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Results for “Consumption--determinants”

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PubMed1983

Effects of verapamil on coronary hemodynamic function and vasomobility relative to its mechanism of antianginal action.

The effect of intravenous verapamil on systemic and coronary hemodynamic function was studied at cardiac catheterization in 12 patients with coronary artery disease. Verapamil was administered as a 2-minute bolus (0.145 mg/kg) followed by an infusion (0.005 mg/kg/min). Cardiac output and coronary sinus blood flow were measured by thermodilution techniques. Caliber of the large coronary arteries and of diseased segments was determined from the coronary angiogram using a computer-assisted method. Verapamil reduced mean arterial pressure 14% (p less than 0.001), systemic vascular resistance 21% (p less than 0.01), and stroke work index 16% (p less than 0.001). Coronary vascular resistance decreased 24% (p less than 0.01) with a small increase in coronary sinus blood flow (+13%, difference not significant [NS]). Myocardial oxygen consumption determined in 5 patients showed no significant change with verapamil. Luminal area in 39 coronary lesions was measured in the "normal" portion of the diseased segment and at its maximal constriction, and an estimate of flow resistance in the stenosis was computed. Overall, 50% of "normal" and of diseased coronary segments dilated significantly with verapamil. Stenosis dilation resulted in an average 14% reduction (p less than 0.01) in estimated flow resistance. In 8 patients, the luminal changes (n = 27) induced by sublingual nitroglycerin were compared with those induced by verapamil. Nitroglycerin induced a significantly greater increase in coronary caliber in both normal and diseased segments; estimated stenosis flow resistance decreased 28% with nitroglycerin compared with 14% with verapamil (p less than 0.01). Thus, verapamil moderately dilates the systemic and coronary small vessel resistance bed without apparently increasing myocardial metabolic demand. Furthermore, verapamil mildly dilates large coronary conductance vessels in both "normal" and diseased segments, although significantly less than does nitroglycerin.

Aged↗

PubMed1983

Myocardial blood flow and oxygen consumption in the empty-beating, fibrillating, and potassium-arrested hypertrophied canine heart.

Myocardial oxygen consumption and blood flow distribution were examined in severely hypertrophied canine hearts in the empty-beating, fibrillating, and pharmacologically arrested states. Hypertrophy was produced using a subcoronary valvular aortic stenosis model that mimics the clinical situation of aortic valvular stenosis. Oxygen content of the total coronary sinus collection was compared with a large volume arterial sample using a Lex-O2-Con-TL analyzer, which had been validated by the Van Slyke-Neill method. Transmural blood flow was measured in each state using microspheres, and perfusion pressure was maintained at 80 mm Hg. Oxygen consumption in the empty-beating hypertrophied heart was found to be the same as that previously reported for normal hearts. Blood flow was evenly distributed in the empty-beating heart, with an endocardial/epicardial ratio of 0.99 +/- 0.15 (SEM) milliliters per minute per gram of left ventricular weight. Oxygen consumption failed to increase significantly with fibrillation; however, blood flow distribution favored the subepicardium, suggesting that oxygen consumption determinations in the fibrillating hypertrophied heart may not accurately reflect metabolic demand. Basal oxygen consumption of the hypertrophied heart as determined by the potassium-arrested, blood-perfused model was the same as that previously described for normal hearts. Blood flow during potassium arrest favored the subendocardium (endocardial/epicardial ratio = 1.14 +/- 0.27 ml/min/gm LV weight).

Animals↗

PubMed1996

Use of N-phenylmethazonium methosulphate oxidation of NADH in the quantification of oxygen uptake by oral bacteria under open-system conditions.

Technically, open systems are more suited than closed systems for the measurement of oxygen uptake by bacteria present at high cell densities as in dental plaque. Moreover, measurements are easier to perform and can be done faster and continuously. However, quantifications is more difficult and, except for steady-state conditions, has been semiquantitative. The stoichiometric oxidation of NADH by N-phenylmethazonium methosulphate (PMS) is a reaction used here to develop a formula that overcomes this problem and makes it possible to relate quantitatively the pO2 measured easily with an oxygen electrode to the amount of oxygen utilized by respiring bacteria provided with a given amount of substrate. The approach and formula consist of the summing of (i) the oxygen decrease observed during the period of bacterial oxygen consumption and (ii) the oxygen simultaneously entering from the atmosphere. To quantify the entry component, the rate of oxygen diffusion into the mixture needed to be determined: this was done by reducing or exhausting the oxygen content of the medium in various ways and determining the rate constant of atmospheric oxygen entry. The relation between the logarithm of the oxygen concentration (determined from pO2 values using the PMS-NADH reaction) and point of time in the oxygen resaturation process proved to be linear. This enabled calculation of a diffusion rate constant, k, for use in the oxygen utilization formula. The validity of this method for quantification of oxygen use was tested by comparing oxygen consumption determined from the pO2 tracing and the derived formula to the oxygen consumed when fixed amounts of NADH are oxidized by PMS. When oxygen uptake/substrate utilization molar ratios were calculated for each of several NADH concentrations, the resulting values were almost identical. The method proved reliable over most of the oxygen concentration range possible in this system.

Bacteria↗

PubMed1997

[Characteristics of patients and use of resource in French pediatric intensive care units. Le groupe francophone de Rèanimation et urgences pédiatriques].

UNLABELLED: Evaluation of case-mix and resource consumption in pediatric intensive care units (ICU) is required. AIMS: This study describes the patterns of pediatric ICU resource consumption, determines the impact of primary clinical characteristics (particularly severity of illness) on resource utilization, and analyses medical efficiency with the frequency of inappropriate stays in French pediatric ICU. METHODS: Prospective study in nine French volunteer multidisciplinary pediatric ICUs from December 1993 to April 1994. Premature neonates were excluded. Resource consumption was expressed using the Omega system and length of stay, from which total Omega per admission, and average daily Omega (total Omega/length of stay) were obtained. RESULTS: Seven hundred and twelve patients were eligible. Twenty-five percent were full-term neonates, 30% infants (1 month to 1 year), and 45% children. Surgical patients constituted 22% of the population. A chronic disease was present in 45% of infants and children. Immunodeficiency was present in 10% of patients. The median length of stay was 4 days (range: 1-155). The mean Omega scores per admission were: total Omega = 92 +/- 124, Omega/day = 14 +/- 9. Sixty-four percent required mechanical ventilation and 37% during more than 2 days. Forty-two percent had a central venous access, and 23% an arterial line. The resource consumption was greater in non-survivors, surgical patients, neonates, and immunosuppressed patients. The mean PRISM score was 9 +/- 9. Mortality was 13%. The Omega/day and the PRISM score correlated. The frequency of inappropriate stays was 7.6% and accounted for 1.0% of the overall Omega activity. CONCLUSIONS: The results of this study can be used for interinstitutional comparison and a broader appraisal of pediatric intensive care. They illustrate the relationship between severity of illness and resource consumption. French pediatric ICU efficiency seems to be high, as compared to North American and Dutch results.

Adolescent↗

PubMed1998

Effect of music on perceived exertion, plasma lactate, norepinephrine and cardiovascular hemodynamics during treadmill running.

We examined the effects of listening to headphone music in ten well trained men (25.1 +/- 6 years) during treadmill running. Maximal oxygen consumption, determined by open circuit spirometry, was followed by two submaximal work bouts 72 hours apart. The work bouts consisted of a supine rest, a 15 minute run at 70% of maximal oxygen consumption, and a three minute active recovery period. Participants listened to music during one of the two trials. Hemodynamic variables and perceived exertion were recorded at three minute intervals during each trial. A venous blood sample, obtained prior to and following each trial, was assayed for norepinephrine and plasma lactate. Analysis of variance revealed significant differences (p < 0.05) between the no music versus the exercise with music trial for (aggregate data 3,6,9,12,15 minutes): heart rate 152.9 +/- 5.3 to 145.9 +/- 4.7 beats x min(-1); systolic blood pressure, 158.1 +/- 3.7 to 151.7 +/- 3.3 mmHg; rate-pressure product 242.2 +/- 11.5 to 222.1 +/- 11.4; exercise lactate 2.75 +/- 0.15 to 2.13 +/- 0.18 mmol x l(-1); and perceived exertion 14.4 +/- 0.4 to 12.9 +/- 0.4. A 17.5% lower level of norepinephrine (841.5 +/- 314.7 to 694.1 +/- 254.5 pg x ml[-1]) in the exercise and music trial was not statistically significant (p<0.05); however a moderate effect size (ES = 0.52) was calculated and may be of practical significance considering the variability of the sample. Higher values for hemodynamics and lactate in the no music trial is suggestive of a greater metabolic demand; however, oxygen consumption was not different. Perhaps the music allowed individuals to relax reducing muscle tension thereby increasing blood flow and lactate clearance while decreasing lactate production in working muscle. The combined results of this study suggest the introduction of music has a psychobiological impact on the exerciser demonstrated by changes in perceived effort, lactate and norepinephrine.

Adult↗

PubMed1988

Thyroid hormone action: early calorigenic effect on dispersed rat liver cells in the absence of protein synthesis.

Isolated dispersed rat liver cells were prepared by hypothyroid Sprague-Dawley rats. The cells were incubated under 95% O2/5% CO2 in Krebs-Ringer-bicarbonate buffer at pH 7.3-7.4 at 37 degrees C. The medium had been enriched with 2% bovine serum albumin (previously stripped of thyroid hormone) and 5-10 mM alanine as substrate. Two hour incubations were carried out with or without added triiodothyronine (T3) at 3 nM or 300-1,000 nM concentrations. Oxygen consumption determined at the end of the period of incubation with the Clark oxygen electrode showed stimulation above control values in the hormone treated flasks; parallel studies in which cycloheximide (100 microM) had been added to cells to block protein synthesis also showed enhanced oxygen consumption in response to T3. The results indicated a response to the hormone not dependent on new protein formation.

Animals↗

PubMed1976

Calorigenic response in obese and nonobese women.

The calorigenic response to a high protein test meal was studied in women with a history of childhood onset obesity. Obese and nonobese individuals were fasted overnight and basal oxygen consumptions determined the following morning. A semisynthetic 823 kcal high protein test meal was ingested within a 1-hr period followed by hourly determinations of oxygen consumption and plasma levels of insulin, free fatty acids, triglycerides, glucose, amino acids, and urea nitrogen. Amino acid levels increased faster and to a higher plateau in the nonobese group, while insulin levels increased and eventually decreased in a similar fashion in both groups. No differences in basal metabolic rate were detected. The postprandial increment in oxygen consumption was significantly less among the obese subjects. Diminished calorigenesis after each meal would result in accumulation of extra calories provided that caloric consumption is not appropriately decreased. These data suggest that a physiological aberration of energy metabolism may contribute to the development of childhood onset obesity.

Adult↗

PubMed1999

Oral clonidine premedication enhances postoperative analgesia by epidural morphine.

UNLABELLED: This study was designed to evaluate the effects of oral clonidine premedication on postoperative analgesia by epidural morphine in a prospective, randomized, double-blinded design. Sixty consenting patients, scheduled for total abdominal hysterectomy, were randomly assigned to one of three groups (n = 20 each); the clonidine-morphine group received oral clonidine 5 microg/kg 90 min before arriving in the operating room and epidural morphine 2 mg before induction of general anesthesia, the clonidine-placebo group received oral clonidine 5 microg/kg and no epidural morphine, and the placebo-morphine group received no clonidine and epidural morphine 2 mg. An epidural catheter was placed at the L1-2 or L2-3 interspace, and 1.5% lidocaine was used for surgical anesthesia in all patients. General anesthesia was then induced with propofol, and maintained with a continuous infusion of propofol and 67% nitrous oxide in oxygen during surgery. Four patients were subsequently withdrawn from the study. After surgery, patient-controlled analgesia using IV morphine was used to assess analgesic requirement. Morphine consumptions determined every 6 h after surgery in the clonidine-morphine and placebo-morphine groups were significantly less than the clonidine-placebo group until 12 h after surgery, whereas those of the clonidine-morphine group were significantly less than the placebo-morphine group from 13 to 42 h after surgery. Visual analog (pain) scale (VAS) scores in the clonidine-morphine group were significantly lower than the placebo-morphine group at 48 h at rest, and at 1, 24, 36, and 48 h with movement. Similarly, VAS scores in the clonidine-morphine group were significantly lower than the clonidine-placebo group at 1 and 6 h both at rest and with movement, whereas VAS scores in the clonidine-placebo group were significantly lower than the placebo-morphine group at 24, 36, and 48 h at rest and with movement. The incidence of nausea and pruritus was similar between groups. We conclude that the combination of oral clonidine and epidural morphine produces more potent and longer lasting postoperative analgesia than either drug alone without increasing the incidence of adverse effects after major gynecologic surgeries. IMPLICATIONS: A small dose of epidural morphine is often used for postoperative analgesia. We found that oral clonidine premedication 5 microg/kg improves the analgesic efficacy of epidural morphine without increasing the incidence of adverse side effects.

Administration, Oral↗

PubMed1999

Risk factors for prolonged length of stay after major elective surgery.

OBJECTIVE: Length of stay (LOS) is an important outcome as a marker of resource consumption. Determining which factors increase LOS may provide information on reducing costs and improving the delivery of care. The purpose of this study was to determine the independent association of intraoperative process of care and postoperative events with prolonged LOS after adjusting for preoperative severity of illness in patients undergoing major elective surgery. METHODS: Cases representing 11 elective operations from the National VA Surgical Quality Improvement Program were analyzed using multivariate logistic regression analysis. The outcome, prolonged LOS, was defined as an LOS greater than or equal to the 75th percentile (in days) for each operation. Hierarchical modeling was used to assess the independent association of groups of variables (preoperative patient characteristics, intraoperative process of care, and postoperative adverse events) with prolonged LOS. RESULTS: For the 11 operations explored, there were 23,919 cases. Common preoperative variables associated with prolonged LOS were functional status, American Society of Anesthesiology class, and age. The most predictive intraoperative and postoperative variables included intraoperative blood transfusion, operative time, return to the operating room, and the number of complications after surgery. CONCLUSIONS: Prolonged LOS is associated with preoperative, intraoperative, and postoperative factors. Although preoperative factors were independently associated with a prolonged LOS, the factors generating the highest risks for a prolonged LOS were the intraoperative process of care and postoperative adverse events. To reduce costs, efforts should be made to improve the intraoperative process of care and to minimize postoperative complications.

Aged↗

PubMed2000

Comparison of methods of measurements of oxygen consumption in mechanically ventilated patients with multiple trauma: the Fick method versus indirect calorimetry.

OBJECTIVE: The purpose of this study was to compare the measurements of whole body oxygen consumption determined by the Fick method and by indirect calorimetry in mechanically ventilated patients with multiple trauma. DESIGN: A prospective, correlational, within-subjects design. SETTING: Surgical intensive care unit of a Level I trauma center. PATIENTS: Thirty-eight mechanically ventilated adults with multiple injuries who received a pulmonary artery catheter within 24 hrs of admission to the surgical intensive care unit. MEASUREMENTS AND MAIN RESULTS: After the initial resuscitation, simultaneous measurements of oxygen consumption (V(O2) by the reverse Fick equation and by indirect calorimetry were performed every 6 hrs for 24 hrs in normothermic patients who were at rest for at least 30 mins. At each measurement period, the mean V(O2) values determined by indirect calorimetry were significantly greater than the mean V(O2) values determined by the Fick method (time 1: 172+/-38 vs. 125+/-47 mL/min/m2, p < .0001; time 2: 170+/-31 vs. 130+/-48 mL/min/m2, p < .0001; time 3: 170+/-32 vs. 132+/-53 mL/min/m2, p < .0001; time 4: 169+/-29 vs. 130+/-60 mL/min/m2, p < .0002). By using the Bland and Altman technique, the mean bias was 41+/-3.95 mL/min/m2. Correlation coefficients of VO2 values between methods of measurements were statistically significant (r2 = .32, p = .0001; r2 = .32, p = .0001; r2 = .33, p = .0001; r2 = .18, p = .0001). CONCLUSIONS: Indirect calorimetry should be the preferred standard for measurement of oxygen consumption in severely injured patients.

Adult↗

PubMed1994

Serum laminin levels offer only a little additional information in liver disease.

We have measured serum laminin, a marker of portal hypertension, in 151 patients with nonmalignant liver diseases, to evaluate its utility in cirrhosis and portal hypertension. There were abnormal serum levels in 43.1% of the patients as a whole and in 62.7% of the cirrhotics. Laminin showed a correlation with many laboratory tests, especially those that reflect liver insufficiency and alcohol intake. Cirrhotics had higher laminin levels than noncirrhotics (p < 0.0001); an association was also found with portal hypertension (p < 0.0001), but laminin was also increased in patients without portal hypertension. Our results suggest that liver dysfunction can also lead to abnormal laminin concentrations, probably through slower metabolization rate. Laminin serum concentrations reflect the severity of the liver disease, and are also a marker of alcohol consumption. Determination of laminin serum levels could play an adjunctive role with respect to other liver tests in the evaluation of these patients although the measure does not really provide more useful information.

Adolescent↗

PubMed1988

Neuropsychological performance and treatment outcome in male alcoholics.

Commonly used neuropsychological tests were administered to 91 detoxified alcoholics at the beginning of treatment. Statistically significant relationships were observed between test scores and post-treatment consumption determined 8 months after completing treatment for 72 patients. The results varied depending upon the particular measure of posttreatment consumption evaluated and the type of statistical analysis used. The most consistent relationships were often counter to the notion that increased neuropsychological performance is correlated with a more favorable treatment outcome. Neuropsychological evaluation is of limited clinical utility in predicting posttreatment alcohol consumption.

Adult↗

PubMed1994

Lactate efflux from fatigued fast-twitch muscle fibres of Xenopus laevis under various extracellular conditions.

1. Isolated, fast-twitch, low-oxidative muscle fibres from the iliofibularis muscle of Xenopus laevis were fatigued by intermittent tetanic stimulation at 20 degrees C in different Ringer solutions and the amount of lactate released was determined. 2. The rate of lactate efflux was constant during 10 min of intermittent stimulation while lactate in the fibres accumulated, and lactate efflux was not hampered by an unstirred layer surrounding the isolated muscle fibre. 3. The rate of lactate efflux at extracellular pH 7.2 was the same as that at pH 7.8, but depended on the type of buffer used; the highest efflux rate (mean +/- S.E.M., 7.4 +/- 2.2 mumol min-1 (g dry weight)-1, n = 8) was observed in bicarbonate-buffered Ringer solution. This rate was about 2.5 times higher than the rate in phosphate-buffered Ringer solution (2.9 +/- 1.3 mumol min-1 (g dry weight)-1, n = 8), indicating that lactate-bicarbonate exchange is the most important route for lactate extrusion in vivo. 4. The highest rate of lactate efflux corresponds to a rate of glycolytic ATP production which is only about 30% of the oxidative rate of ATP production (calculated from the maximum rate of oxygen consumption determined previously). 5. In the presence of 5 mM alpha-cyano-4-hydroxycinnamate (CHC) the lowest lactate efflux rate (1.5 +/- 0.6 mumol min-1 (g dry weight)-1, n = 16) was found. This rate was independent of the composition of the Ringer solution. Assuming that 5 mM CHC completely inhibits lactate transporters in the sarcolemma, the rate of lactate efflux in the presence of 5 mM CHC can be explained by passive diffusion, but only if most lactate is extruded via the T-tubules.

Animals↗

PubMed1978

Myoglobin function in the isolated fluorocarbon-perfused dog heart.

An isolated dog heart preparation perfused with hemoglobin-free fluorocarbon suspension has been developed to study the role of myoglobin in myocardial function. The coronary vasculature was perfused at constant flow, with oxygen consumption determined from arteriovenous PO2 differences. Muscle function was assessed by measurement of pressures generated in a latex balloon placed in the left ventricle. The perfusate consisted of 20% perfluorotributylamine and 80% Ringer's lactate with 16 mM glucose. Steady-state oxygen consumption decreased from 0.30 to 0.11 ml/min per gram dry weight left ventricle, as perfusate PO2 decreased from 690 to 150 mmHg. Left ventricular pressure generation and oxygen consumption were determined before and after addition of 8 mM sodium nitrite, which changed functional ferrous myoglobin to high-spin ferric myoglobin. Over the range of perfusate PO2 studied, nitrite addition did not alter mechanical performance or myocardial oxygen consumption. These data suggest that those conditions necessary for substantial myoglobin-facilitated diffusion of oxygen in the myocardium are not present in the isolated fluorocarbon-perfused dog heart.

Animals↗

PubMed2000

Influence of training on sweating responses during submaximal exercise in horses.

Sweating responses were examined in five horses during a standardized exercise test (SET) in hot conditions (32-34 degrees C, 45-55% relative humidity) during 8 wk of exercise training (5 days/wk) in moderate conditions (19-21 degrees C, 45-55% relative humidity). SETs consisting of 7 km at 50% maximal O(2) consumption, determined 1 wk before training day (TD) 0, were completed on a treadmill set at a 6 degrees incline on TD0, 14, 28, 42, and 56. Mean maximal O(2) consumption, measured 2 days before each SET, increased 19% [TD0 to 42: 135 +/- 5 (SE) to 161 +/- 4 ml. kg(-1). min(-1)]. Peak sweating rate (SR) during exercise increased on TD14, 28, 42, and 56 compared with TD0, whereas SRs and sweat losses in recovery decreased by TD28. By TD56, end-exercise rectal and pulmonary artery temperature decreased by 0.9 +/- 0.1 and 1.2 +/- 0.1 degrees C, respectively, and mean change in body mass during the SET decreased by 23% (TD0: 10.1 +/- 0.9; TD56: 7.7 +/- 0.3 kg). Sweat Na(+) concentration during exercise decreased, whereas sweat K(+) concentration increased, and values for Cl(-) concentration in sweat were unchanged. Moderate-intensity training in cool conditions resulted in a 1.6-fold increase in sweating sensitivity evident by 4 wk and a 0.7 +/- 0.1 degrees C decrease in sweating threshold after 8 wk during exercise in hot, dry conditions. Altered sweating responses contributed to improved heat dissipation during exercise and a lower end-exercise core temperature. Despite higher SRs for a given core temperature during exercise, decreases in recovery SRs result in an overall reduction in sweat fluid losses but no change in total sweat ion losses after training.

Animals↗

PubMed1992

Does the severity of leukoaraiosis contribute to senile dementia? A comparative computerized and positron emission tomographic study.

The present study evaluates the origin, severity and location of leukoaraiosis in senile dementia and in normal ageing. The regional white-matter lucency scores, determined on computed-tomographic scan of the brain, are compared to the regional blood flow, oxygen extraction rate and oxygen consumption, determined by the [15O] steady-state technique with positron emission tomography. Thirty patients, classified according to the presence or absence of leukoaraiosis and their mental status, are examined. The occurrence and severity of dementia appear to be mainly correlated to decreased blood flow and oxygen metabolism in the frontal, temporal and parietal cerebral cortex. Leukoaraiosis in demented and nondemented patients is associated with lowered blood flow in the frontal and parietal white matter. The regional lucency score is increased, and blood flow and oxygen consumption decreased in the frontal white matter of severely demented patients. Frontal leukoaraiosis contributes to dementia and is probably of ischemic origin, while parietal and occipital leukoaraiosis is due to wallerian degeneration.

Aged↗

PubMed1984

Oxygen consumption of infants with respiratory distress syndrome.

The objective of this research was to determine the oxygen consumption of newborn infants with respiratory distress syndrome in the first 4 days of life. Serial determinations of oxygen consumption were made in 14 infants with respiratory distress syndrome receiving positive end-expiratory pressures. The mean (+/- SE) oxygen consumption determined at 24, 48, 72, and 96 h postnatal age were 8.3 +/- 0.9, 6.5 +/- 0.8, 5.5 +/- 0.5, and 5.3 +/- 0.6 ml/min/kg, respectively. The level of oxygen consumption at 24 h postnatal age was significantly greater than the levels determined at 48, 72, and 96 h (p less than 0.03). The oxygen levels found at 72 and 96 h of age were comparable to those determined for healthy preterm infants. A linear regression of serial oxygen consumption and weight loss yielded a 'fair' (r = 0.5) correlation with a significant inference (p less than 0.01).

Body Weight↗

PubMed1982

The effects of atrial fibrillation on atrial pressure-volume and flow relationships.

To study whether atrial fibrillation might produce local changes in the atrium which could facilitate the tendency of this arrhythmia to become chronic and self-perpetuating, we compared the effect of atrial fibrillation, atrial pacing, and acute volume loading on the perfusion and oxygen consumption of the atrium in anesthetized dogs. Measurement of atrial perfusion with microspheres indicates that during atrial fibrillation, atrial blood flow increases 2- to 3-fold. Right atrial pacing is a significantly less potent metabolic stimulus for atrial vasodilation. Using Doppler velocity recordings of sinus node artery blood flow velocity, a marked increase in velocity is observed within 5 seconds after the initiation of atrial fibrillation. During atrial fibrillation, the sinus node artery reactive hyperemia response is markedly attenuated. Atrial fibrillation acutely decreases atrial distensibility; atrial pressure increased 81 +/- 19% with only a small increase (9.7 +/- 3%) in atrial diameter measured by echocardiography. During sinus rhythm, volume expansion to equivalent levels of atrial pressure as seen during atrial fibrillation increased atrial diameter 21 +/- 5% P less than 0.05. Atrial oxygen consumption determined by the microspectrophotometric method markedly increases during atrial fibrillation, compared to control conditions (12.3 +/- 2.8 vs. 3.9 +/- 0.6 ml O2/min per 100 g, respectively) P less than 0.05. Atrial O2 extraction was 5.5 +/- 0.4 ml O2/ml blood in the control state, and did not change with interventions. There was a linear relationship between left atrial O2 consumption and blood flow in all experimental conditions. Atrial fibrillation therefore alters atrial hemodynamics and metabolism by increasing atrial blood flow and oxygen consumption and decreasing atrial distensibility. Since atrial perfusion during atrial fibrillation is high and atrial flow reserve is limited, it is possible that additional atrial metabolic requirements might lead to atrial ischemia, fibrosis, and, thereby, perpetuation of the arrhythmia.

Animals↗