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PubMed1987

Directly measured tissue oxygen tension and arterial oxygen tension assess tissue perfusion.

Mean subcutaneous tissue PO2 (PsqO2) measurements were obtained in dogs with an unheated electrode placed in an implanted Silastic tonometer, while PaO2 was increased in increments from 40 to 600 torr during normal, increased, and reduced blood volume. These changes reflect that the mean PsqO2 is approximately 10 torr below the PO2 of venous blood draining that tissue. Since PaO2 was already known, the oxygen content of arterial and venous blood entering and leaving this tissue could be determined by reference to blood-oxygen dissociation curves. Therefore, relative changes in blood flow could be calculated using the Fick principle. After a 20% blood loss, the PsqO2 measured during breathing of room air fell to 20% of baseline, corresponding to an 80% fall in sc blood flow; it remained low until the shed blood was returned despite compensatory changes in cardiac output. Rapid infusion of electrolyte solutions in normovolemic animals produced a temporary increase in local blood flow. Subcutaneous oximetry seems capable of quantifying peripheral perfusion and may be clinically useful.

Animals↗
PubMed2005

Dynamic tissue perfusion measurement: a novel tool in follow-up of renal transplants.

BACKGROUND: The authors applied the novel method of noninvasive dynamic color Doppler sonographic parenchymal perfusion measurement to renal transplants. METHODS: Color Doppler sonographic videos of renal transplants from 38 renal transplant recipients were recorded under defined conditions. Specific tissue perfusion was calculated as mean flow velocity encoded by color Doppler signals of a region of interest during one full heart cycle. RESULTS: The authors could demonstrate significant differences of central versus peripheral cortical perfusion intensity (1.36 vs. 0.60 cm/sec) and a significant loss of perfusion intensity in the posttransplantation period in the peripheral cortex from 1.06 cm/sec in the first year to a minimum of 0.39 cm/sec in the 3- to 5-year interval, with stronger perfusion in longer surviving transplants: 0.71 cm/sec more than 9 years after transplantation. In the central cortex, a similar but less pronounced pattern could be demonstrated. A significant drop of parenchymal perfusion was found in patients with elevated serum creatinine (1.36 cm/sec in cases with normal and 0.82 cm/sec in those with elevated creatinine at the proximal cortical level). The perfusion ratio of the central 50% and the peripheral 50% shows marked changes over time: in the first year, the ratio was 2.99, climbing to 5.56 at the 3- to 5-year interval and declining later on. CONCLUSIONS: Cortical tissue perfusion in renal transplants was quantified noninvasively from color Doppler signal data in an easily accomplishable manner. Renal transplants showed a marked decline in tissue perfusion after transplantation. Perfusion is significantly lower in transplant function loss with elevated serum creatinine.

Adolescent↗
PubMed1996

Enhancement of perioperative tissue perfusion as a therapeutic strategy for major surgery.

Multiple organ dysfunction syndrome (MODS) accounts for most surgical deaths which occur some days postoperatively. Current hypotheses concerning the pathophysiology of MODS place tissue hypoxia and reperfusion as a central feature of the initiation and continuation of the syndrome. Surgical patients are at risk of developing overt and covert tissue hypoxia and hypoperfusion due to anesthetic, surgical, and other factors; and it is known that surgical patients with poor cardiovascular reserve have a worse outcome postoperatively. A number of clinical studies have attempted to intervene early in surgical patients to prophylactically improve tissue perfusion in the perioperative period by augmentation of cardiac output. These studies demonstrate a reduction in mortality and morbidity in these groups of patients. A similar approach has been tried in other groups of critically ill patients, at a later state in the evolution of their illness; these studies have not shown any improvement in outcome. In surgical patients, data show that those with more coexisting pathology and worse cardiac function may benefit most from a treatment approach aimed at improving tissue perfusion; furthermore, this may result in cost savings. The implications for the management of the higher risk surgical patient are obvious. It may no longer be acceptable to undertake surgery in these patients without facilities to monitor and improve cardiac output and tissue perfusion.

Blood Circulation↗
PubMed1992

The influence of different levels of PEEP on peripheral tissue perfusion measured by subcutaneous and transcutaneous oxygen tension.

OBJECTIVE: To compare subcutaneous (PscO2) and transcutaneous (PtcO2) oxygen tension measurements in relation to hemodynamic variables at different levels of PEEP, and to evaluate the usefulness of these measurements as monitors of peripheral tissue perfusion. DESIGN: Prospective trial. SETTING: Intensive care unit in a university hospital. PATIENTS: Seven patients with gastric cancer who where undergoing total gastrectomy. INTERVENTIONS: Silicone catheter was placed in the upper arm and transcutaneous oxygen monitor was placed on the upper part of the chest. A pulmonary artery catheter was placed in the right pulmonary artery. MEASUREMENTS AND RESULTS: PscO2 and PtcO2 together with hemodynamic variables were measured at different levels of PEEP. Progressive increase of PEEP reduced cardiac index (CI) (p < 0.05) with a concomitant decrease of PscO2 (p < 0.05) and oxygen delivery (DO2) (p < 0.05). Changes in PtcO2 paralleled changes in arterial oxygen tension (PaO2), but no correlation was found between PtcO2, CI and DO2. CONCLUSION: PscO2 is a sensitive indicator of subcutaneous tissue perfusion, which can be used to identify the PEEP level, with optimum peripheral perfusion. PscO2 seems to be a more reliable indicator of tissue perfusion than PtcO2.

Aged↗
PubMed1985

Assisted ventilation in patients with preexisting cardiopulmonary disease. The effect on systemic oxygen consumption, oxygen transport, and tissue perfusion variables.

We have evaluated systemic oxygen consumption (VO2), systemic oxygen transport, and tissue perfusion variables in 30 patients with preexisting cardiac and underlying pulmonary disease during continuous positive-pressure ventilation and positive end-expiratory pressure [PEEP], during intermittent mandatory ventilation (IMV and PEEP), and during spontaneous ventilation (continuous positive airway pressure [CPAP]), with end-expiratory pressure held constant during all ventilatory modes. Using radionuclide angiography together with invasive determinations of pressure and flow, we also measured left and right ventricular ejection fractions and calculated the end-systolic (ESVI) and end-diastolic (EDVI) volume indices of both ventricles. We found that oxygen transport was significantly greater during CPAP (583 +/- 172 ml/min/M2)(mean +/- SD) than during either IMV and PEEP (543 +/- 151 ml/min/sq; p less than 0.01) or CPPV and PEEP (526 +/- 159 ml/min/M2; p less than 0.01); however, we found no significant change in systemic VO2 with conversion from CPPV and PEEP to CPAP. The increase in oxygen transport was related to a greater cardiac index and, more specifically, to a higher heart rate during CPAP (CPAP, 106 +/- 16 beats per minute; CPPV and PEEP, 97 +/- 14 beats per minute) (p less than 0.01). Enhanced oxygen transport during CPAP was also associated with an increase in mixed venous oxygenation and a decrease in arterial lactate. Although neither the mean left ventricular EDVI nor ESVI changed from CPPV and PEEP to CPAP, the mean pulmonary capillary wedge pressure increased (CPPV and PEEP, 12 +/- 5 mm Hg; CPAP, 14 +/- 7 mm Hg) (p less than 0.01), suggesting the possibility of a decrease in left ventricular compliance with the spontaneous ventilatory mode. This study suggests that in the absence of ventilatory failure, spontaneous ventilation provides for better systemic oxygen transport and overall tissue perfusion than either controlled ventilation or IMV; however, this benefit of enhanced oxygen delivery with spontaneous ventilation may potentially be offset by a decrease in left ventricular compliance.

Aged↗
PubMed2001

Noninvasive determination of spatially resolved and time-resolved tissue perfusion in humans during nitric oxide inhibition and inhalation by use of a visible-reflectance hyperspectral imaging technique.

BACKGROUND: Vascular disease is commonly associated with reduced local synthesis of nitric oxide (NO) and impaired tissue perfusion. We introduce a novel noninvasive, visible-reflectance, hyperspectral imaging technique for quantifying the percentage of hemoglobin existing as oxyhemoglobin (HbO(2)) as an index of skin tissue perfusion. METHODS AND RESULTS: To simulate vascular endothelial dysfunction, N(G)-monomethyl-L-arginine (L-NMMA) was infused into the brachial arteries of 9 healthy subjects for 5 minutes to inhibit forearm NO synthesis, first with the subject breathing room air and subsequently during NO inhalation at 80 ppm for 1 hour. Blood flow was measured by venous occlusion plethysmography, and the percentage of HbO(2) perfusing skin tissue was imaged noninvasively with a visible-reflectance hyperspectral technique. L-NMMA reduced blood flow by 31.7+/-4.9% and percentage of HbO(2) by 6.5+/-0.1 (P=0.002 and P<0.001 versus baseline, respectively). With subjects inhaling NO, blood flow fell during L-NMMA infusion by only 10.9+/-7.3%, and the percentage of HbO(2) decreased by 3.6+/-0.1 (P=0.007 and P<0.001, respectively, versus room air L-NMMA responses). CONCLUSIONS: Visible-reflectance hyperspectral imaging demonstrates (1) a significant decline in the percentage of HbO(2) in skin tissue when blood flow is reduced after inhibition of forearm NO synthesis and (2) restoration of HbO(2) toward basal values with improved blood flow during inhalation of NO. This imaging method may provide an effective approach for time-resolved noninvasive monitoring of skin hemoglobin oxygen saturation and assessment of responses to therapeutic interventions in patients with vascular disease.

Administration, Inhalation↗
PubMed1991

Oxygen transport measurements to evaluate tissue perfusion and titrate therapy: dobutamine and dopamine effects.

BACKGROUND: Increased cardiac index, oxygen delivery (DO2), and oxygen consumption (VO2) patterns were shown to characterize the physiologic status of surviving high-risk surgical patients, and indicate increased metabolic needs; relatively normal DO2 and VO2 values were found to characterize the sequential pattern of nonsurvivors who developed an early oxygen debt followed by lethal organ failure. The cardiac index, DO2, and VO2 values empirically determined from survivors' patterns were shown to improve outcome in prospective randomized trials. The present study considers these criteria to evaluate the tissue perfusion status as well as the effects of therapy on tissue perfusion and oxygenation. OBJECTIVE: To summarize new information on the temporal patterns of DO2, VO2, and oxygen debt on outcome and the effects of fluids and inotropes on these patterns in a wide range of clinical, temporal, and physiologic conditions. DESIGN: Descriptive analysis based on data gathered prospectively using a specified protocol. PATIENTS: High-risk patients with accidental or elective surgical trauma, and patients with or without sepsis or septic shock and organ failure. SETTING: University-run county hospital with a large trauma service. INTERVENTIONS: Fluids, dobutamine, and dopamine at various times and at various doses throughout critical illness of postoperative, posttraumatic, septic, and hypovolemic patients with and without lethal and nonlethal organ failure. MEASUREMENTS AND MAIN RESULTS: The pattern of DO2 plotted against the corresponding VO2 values in 437 consecutive critically ill surgical patients showed a wide variability and poor correlation probably because complex clinical conditions may obscure the supply-dependent and supply-independent VO2 relationships observed in normal dogs bled or given bacterial infusions. However, the use of specific therapy by well-defined protocols was shown to provide objective evidence of efficacy. Significant increases in DO2 and VO2 were previously shown after whole blood, packed red cells, and colloid administration, but not after crystalloid administration. Dobutamine administration in 715 circumstances in postoperative, traumatic, septic patients and patients with adult respiratory distress syndrome, renal failure, and multiple organ failure significantly improved DO2 and VO2. Dopamine under comparable conditions produced less improvement in DO2 and VO2 than that of dobutamine; most of the VO2 changes were not significant. CONCLUSIONS: The monitored patterns of cardiac index, DO2, and VO2 may be used to evaluate the adequacy of tissue perfusion as well as the relative effectiveness of alternative therapies. Second, these physiologic criteria may be used to titrate therapy in order to achieve optimal outcome. Third, after colloids optimally expand the plasma volume, dobutamine may be used to enhance flow and the distribution of flow in order to improve tissue oxygenation. Vasodilators may be used when hypertensive episodes occur or there is an inadequate response to inotropic agents. Vasopressors are used as a last resort, usually in the terminal or preterminal state.

Acute Kidney Injury↗
PubMed2000

Contribution of the portal flow on hepatic tissue perfusion increases in reduced hepatic vascular bed.

Background: A hepatic artery-portal vein reciprocal response and hepatic hemodynamics have well been investigated under normal condition, but not under pathologic condition with decreased vascular bed. This study was designed to determine the hemodynamic changes in the hepatic blood flow, tissue perfusion and interrelationship between portal venous flow (PVF) and hepatic arterial flow (HAF) after inflow interruption in the various size of hepatic vascular bed. Methods: Anesthetized dogs were used to measure PVF and HAF using a transit time flow meter and hepatic tissue flow (HTF) using a laser Doppler flow meter before and after portal venous (PVO) or hepatic arterial occlusion (HAO) under various range of portal triad occlusion (PTO). Results: The ratio of HAF/TLF (total liver flow) was 38+/-14% under the basal condition. This ratio did not change under the 30% PTO where there was a similar decrease in PVF and HAF, but reduced to 25+/-12% under the 70% PTO where there was more selective reduction in HAF than PVF. Although a reciprocal HAF increase was observed under any conditions after PVO, the TLF and HTF decreases after PVO were largest under the 70% PTO with the highest PVF/TLF ratio. On the other hand, there was no reciprocal PVF increase in any conditions after HAO, and the TLF and HTF decreases after HAO were minimal under the 70% PTO with the lowest HAF/TLF ratio. Conclusions: With decreasing hepatic vascular bed, dependency of the remnant hepatic hemodynamics and tissue perfusion on the portal blood flow increased. These findings suggest that an integrity of portal venous flow becomes crucial in the remnant hepatic tissue perfusion after extensive hepatic resection.

Journal Article↗
PubMed2004

A laser speckle imaging technique for measuring tissue perfusion.

Laser Doppler imaging (LDI) has become a standard method for optical measurement of tissue perfusion, but is limited by low resolution and long measurement times. We have developed an analysis technique based on a laser speckle imaging method that generates rapid, high-resolution perfusion images. We have called it laser speckle perfusion imaging (LSPI). This paper investigates LSPI output and compares it to LDI using blood flow models designed to simulate human skin at various levels of pigmentation. Results show that LSPI parameters can be chosen such that the instrumentation exhibits a similar response to changes in red blood cell concentration (0.1%-5%, 200 microL/min) and velocity (0-800 microL/min, 1% concentration) and, given its higher resolution and quicker response time, could provide a significant advantage over LDI for some applications. Differences were observed in the LDI and LSPI response to tissue optical properties. LDI perfusion values increased with increasing tissue absorption, while LSPI perfusion values showed a slight decrease. This dependence is predictable, owing to the perfusion algorithms specific to each instrument, and, if properly compensated for, should not influence each instrument's ability to measure relative changes in tissue perfusion.

Algorithms↗
PubMed2000

Ibuprofen modulates tissue perfusion in partial-thickness burns.

INTRODUCTION: The anti-inflammatory and anticoagulant effects of ibuprofen and heparin may enhance skin perfusion in cutaneous scald burns. To test this hypothesis, skin perfusion and edema formation in scald burned rabbit ears were measured. METHOD: Eighteen rabbits (3.5-4.5 kg) received partial-thickness scald burns to one ear and then were given normal saline, n = 6, 20 mg/kg ibuprofen, n = 6, or 700 IU/kg heparin, n = 6. Skin perfusion, blood flow and edema formation in the burned ear were measured with laser Doppler, ultrasound flowmeter and skin calipers, respectively. Statistical analysis was performed using repeated measures ANOVA with post hoc Scheffe's test for comparison between groups. RESULTS: Blood flow to the scald burned ear increased 10-15 times that of baseline with tissue perfusion increasing by 70% within 0.5 h compared to pre-burn. Ibuprofen maintained the elevated tissue perfusion for 5 h while the heparin and saline groups showed decreases to 95 and 35% of pre-burn values, respectively. The heparin and ibuprofen groups demonstrated significant increases in ear perfusion at 4 and 5 h postburn. Ibuprofen also showed a significant difference within the first hour postburn, p<0.01. Wet to dry weight ratios in burned ear tissue were greater in rabbits receiving saline or heparin compared to ibuprofen at 3.6+/-0.2 and 2.9+/-0.3 vs. 2.1+/-0.1, respectively (p<0.001). CONCLUSION: Ibuprofen increases tissue perfusion and reduces edema formation in scald burned rabbit ears.

Analysis of Variance↗
PubMed2007

Blood flow occlusion via ultrasound image-guided high-intensity focused ultrasound and its effect on tissue perfusion.

This study investigated the induction of tissue necrosis by arterial blood flow occlusion using ultrasound image-guided high-intensity focused ultrasound (HIFU). We constructed a prototype HIFU transducer in combination with an imaging probe that provided color Doppler imaging and ultrasound contrast imaging. The HIFU beam was aimed into a branch of the renal artery in vivo. The renal artery branches of eight rabbits were occluded by HIFU at an intensity of 4 kW/cm(2) (from 2 to 10 times of each sonication for 5 s). When the HIFU exposure was successful, complete cessation of blood flow was observed by color Doppler imaging with success rate of 100% (8/8). Furthermore, lack of perfusion was observed in the renal cortex with a contrast-enhanced image. Postmortem histologic evaluation showed a wedge-shaped area of infarction in six of seven cases, corresponding to the lack of the contrast medium in the ultrasound image. These results demonstrated that ultrasound image-guided HIFU can be used to induce arterial occlusion, thus producing infarction and necrosis of the perfused tissue.

Albumins↗
PubMed1980

Hepatic tissue perfusion studies during distal splenorenal shunt.

Hepatic tissue perfusion was measured by the krypton-85 clearance technique during surgery in four patients with bleeding esophageal varices before and immediately after Warren distal splenorenal shunt. No significant reduction in perfusion was found in any patient, thus confirming the concept that this type of portasystemic shunt maintains portal flow to the liver.

Adult↗
PubMed2006

Successful thrombus extraction with the Rescue thrombus management system during acute percutaneous coronary intervention improves flow but does not necessarily restore optimal myocardial tissue perfusion.

UNLABELLED: We determined the effectiveness of the Rescue device in restoring flow and achieving optimal tissue perfusion during percutaneous coronary intervention (PCI) in thrombus-laden coronary arteries. METHODS: A total of 30 patients with an acute coronary syndrome underwent PCI using the Rescue device. RESULTS: The mean age was 65.5 +/- 9.8 years. Although the Rescue device could not be passed across the lesion in 6 (20%) cases, debris was aspirated in 26 (87%). The uncorrected TIMI frame count improved following the use of the Rescue device and improved further at the completion of PCI (92.2 +/- 23.9 pre-PCI vs. 38.7 +/- 31.3 post-Rescue vs. 21.96 +/- 24 post-PCI, P < 0.0001). The thrombus score improved from 4 +/- 0 to 2.2 +/- 1.29 to 0.86 +/- 1.4 (P < 0.0001). TIMI flow grade (TFG) 3 was restored in 60% of cases following the Rescue device and in 87% after PCI. Myocardial blush grade 3 occurred in only 13% of patients following the Rescue device and 37% of patients after PCI. CONCLUSION: These data suggest that the Rescue device can aspirate considerable amounts of debris in the majority of patients and significantly improves the angiographic epicardial coronary blood flow. How effective such a device is in improving tissue perfusion and, thereby, clinical outcomes for patients remains to be seen.

Aged↗
PubMed2005

Hormone replacement therapy in postmenopausal women: breast tissue perfusion determined with MR imaging--initial observations.

PURPOSE: To use magnetic resonance (MR) imaging to evaluate tissue perfusion in the normal breast parenchyma of postmenopausal women with current or recent hormone replacement therapy (HRT). MATERIALS AND METHODS: The study was approved by the institutional subcommittee on human studies, and informed consent was obtained from all patients prior to MR imaging. Sixty postmenopausal women (age range, 44-77 years) were grouped according to HRT received: estrogen replacement therapy (ERT) (n = 13), combined (estrogen and progesterone) replacement therapy (CRT) (n = 16), selective estrogen receptor modulator (SERM) therapy (n = 8), and no (hormone replacement) therapy (NT) (n = 23). MR imaging with a 1.5-T magnet was performed by using gradient-echo and dynamic contrast material-enhanced echo-planar pulse sequences before and after gadopentetate dimeglumine injection. Precontrast T1 relaxation times were measured, after which extraction-flow product (EFP) maps were calculated with a multicompartmental model. Analysis of variance was performed. RESULTS: Age did not significantly differ between the groups (P > .3). Women receiving ERT or CRT at the time of MR imaging had higher EFP values (7.3 mL . 100 g(-1) . min(-1)+/- 2.6 and 7.1 mL . 100 g(-1) . min(-1)+/- 3.8, respectively) than did women receiving NT (4.4 mL . 100 g(-1) . min(-1)+/- 2.1) (P = .012 and P = .008, respectively) or SERM therapy (3.9 mL . 100 g(-1) . min(-1)+/- 1.1) (P = .015 and P = .013, respectively). Women who ended ERT or CRT 1-47 months before MR examination had lower EFP values than did women with current ERT or CRT and had higher EFP values than did women receiving NT or SERM therapy (6.2 mL . 100 g(-1) . min(-1)+/- 2.4 and 5.9 mL . 100 g(-1) . min(-1)+/- 3.8, respectively), but the observed differences were not significant (P > .1). Differences in T1 between all groups were not significant (P > .5). CONCLUSION: Higher breast tissue perfusion is observed in postmenopausal women receiving HRT.

Adult↗
PubMed1995

[Improving tissue perfusion without invasive monitoring. Apropos of a case].

A case is reported of a 64 year old patient who suffered a septic shock after surgical treatment of a biliary peritonitis. Increasing myocardial contractility and aortic blood flow by dobutamine appeared ineffective; added norepinephrine infusion improved the peripheral perfusion. This clinical improvement in tissue perfusion was evaluated by non-invasive continuous monitoring of the haemodynamic profile, combining aortic blood flow measurement by a transoesophageal echo-Doppler and continuous measurement of end-tidal carbon dioxide.

Carbon Dioxide↗
PubMed2003

Noninvasive, near infrared spectroscopic-measured muscle pH and PO2 indicate tissue perfusion for cardiac surgical patients undergoing cardiopulmonary bypass.

OBJECTIVE: To determine whether near infrared spectroscopic measurement of tissue pH and Po2 has sufficient accuracy to assess variation in tissue perfusion resulting from changes in blood pressure and metabolic demand during cardiopulmonary bypass. DESIGN: Prospective clinical study. SETTING: Academic medical center. SUBJECTS: Eighteen elective cardiac surgical patients. INTERVENTION: Cardiac surgery under cardiopulmonary bypass. MEASUREMENTS AND MAIN RESULTS: A near infrared spectroscopic fiber optic probe was placed over the hypothenar eminence. Reference Po2 and pH sensors were inserted in the abductor digiti minimi (V). Data were collected every 30 secs during surgery and for 6 hrs following cardiopulmonary bypass. Calibration equations developed from one third of the data were used with the remaining data to investigate sensitivity of the near infrared spectroscopic measurement to physiologic changes resulting from cardiopulmonary bypass. Near infrared spectroscopic and reference pH and Po2 measurements were compared for each subject using standard error of prediction. Near infrared spectroscopic pH and Po2 at baseline were compared with values during cardiopulmonary bypass just before rewarming commenced (hypotensive, hypothermic), after rewarming (hypotensive, normothermic) just before discontinuation of cardiopulmonary bypass, and at 6 hrs following cardiopulmonary bypass (normotensive, normothermic) using mixed-model analysis of variance. Near infrared spectroscopic pH and Po2 were well correlated with the invasive measurement of pH (R2 =.84) and Po2 (R 2 =.66) with an average standard error of prediction of 0.022 +/- 0.008 pH units and 6 +/- 3 mm Hg, respectively. The average difference between the invasive and near infrared spectroscopic measurement was near zero for both the pH and Po2 measurements. Near infrared spectroscopic Po2 significantly decreased 50% on initiation of cardiopulmonary bypass and remained depressed throughout the bypass and monitored intensive care period. Near infrared spectroscopic pH decreased significantly during cardiopulmonary bypass, decreased significantly during rewarming, and remained depressed 6 hrs after cardiopulmonary bypass. Diabetic patients responded differently than nondiabetic subjects to cardiopulmonary bypass, with lower muscle pH values (p =.02). CONCLUSIONS: Near infrared spectroscopic-measured muscle pH and Po2 are sensitive to changes in tissue perfusion during cardiopulmonary bypass.

Aged↗
PubMed2000

Effects of dobutamine on splanchnic tissue perfusion during partial superior mesenteric artery occlusion.

OBJECTIVE: To evaluate the effects of dobutamine and fluid treatment on splanchnic hemodynamics and tissue oxygenation during partial superior mesenteric artery occlusion. DESIGN: Prospective, open randomized, full-factorial design. SETTING: University research laboratory. SUBJECTS: Forty-eight female pigs. INTERVENTIONS: In 24 anesthetized pigs (ischemic group), superior mesenteric artery (SMA) blood flow was reduced to 30% from the baseline for 120 mins; 24 pigs (sham group) served as nonischemic controls. The animals were further assigned into four treatment arms. In the control arm, the animals were administered only basic fluid therapy. In the fluid therapy arm, pulmonary artery occlusion pressure was maintained at 10 mm Hg with fluids. In the dobutamine treatment arm, dobutamine hydrochloride was infused at a dose of 10 microg/min/kg. In the combined dobutamine-fluid therapy arm, dobutamine at 10 microg/min/kg was administered and pulmonary artery occlusion pressure was maintained at 10 mm Hg with fluids. MEASUREMENTS AND MAIN RESULTS: Systemic and regional hemodynamics and oxygen transport, as well as jejunal intramucosal pH, intramucosal-arterial PCO2 gradient, and portal venous-arterial lactate gradient were measured. Ischemia did not modify the effects of fluids or dobutamine on systemic hemodynamics and oxygen transport. Dobutamine-treated animals had a higher cardiac index compared with control animals (218 +/- 22 vs. 135 +/- 13 mL/min/kg; p = .012), and the effect was enhanced when dobutamine was combined with fluid treatment (365 +/- 23 mL/ min/kg; p = .019). Fluid treatment alone did not influence cardiac index, whereas it increased SMA blood flow compared with control groups (15 +/- 2 vs. 12 +/- 2 mL/min/kg; p = .023). Dobutamine also decreased the proportion of SMA blood flow of cardiac output compared with control groups (6 +/- 1 vs. 9% +/- 1%; p = .024). Other treatments had no effect on SMA blood flow. Ischemia increased intramucosal-arterial Pco2 gradient to 54.8 +/- 10.7 torr (7.31 +/- 1.43 kPa) (p = .002 vs. sham control) and decreased intramucosal pH to 7.13 +/- 0.06 (p = .028 vs. sham control). In the ischemic animals, dobutamine without fluid therapy reduced intramucosal pH further to 7.00 +/- 0.09 (p = .023 vs. ischemic control) and increased portal venous-arterial lactate gradient (p = .033). CONCLUSIONS: Dobutamine alone worsened splanchnic tissue perfusion during partial superior mesenteric artery occlusion. As compared with fluid treatment alone, the combination of fluid and dobutamine therapy did not improve tissue perfusion.

Animals↗
PubMed1994

Formulation of a statistical model of heat transfer in perfused tissue.

A new model of steady-state heat transport in perfused tissue is presented. The key elements of the model are as follows: (1) a physiologically-based algorithm for simulating the geometry of a realistic vascular tree containing all thermally significant vessels in a tissue; (2) a means of solving the conjugate heat transfer problem of convection by the blood coupled to three-dimensional conduction in the extravascular tissue, and (3) a statistical interpretation of the calculated temperature field. This formulation is radically different from the widely used Pennes and Weinbaum-Jiji bio-heat transfer equations that predict a loosely defined local average tissue temperature from a local perfusion rate and a minimal representation of the vascular geometry. Instead, a probability density function for the tissue temperature is predicted, which carries information on the most probable temperature at a point and uncertainty in that temperature due to the proximity of thermally significant blood vessels. A sample implementation illustrates the dependence of the temperature distribution on the flow rate of the blood and the vascular geometry. The results show that the Pennes formulation of the bio-heat transfer equation accurately predicts the mean tissue temperature except when the arteries and veins are in closely spaced pairs. The model is useful for fundamental studies of tissue heat transport, and should extend readily to other forms of tissue transport including oxygen, nutrient, and drug transport.

Algorithms↗