Measurement Of Pulmonary Blood Flow Research Articles

Sources of error in partial rebreathing pulmonary blood flow measurements in lungs with emphysema and pulmonary embolism

Studies of the accuracy of partial rebreathing measurements of pulmonary blood flow (PBF) in patients with abnormal lungs have not fully explained the sources of error. We used computer models of emphysema and pulmonary embolism incorporating both ventilation-perfusion (V/Q) and ventilation-volume (V/V) heterogeneity to investigate systematic errors in partial rebreathing PBF measurements. We studied (i) errors produced under usual conditions, (ii) effects of recirculation, (iii) effects of alveolar-proximal airway and alveolar-capillary PCO2 and VCO2 differences, (iv) effects of alveolar V/Q inhomogeneity and (v) effects of rebreathing time. In the pulmonary embolism model the systematic error is only acceptable (<10%) when the simulated PBF is low (2-3 litre min(-1)). In the emphysema model PBF is underestimated by more than 20% at all cardiac outputs studied. Four sources of systematic errors were found. (i) Alveolar-proximal airway PCO2 gradients and flux differences between the proximal airway and alveolar compartments contribute most to the systematic error. (ii) V/Q inhomogeneity causes PCO2 gradients between the alveolar compartments and pulmonary capillary blood, and between pulmonary capillary compartments. (iii) Rebreathing times are inadequate in the presence of V/V mismatch. (iv) The apparent effect of venous blood recirculation is small in emphysema but significant in pulmonary embolism. We conclude that PBF cannot be measured accurately by partial rebreathing in lungs with emphysema or embolism. Systematic errors are caused mainly by errors in end-tidal PCO2 values.

Noninvasive, Automated and Continuous Cardiac Output Monitoring by Pulmonary Capnodynamics

Cardiac output monitoring is most important where cardiovascular stability is potentially threatened, such as during major surgery and in critically ill patients. However, continuous monitoring of cardiac output is still not performed routinely during anesthesia and critical care, because of invasiveness, expense, and inaccuracy of available technologies. A technique termed the capnodynamic method was tested for breath-to-breath measurement of pulmonary blood flow from lung carbon dioxide mass balance, using measured carbon dioxide elimination and end-tidal concentration. A prototype measurement system was constructed for a feasibility study in six anesthetized sheep. Large and rapid fluctuations in cardiac output were generated by repeated dobutamine and esmolol challenge. Measurements were compared with an indwelling ultrasonic flow probe placed on the ascending aorta or pulmonary artery. Cardiac output measured by the flow probe varied between zero and 8.67 l/min, with a mean of 3.50 l/min. Overall mean bias [SD of the difference] between the methods (capnodynamic - flow probe) was -0.25 [0.94] l/min, r = 0.79 (P < 0.001). During periods of stability in cardiac output of 5 min or more, mean bias was -0.20 [0.55] l/min. The method successfully indicated two cardiac arrest events, which were induced in one of the animals. The method satisfactorily tracked wide fluctuations in cardiac output in real time. The capnodynamic method may have potential for continuous noninvasive cardiac output monitoring in patients undergoing anesthesia for major surgery, and in critical care, on a routine basis.

Capnography: Clinical Aspects.

Capnography: Clinical Aspects.

Comparison of two systems for measurement of pulmonary capillary blood flow by partial CO2 rebreathing

de Abreu, Gama M.; Winkler, T.; Pahlitzsch, T.; Weismann, D.; Koch, T. Author Information

Non-invasive measurement of intrapulmonary shunt during inert gas rebreathing

We tested the agreement between non-invasive measurement of intrapulmonary shunt, using oxygen uptake and pulmonary capillary blood flow measurement obtained by nitrous oxide rebreathing, with that measured using mixed venous blood sampling. Nine patients were recruited pre- and post-cardiac surgery resulting in 20 sets of measurements overall. Mean shunt fraction was 12.5%, and bias between methods (±95% confidence limits) was −0.7% (±0.8%). The standard deviation of the difference was 1.7% with limits of agreement between the two methods of +2.6% and −3.9%. Correlation coefficient r was 0.90. Agreement with the invasive standard was less accurate and precise where cardiac output was measured by bolus thermodilution (mean bias +1.6%, standard deviation of the difference 2.2%, limits of agreement between the two methods of +5.8% and −2.8%, r = 0.86). Good agreement was demonstrated between the non-invasive method and the invasive reference standard.

Agreement of an Inert Gas Rebreathing Device with Thermodilution and the Direct Oxygen Fick Method in Measurement of Pulmonary Blood Flow

Inert gas rebreathing is a well established method for the non-invasive measurement of pulmonary blood flow. We tested the agreement in measurement of pulmonary blood flow (Qt rb) by a new inert soluble gas rebreathing device, the Innocor (Innovision, Copenhagen), with bolus thermodilution (Qt td) and the direct oxygen Fick (Qt Fick) method. 9 patients pre- and post-cardiac surgery were recruited resulting in 20 sets of measurements overall. Arterial and mixed venous blood samples were collected simultaneously with a thermodilution measurement and rebreathing manoeuvre to measure both V*O2 and effective pulmonary capillary blood flow. Mean bias (95% confidence limits) was: Qt rb - Qt td 0.01 (+/- 0.42) L/min; Qt rb - Qt Fick + 0.34 (+/-0.59) L/min. The standard deviation of the difference between paired measurements was: Qt td - Qt rb +/- 0.89 L/min; Qt Fick - Qt rb +/- 1.26 L/min. Acceptable overall agreement between the Innocor and these reference standards was demonstrated.

A noninvasive partial carbon dioxide rebreathing technique for measurement of pulmonary capillary blood flow is also a useful oxygenation monitor during one-lung ventilation

Study objectives To test the hypothesis that effective pulmonary capillary blood flow can be a useful indicator for estimating appropriate oxygenation and ventilation during one-lung ventilation in lung surgery. Design Prospective data analysis. Setting A 770-bed general teaching hospital. Patients 15 ASA physical status II and III patients undergoing elective lung surgery. Interventions Patients received general and thoracic epidural anesthesia and underwent lung operation with one-lung ventilation. Measurements We measured effective pulmonary capillary blood flow by a partial CO 2 rebreathing method and oxygenation parameters during two-lung ventilation before surgery, during one-lung ventilation, and during two-lung ventilation after lung surgery. Main results The effective pulmonary capillary blood flow index significantly decreased by 31.6%, which was associated with a significant decrease in arterial oxygen tension (PaO 2). The pulmonary shunt fraction increased to 46.3% during one-lung ventilation. During two-lung ventilation, after chest closure, effective pulmonary capillary blood flow index divided by heart rate (i.e., effective pulmonary blood stroke flow index) was still significantly lower than that seen during two-lung ventilation before thoracotomy. There were significant correlations between effective pulmonary capillary blood flow, pulmonary blood stroke flow index, and PaO 2. Conclusions Effective pulmonary capillary blood flow index and effective pulmonary blood stroke flow index are useful indicators for determining appropriate oxygenation therapy during one-lung ventilation.

Measurement of pulmonary capillary blood flow by partial CO2 rebreathing during one-lung ventilation

Measurement of pulmonary capillary blood flow by partial CO2 rebreathing during one-lung ventilation

Noninvasive measurement of intrapulmonary shunting

Objective: To investigate the accuracy and precision of a noninvasive approach to measurement of pulmonary shunt fraction using simultaneous application of 2 fundamental respiratory mixing equations: the direct Fick equation for oxygen and the shunt equation of Berggren. This can be performed without mixed venous blood sampling and requires measurement of oxygen uptake and pulmonary blood flow. Design: Comparison with invasive shunt fraction measured using mixed venous blood sampling and with estimated shunt fraction using an assumed arteriovenous O 2 content difference. Setting: Major teaching hospital. Participants: Nine patients undergoing anesthesia for cardiac surgery. Interventions: Pulmonary blood flow was measured using an indirect Fick technique (nitrous oxide throughflow) and by bolus thermodilution for comparison. Measurements and Main Results: The mean shunt fraction measured by the invasive method was 0.145 (range 0.057–0.263). When pulmonary blood flow was measured using an indirect Fick technique (nitrous oxide throughflow), the absolute mean bias for noninvasive shunt fraction was −0.005 with a standard deviation of 0.012. Correlation was excellent ( r 2 = 0.95, p < 0.001). Agreement was less precise when pulmonary blood flow was measured using thermodilution (mean bias + 0.001 with a standard deviation of 0.018). Conclusions: The noninvasive method is an accurate substitute for invasive shunt fraction measurement with mixed venous blood sampling.

THIS MONTH IN ANESTHESIOLOGY

THIS MONTH IN ANESTHESIOLOGY

Sources of error in noninvasive pulmonary blood flow measurements by partial rebreathing: a computer model study.

Partial rebreathing is a noninvasive method for measuring pulmonary blood flow (PBF). This study examines the systematic errors produced by the partial rebreathing technique utilizing a comprehensive mathematical model of the cardiorespiratory system of a healthy, 70-kg adult male. The model simulates tidal breathing through a branched respiratory tree and incorporates the effects on carbon dioxide dynamics of lung tissue mass, vascular transport delays, multiple body compartments, and realistic blood-gas dissociation curves. Four studies were performed: (1) errors produced under standard conditions, (2) effects of recirculation, (3) effects of alveolar-proximal airway partial pressure of carbon dioxide (Pco(2)) differences, and (4) effects of rebreathing time. Systematic errors are less than 10% when the simulated PBF is between 3 and 6 l/min. At 2 l/min, PBF is overestimated by approximately 35%. At 14 l/min, PBF is underestimated by approximately 40%. At PBF of greater than 6 l/min, recirculation causes approximately 60% of the systematic error, alveolar-proximal airway differences cause approximately 20%, and alveolar-arterial differences cause approximately 20%. The standard rebreathing time of 50 s is shown to be excessive for PBF of greater than 6 l/min. At PBF of less than 3 l/min, errors are caused by inadequate rebreathing time and alveolar-arterial gradients. Systematic errors in partial rebreathing cardiac output measurements have multiple causes. Our simulations suggest that errors can be reduced by using a variable rebreathing time, which should be increased at low PBF so that quasi-equilibrium in the alveoli can be achieved and decreased at high PBF to reduce the effects of recirculation.

Pulmonary vascular dysfunction in preterm lambs with chronic lung disease.

Chronic lung injury from prolonged mechanical ventilation after premature birth inhibits the normal postnatal decrease in pulmonary vascular resistance (PVR) and leads to structural abnormalities of the lung circulation in newborn sheep. Compared with normal lambs born at term, chronically ventilated preterm lambs have increased pulmonary arterial smooth muscle and elastin, fewer lung microvessels, and reduced abundance of endothelial nitric oxide synthase. These abnormalities may contribute to impaired respiratory gas exchange that often exists in infants with chronic lung disease (CLD). Nitric oxide inhalation (iNO) reduces PVR in human infants and lambs with persistent pulmonary hypertension. We wondered whether iNO might have a similar effect in lambs with CLD. We therefore studied the effect of iNO on PVR in lambs that were delivered prematurely at approximately 125 days of gestation (term = 147 days) and mechanically ventilated for 3 wk. All of the lambs had chronically implanted catheters for measurement of pulmonary vascular pressures and blood flow. During week 2 of mechanical ventilation, iNO at 15 parts/million for 1 h decreased PVR by approximately 20% in 12 lambs with evolving CLD. When the same study was repeated in eight lambs at the end of week 3, iNO had no significant effect on PVR. To see whether this loss of iNO effect on PVR might reflect dysfunction of lung vascular smooth muscle, we infused 8-bromo-guanosine 3',5'-cyclic monophosphate (cGMP; 150 microg. kg(-1). min(-1) iv) for 15-30 min in four of these lambs at the end of week 3. PVR consistently decreased by 30-35%. Lung immunohistochemistry and immunoblot analysis of excised pulmonary arteries from lambs with CLD, compared with control term lambs, showed decreased soluble guanylate cyclase (sGC). These results suggest that loss of pulmonary vascular responsiveness to iNO in preterm lambs with CLD results from impaired signaling, possibly related to deficient or defective activation of sGC, the intermediary enzyme through which iNO induces increased vascular smooth muscle cell cGMP and resultant vasodilation.

Direct and transoesophageal ECHO measurements of pulmonary blood flow

s: European Association of Cardiothoracic Anaesthesiologists; 17th Annual Meeting; Dublin, Ireland; June 12-15, 2002: Measurement

Pulmonary blood flow is inhomogeneously reduced after Euro Collins-preservation and lung transplantation

Background. Vasoconstriction after lung transplantation is a well-known phenomenon, but only limited information is available on blood flow distribution after ischemia and reperfusion. The aim of our study was to determine the regional flow characteristics in transplanted and native dog lungs after 24 hours of cold storage and preservation with Euro Collins-solution. Methods. Six pairs of weight-matched Foxhounds (25 to 30 kg) were used. In donors and recipients, aortic and pulmonary artery catheters were inserted percutaneously and a reference withdrawal catheter was placed into the main pulmonary artery. For preservation, the lungs were perfused with modified Euro Collins-solution and stored at 4°C. After 24 hours, the left lung was transplanted. Regional pulmonary blood flow was assessed by injection of colored microspheres into the right atrium using the reference withdrawal technique. Measurements of regional pulmonary blood flow were conducted twice in donors and recipients (baseline and 3 hours after reperfusion). Tissue samples from five distinct regions (apical, medial, dorsal, ventral, and lateral) were taken to assess regional pulmonary blood flow and wet–dry ratios. Results. The relative (‰ Confidence Intervals/100 mg dry weight) regional pulmonary blood flow was significantly reduced in the transplanted lung but not in the native organ. This reduction was most pronounced in apical regions and smallest in regions close to the hilum. Edema formation occurred in both lungs, as judged from wet-to-dry ratios of lung tissue specimen. Conclusions. Two separate processes can be observed after single lung transplantation: (1) reduced regional pulmonary blood flow, which is a regional phenomenon restricted to the transplanted organ, and (2) extensive edema affecting both the transplanted and the native lung.

Intrapulmonary Instillation of Perfluorocarbon in Experimental Acute Lung Injury

Intrapulmonary Instillation of Perfluorocarbon in Experimental Acute Lung Injury Max et al.(page 1437) Max et al. used an experimental model to induce acute lung injury in 20 pigs to study the effects of partial liquid ventilation (PLV) with perfluorocarbon on the distribution of pulmonary blood flow. Gas exchange and hemodynamic and pulmonary blood flow were assessed in all animals before and after induction of acute lung injury with use of a saline lavage. Then, the animals were assigned randomly to one of two groups: a group of 10 who were submitted to PLV by administering 15 ml/kg of perfluorocarbon through the endotracheal tube at 1 and 2 h after injury, and a group of 10 in whom controlled mechanical ventilation was continued with no changes in respirator settings. Measurements were performed 1 and 2 h after injury in the latter group, as well. At specific points in the study protocol, researchers also injected radioactive-labeled macroaggregates of human serum albumin to enable measurement of pulmonary blood flow using single photon emission computed tomography. With use of specialized software, they generated 12 lung segments (four transaxial slices consisting of ventral, middle and dorsal segments) for each animal to be examined for distribution of blood flow. Arterial carbon dioxide tension increased from 32 ± 4 to 57 ± 13 mmHg after acute lung injury was induced, but, after the initial changes, arterial carbon dioxide tension and pH remained constant in groups 1 and 2. When all 20 pigs, either in gaseous ventilation or in PLV groups, were analyzed together, acute lung injury was shown to cause an increase of pulmonary blood flow to the ventral segment of slice 2 and to the middle segments of slices 1 and 2. Blood flow increased in the combined middle segments but decreased in the dorsal ones. Neither PLV nor gaseous ventilation resulted in a redistribution of blood flow to any of the 12 segments when values at 1 and 2 h after injury were compared with those measured immediately after acute lung injury. In a third group of five pigs, the attenuation control group, a similar number of lung lavages (11 ± 2) were needed to induce acute lung injury with an arterial oxygen tension of 52 ± 14 mmHg. Arterial oxygenation improved significantly after PLV with perfluororcarbon, which may be caused by an improvement in ventilation/perfusion ratios.

Heart Transplantation in Neonates: Achievements, Controversies, and Challenges for the Future

After completing this article, readers should be able to: 1. Compare the results of pediatric heart transplantation with those of transplantation in adults, including the survival rates. 2. Compare and contrast the indications for pediatric heart transplant among those younger and older than 1 year of age. 3. List the common complications after pediatric heart transplantation. 4. Compare and contrast new immunosuppressive agents (tacrolimus, mycophenolate, humanized anti-Tac antibodies) and standard therapies (cyclosporine, azathioprine, prednisone, antithymocyte globulin). 5. Describe the controversy surrounding the proper management of infants who have hypoplastic left heart syndrome. Not long after the first successful human heart transplant was performed, the first neonatal heart transplant was attempted. In December of 1967, Kantrowitz and colleagues at Maimonides Hospital in New York transplanted the heart of an anencephalic infant into a 3-week-old who had tricuspid atresia. Although the recipient survived only 6.5 hours, the technical feasibility of cardiac transplantation in the pediatric patients was proven. Thirty-three years later, heart transplantation has gained widespread acceptance as a standard treatment modality for end-stage cardiomyopathy or noncorrectable congenital heart disease in infants and children. The 2 years following Barnard’s pioneering first transplant saw explosive growth in the field of adult heart transplantation, but poor 1-year survival dampened much of the initial enthusiasm and with it, any hope for bringing heart transplantation to the pediatric population. Most centers eventually abandoned the procedure, and many physicians denounced the concept. However, a few centers persisted, most notably Dr Norman Shumway and colleagues at Stanford, gradually improving survival through strong collaborations with basic immunologists and cardiac pathologists. By the mid-1970s, heart transplantation had been extended successfully to teenagers. The introduction of the “wonder drug” cyclosporine in 1980 so dramatically improved survival in adult cardiac transplant recipients that the extension of transplantation to even younger patients became feasible. Almost as important as …

Evaluation of a new real continuous cardiac output pulmonary artery catheter

None of the currently available pulmonary artery (PA) catheters allows instantaneous and continuous measurement of pulmonary blood flow. At best, the so-called continuous cardiac output (CO) catheters (and associated software) indicate continuously an averaged value of CO measured over several minutes. A new catheter has been introduced recently, and animal experiments have shown that it allows instantaneous detection of changes in pulmonary blood flow. In this catheter, blood flow is derived from the power required to maintain a temperature gradient between two thermistors that are insulated differently. The technology also allows the clinician to measure CO using the standard thermodilution technique. The aim of the present study was to demonstrate the clinical safety and efficacy of this new PA catheter.

Vascular structure determines pulmonary blood flow distribution.

Scientific knowledge develops through the evolution of new concepts. This process is usually driven by new methodologies that provide observations not previously available. Understanding of pulmonary blood flow determinants advanced significantly in the 1960s and is now changing rapidly again, because of increased spatial resolution of regional pulmonary blood flow measurements.

Pulmonary arterial resistance: noninvasive measurement with indexes of pulmonary flow estimated at velocity-encoded MR imaging--preliminary experience.

Cardiac output and pulmonary vascular resistance (PVR) were measured in 19 patients by means of catheterization of the right side of the heart. Results were compared with the cardiac output and indexes of pulmonary arterial blood flow estimated with velocity-encoded magnetic resonance (MR) imaging. Correlations were good between estimates with right-sided heart catheterization and those with velocity-encoded MR imaging. By providing accurate pulmonary arterial blood flow measurements, velocity-encoded MR imaging allowed distinction of patients with high PVR from subjects with normal PVR.

The role of bidirectional cavopulmonary shunt on selection of Fontan patients

There are no objection against that pulmonary vascular resistance index (PVRI) is one of the most important factors for completion of successful application of Fontan-type operation. However, calculated PVRI in single ventricle physiology in often unreliable because of difficulty in accurate measurement of pulmonary blood flow, especially in patients with decreased pulmonary blood flow. Although the role of bidirectional cavopulmonary shunt (BCPS) in such patients has been increasingly recognized, the impact of BCPS on PVRI has not been fully understood. Between November 1993 and November 1996, 24 patients, aged between 0.54 and 22.2 years, with a wide variety of cardiac malformations underwent BCPS, and were followed up for the mean of 15.1 months. There were four hospital deaths (16.7%) and three deaths in follow-up (12.5%). Serial catheterization revealed that significant increase in mean arterial oxygen saturation from 75.8% to 83.9% (p = 0.005), and decrease in mean Nakata's index from 433 to 311 (p < 0.0001). PVRI calculated by using formulas derived from Ohm's law before BCPS (Pulmonary flow was derived from Fick formula) was highly (greater than 10 u.m2) or moderately (between 4 and 10 u.m2) elevated in 6 and 7 patients, respectively. However, PVRI in these patients was normal after BCPS. Fourteen out of 24 patients underwent total cavopulmonary connection (TCPC) with 8 to 15 months of interval from BCPS, and have been currently surviving, and in NYHA functional class I or II, except 2 patients who underwent take-down. In conclusion, early and midterm outcome after staged operation appears to be excellent. BCPS is a good interim procedure, in part because one can more properly select patients undergoing Fontan operations from the PVRI point of view.