The relationship between oxygen extraction and extravascular mean transit time in the canine heart

1977 ◽  
Vol 55 (3) ◽  
pp. 478-481 ◽  
Author(s):  
R. R. Mildenberger ◽  
A. L'Abbate ◽  
D. T. Zborowska-Sluis ◽  
G. A. Klassen
Keyword(s):  
Transit Time ◽  
Myocardial Oxygen Consumption ◽  
Mean Transit Time ◽  
Time Dependent ◽  
Oxygen Extraction ◽  
Canine Heart ◽  
Myocardial Oxygen Extraction ◽  
The Relationship ◽  
Mean Time ◽  
Critical Link

A significant relationship was observed between myocardial oxygen extraction and the extravascular mean time transit time. This relationship implies that oxygen extraction by the myocardium is a time-dependent process, and emphasizes the critical link between blood flow and myocardial oxygen consumption.

scholarly journals Aggregation in environmental systems: seasonal tracer cycles quantify young water fractions, but not mean transit times, in spatially heterogeneous catchments

2015 ◽  
Vol 12 (3) ◽  
pp. 3059-3103 ◽  
Author(s):  
J. W. Kirchner
Keyword(s):  
Transit Time ◽  
Mean Transit Time ◽  
Strong Nonlinearity ◽  
Isotopic Tracers ◽  
Water Fraction ◽  
Benchmark Tests ◽  
Environmental Systems ◽  
Transit Times ◽  
Event Based ◽  
The Relationship

Abstract. Environmental heterogeneity is ubiquitous, but environmental systems are often analyzed as if they were homogeneous instead, resulting in aggregation errors that are rarely explored and almost never quantified. Here I use simple benchmark tests to explore this general problem in one specific context: the use of seasonal cycles in chemical or isotopic tracers (such as Cl−, δ18O, or δ2H) to estimate timescales of storage in catchments. Timescales of catchment storage are typically quantified by the mean transit time, meaning the average time that elapses between parcels of water entering as precipitation and leaving again as streamflow. Longer mean transit times imply greater damping of seasonal tracer cycles. Thus, the amplitudes of tracer cycles in precipitation and streamflow are commonly used to calculate catchment mean transit times. Here I show that these calculations will typically be wrong by several hundred percent, when applied to catchments with realistic degrees of spatial heterogeneity. This aggregation bias arises from the strong nonlinearity in the relationship between tracer cycle amplitude and mean travel time. I propose an alternative storage metric, the young water fraction in streamflow, defined as the fraction of runoff with transit times of less than roughly 0.2 years. I show that this young water fraction (not to be confused with event-based "new water" in hydrograph separations) is accurately predicted by seasonal tracer cycles within a precision of a few percent, across the entire range of mean transit times from almost zero to almost infinity. Importantly, this relationship is also virtually free from aggregation error. That is, seasonal tracer cycles also accurately predict the young water fraction in runoff from highly heterogeneous mixtures of subcatchments with strongly contrasting transit time distributions. Thus, although tracer cycle amplitudes yield biased and unreliable estimates of catchment mean travel times in heterogeneous catchments, they can be used reliably to estimate the fraction of young water in runoff.

Is Calcium a Coronary Vasoconstrictor In Vivo? 

1998 ◽  
Vol 88 (3) ◽  
pp. 735-743 ◽  
Author(s):  
George J. Crystal ◽  
Xiping Zhou ◽  
Ramez M. Salem
Keyword(s):  
Blood Flow ◽  
Oxygen Consumption ◽  
Coronary Blood Flow ◽  
Myocardial Oxygen Consumption ◽  
Extraction Ratio ◽  
Oxygen Extraction ◽  
Oxygen Extraction Ratio ◽  
Myocardial Oxygen Extraction ◽  
Dose Dependent

Background Calcium produces constriction in isolated coronary vessels and in the coronary circulation of isolated hearts, but the importance of this mechanism in vivo remains controversial. Methods The left anterior descending coronary arteries of 20 anesthetized dogs whose chests had been opened were perfused at 80 mmHg. Myocardial segmental shortening was measured with ultrasonic crystals and coronary blood flow with a Doppler flow transducer. The coronary arteriovenous oxygen difference was determined and used to calculate myocardial oxygen consumption and the myocardial oxygen extraction ratio. The myocardial oxygen extraction ratio served as an index of effectiveness of metabolic vasodilation. Data were obtained during intracoronary infusions of CaCl2 (5, 10, and 15 mg/min) and compared with those during intracoronary infusions of dobutamine (2.5, 5.0, and 10.0 microg/min). Results CaCl2 caused dose-dependent increases in segmental shortening, accompanied by proportional increases in myocardial oxygen consumption. Although CaCl2 also increased coronary blood flow, these increases were less than proportional to those in myocardial oxygen consumption, and therefore the myocardial oxygen extraction ratio increased. Dobutamine caused dose-dependent increases in segmental shortening and myocardial oxygen consumption that were similar in magnitude to those caused by CaCl2. In contrast to CaCl2, however, the accompanying increases in coronary blood flow were proportional to the increases in myocardial oxygen consumption, with the result that the myocardial oxygen extraction ratio remained constant. Conclusions Calcium has a coronary vasoconstricting effect and a positive inotropic effect in vivo. This vasoconstricting effect impairs coupling of coronary blood flow to the augmented myocardial oxygen demand by metabolic vascular control mechanisms. Dobutamine is an inotropic agent with no apparent direct action on coronary resistance vessels in vivo.

scholarly journals Granulocyte Transit from Bone Marrow to Blood

Blood ◽  
1968 ◽  
Vol 31 (2) ◽  
pp. 195-201 ◽  
Author(s):  
MARY A. MALONEY ◽  
HARVEY M. PATT
Keyword(s):  
Bone Marrow ◽  
Transit Time ◽  
Peripheral Blood ◽  
Tritiated Thymidine ◽  
Mean Transit Time ◽  
Cell Loss ◽  
Single Generation ◽  
The Mean ◽  
Mean Time ◽  
Normally Distributed

Abstract The release of granulocytes from marrow to blood was studied in the dog by hourly sampling of the peripheral blood from 48 to 143 hours after injection of tritiated thymidine. Labeled granulocytes were classified by grain count and cells with 30 or more grains were considered to represent the progeny of a single generation. The blood curve for the most heavily labeled cells was corrected for exponential cell loss with a T½ of 6 hours. It was possible in this way to determine that granulocyte release from bone marrow was normally distributed with a mean time from labeling as a myelocyte to appearance in blood of 102 ± 13.8 hours. The mean transit time of segmented granulocytes in marrow is about 50 hours, which is indicative of a much larger pool of mature cells than formerly thought.

Selective blockade of mitochondrial KATPchannels does not impair myocardial oxygen consumption

2001 ◽  
Vol 281 (2) ◽  
pp. H738-H744 ◽  
Author(s):  
Yingjie Chen ◽  
Jay H. Traverse ◽  
Jianyi Zhang ◽  
Robert J. Bache
Keyword(s):  
Oxygen Consumption ◽  
Myocardial Oxygen Consumption ◽  
Atp Synthesis ◽  
Oxygen Extraction ◽  
Channel Blockade ◽  
Inner Mitochondrial Membrane ◽  
Resistance Vessel ◽  
Selective Blockade ◽  
Myocardial Oxygen Extraction ◽  
Matrix Contraction

Opening of mitochondrial ATP-sensitive potassium (KATP) channels has been postulated to prevent inhibition of respiration resulting from matrix contraction during high rates of ATP synthesis. Glibenclamide, which blocks KATP channels on the sarcolemma of vascular smooth muscle cells and myocardial myocytes as well as on the inner mitochondrial membrane, results in a decrease of myocardial oxygen consumption (MV˙o 2) both at rest and during exercise. This study examined whether this represents a primary effect of blockade of mitochondrial KATP channels or occurs secondary to coronary resistance vessel constriction with a decrease of coronary blood flow (CBF) and myocardial oxygen availability. MV˙o 2 was measured at rest and during treadmill exercise in 10 dogs during control conditions, after selective mitochondrial KATP channel blockade with 5-hydroxydecanoate (5-HD), and after nonselective KATPchannel blockade with glibenclamide. During control conditions, exercise resulted in progressive increases of CBF and MV˙o 2. Glibenclamide (50 μg · kg−1 · min−1 ic) resulted in a 17 ± 6% decrease of resting CBF with a downward shift of CBF during exercise and a decrease of coronary venous Po 2, indicating increased myocardial oxygen extraction. In contrast with the effects of glibenclamide, 5-HD (0.7 mg · kg−1 · min−1 ic) had no effect on CBF, MV˙o 2, or myocardial oxygen extraction. These findings suggest that glibenclamide decreased MV˙o 2 by causing resistance vessel constriction with a decrease of CBF and oxygen available to the myocardium rather than to a primary reduction of mitochondrial respiration.

scholarly journals Aggregation in environmental systems – Part 1: Seasonal tracer cycles quantify young water fractions, but not mean transit times, in spatially heterogeneous catchments

2016 ◽  
Vol 20 (1) ◽  
pp. 279-297 ◽  
Author(s):  
J. W. Kirchner
Keyword(s):  
Transit Time ◽  
Mean Transit Time ◽  
Strong Nonlinearity ◽  
Isotopic Tracers ◽  
Water Fraction ◽  
Benchmark Tests ◽  
Environmental Systems ◽  
Transit Times ◽  
Event Based ◽  
The Relationship

Abstract. Environmental heterogeneity is ubiquitous, but environmental systems are often analyzed as if they were homogeneous instead, resulting in aggregation errors that are rarely explored and almost never quantified. Here I use simple benchmark tests to explore this general problem in one specific context: the use of seasonal cycles in chemical or isotopic tracers (such as Cl−, δ18O, or δ2H) to estimate timescales of storage in catchments. Timescales of catchment storage are typically quantified by the mean transit time, meaning the average time that elapses between parcels of water entering as precipitation and leaving again as streamflow. Longer mean transit times imply greater damping of seasonal tracer cycles. Thus, the amplitudes of tracer cycles in precipitation and streamflow are commonly used to calculate catchment mean transit times. Here I show that these calculations will typically be wrong by several hundred percent, when applied to catchments with realistic degrees of spatial heterogeneity. This aggregation bias arises from the strong nonlinearity in the relationship between tracer cycle amplitude and mean travel time. I propose an alternative storage metric, the young water fraction in streamflow, defined as the fraction of runoff with transit times of less than roughly 0.2 years. I show that this young water fraction (not to be confused with event-based "new water" in hydrograph separations) is accurately predicted by seasonal tracer cycles within a precision of a few percent, across the entire range of mean transit times from almost zero to almost infinity. Importantly, this relationship is also virtually free from aggregation error. That is, seasonal tracer cycles also accurately predict the young water fraction in runoff from highly heterogeneous mixtures of subcatchments with strongly contrasting transit-time distributions. Thus, although tracer cycle amplitudes yield biased and unreliable estimates of catchment mean travel times in heterogeneous catchments, they can be used to reliably estimate the fraction of young water in runoff.

Regional differences in erythrocyte transit in normal lungs

1985 ◽  
Vol 59 (4) ◽  
pp. 1266-1271 ◽  
Author(s):  
J. C. Hogg ◽  
B. A. Martin ◽  
S. Lee ◽  
T. McLean
Keyword(s):  
Blood Volume ◽  
Transit Time ◽  
Regional Differences ◽  
Regional Blood Flow ◽  
Mean Transit Time ◽  
Vascular Bed ◽  
Transit Times ◽  
Regional Blood Volume ◽  
The Relationship ◽  
Normal Lungs

We measured regional blood volume and flow in the lungs of nine mongrel dogs. The time taken for the erythrocytes to transit through individual lung regions was calculated from the relationship t = V/Q, where V is blood volume and Q is flow. The data show that the total pulmonary blood volume was 82 +/- 6 ml and that the average time spent in the pulmonary vascular bed was 2.86 +/- 0.31 s. The frequency distribution of the transit times ranged from 0.41 to 6 s in the experiment with the shortest mean transit (1.62 s) and from 0.9 to greater than 20 s in the experiment with the longest mean transit time (4.6 s). The regional data show that the longer transit times were in the upper lung and that expansion of the blood volume as flow increased down the lung prevented an excessive shortening of the transit time. We conclude that increasing regional blood flow is associated with an expansion of regional blood volumes so that the transit times remain relatively constant.

Analysis of the Relationship Between Age and Treatment Response in Migraine

Cephalalgia ◽  
2009 ◽  
Vol 29 (7) ◽  
pp. 772-780 ◽  
Author(s):  
HJ Maas ◽  
M Danhof ◽  
OE Della Pasqua
Keyword(s):  
Transit Time ◽  
Drug Exposure ◽  
Mean Transit Time ◽  
Clinical Observations ◽  
Headache Severity ◽  
Adolescents And Adults ◽  
The Mean ◽  
Using Data ◽  
The Relationship ◽  
Free Status

In migraine, headache severity varies with age. As a consequence, the effectiveness of medication may also depend on a patient's age. The purpose of this study was to assess the combined effect of age and drug treatment on headache characteristics. Using data from clinical trials of sumatriptan in adolescents and adults, we show how the interaction between age and drug exposure can be parameterised as a covariate on a Markov model that describes the decline of headache severity over three clinically defined stages (no relief, relief and pain-free status). The model explains important clinical observations: (i) the rates at which the pain relief and pain-free status were attained were found to be inversely related to age; (ii) in placebo-treated patients, the mean transit time from ‘no relief’ to ‘relief’ is 3 h for young adolescents and increases to 6 h for patients aged ≥ 30 years; and (iii) sumatriptan reduces the transit time to 2 h, irrespective of age. These findings indicate that the therapeutic gain over placebo increases with age. Prospective studies of antimigraine drugs should take this relationship into account when extrapolating efficacy data from adults to adolescents.

Cerebral vascular mean transit time determined by PET and DSC-MRI

2005 ◽  
Vol 25 (1_suppl) ◽  
pp. S676-S676
Author(s):  
Masanobu Ibaraki ◽  
Hiroshi Ito ◽  
Eku Shimosegawa ◽  
Hideto Toyoshima ◽  
Keiichi Ishigame ◽  
...  
Keyword(s):  
Transit Time ◽  
Mean Transit Time ◽  
Dsc Mri ◽  
Cerebral Vascular

Plasminogen Depletion during Streptokinase Treatment or Two-Chain Urokinase Incubation Correlates with Decreased Clot Lysability Ex Vivo and In Vitro

1993 ◽  
Vol 70 (06) ◽  
pp. 0998-1004 ◽  
Author(s):  
Páll T Önundarson ◽  
H Magnús Haraldsson ◽  
Lena Bergmann ◽  
Charles W Francis ◽  
Victor J Marder
Keyword(s):  
Myocardial Infarction ◽  
Ex Vivo ◽  
Time Dependent ◽  
State Variables ◽  
Thrombolytic Treatment ◽  
Direct Proportion ◽  
Plasmin Activity ◽  
Plasma Exposure ◽  
The Relationship

SummaryThe relationship between lytic state variables and ex vivo clot lysability was investigated in blood drawn from patients during streptokinase administration for acute myocardial infarction. A lytic state was already evident after 5 min of treatment and after 20 min the plasminogen concentration had decreased to 24%, antiplasmin to 7% and fibrinogen 0.2 g/1. Lysis of radiolabeled retracted clots in the patient plasmas decreased from 37 ± 8% after 5 min to 21 ± 8% at 10 min and was significantly lower (8 ± 9%, p <0.005) in samples drawn at 20, 40 and 80 min. Clot lysability correlated positively with the plasminogen concentration (r = 0.78, p = 0.003), but not with plasmin activity. Suspension of radiolabeled clots in normal plasma pre-exposed to 250 U/ml two-chain urokinase for varying time to induce an in vitro lytic state was also associated with decreasing clot lysability in direct proportion with the duration of prior plasma exposure to urokinase. The decreased lysability correlated with the time-dependent reduction in plasminogen concentration (r = 0.88, p <0.0005). Thus, clot lysability decreases in conjunction with the development of the lytic state and the associated plasminogen depletion. The lytic state may therefore limit reperfusion during thrombolytic treatment.

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