Bronchopulmonary anastomotic and noncoronary collateral blood flow in humans during cardiopulmonary bypass

A Case of an Apical Aneurysm Caused by a Cardiac Event Involving Noncoronary Collateral Blood Flow

An 87-year-old man presented with exertional dyspnea and was admitted due to congestive heart failure. Echocardiography and left ventriculography performed after his condition improved showed an aneurysm at the left ventricular apex. However, coronary angiography showed no significant lesions and an avascular field at the apex. Computed tomography angiography revealed that the enlarged left inferior phrenic artery reached the heart and nourished the apex wall where the aneurysm was present. Looking back retrospectively, he was previously hospitalized nine years ago for epigastric pain with elevated myocardial deviation enzymes and electrocardiographic changes but no coronary artery lesions. Moreover, abnormal vascularization had already been observed 13 years ago when the aneurysm did not exit. Considering these findings, we concluded that the ventricular aneurysm in this case was caused by a vascular event involving collateral circulation from outside the heart.

The ongoing quest for the first total artificial heart as destination therapy

Many patients with end-stage heart disease die because of the scarcity of donor hearts. A total artificial heart (TAH), an implantable machine that replaces the heart, has so far been successfully used in over 1,700 patients as a temporary life-saving technology for bridging to heart transplantation. However, after more than six decades of research on TAHs, a TAH that is suitable for destination therapy is not yet available. High complication rates, bulky devices, poor durability, poor biocompatibility and low patient quality of life are some of the major drawbacks of current TAH devices that must be addressed before TAHs can be used as a destination therapy. Quickly emerging innovations in battery technology, wireless energy transmission, biocompatible materials and soft robotics are providing a promising opportunity for TAH development and might help to solve the drawbacks of current TAHs. In this Review, we describe the milestones in the history of TAH research and reflect on lessons learned during TAH development. We summarize the differences in the working mechanisms of these devices, discuss the next generation of TAHs and highlight emerging technologies that will promote TAH development in the coming decade. Finally, we present current challenges and future perspectives for the field.

Association of Passive Lung Insufflation Oxygen Fraction in Adult Patients on Cardiopulmonary Bypass with Postoperative Pulmonary Outcomes: A Retrospective Cohort Study

OBJECTIVES

To determine whether F_IO₂ of passive lung insufflation during cardiopulmonary bypass correlates with postoperative pulmonary function.

DESIGN

A retrospective, observational study SETTING: A single-center, university-affiliated, specialist cardiothoracic center in the United Kingdom.

PARTICIPANTS

Adult patients presenting for nonemergency, nontransplant cardiac surgery requiring cardiopulmonary bypass without the need for deep hypothermic circulatory arrest between January 1, 2018, and December 31, 2018.

INTERVENTIONS

Passive insufflation of the lungs during cardiopulmonary bypass with fresh gas flow of varying F_IO₂. Patients were sorted retrospectively into low F_IO₂ (0.21-0.44), intermediate F_IO₂ (0.45-0.69), and high F_IO₂ (0.7-1.0) groups. The primary outcome was the difference between the PaO₂:F_IO₂ on the first postinduction blood gas and on the first blood gas recorded postoperatively in the intensive care unit (ICU) (delta PaO₂:F_IO₂). Secondary outcomes were ICU and hospital lengths of stay, requirement for respiratory support, and 30-day mortality.

MEASUREMENTS AND MAIN RESULTS

Nine hundred patients were included in the authors' analysis (low F_IO₂ n = 307, intermediate F_IO₂ n = 459, high F_IO₂ n = 134). There was no significant difference in delta PaO₂:F_IO₂ among the groups (low F_IO₂ = 52.5 [-38.8 to 152.4], intermediate F_IO₂ = 71.8 [-39.4 to 165.1], high F_IO₂ = 60.2 [-19.2 to 184.0], p = 0.25). There were no significant differences among groups for any secondary outcomes.

CONCLUSION

Fresh gas flow with a low F_IO₂ delivered to the lungs without positive airway pressure during cardiopulmonary bypass was not associated with improved postoperative pulmonary function when compared to higher F_IO₂ levels.

Practical conduct of open heart procedures for congenital heart lesions

Open heart surgery on infants with congenital heart lesions can be challenging not only in terms of the surgical procedure itself but also for setting up ideal conditions for safe and smooth conduct of cardiopulmonary bypass (CPB). The surgeon has to deal with a variety of lesions in a subgroup of patients who offer little room for any error. Familiarity with the principles of CPB, check lists and protocols go a long way in improving outcome in this critical group of patients.

The Human Coronary Collateral Circulation, Its Extracardiac Anastomoses and Their Therapeutic Promotion

Cardiovascular disease remains the leading global cause of death, and the number of patients with coronary artery disease (CAD) and exhausted therapeutic options (i.e., percutaneous coronary intervention (PCI), coronary artery bypass grafting (CABG) and medical treatment) is on the rise. Therefore, the evaluation of new therapeutic approaches to offer an alternative treatment strategy for these patients is necessary. A promising research field is the promotion of the coronary collateral circulation, an arterio-arterial network able to prevent or reduce myocardial ischemia in CAD. This review summarizes the basic principles of the human coronary collateral circulation, its extracardiac anastomoses as well as the different therapeutic approaches, especially that of stimulating the extracardiac collateral circulation via permanent occlusion of the internal mammary arteries.

Noncoronary Collateral Myocardial Blood Flow: The Human Heart's Forgotten Blood Supply

The “noncoronary collateral circulation” (NCCC) or “noncoronary collateral myocardial blood flow” (NCCMBF), reaches the heart through a micro-vascular network arising from the bronchial, esophageal, pericardial, diaphragmatic, and aortic arteries. The left and right internal thoracic arteries (ITAs) along with their collateral branches also serve as a source of NCCMBF-a feature seen in other mammals. Under certain circumstances the ITAs have a high potential for developing collateral branches. In the case of severe Leriche syndrome or with chronic obstruction of the abdominal aorta, the ITAs can serve as the main or even sole source of blood supply to the lower limbs. It is also possible for the ITAs to develop angiographically visible branches that directly connect with the coronary arteries. In ischemic conditions there is a functional, ischemia-reducing extracardiac coronary artery supply via natural ipsilateral ITA anastomosis. To date we know little about NCCMBF and its potential benefits in clinical applications, which makes this a challenging and intriguing field of research. This paper reviews all available data on noncoronary collateral blood supply to the human heart.

Risk Factors Associated with Prolonged Mechanical Ventilation after Corrective Surgery for Tetralogy of Fallot

INTRODUCTION

This study examined early postoperative results to identify perioperative factors that are associated with prolonged mechanical ventilation (PMV) in tetralogy of Fallot (TOF) patients undergoing corrective surgery.

METHODS

We retrospectively examined the role of perioperative variables in determining the period of mechanical ventilatory support in TOF patients undergoing corrective surgery. A total of 821 patients were included in the study. The cohort was divided into a PMV group that included patients with >90th percentile for duration of mechanical ventilation and a non-PMV group which included all other patients.

RESULTS

Non-PMV group consisted of 751 patients (454 males, 297 females; median age 12 months, interquartile range 8-19 months; mean weight 9.60 ± 2.98 kg). PMV group consisted of 70 patients (51 males, 19 females; median age 8 months, interquartile range 6.75-13 months; mean weight 8.64 ± 1.95 kg). No patients died in the non-PMV group compared with two deaths due to acute respiratory distress syndrome in the PMV group. Univariate risk factors for PMV included age, weight, left ventricular end-diastolic volume index (LVEDVI), McGoon ratio, Nakata index, previous palliative operations, cardiopulmonary bypass (CPB) time, aortic cross-clamp (ACC) time, preoperative major aortopulmonary collateral arteries (MAPCAs) occlusion by coils in hybrid procedure, postoperative right ventricular/left ventricular systolic pressure ratio, central venous pressure (CVP), left atrial pressure (LAP), endotracheal reintubation, vasoactive-inotropic score (VIS), renal replacement therapy, and early-onset ventilator-associated pneumonia (VAP). In a multivariable model, age, LVEDVI, McGoon ratio, Nakata index, previous palliative operations, CPB time, blood returning to left atrium during surgery as a surrogate marker for significant aortopulmonary collateral presence, and early-onset VAP were the independent risk factors for PMV.

CONCLUSIONS

The risk factors for PMV were age, LVEDVI, McGoon ratio, Nakata index, previous palliative operations, CPB time, VIS, LAP, blood returning to left atrium during surgery, and early-onset VAP.

Does Pulmonary Artery Venting Decrease the Incidence of Postoperative Atrial Fibrillation after Conventional Aortocoronary Bypass Surgery?

<strong>Objectives</strong>: In this study, we tested the hypothesis that<br />pulmonary artery venting would decrease the incidence of<br />atrial fibrillation after coronary artery bypass surgery.<br /><strong>Methods</strong>: This prospective study included 301 patients<br />who underwent complete myocardial revascularization with<br />cardiopulmonary bypass in our department during a 2-year<br />period. The patients were randomly divided into 2 groups:<br />group I included 151 patients who underwent aortic root<br />venting and group II included 150 patients who underwent<br />pulmonary arterial venting for decompression of the left<br />heart. Pre-, peri-, and postoperative risk factors for atrial<br />fibrillation were assessed in both groups.<br /><strong>Results</strong>: The mean age was similar in the 2 groups. The<br />mean number of anastomoses was significantly higher in<br />group I (2.8 ± 0.8) than in group II (2.4 ± 0.8) (P = 0.001).<br />The mean cross-clamp time was 42.7 ± 17.4 minutes in group<br />I and 54.1 ± 23.8 minutes in group II (P = 0.001). The mean<br />cardiopulmonary bypass time was 66.4 ± 46.1 minutes in<br />group I and 77.4 ± 28.6 minutes in group II (P = 0.08). The<br />incidence of atrial fibrillation was 14.5% (n = 21) in group I<br />and 6.5% (n = 10) in group II (P = 0.02). Multivariate regression<br />analysis showed that pulmonary artery venting decreased<br />the postoperative incidence of atrial fibrillation by 17.6%.<br /><strong>Conclusions</strong>: Pulmonary arterial venting may be used as<br />an alternative to aortic root venting during on-pump coronary<br />bypass surgery, especially in patients at high risk of postoperative<br />atrial fibrillation.

Computed tomography and magnetic resonance imaging of pulmonary hypertension: Pulmonary vessels and right ventricle

Pulmonary hypertension (PH) is very heterogeneous and the classification identifies five major groups including many associated disease processes. The treatment of PH depends on the underlying cause and accurate classification is paramount. A comprehensive assessment to identify the cause and severity of PH is therefore needed. Furthermore, follow-up assessments are required to monitor changes in disease status and response to therapy. Traditionally, the diagnostic imaging work-up of PH comprised mainly echocardiography, invasive right heart catheterization, and ventilation/perfusion scintigraphy. Due to technical advances, multidetector row computed tomography (CT) and magnetic resonance imaging (MRI) have become important and complementary investigations in the evaluation of patients with suspected PH. Both modalities are reviewed and recommendations for clinical use are given.

Pulmonary vascular resistance, collateral flow, and ventricular function in patients with a Fontan circulation at rest and during dobutamine stress

BACKGROUND

The role, interplay, and relative importance of the multifactorial hemodynamic and myocardial mechanisms causing dysfunction of the Fontan circulation remain incompletely understood.

METHODS AND RESULTS

Using an MRI catheterization technique, we performed a differential analysis of pulmonary vascular resistance and aortopulmonary collateral blood flow in conjunction with global ventricular pump function, myocontractility (end-systolic pressure-volume relation), and diastolic compliance (end-diastolic pressure-volume relation) in 10 patients with a Fontan circulation at rest and during dobutamine stress. Pulmonary and ventricular pressures were measured invasively and synchronized with velocity-encoded MRI-derived pulmonary and aortic blood flows and cine MRI-derived ventricular volumes. Pulmonary vascular resistance and end-systolic and end-diastolic pressure-volume relations were then determined. Aortopulmonary collateral flow was calculated as the difference between aortic and pulmonary flow. Compared to rest, dobutamine caused a small increase in mean pulmonary pressures (P<0.05). Collateral flow was significantly augmented (P<0.001) and contributed importantly to an increase in pulmonary flow (P<0.01). Pulmonary vascular resistance decreased significantly (P<0.01). Dobutamine did not increase stroke volumes significantly despite slightly enhanced contractility (end-systolic pressure-volume relation). Active early relaxation (τ) was inconspicuous, but the end-diastolic pressure-volume relation shifted upward, indicating reduced compliance.

CONCLUSIONS

In patients with a Fontan circulation, aortopulmonary collateral flow contributes substantially to enhanced pulmonary flow during stress. Our data indicate that pulmonary vascular response to augmented cardiac output was adequate, but decreased diastolic compliance was identified as an important component of ventricular dysfunction.

Enhancement of noncoronary collateral circulation: the hypothesis of an alternative treatment for ischemic heart disease

The internal thoracic arteries (ITAs) are a source of "noncoronary collateral circulation" (NCCC), or "noncoronary collateral blood flow" (NCCBF). The hypothesis herein is that enhancement of NCCC may represent an alternative means of myocardial blood supply: (1) Ligature of the ITAs creates a local hypertensive status and increases the perfusion pressure within the channels leading to the heart; (2) Myocardial ischemic stimulus diverts most ITA-related collateral flow to the heart rather than to the chest wall; (3) The ITAs may develop neo-collaterals owing to their ischemia-related plastic potential; (4) Angiogenic growth factor administration within the ITAs enhances neo-collateral development. These elements may pave the way for a new field of cardiovascular research aimed at enhancing NCCC as a new therapeutic option for ischemic heart disease.

Indirect Bronchial Shunt Flow Measurements in AbioCor Implantable Replacement Heart Recipients

Bronchial shunt flows in the recipients of the electrohydraulic AbioCor implantable replacement heart have been measured indirectly. A built-in compliance chamber accommodates the differential flow output required of the two ventricles of the AbioCor. An occluder mechanism regulates the flow differential. For a thoracic unit, given a beat rate, an occluder setting, and the pressure differentials across the replacement heart ventricles, the atrial pressure difference depends only on the level of shunt flow present in the vasculature. For a replacement heart recipient, the bronchial shunt is the dominant shunt flow. For patients implanted with the AbioCor, the beat rates and the occluder settings are known and the pressure differentials across the ventricles are estimated. Atrial pressures were measured using catheters. The bronchial shunt flow was deduced from in vitro characterization data based on these parameters. Available data from five patients in the ongoing clinical trial of AbioCor showed 0-1.4 L/minute bronchial shunt flows. Maximum variation for any individual patient was 1.1 L/minute.

Effect of bronchial artery blood flow on cardiopulmonary bypass-induced lung injury

Cardiovascular surgery requiring cardiopulmonary bypass (CPB) is frequently complicated by postoperative lung injury. Bronchial artery (BA) blood flow has been hypothesized to attenuate this injury. The purpose of the present study was to determine the effect of BA blood flow on CPB-induced lung injury in anesthetized pigs. In eight pigs (BA ligated) the BA was ligated, whereas in six pigs (BA patent) the BA was identified but left intact. Warm (37°C) CPB was then performed in all pigs with complete occlusion of the pulmonary artery and deflated lungs to maximize lung injury. BA ligation significantly exacerbated nearly all aspects of pulmonary function beginning at 5 min post-CPB. At 25 min, BA-ligated pigs had a lower arterial Po2at a fraction of inspired oxygen of 1.0 (52 ± 5 vs. 312 ± 58 mmHg) and greater peak tracheal pressure (39 ± 6 vs. 15 ± 4 mmHg), pulmonary vascular resistance (11 ± 1 vs. 6 ± 1 mmHg·l–1·min), plasma TNF-α (1.2 ± 0.60 vs. 0.59 ± 0.092 ng/ml), extravascular lung water (11.7 ± 1.2 vs. 7.7 ± 0.5 ml/g blood-free dry weight), and pulmonary vascular protein permeability, as assessed by a decreased reflection coefficient for albumin (σalb; 0.53 ± 0.1 vs. 0.82 ± 0.05). There was a negative correlation ( R = 0.95, P < 0.001) between σalband the 25-min plasma TNF-α concentration. These results suggest that a severe decrease in BA blood flow during and after warm CPB causes increased pulmonary vascular permeability, edema formation, cytokine production, and severe arterial hypoxemia secondary to intrapulmonary shunt.

Bronchopulmonary shunts in patients with chronic thromboembolic pulmonary hypertension: evaluation with helical CT and MR imaging

OBJECTIVE

The purpose of our study was to compare differences in flow between the pulmonary and systemic circulations by assessing MR phase-contrast flow measurements and CT measurements of dilated bronchial arteries in patients with chronic thromboembolic pulmonary hypertension.

MATERIALS AND METHODS

Seventeen patients were included in this study. MR phase-contrast flow measurements were used to calculate the net forward volumes in the right and left pulmonary arteries and in the ascending aorta. Single-detector helical CT scans were assessed for the presence of dilated bronchial arteries that could be delineated from the descending aorta to the mainstem bronchi. Their perpendicular cross-sectional area at the level of the main bronchi was measured using a double-threshold region of interest (> or =100-3072 H).

RESULTS

The mean net forward volume in the aorta was 44.6 mL per heartbeat (R-R interval) and in the pulmonary arteries, 30 mL per R-R interval. Thus, the mean difference was 14.6 mL per R-R interval; this value represents the shunt volume between the systemic arterial and pulmonary venous circulations. On CT, dilated bronchial arteries were depicted in all patients (mean, three arteries per patient). The mean cross-sectional area of the bronchial arteries was 0.19 cm(2). Pearson's correlation coefficient (r) between cross-sectional area and shunt volume was 0.86 (p < 0.01).

CONCLUSION

MR imaging was able to reveal substantial differences in flow between the systemic arterial and pulmonary venous circulations in patients with chronic thromboembolic pulmonary hypertension. These differences correlated well with the diameters of the bronchial arteries seen on helical CT. Furthermore, these differences resolved after pulmonary thromboendarterectomy. MR imaging enables the accurate estimation of flow in the bronchial arteries in patients with chronic thromboembolic pulmonary hypertension.

Lung protection during total cardiopulmonary bypass by isolated lung perfusion: preliminary results of a novel perfusion strategy

BACKGROUND

The present pilot study was conducted to evaluate the effect of isolated short-term lung perfusion during cardiopulmonary bypass (CPB) on inflammatory response and oxygenation.

METHODS

A total of 24 patients undergoing elective cardiac surgery with routine CPB were prospectively assigned to three groups. Group I (n = 7), control subjects receiving neither lung perfusion nor ultrafiltration; group II (n = 9), patients undergoing lung perfusion; and group III (n = 8), patients undergoing lung perfusion plus ultrafiltration. Lung perfusion consisted of single-shot hypothermic pulmonary artery perfusion with oxygenated blood. Proteins indicative of leukocyte activation and lung injury were measured in plasma and bronchoalveolar lavage fluid (BALF). The alveolar-arterial oxygen gradient (A-aDO2) and the oxygenation index (PO2/FiO2) were also determined.

RESULTS

Oxygenation values were best preserved in group III, followed by group II. After CPB, elastase-alpha1-proteinase inhibitor complex had increased in plasma in all groups; in BALF it increased in groups I and II, but not in group III. Alpha2-macroglobulin increased significantly in BALF in group I but not in groups II and III.

CONCLUSIONS

These preliminary results provide some evidence that single-shot hypothermic lung perfusion with oxygenated blood at the beginning of CPB may have a protective effect on the lungs, especially when combined with ultrafiltration.

Cardiopulmonary bypass reduction of bronchial blood flow: a potential mechanism for lung injury in a neonatal pig model

BACKGROUND

During total cardiopulmonary bypass, blood flow to the lungs is limited to flow through the bronchial arteries. We tested the hypothesis that bronchial blood flow during cardiopulmonary bypass is insufficient to prevent ischemia of the lung and that perfusion of the pulmonary arteries with oxygenated blood during bypass would reduce lung injury.

METHODS

Eighteen piglets (5.0 +/- 0.5 kg) were subjected to 120 minutes of normothermic total cardiopulmonary bypass, followed by 60 minutes of postbypass perfusion. Nine of them received continuous pulmonary perfusion with oxygenated blood during bypass. Six additional piglets served as a control group and were mechanically ventilated after sternotomy for 180 minutes only. We quantitated bronchial arterial blood flow, tissue lactate content, and alveolar septal thickness and surface area. We also obtained bronchioalveolar lavage fluid samples.

RESULTS

With the beginning of cardiopulmonary bypass, bronchial arterial blood flow decreased to 13% of baseline (42.1 +/- 10.4 to 5.6 +/- 1.0 mL/min). It remained decreased until the end of bypass and returned to starting levels 60 minutes after bypass. The decrease in bronchial blood flow was associated with a 3-fold increase in tissue lactate content. At the end of reperfusion there was a 2-fold increase in alveolar septal thickness and significant accumulations relative to control in the bronchoalveolar lavage fluid of albumin, lactate dehydrogenase, neutrophils, and elastase. Controlled pulmonary perfusion significantly ameliorated all the observed changes.

CONCLUSION

Cardiopulmonary bypass caused a reduction in bronchial arterial blood flow, which was associated with injury of the lung. Controlled pulmonary perfusion reduced injury to the lung during bypass. The inflammatory response, as evidenced by bronchoalveolar lavage fluid, may be caused by ischemia.

Bronchial artery perfusion during cardiopulmonary bypass does not prevent ischemia of the lung in piglets: assessment of bronchial artery blood flow with fluorescent microspheres

OBJECTIVE

Blood supply of the lungs during total cardiopulmonary bypass (CPB) is limited to flow through the bronchial arteries. This study was undertaken to assess the bronchial artery blood flow during CPB with fluorescent microspheres in a piglet model.

METHODS

We subjected ten piglets (mean weight 5.0+/-0.5 kg) to 120 min of normothermic, total CPB without aortic cross-clamping, followed by 60 min of post-bypass perfusion. Fluorescent microspheres were injected into the left atrium or the aortic cannula or distal to the cannula to assess bronchial artery blood flow before, during and after CPB. The reference samples were taken from the descending aorta. We compared the different sites of injection. Tissue samples of the lungs were taken before and 60 min after CPB.

RESULTS

Before CPB, total bronchial artery perfusion was 43.6+/-14.1 ml/min (4.8+/-1.3% of cardiac output) as by injection distal to the aortic cannula. These values were not different when microspheres were injected into the left atrium or the aortic cannula. There was no difference in scatter or in the amount of microspheres in the reference samples among the three injections sites. During CPB, bronchial artery perfusion was significantly decreased (4.4+/-2.4 ml/min vs. 40.0+/-5.0 ml/min before CPB) and returned to baseline values 60 min after CPB. Light microscopy of the tissue samples revealed alveolar septal thickening and a decrease in alveolar surface area after 60 min of reperfusion which was associated with a decreased capacity to oxygenate blood.

CONCLUSIONS

(1) Bronchial artery blood flow can quantitatively be assessed during CPB when microspheres are injected into the ascending aorta and the reference samples are taken from the descending aorta. (2) Despite adequate perfusion pressure bronchial artery blood flow is decreased substantially during CPB. (3) The decrease in blood flow and the ultrastructural changes present at the end of CPB suggest the presence of low-flow ischemia of the lung during total CPB.

Effects of ventilation and nonventilation on pulmonary venous blood gases and markers of lung hypoxia in humans undergoing total cardiopulmonary bypass

OBJECTIVE

To assess the effects of lung oxygenation and ventilation vs. lung collapse on pulmonary markers of lung hypoxia.

DESIGN

A prospective, nonrandomized, nonblinded comparative study.

SETTING

University department of anesthesiology and cardiothoracic surgery.

SUBJECTS

Twelve adult patients undergoing coronary bypass grafting requiring total cardiopulmonary bypass.

INTERVENTIONS

Single lung ventilation during total cardiopulmonary bypass (tidal volume, 150 mL; respiratory rate, 6 breaths/min; inspiratory oxygen fraction, 0.5) while the contralateral lung was allowed to collapse completely without oxygenation.

MEASUREMENTS AND MAIN RESULTS

At the beginning and at the end of total cardiopulmonary bypass (duration, 59-65 mins), blood was aspirated from the right and left pulmonary veins and the radial artery for measurement of blood gases and concentrations of endothelin-1, big-endothelin, thromboxane B2, lactate, and lactate dehydrogenase. Nonventilation during total cardiopulmonary bypass compared with ventilation resulted in lower pulmonary venous P(O2) values (57+/-15 torr [7.6+/-2.0 kPa] vs. 103+/-23 torr [13.7+/-3.1 kPa]) and higher thromboxane B2 concentrations (488+/-95 pg/mL vs. 434+/-92 pg/mL). The concentrations of endothelin-1, big-endothelin, lactate, and lactate dehydrogenase in the pulmonary veins did not differ significantly between nonventilated and ventilated lungs.

CONCLUSIONS

Development of pulmonary tissue hypoxia during 1 hr of nonventilation and cardiopulmonary bypass with completely inhibited pulmonary arterial blood flow is unlikely, suggesting that enough oxygen is stored in or is provided to the collapsed lung. Thus, nonventilation during total cardiopulmonary bypass does not appear to contribute to postoperative respiratory dysfunction by causing pulmonary tissue hypoxia. These results, however, do not exclude that mechanical factors of ventilation might benefit the lung during cardiopulmonary bypass.

Human bronchial artery blood flow after lung Tx with direct bronchial artery revascularization

The inaccuracy of measuring human bronchial artery blood flow has previously been considerable. En bloc double-lung transplantation with bronchial artery revascularization (BAR) using a single conduit offers the unique opportunity of direct measurement of the total bronchial artery blood flow. In eight en bloc double-lung-transplanted patients with complete BAR, the basal blood flow was measured by using a 0.014-in. Doppler guide wire and arteriography. The average peak velocity in the conduit was 12-73 cm/s [+/-2.1 (SD) cm/s], and the conduit diameter was 1.7-3.1 mm [+/-0.10 (SD) mm], giving individual basal flow values between 19 and 67 ml/min [+/-5 (SD) ml/min], or 0.2-1.9% of estimated cardiac output. In three patients basal measurements were followed by injection of nitroglycerin and verapamil into the conduit. This increased the bronchial artery flow to 121-262% of basal values (31-89 ml/min). The measured values appear more physiologically plausible than previous bronchial artery blood flow measurements in humans.

Partial pressure of oxygen is lower in the left upper pulmonary vein than in the right in adults with atrial septal defect: difference in P(O2) between the right and left pulmonary veins

BACKGROUND

The right-to-left shunt at the atrial level is responsible for arterial hypoxemia in patients with atrial septal defect.

OBJECTIVES

This study investigated the mechanism of arterial hypoxemia in patients with atrial septal defect by measuring the P(O2) in both the right and left upper pulmonary veins.

SUBJECTS AND METHOD

We prospectively measured the P(O2) in the femoral artery and the right and left upper pulmonary veins during cardiac catheterization in 13 adults (median age, 53 years) and 7 children (median age, 7 years) with secundum atrial septal defect. The adults and children were studied consecutively. Contrast echocardiography was performed to evaluate right-to-left shunt in all adults.

RESULTS

Among the children, there were no patients showing arterial hypoxemia, and there was no difference in the P(O2) (+/-SD) between the right and left upper pulmonary veins (right, 100+/-3.8 mm Hg vs left, 100+/-7.8 mm Hg; p = 0.92). However, arterial hypoxemia was present in 11 of the 13 adult patients, although contrast echocardiography showed more than a moderate degree of right-to-left shunt in only four adults. The P(O2) was lower in the left upper pulmonary vein than it was in the right upper pulmonary vein in all adult patients (right, 91.6+/-13.8 mm Hg vs left, 73.0+/-11.5 mm Hg; p < 0.0001).

CONCLUSION

The P(O2) was lower in the left upper pulmonary vein than it was in the right upper pulmonary vein in adults with atrial septal defect. Care must be taken in measuring pulmonary blood flow if the P(O2) in the left upper pulmonary vein is low enough to influence oxygen content. The decreased P(O2) in the left upper pulmonary vein may contribute to arterial hypoxemia in addition to right-to-left shunt at the atrial level in adults with atrial septal defect.

Revascularization of the bronchial arteries in lung transplantation: an overview

Development of the surgical technique has minimized the incidence of airway problems associated with single as well as sequential bilateral lung transplantation. Although early results are good, long-term results remain unsatisfactory. The main problems after lung transplantation are pulmonary infections and the bronchiolitis obliterans syndrome. The bronchiolitis obliterans syndrome is usually considered to be chronic rejection, but a multifactorial genesis including airway ischemia has been suggested. We reviewed the literature relevant to direct bronchial artery revascularization during lung transplantation. Although information is limited, there are good reasons to believe that reestablishment of the dual blood supply to the transplanted lung is beneficial not only for healing of the airway anastomoses, but also for the airway and the lung responses to pathologic conditions. In small series, methods of bronchial artery revascularization have proved successful and have been associated with good early results. We believe it is justified to test the impact of direct bronchial artery revascularization on outcome after lung transplantation in large clinical series.

Systemic to pulmonary bronchial blood flow in heart failure

STUDY OBJECTIVE

The aim of this study was to measure systemic to pulmonary blood flow from bronchial circulation (Qbr[s-p]) in patients with heart failure.

DESIGN

In the absence of pulmonary and coronary flows, Qbr(s-p) is the volume of blood accumulating in the left side of the heart; Qbr(s-p) was measured during total cardiopulmonary bypass for coronary artery surgery; bronchial blood was vented through a cannula introduced into the left side of the heart and its volume was measured.

PATIENTS

Patients were subdivided according to the presence for more than 6 months (group 1, n = 6) or less than 2 months (group 2, n = 7), or the absence of heart failure (group 2, n = 15).

MEASUREMENTS AND RESULTS

Qbr(s-p) was 89 +/- 18* mL/min, 27 +/- 3, 22 +/- 2, in groups 1, 2, and 3, respectively (* = p < 0.01 group 1 vs groups 2 and 3). During total cardiopulmonary bypass, pulmonary venous pressure approximates atmospheric pressure and no differences between groups were observed in systemic artery pressure, extracorporeal circulation pump flow, and airway pressure. Therefore, vascular resistance through the bronchial vessels draining into the pulmonary circulation is reduced in patients with heart failure for more than 6 months (group 1).

CONCLUSIONS

During total cardiopulmonary bypass, Qbr(s-p) is increased in patients with chronic heart failure. Since with elevated pulmonary vascular pressure blood flow through Qbr(s-p) vessels is from the pulmonary to the systemic circulation, the lower resistance observed in group 1 suggests that bronchial vessels might contribute to reduced lung fluid overload in patients with chronic heart failure.

Airway obstruction and bronchial hyperresponsiveness in left ventricular failure and mitral stenosis

Small and large airways narrow in LVF and the term cardiac asthma is often used. However, current usage of this term is inconsistent and its meaning is therefore ambiguous. The term is better avoided despite several emerging similarities with bronchial asthma. Airway narrowing may be precipitated by acute elevation of pulmonary or bronchial vascular pressures. This appears to be mainly due to reflex bronchoconstriction. The afferents of this reflex are C-fibers with their endings in the lung parenchyma, bronchi, and pulmonary blood vessels and RAR in the larger airways, and they run in the vagus nerves, as do the efferent bronchoconstrictor fibers. Chronic elevation of pulmonary vascular pressures, as in mitral stenosis, are also associated with airway narrowing. Pulmonary edema (in the absence of vascular hypertension) also causes reflex bronchoconstriction. Bronchial responsiveness to bronchoconstrictor drugs is increased in LVF, partly, at least, due to reflex mechanisms. Bronchial mucosal swelling may also contribute. Narrowing by nonreflex mechanisms definitely occurs and there is direct evidence that decreased lung volume caused by pulmonary edema may cause this. There is little evidence for bronchial narrowing due to the mechanical effect of peribronchial edema, or by swelling of the bronchial mucosa. However, edema foam may terminally cause grave obstruction. Patients with LVF are commonly treated with bronchodilator drugs, but the basis for this approach needs further clarification.

Systemic to pulmonary bronchial blood flow in mitral stenosis

We measured systemic to pulmonary bronchial blood flow [Qbr(s-p)] during total cardiopulmonary bypass in 15 patients with mitral stenosis and elevated pulmonary venous pressure (group A, mean pulmonary wedge pressure = 22.2 +/- 5.4 mm Hg, mean +/- SD) and in 15 patients with coronary artery diseases and normal pulmonary venous pressure (group B). Qbr(s-p) is the volume of blood accumulating in the left side of the heart in the absence of pulmonary and coronary flows. This blood was vented through a cannula introduced into the left atrium and measured. Qbr(s-p) was 76.3 +/- 13.9 ml/min (2.18 +/- 0.37 percent of extracorporeal circulation pump flow) and 22.3 +/- 2.1 (0.63 +/- 0.15) in group A and B, respectively (p less than 0.01). During total cardiopulmonary bypass, pulmonary venous pressure is approximately atmospheric pressure, and no differences in systemic blood pressure, extracorporeal circulation pump flow, and airways pressure were observed between group A and B. Therefore, vascular resistance through the bronchial vessels draining into the pulmonary circulation is reduced in patients with mitral stenosis and elevated pulmonary venous pressure.

Inspired gas relative humidity affects systemic to pulmonary bronchial blood flow in humans

To our knowledge, the effects of humidity of inspired air on bronchial blood flow in humans are unknown. During total cardiopulmonary bypass, we measured systemic to pulmonary bronchial blood flow (Qbr[s-p]) which is the volume of blood accumulating into the left side of the heart in the absence of pulmonary and coronary flow. A cannula was introduced into the right upper pulmonary vein and advanced into the lowermost portion of the left side of the heart. From this cannula Qbr(s-p) was vented by gravity and measured. Inspired gas (10 L/min, endotracheal tube, 50 percent O2 + 50 percent N2O) relative humidity was less than 20 percent and greater than 85 percent in group A (n = 25) and in group B (n = 25), respectively. Mean (+/- SE) Qbr(s-p) was 40.7 +/- 0.06 ml/min or 1.32 +/- 0.12 ml/min (percent cardiac output) in group A and 21.7 +/- 1.8 ml/min or 0.68 +/- 0.06 ml/min in group B. These data indicate that under these conditions Qbr(s-p) is increased by dry gas lung inflation in humans.

Increase of alveolar pressure reduces systemic-to-pulmonary bronchial blood flow in humans

We studied the effect of positive alveolar pressure (PA) on systemic to pulmonary bronchial blood flow, Q?? in humans. The Q?? was measured during total cardiopulmonary bypass as the volume of blood accumulating in the left heart. This blood was vented by gravity from the left heart via a cannula introduced in the right upper pulmonary vein and advanced to the lowest portion of the left heart. In group A (n = 10) the Qbr(s-p) was measured for 25 to 95 min with constant PA (4.0 +/- 0.2 cm H2O, mean +/- SE). In group B (n = 10) Qbr(s-p) was measured for 20 min with PA = 4.1 +/- 0.2 cm H2O and for a further 20 min with PA = 14.1 +/- 0.4 cm H2O. The Qbr(s-p) ranged between 0.32 and 2.76 percent of cardiac output (pump flow) and remained constant with time (group A). The increase of PA from 4.1 +/- 0.2 to 14.1 +/- 0.4 cm H2O reduced Qbr(s-p) by approximately 40 percent (p less than 0.01, group B). We conclude that positive PA reduces Qbr(s-p) during total cardiopulmonary bypass. Therefore, we advise using low PA during assisted ventilation to preserve bronchial blood flow.

Phrenic nerve function and its relationship to atelectasis after coronary artery bypass surgery

Atelectasis following coronary artery bypass surgery (CAB) occurs in the majority of patients. To determine the importance of operative variables in the development of postoperative atelectasis and the incidence of phrenic nerve injury caused by topical cold cardioplegic solution, we studied 57 patients (53 male, four female) undergoing CAB. Their mean age, +/- SD, was 58 +/- 13 years. Transcutaneous stimulation was used to evaluate phrenic nerve function preoperatively and postoperatively in 52 patients. An unequivocal paresis of the phrenic nerve was documented in five patients. In an additional 27 patients, the amplitude of the compound diaphragm action potential was reduced postoperatively. However, methodologic limitations did not allow the conclusion that this was secondary to a phrenic axonal degeneration. Discriminant analysis of intraoperative variables showed more severe atelectasis with a larger number of grafts, with a longer operative and bypass time, when the pleural space was entered, when a right atrial drain and a cardiac insulating pad were not used, and with a lower body temperature. It is concluded that phrenic paresis may occur after CAB and topical cold cardioplegia, but that other factors must explain the atelectasis found in the majority of patients.

Cardiac temperature and cardioplegic volume during cardiopulmonary bypass

This study was designed to compare two methods of cardiac drainage on the rate of change of cardiac temperature and volume of cardioplegic solution required to maintain the cardiac temperature less than or equal to 12 degrees C in patients undergoing coronary artery bypass surgery. Two groups of 10 patients were studied who were comparable in age, sex, and smoking history. In Group 1, cardiac drainage was achieved by using single-port drainage cannulae in the superior and inferior vena cava with caval tapes. Group 2 patients had a caval atrial cannula to drain the noncoronary collateral flow from the right atrium as well as that from the venae cavae. Both groups had a sump line in the left ventricle to drain the bronchopulmonary anastomotic blood flow. Results from the study showed that there was no difference between groups in the initial amount of cold cardioplegic solution required to arrest and cool the heart or the initial recording of ventricular temperatures. However, the volume of cardioplegic solution required to maintain the cardiac temperature at less than or equal to 12 degrees C after administration of the initial volume was less (P less than 0.05) for Group 2 than Group 1. Group 2 also had a slower rate of increase in cardiac temperature than Group 1 (P less than 0.01). Results from this study indicate that the constant removal of blood from both cardiac chambers during coronary artery bypass surgery significantly reduces the rate of myocardial rewarming and decreases the amount of cardioplegic solution required to maintain a given cardiac temperature.