Distribution of pulmonary blood flow after myocardial ischemia and infarction

A new approach to improve the hemodynamic assessment of cardiac function independent of respiratory influence

Cardiovascular and respiratory systems are anatomically and functionally linked; inspiration produces negative intrathoracic pressures that act on the heart and alter cardiac function. Inspiratory pressures increase with heart failure and can exceed the magnitude of ventricular pressure during diastole. Accordingly, respiratory pressures may be a confounding factor to assessing cardiac function. While the interaction between respiration and the heart is well characterized, the extent to which systolic and diastolic indices are affected by inspiration is unknown. Our objective was to understand how inspiratory pressure affects the hemodynamic assessment of cardiac function. To do this, we developed custom software to assess and separate indices of systolic and diastolic function into inspiratory, early expiratory, and late expiratory phases of respiration. We then compared cardiac parameters during normal breathing and with various respiratory loads. Variations in inspiratory pressure had a small impact on systolic pressure and function. Conversely, diastolic pressure strongly correlated with negative inspiratory pressure. Cardiac pressures were less affected by respiration during expiration; late expiration was the most stable respiratory phase. In conclusion, inspiration is a large confounding influence on diastolic pressure, but minimally affects systolic pressure. Performing cardiac hemodynamic analysis by accounting for respiratory phase yields more accuracy and analytic confidence to the assessment of diastolic function.

Relationship between mean right atrial pressure and Doppler parameters in patients with right ventricular infarction

BACKGROUND

The incidence of an inferior left ventricular infarction involving the right ventricle is very high, ranging from 14 to 84%. Isolated right ventricular infarction accounts for < 3% of all cases of infarction.

HYPOTHESIS

The aim of the present study was to assess the relationship between Doppler parameters of hepatic vein and tricuspid inflow, as well as mean right atrial (RA) pressure in patients with right ventricular infarction.

METHODS

In all, 59 consecutive patients with inferior left ventricular infarction involving the right ventricle were selected for the study. All patients underwent Doppler echocardiographic evaluation of tricuspid and hepatic vein parameters and catheterization of the right side of the heart. Patients were divided into two groups according to the presence or absence of severe tricuspid regurgitation.

RESULTS

In patients with severe tricuspid regurgitation, a significant correlation (r = 0.64; p < 0.001) between RA maximal volume and mean right atrial pressure (RAP) was found, and the sensitivity of RA maximal volume in identifying mean RAP > 7 mmHg was 64% with a specificity of 78%. In patients without severe tricuspid regurgitation, the most significant relationship was observed between mean RAP and inferior vena cava collapse index. Significant correlations between maximal and minimal diameters of the inferior vena cava were also observed.

CONCLUSIONS

Echocardiographic and Doppler parameters may be useful for evaluating mean RAP in patients with right ventricular infarction. In patients with severe tricuspid regurgitation, the more important parameters are maximal and minimal RA volumes. In patients without severe tricuspid regurgitation together with right atrial volume, the important parameters are acceleration and deceleration time of the tricuspid inflow peak E velocity and hepatic systolic and diastolic venous flow.

Radionuclide-determined changes in pulmonary blood volume and thallium lung uptake in patients with coronary artery disease

Exercise-induced increases in radionuclide-determined pulmonary blood volume (PBV) and thallium lung uptake have been described in patients with coronary artery disease (CAD) and have been shown to correlate with transient exercise-induced left ventricular dysfunction. To compare these 2 techniques in the same patients, 74 patients (59 with and 15 without significant CAD) underwent supine bicycle exercise twice on the same day--first for thallium myocardial and lung imaging and then for technetium-99m gated blood pool imaging for the PBV ratio determination. Thallium activity of lung and myocardium was determined to calculate thallium lung/heart ratio. Relative changes in PBV from rest to exercise were expressed as a ratio of pulmonary counts (exercise/rest). Previously reported normal ranges for thallium lung/heart ratio and PBV ratio were used. The PBV ratio and thallium lung/heart ratio were abnormal in 71 and 36%, respectively, of patients with CAD (p less than 0.01). Both ratios were normal in all patients without CAD. Although the resting ejection fractions did not differ significantly in patients with normal versus those with abnormal PBV ratios or thallium lung/heart ratios, abnormal PBV ratios and thallium lung/heart ratios were associated with an exercise-induced decrease in ejection fraction. Propranolol use was significantly higher in patients with abnormal than in those with normal thallium lung/heart ratios (p less than 0.01). No significant difference in propranolol use was present in patients with abnormal or normal PBV ratios.

IN CONCLUSION

(1) the prevalence of an abnormal thallium lung/heart ratio is less than that of the PBV ratio in patients with CAD; (2) both tests are normal in normal control subjects; (3) propranolol does not cause abnormal results in normal control subjects; however, propranolol may influence lung thallium uptake in patients with CAD; and (4) when both tests are abnormal, there is a high likelihood of multivessel disease.

Clinical ventilation-perfusion scintigraphy

Ventilation-perfusion scintigraphy is an established procedure for the investigation of lung disease. Perfusion scans are commonly obtained with a gamma-camera following injection of 99mTc-labelled microspheres. For the assessment of regional lung ventilation, a number of techniques are now being employed, i.e. 133Xe and 127Xe single breath/washout studies, continuous inhalation of 81mKr and inhalation of radioactive aerosols. The latter two methods are now gaining consideration in clinical practice. Lung perfusion scanning is highly sensitive for detection of regional abnormalities of blood flow; the diagnosis of pulmonary embolism remains the most important clinical application of the technique. In this context, the use of a ventilation scan is required in order to increase the specificity of the procedure. In general, lung ventilation-perfusion scintigraphy is of great value for the management of patients with both primary lung disease and heart disease, by providing pathophysiological information of importance for the diagnosis, follow up and the functional evaluation of the patient.

Pulmonary gas exchange during acute myocardial ischaemia a study in the closed chest anaesthetized dog

The occurrence and the cause of arterial hypoxaemia were studied in spontaneously breathing dogs in which myocardial ischaemia was induced during anaesthesia. Changes in several circulatory and ventilatory variables and in parameters of gas exchange were assessed in twelve dogs in the two 1st h after the intervention; these included changes in the distribution of ventilation-perfusion ratios determined with an inert tracer gas method. Eight out of 12 dogs developed haemodynamic signs of an acute myocardial infarction after occlusion of a branch of the left coronary artery; the circulatory changes were moderate in 6 and severe in 2 animals. A drop in Pa,O2 occurred in 5 dogs. In one without significant haemodynamic changes it was largely due to a decrease in alveolar ventilation. The ventilation-perfusion ratio distribution in the other 4 dogs did not change in a consistent way; appreciable shunt circulation (6.6%) developed in one dog. Neither ventilation-perfusion mismatch nor shunt circulation contributed much to the hypoxaemia. The most consistent finding in the 5 dogs in whom Pa,O2 fell, was a drop in Pv,O2 (mean 1.3 kPa); it accounted for 86% of the drop in Pa,O2.

Radionuclide-determined change in pulmonary blood volume with exercise. Improved sensitivity of multigated blood-pool scanning in detecting coronary-artery disease

To assess the clinical usefulness of radionuclide-determined changes in pulmonary blood volume in patients with or without substantial coronary-artery disease, we determined the ratio of pulmonary blood volume at rest as compared with that during exercise. We used multigated blood-pool images obtained at rest and during supine exercise to determine the blood-volume ratio in patients subsequently undergoing coronary arteriography for evaluation of chest pain. Exercise tests were performed by use of a submaximal-workload protocol, although all tests were limited according to each patient's symptoms. The mean exercise/rest pulmonary-blood-volume ratios were lower for persons without coronary-artery disease (0.94 +/- 0.06 [S.D.], 10 patients) and for those with disease confined to the right coronary artery (0.99 +/- 0.12, five patients), as compared with all others with coronary-artery disease (1.14 +/- 0.15, 37 patients) (P less than 0.01). A pulmonary-blood-volume ratio equal to or greater than 1.06 had a sensitivity of 79 per cent. Patients with coronary-artery disease not confined to the right coronary artery usually show an increase in pulmonary blood volume during supine exercise. No such change occurs in persons without coronary-artery disease.

Clinical significance of pulmonary function tests. Pulmonary function after uncomplicated myocardial infarction

Derangement of pulmonary function following myocardial infarction is related to the severity of hemodynamic dysfunction. Abnormalities of pulmonary function appear even in patients without clinical or radiologic evidence of congestive failure. There is a reduction in vital capacity and rates of air flow. There is evidence for dysfunction of "small airways" and diminished ventilation to dependent parts of the lung. Total lung capacity may be normal or reduced, and residual volume may be increased slightly in uncomplicated myocardial infarction. Residual volume falls with more pronounced pulmonary congestion and edema. Distribution of pulmonary perfusion is altered after myocardial infarction, with a shift of perfusion away from the dependent parts of the lung (bases) towards the apices. Pulmonary gas exchange is impaired, with hypoxemia (due to both ventilation-perfusion inequality and increased shunting); and the diffusing capacity for carbon monoxide is diminished. Dead space is increased. The basic pathophysiologic mechanism responsible for abnormalities of pulmonary function is increased pulmonary water, which may be very minimal with uncomplicated myocardial infarction and stay primarily in the pulmonary interstitial space, but becomes progressively more severe with eventual alveolar flooding and marked impairment of pulmonary function.

Hypoxemia and lung water in acute myocardial infarction

Pulmonary extravascular volume or lung water (PEV), arterial blood gases, and cardiac hemodynamics were measured in 88 patients with acute myocardial infarction. A progressive increase in PEV and a decrease in arterial oxygen tension (PaO2) were observed from Class I (uncomplicated) patients to Class III (frank pulmonary edema) patients. Heart rate and pulmonary wedge pressure (Pw) rose and cardiac index declined with increasing severity of heart failure by clinical classification. There was a significant correlation between PEV and Pw independent of clinical class (r = 0.47, p less than 0.01). PaO2 had a negative correlation with Pw (r = -0.28, p less than 0.01) as well as PEV (r = -0.26, p less than 0.02). We conclude therefore that increased pulmonary hydrostatic pressure secondary to pulmonary venous hypertension in patients with acute myocardial infarction is a major determinant of interstitial edema. At higher values of PEV, PaO2 was lower. The mechanism of hypoxemia in the presence of excessive lung water may be due to multiple factors, including small airway dysfunction and intrapulmonary shunting.

Estimation of blood gas contents from expired air under normal and pathologic conditions

Methods of estimating arterial-venous O2 content difference, mixed venous CO2 content and tension, and average arterial CO2 content are presented. They are based on the continuous gas analysis of expired air during a prolonged expiration. The influence of CO2 storage in lung tissue and certain pathophysiologic conditions on the accuracy of these methods was systematically investigated with a comprehensive multi-chamber computer simulation of the lung. For normal levels of CO2 storage capacity, satisfactory estimates of arterial-venous O2 content difference are feasible for differences less than 8 volumes percent; with high levels of CO2 storage capacity, large errors can occur. Storage of CO2 in lung tissue causes large errors in the estimates of mixed venous CO2 content and tension, and average arterial CO2 content; reliable estimates do not appear to be feasible from analysis of expired gas. Simulated pathophysiologic conditions of interstitial pulmonary edema or atelectasis also introduce large errors. This analysis delineates the theoretic limitations of an estimation technique in clinical applications where acute respiratory dysfunctions occur.

Regional pulmonary function before and after pneumonectomy using 133xenon

Regional pulmonary function studies using 133xenon gas, spirometry, and arterial blood gas levels were performed before and 1 to 47 months after pneumonectomy for bronchogenic carcinoma in 27 patients. The mean loss in forced vital capacity was more after right pneumonectomy (44.9 percent of preoperative value) than after left lung resection (41.4 percent). There was no significant change in regional pulmonary function distribution within the remaining lung in 24 patients. Two patients developed significant changes in regional pulmonary blood flow; one had hepatic cirrhosis, and the other sustained a myocardial infarction after pneumonectomy. The third patient with significant apical hyperperfusion before pneumonectomy gradually developed abnormal distribution of ventilation concomitant with electrocardiographic evidence of cor pulmonale within two years after pneumonectomy. The mean ventilation of the apical zones was significantly lower than the mean of 14 healthy subjects. This finding and the higher incidence of ventilatory defects were related to old age and heavy smoking. Seven patients with marked reduction of pulmonary blood flow to the tumor-bearing lung (9 to 33 percent of cardiac output) had technically successful pneumonectomy. A formula and nomogram were developed to estimate the prognostically significant forced expiratory volume in one second after pneumonectomy from the preoperative studies.

Interrelation between alterations in pulmonary mechanics and hemodynamics in acute myocardial infarction

Pulmonary mechanics were evaluated in 30 patients with acute myocardial infarction by measuring forced expiratory flow rates and total pulmonary resistance (R(T)) with the oscillometric method at the resonant frequency of the chest (6-8) cycle/s). During the first 3 days after infarction, forced expiratory volume (FEV) and forced mid-expiratory flow rate (FEF(25-75%)) were 69% and 60% of predicted values, respectively. 10 or more wk later these values were 95% and 91%. Initially, R(T) was 52% greater than predicted, but was only 4% greater 10 or more wk later. In 11 patients R(T) was measured at both resonant frequency and at 3 cycle/s. Five of these patients had no clinical signs of heart failure, but nine had abnormally high values of pulmonary artery pressure, "wedge" pressure and pulmonary extravascular water volume. All of these patients recovered. Initially, R(T) at resonance was 50% and R(T) at 3 cycle/s was 130% greater than predicted values. 2-3 wk later these figures were -3% and +6% of those predicted, respectively. At 10 wk or more, significant frequency dependence of R(T) had disappeared (R(T) at 3 cycle/s was 7% greater than R(T) at resonance). Isoproterenol inhalation in six patients caused no change in flow rates, R(T) at resonance, or R(T) at 3 cycle/s. R(T) at resonance and at 3 cycle/s, FEV, and FEF(25-75%) correlated significantly with the pulmonary vascular pressures. Patients with more marked arterial hypoxia and larger values for extravascular water volume had greater elevations of R(T) and depression of FEF(25-75%), but linear correlations were not significant. Clinical signs of congestive heart failure significantly correlated with a fall in FEV and FEF(25-75%), the development of frequency dependence of R(T), and elevation of the pulmonary wedge pressure. The initial elevation of R(T) and low flow rates indicate a modest degree of airway obstruction in acute myocardial infarction. Lack of response to isoproterenol suggests that bronchial muscular constriction is not a major factor. Frequency dependence of R(T) accompanied by elevated pulmonary vascular pressures and extravascular water volume indicates that pulmonary congestion causes the development of uneven time constants in the airways. Vascular engorgement and interstitial edema from elevated vascular pressures causing narrowing of the peripheral airways and closure of collateral airways could account for the above findings.