paced with submaximal levels of stimulation at various duty cycles (DC) to achieve tension-time index below and above the fatigue threshold (0.03–0.60). Left Qpha was measured via Doppler technique during control (inactive diaphragm) and during two submaximal levels of bilateral phrenic nerve stimulation sustained for 1 min. Measurements were done when Qpha reached steady state in each run. The frequency of pacing of each run was 10/min, and the DC ranged from 0.1 to 0.9 in 0.1 increments. Shortening of costal and crural segments was measured by sonomicrometry. It was found that Qpha during the diaphragmatic contraction phase (QphaC) was a sigmoidal function of DC and was not affected by the levels of transdiaphragmatic pressure (Pdi) explored (34–64% of maximal Pdi). Qpha during the diaphragmatic relaxation phase (QphaR) was a parabolic function of the DC, reaching an optimal value at DC of approximately 0.3 at any given Pdi. QphaR increased significantly with the preceding level of Pdi. QphaT (the sum of QphaC and QphaR) was a parabolic function of DC, reaching peak values at DC of 0.4–0.6 and then decreasing. This function was similar at two levels of Pdi. Post-pacing hyperemia was directly related to tension-time index greater than 0.20.

Diaphragmatic blood flow in the dog

1986 ◽  
Vol 60 (2) ◽  
pp. 554-561 ◽  
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.

Contraction-dependent modulations in regional diaphragmatic blood flow

1990 ◽  
Vol 68 (5) ◽  
pp. 2019-2028 ◽  
Author(s):  
F. Hu ◽  
A. Comtois ◽  
A. E. Grassino
Keyword(s):  
Blood Flow ◽  
Duty Cycle ◽  
Time Course ◽  
Azygos Vein ◽  
Transdiaphragmatic Pressure ◽  
Parabolic Function ◽  
Internal Mammary ◽  
Anesthetized Dogs ◽  
Phrenic Artery ◽  
Artery Flow

Blood flow (Q) of the diaphragm was measured simultaneously with Doppler probes placed on diaphragmatic veins and an artery and by direct volumetric measurements obtained from cannulation of diaphragmatic blood vessels. The Doppler converting coefficients obtained were 6.27, 7.25, 4.21, and 41.07 ml.min-1.kHz-1 for left phrenic artery flow (Qpha), phrenic vein flow (Qphv), internal mammary vein flow (Qimv), and azygos vein flow (Qazv), respectively. The time course of Qpha, Qphv, Qimv, and Qazv after imposed patterns of diaphragmatic contraction was measured in nine anesthetized dogs. Each pattern consisted of various combinations of transdiaphragmatic pressure (Pdi), frequency of pacing (f), and duty cycle obtained by bilateral phrenic nerve stimulation. The dogs were prepared with chests open and loosely casted abdomens. Qpha, Qphv, Qimv, and Qazv were measured at rest (control, passive diaphragm, mechanical ventilation) and at two submaximal levels of stimulation (30 and 60% of Pdimax). The f was 10 or 30 cycles/min and the duty cycle was 0.25, 0.50, and 0.75. The results show 1) Qpha, Qphv, Qimv, and Qazv reached stable values (equilibration) after 30-36 s of pacing; 2) the steady Qpha, Qphv, and Qimv were linearly related to Pdi, and they were related by a parabolic function to duty cycle, whereas Qazv was not significantly affected by Pdi and increased linearly as a function of the duty cycle; 3) the diaphragmatic blood drainage was approximately 60% through the intercostal veins leading into the azygos trunk, 25% through the phrenic vein, and 15% through the internal mammary vein during pacing of the diaphragm at a duty cycle of 0.50 and 60% Pdimax; and 4) for a given pacing pattern, Qpha and Qphv increased with f, but Qimv and Qazv did not.

Changes in relaxation rate with diaphragmatic fatigue in humans

1983 ◽  
Vol 54 (5) ◽  
pp. 1353-1360 ◽  
Author(s):  
S. A. Esau ◽  
F. Bellemare ◽  
A. Grassino ◽  
S. Permutt ◽  
C. Roussos ◽  
...  
Keyword(s):  
Relaxation Rate ◽  
Time Course ◽  
Low Frequency ◽  
Base Line ◽  
Experimental Setting ◽  
Inspiratory Time ◽  
Transdiaphragmatic Pressure ◽  
Diaphragmatic Fatigue ◽  
Tension Time ◽  
Male Subjects

Maximum relaxation rate (MRR) and the time constant of relaxation (tau) of transdiaphragmatic pressure (Pdi) was measured in four male subjects and compared with the high-to-low frequency ratio (H/L) of the diaphragmatic electromyogram (EMG) as a predictor of diaphragmatic fatigue. Pdi and inspiratory time-to-total breath duration ratios (TI/TT) were varied, and TT and tidal volume were held constant; inspiratory resistances were used to increase Pdi. Studies were performed at various tension-time indices (TTdi = Pdi/Pdimax X TI/TT). Base-line MRR/Pdi was 0.0100 +/- 0.0004 (SE) ms-1, and baseline tau was 53.2 +/- 3.2 ms. At TTdi greater than 0.20, MRR and H/L decreased and tau increased, with maximum changes at the highest TTdi. At TTdi less than 0.20, there was no change in H/L, MRR, or tau. The time course of changes in H/L correlated with those of MRR and tau under fatiguing conditions. In this experimental setting, change in relaxation rate was as useful a predictor of diaphragmatic fatigue as fall in H/L of the diaphragmatic EMG.

Effects of contraction frequency and duty cycle on diaphragmatic blood flow

1985 ◽  
Vol 58 (1) ◽  
pp. 265-273 ◽  
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.

Validation of a noninvasive tension-time index of inspiratory muscles

1995 ◽  
Vol 78 (2) ◽  
pp. 646-653 ◽  
Author(s):  
M. Ramonatxo ◽  
P. Boulard ◽  
C. Prefaut
Keyword(s):  
Chronic Obstructive Pulmonary Disease ◽  
Pulmonary Disease ◽  
Transpulmonary Pressure ◽  
Chronic Obstructive ◽  
Obstructive Pulmonary Disease ◽  
Transdiaphragmatic Pressure ◽  
Time Index ◽  
Inspiratory Muscles ◽  
Tension Time ◽  
Pressure Swing

The aim of this study was to validate a noninvasive tension-time index (TT) for all the inspiratory muscles estimated from the measurement of mouth occlusion pressure (P0.1), i.e., TT of inspiratory muscles (TTmus = PI/PImax x TI/TT, where PI is mean inspiratory pressure, PImax is maximal PI, TI is time of muscle contraction, and TT is total time of respiratory cycle) compared with TT of the diaphragm (TTdi = Pdi/Pdimax x TI/TT, where Pdi is mean transdiaphragmatic pressure and Pdimax is maximal Pdi). PI was estimated as PI = 5 P0.1 x TI. Eleven patients with chronic obstructive pulmonary disease and seven normal subjects were studied at rest in the sitting position. After 5 min of steady state, we measured breathing pattern, gastric and esophageal pressures, Pdi, mean inspiratory transpulmonary pressure swing, PImax, and Pdimax. By linear regression analysis, significant positive correlations were found between PI and mean inspiratory transpulmonary pressure swing, PI and Pdi, PImax and Pdimax, and PI/PImax and Pdi/Pdimax, with P < 0.001 for all subjects combined. These led to the highly significant correlation between TTmus and TTdi for all subjects combined (TTmus = 2.1 TTdi + 0.012; r = 0.97; P < 0.001) and for patients only (TTmus = 2.0 TTdi + 0.024; r = 0.97; P < 0.001). Therefore, patterns of breathing that lie near fatigue thresholds can be identified with TTmus or TTdi. In conclusion, noninvasive and clinically easily determined TTmus seems valid for situating patients of chronic obstructive pulmonary disease in reference to the inspiratory muscle fatigue.

Abstract 2432: Effect of Left Ventricular Systolic Dysfunction on Wasted Left Ventricular Energy and Tension-Time Index

Circulation ◽  
2008 ◽  
Vol 118 (suppl_18) ◽  
Author(s):  
Scott J Denardo ◽  
Wilmer W Nichols
Keyword(s):  
Heart Failure ◽  
Left Ventricular Systolic Dysfunction ◽  
Systolic Dysfunction ◽  
Aortic Pressure ◽  
Left Ventricular ◽  
Systemic Hypertension ◽  
Pressure Waveform ◽  
Ventricular Systolic Dysfunction ◽  
Time Index ◽  
Tension Time

Information obtained from the aortic pressure waveform is affected by age, physical condition, systemic hypertension, diabetes mellitus and coronary artery disease. However, alterations in the aortic pressure waveform in patients (pts) with heart failure and left ventricular systolic dysfunction (LVSD) have not been fully described, including a description of the effect on wasted LV pressure energy and tension-time index. Non-invasive high-fidelity radial artery tonometry was used for data acquisition, and a mathematical transfer function used to generate aortic pressure waveforms (see figure ). Pulse wave analysis (PWA) of the aortic pressure waveform was used to obtain information associated with LV/vascular coupling in 23 pts age 55±9.5 yrs with LVSD (mean LV ejection fraction, 22±6%) and compared to data collected from 23 normal subjects matched for age, gender, height, weight and heart rate. Measurements obtained using PWA in heart failure pts with LVSD demonstrate decreased wasted LV energy and tension time index, consistent with poor LV mechanical performance, in addition to decreased unaugmented pressure, pulse pressure, ejection duration and augmentation index. Further standardization of these aortic pressure waveform findings in heart failure pts may allow for the clinical use of arterial PWA to non-invasively estimate LVSD.

Sustainable inspiratory pressures over varying flows, volumes, and duty cycles

1990 ◽  
Vol 69 (5) ◽  
pp. 1875-1882 ◽  
Author(s):  
T. L. Clanton ◽  
B. T. Ameredes ◽  
D. B. Thomson ◽  
M. W. Julian
Keyword(s):  
Tidal Volume ◽  
Duty Cycle ◽  
Dynamic Pressure ◽  
Breathing Patterns ◽  
Transdiaphragmatic Pressure ◽  
Lung Inflation ◽  
Duty Cycles ◽  
Pressure Time ◽  
Endurance Tests ◽  
Normal Humans

This study identifies the influence of flow (0.5-2.0 l/s), duty cycle (0.29-0.57), and tidal volume (1.08-2.16 liters) on sustainable inspiratory muscle pressure (Pmus) and transdiaphragmatic pressure (Pdi) development. Six normal humans performed endurance tests using an isoflow method, which allowed for measurements of maximum dynamic Pmus and Pdi, with controlled lung inflation. The subjects repeated maximum dynamic voluntary inspirations for 10 min. Pressures dropped exponentially from initial measurements at rest (Pmusi or Pdi) to sustainable values (Pmus or Pdis). As flow and tidal volume increased, maximum initial and sustainable pressures decreased significantly. However, at a constant duty cycle, the sustainable dynamic pressures remained predictable fractions of initial dynamic pressures (i.e., Pmuss/Pmusi or Pdis/Pdii), regardless of changes in flow and tidal volume. In contrast, as duty cycle increased, the sustainable fractions significantly decreased for both Pdi and Pmus. For example, at a duty cycle of 0.29, Pmuss/Pmusi was approximately 0.71, and at a duty cycle of 0.57, Pmuss/Pmusi was approximately 0.62. Calculated sustainable pressure-time indexes varied significantly between 0.16 to 0.32 for Pmus and 0.11 to 0.22 for Pdi over the breathing patterns studied. We conclude that 1) the maximum dynamic pressure that can be sustained at a given duty cycle is a predictable fraction of the maximum dynamic pressure that can be generated at rest when measured under the same conditions of inspiration and 2) the sustainable fraction of initial dynamic pressure significantly decreases with increasing duty cycle.

scholarly journals Bioenergetics of contracting skeletal muscle after partial reduction of blood flow

1998 ◽  
Vol 84 (6) ◽  
pp. 1882-1888 ◽  
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.

Velocity-length-time relations in canine tracheal smooth muscle

1988 ◽  
Vol 64 (5) ◽  
pp. 2053-2057 ◽  
Author(s):  
C. Y. Seow ◽  
N. L. Stephens
Keyword(s):  
Smooth Muscle ◽  
Goodness Of Fit ◽  
Time Course ◽  
Muscle Length ◽  
Tracheal Smooth Muscle ◽  
Minimum Length ◽  
Shortening Velocity ◽  
Contracting Muscle ◽  
Parabolic Function ◽  
The Moment

Zero-load velocity (V0) as a function of the length of canine tracheal smooth muscle was obtained by applying zero-load clamps to isotonically contracting muscle under various loads. The load clamps were applied at a specific time after onset of contraction. The magnitude of the isotonic load therefore determines the length of the muscle at the moment of release or at the moment the unloaded shortening velocity was measured. A family of such V0-muscle length (L) curves was obtained at 1-s intervals in the time course of contraction. The V0-L curve was fitted by a parabolic function with satisfactory goodness of fit. The maximum shortening velocity at optimum muscle length varied with time, but the minimum length at which V0 diminished to zero was time independent.

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

1980 ◽  
Vol 49 (3) ◽  
pp. 444-449 ◽  
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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