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.

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.

Effects of tension, duty cycle, and arterial pressure on diaphragmatic blood flow in dogs

1989 ◽  
Vol 66 (2) ◽  
pp. 968-976 ◽  
Author(s):  
S. N. Hussain ◽  
C. Roussos ◽  
S. Magder
Keyword(s):  
Blood Flow ◽  
Arterial Pressure ◽  
Duty Cycle ◽  
Phrenic Nerve Stimulation ◽  
Gradual Decline ◽  
Transdiaphragmatic Pressure ◽  
Duty Cycles ◽  
Severe Hypotension ◽  
Internal Mammary ◽  
Pressure Part

We investigated the selective effects of changes in transdiaphragmatic pressure (Pdi) and duty cycle on diaphragmatic blood flow in supine dogs at normal arterial pressure (N), moderate hypotension (MH), and severe hypotension (SH) [mean arterial pressure (Part) of 116, 75, and 50 mmHg, respectively]. The diaphragm was paced at a rate of 12/min by bilateral phrenic nerve stimulation. Left phrenic (Qphr-T) and left internal mammary (Qim-T) arterial flows were measured by electromagnetic flow probes. Changes in Pdi and duty cycle were achieved by changing the stimulation frequencies and the duration of contraction, whereas Part changes were produced by bleeding. With N and at a duty cycle of 0.5, incremental increases in Pdi produced peaks in Qphr-T and Qim-T at 30% maximum diaphragmatic pressure (Pdimax) with a gradual decline at higher Pdi. With MH and SH, blood flow peaked at 10% Pdimax. At any given Pdi, blood flow was lower with MH and SH in comparison to N. The effect of duty cycle was tested at two levels of Pdi. With N and at low Pdi (25% Pdimax), blood flow rose progressively with increases in duty cycle, whereas at moderate Pdi level (50% Pdimax) blood flow peaked at a duty cycle of 0.3, with no increase thereafter. With MH, blood flow at low Pdi rose linearly with increasing duty cycle but to a lesser extent than with N, and at a moderate Pdi flow peaked at a duty cycle of 0.3. With SH, blood flow at low and moderate Pdi was limited at duty cycles greater than 0.3 and 0.1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

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.

Autoregulation of diaphragmatic blood flow in dogs

1988 ◽  
Vol 64 (1) ◽  
pp. 329-336 ◽  
Author(s):  
S. N. Hussain ◽  
C. Roussos ◽  
S. Magder
Keyword(s):  
Blood Flow ◽  
Venous Blood ◽  
Muscular Activity ◽  
Work Load ◽  
Quiet Breathing ◽  
Transdiaphragmatic Pressure ◽  
Arterial Blood ◽  
Normal Ranges ◽  
Phrenic Artery ◽  
Spontaneously Breathing

In eight anesthetized spontaneously breathing dogs, we determined whether diaphragmatic blood flow is dependent on arterial blood pressure (Pa) or whether it is autoregulated. We also determined whether diaphragmatic muscular activity affects the degree of autoregulation. We measured blood flow through the left phrenic artery (Qphr) with an electromagnetic flow probe and decreased Pa in steps by controlled hemorrhage. Phrenic venous blood was sampled to allow the calculation of diaphragmatic O2 consumption (VO2phr). Diaphragmatic energy demands were varied by using three inspiratory resistances (R1, R2, and R3), which increased peak transdiaphragmatic pressure two-, three-, and fourfold, respectively. During quiet breathing, Qphr was independent of Pa between Pa of 90 and 120 mmHg (i.e., plateau of pressure-flow relation), but at lower Pa, Qphr was directly related to Pa. During inspiratory loading, the Qphr plateau ended at a higher Pa than with quiet breathing, but within the normal ranges of Pa there still was a plateau. VO2phr at a given work load was constant between Pa of 70 and 120 mmHg, but at Pa of 50-55 mmHg, VO2phr declined with all work loads. We conclude that in spontaneously breathing dogs 1) Qphr is autoregulated over the normal range of blood pressures and 2) VO2phr is maintained over wider ranges of Pa than Qphr.

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

2003 ◽  
Vol 95 (3) ◽  
pp. 1139-1144 ◽  
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.

An ATP-sensitive potassium channel blocker decreases diaphragmatic circulation in anesthetized dogs

1994 ◽  
Vol 77 (1) ◽  
pp. 127-134 ◽  
Author(s):  
A. Comtois ◽  
C. Sinderby ◽  
N. Comtois ◽  
A. Grassino ◽  
J. M. Renaud
Keyword(s):  
Blood Flow ◽  
Phrenic Nerve ◽  
Spontaneous Breathing ◽  
Arterial Blood Flow ◽  
Control Group ◽  
Transdiaphragmatic Pressure ◽  
K Channels ◽  
Arterial Blood ◽  
Tension Time ◽  
Experimental Group

The goal of this study was to determine whether in the dog ATP-sensitive K+ channels blocked with glibenclamide affect diaphragmatic blood flow [phrenic arterial blood flow (Qpa)] during both spontaneous breathing at rest and increased diaphragmatic activity. A control group (no glibenclamide; n = 4) and an experimental group (50 mg/kg of glibenclamide; n = 5) were studied. During spontaneous breathing at rest, Qpa was 15.0 ml.min-1 x 100 g-1 and decreased by 5% in the presence of glibenclamide. Diaphragmatic pacing (30 min-1) generated by phrenic nerve pacing produced an initial diaphragmatic tension-time index of 0.25 in both groups. A 50% decay in transdiaphragmatic pressure was reached at 165 s in the experimental group compared with 421 s in the control group. Diaphragmatic pacing increased Qpa by 46% in the experimental group and 65% in the control group, yielding a 63% greater vascular resistance in the experimental group. Phrenic vein K+ content at rest was unchanged by the presence of glibenclamide, being 3.6 +/- 0.16 mmol/l compared with 3.5 +/- 0.19 mmol/l in the control group. Phrenic nerve pacing in the control group produced a 13% increase in phrenic vein K+ content, whereas in the experimental group a 16% decrease was observed. We suggest that ATP-sensitive K+ channels play an important role in the modulation of Qpa.

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

1987 ◽  
Vol 62 (1) ◽  
pp. 291-299 ◽  
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.

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

1983 ◽  
Vol 54 (6) ◽  
pp. 1597-1606 ◽  
Author(s):  
F. Bellemare ◽  
D. Wight ◽  
C. M. Lavigne ◽  
A. Grassino
Keyword(s):  
Animal Model ◽  
Blood Flow ◽  
Duty Cycle ◽  
Cycle Time ◽  
Contraction Time ◽  
Initial Length ◽  
Time Index ◽  
Tension Time ◽  
Residual Capacity ◽  
Intermittent Contractions

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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