Small-airways function in myocardial infarction

Metabolic labeling of cardiomyocyte-derived small extracellular-vesicle (sEV) miRNAs identifies miR-208a in cardiac regulation of lung gene expression

Toxoplasma gondii uracil phosphoribosyltransferase (UPRT) converts 4-thiouracil (4TUc) into 4-thiouridine (4TUd), which is incorporated into nascent RNAs and can be biotinylated, then labelled with streptavidin conjugates or isolated via streptavidin-affinity methods. Here, we generated mice that expressed T. gondii UPRT only in cardiomyocytes (CM UPRT mice) and tested our hypothesis that CM-derived miRNAs (CM miRs) are transferred into remote organs after myocardial infarction (MI) by small extracellular vesicles (sEV) that are released from the heart into the peripheral blood (PB sEV). We found that 4TUd was incorporated with high specificity and sensitivity into RNAs isolated from the hearts and PB sEV of CM UPRT mice 6 h after 4TUc injection. In PB sEV, 4TUd was incorporated into CM-specific/enriched miRs including miR-208a, but not into miRs with other organ or tissue-type specificities. 4TUd-labelled miR208a was also present in lung tissues, especially lung endothelial cells (ECs), and CM-derived miR-208a (CM miR-208a) levels peaked 12 h after experimentally induced MI in PB sEV and 24 h after MI in the lung. Notably, miR-208a is expressed from intron 29 of α myosin heavy chain (αMHC), but αMHC transcripts were nearly undetectable in the lung. When PB sEV from mice that underwent MI (MI-PB sEV) or sham surgery (Sham-PB sEV) were injected into intact mice, the expression of Tmbim6 and NLK, which are suppressed by miR-208a and cooperatively regulate inflammation via the NF-κB pathway, was lower in the lungs of MI-PB sEV-treated animals than the lungs of animals treated with Sham-PB sEV or saline. In MI mice, Tmbim6 and NLK were downregulated, whereas endothelial adhesion molecules and pro-inflammatory cells were upregulated in the lung; these changes were significantly attenuated when the mice were treated with miR-208a antagomirs prior to MI surgery. Thus, CM UPRT mice enables us to track PB sEV-mediated transport of CM miRs and identify an miR-208a-mediated mechanism by which myocardial injury alters the expression of genes and inflammatory response in the lung.

Small airway dysfunction in smokers with stable ischemic heart disease

BACKGROUND

A higher prevalence of airflow limitation (AL) has been described in patients with ischemic heart disease (IHD). Although small airway dysfunction (SAD) is an early feature of AL, there is little information about its occurrence in IHD patients. Our objective was to describe the prevalence of SAD in IHD patients, while comparing patient-related outcomes and future health risk among IHD patients with AL, SAD and normal lung function.

METHODS

In 118 consecutive smoking patients with stable IHD, comorbidities, utilization of healthcare resources, current treatment, blood biochemistry and health status were recorded. SAD was evaluated by impulse oscillometry, and pre- and post-bronchodilator spirometry was performed.

RESULTS

The prevalence of AL and SAD were 20.3 (95% CI, 13.1-27.6%) and 26.3% (95% CI, 18.3-34.2%), respectively. Compared to the normal lung function group, patients with SAD and without AL had lower spirometric values, poorer quality of life and higher levels of C-reactive protein (CRP), as well as increased cardiovascular risk and more vascular age. In patients with normal spirometry, the presence of SAD was independently associated with pack-years, HDL-cholesterol and CRP levels.

CONCLUSION

In patients with IHD, the presence of SAD is common and that it is associated with reduced health status and increased future cardiac risk.

Magnetic resonance elastography of the lung parenchyma in an in situ porcine model with a noninvasive mechanical driver: correlation of shear stiffness with trans-respiratory system pressures

Quantification of the mechanical properties of lung parenchyma is an active field of research due to the association of this metric with normal function, disease initiation and progression. A phase contrast MRI-based elasticity imaging technique known as magnetic resonance elastography is being investigated as a method for measuring the shear stiffness of lung parenchyma. Previous experiments performed with small animals using invasive drivers in direct contact with the lungs have indicated that the quantification of lung shear modulus with (1) H based magnetic resonance elastography is feasible. This technique has been extended to an in situ porcine model with a noninvasive mechanical driver placed on the chest wall. This approach was tested to measure the change in parenchymal stiffness as a function of airway opening pressure (P(ao) ) in 10 adult pigs. In all animals, shear stiffness was successfully quantified at four different P(ao) values. Mean (±STD error of mean) pulmonary parenchyma density corrected stiffness values were calculated to be 1.48 (±0.09), 1.68 (±0.10), 2.05 (±0.13), and 2.23 (±0.17) kPa for P(ao) values of 5, 10, 15, and 20 cm H2O, respectively. Shear stiffness increased with increasing P(ao) , in agreement with the literature. It is concluded that in an in situ porcine lung shear stiffness can be quantitated with (1) H magnetic resonance elastography using a noninvasive mechanical driver and that it is feasible to measure the change in shear stiffness due to change in P(ao) .

Phenotypic heterogeneity in lung capillary and extra-alveolar endothelial cells. Increased extra-alveolar endothelial permeability is sufficient to decrease compliance

BACKGROUND

In acute respiratory distress syndrome, pulmonary vascular permeability increases, causing intravascular fluid and protein to move into the lung's interstitium. The classic model describing the formation of pulmonary edema suggests that fluid crossing the capillary endothelium is drawn by negative interstitial pressure into the potential space surrounding extra-alveolar vessels and, as interstitial pressure builds, is forced into the alveolar air space. However, the validity of this model is challenged by animal models of acute lung injury in which extra-alveolar vessels are more permeable than capillaries under a variety of conditions. In the current study, we sought to determine whether extravascular fluid accumulation can be produced because of increased permeability of either the capillary or extra-alveolar endothelium, and whether different pathophysiology results from such site-specific increases in permeability.

MATERIALS AND METHODS

We perfused isolated lungs with either the plant alkaloid thapsigargin, which increases extra-alveolar endothelial permeability, or with 4alpha-phorbol 12, 13-didecanoate, which increases capillary endothelial permeability.

RESULTS

Both treatments produced equal increases in whole lung vascular permeability, but caused fluid accumulations in separate anatomical compartments. Light microscopy of isolated lungs showed that thapsigargin caused fluid cuffing of large vessels, while 4alpha-phorbol 12, 13-didecanoate caused alveolar flooding. Dynamic compliance was reduced in lungs with cuffing of large vessels, but not in lungs with alveolar flooding.

CONCLUSIONS

Phenotypic differences between vascular segments resulted in site-specific increases in permeability, which have different pathophysiological outcomes. Our findings suggest that insults leading to acute respiratory distress syndrome may increase permeability in extra-alveolar or capillary vascular segments, resulting in different pathophysiological sequela.

Effects of positive end-expiratory pressure in an experimental model of acute myocardial infarct in wistar rats

Our purpose in this study was to access the pulmonary effects of mechanical ventilation with positive end-expiratory pressure (PEEP; 10 cmH2O) or without PEEP (zero PEEP-ZEEP) in a rat model of acute myocardial infarction that resulted in hypotension but not in pulmonary congestion.

METHODS

Wistar rats were anesthetized (1.5% isoflurane) and myocardial infarct was induced by ligature of the anterior interventricular coronary artery. Rats with myocardial infarct were compared with sham-operated (Sham) and closed thorax groups.

RESULTS AND CONCLUSION

There was a significant decrease in MAP in the acute myocardial infarct group (92.5 +/- 4.2 mmHg) when compared with closed chest group (113.0 +/- 4.4 mmHg). There was no significant difference between acute myocardial infarct and Sham groups in PEEP or ZEEP. Mechanical ventilation for 120 min resulted in a significant increase in respiratory system elastance in the groups ventilated with ZEEP (2.59 +/- 0.17 and 2.32 +/- 0.17 cmH2O.mL, Sham and acute myocardial infarct groups, respectively). This effect of mechanical ventilation was not observed in the presence of PEEP in both groups. There was no significant increase in the amount of perivascular pulmonary edema measured in all groups studied. Mean airspace linear intercept and lung tissue distortion index also did not show statistically significant difference between Sham and acute myocardial infarct groups. We conclude that in this experimental model of acute myocardial infarct (12.4 +/- 4.1% area of necrotic tissue and 26.4 +/- 4.0% area of ischemic tissue), there was a protective pulmonary effect of PEEP.

Serial changes in spirometry during an ascent to 5,300 m in the Nepalese Himalayas

The aims of the present study were to determine the changes in forced vital capacity (FVC), forced expiratory volume in 1 sec (FEV1) and peak expiratory flow (PEF), during an ascent to 5,300 m in the Nepalese Himalayas, and to correlate the changes with arterial oxygen saturation measured by pulse oximetry (SpO2) and symptoms of acute mountain sickness (AMS). Forty-six subjects were studied twice daily during an ascent from 2,800 m (mean barometric pressure 550.6 mmHg) to 5,300 m (mean barometric pressure 404.3 mmHg) during a period of between 10 and 16 days. Measurements of FVC, FEV1, PEF, SpO2, and AMS were recorded. AMS was assessed using a standardized scoring system. FVC fell with altitude, by a mean of 4% from sea level values [95% confidence intervals (CI) 0.9% to 7.4%] at 2,800 m, and 8.6% (95% CI 5.8 to 11.4%) at 5,300 m. FEV1 did not change with increasing altitude. PEF increased with altitude by a mean of 8.9% (95% CI 2.7 to 15.1%) at 2,800 m, and 16% (95% CI 9 to 23%) at 5,300 m. These changes were not significantly related to SpO2 or AMS scores. These results confirm a progressive fall in FVC and increase in PEF with increasing hypobaric hypoxia while FEV1 remains unchanged. The increase in PEF is less than would be predicted from the change in gas density. The fall in FVC may be due to reduced inspiratory force producing a reduction in total lung capacity; subclinical pulmonary edema; an increase in pulmonary blood volume, or changes in airway closure. The absence of a correlation between the spirometric changes and SpO2 or AMS may simply reflect that these measurements of pulmonary function are not sufficiently sensitive indicators of altitude-related disease. Further studies are required to clarify the effects of hypobaric hypoxia on lung volumes and flows in an attempt to obtain a unifying explanation for these changes.

The effects of cardiac surgery on early and late pulmonary functions

BACKGROUND

Impaired pulmonary functions are common in cardiac patients. Early and late effects of cardiac surgery on pulmonary function tests (PFTs) are presented.

METHODS

Fifty patients undergoing cardiac surgery (coronary artery bypass grafting [CABG, 74%], valve replacement or valvuloplasty [20%] and combined procedures [6%]) were studied. Anginal and cardiac failure symptoms severity, and smoking history, were evaluated preoperatively. PFTs were studied and compared pre-, and 3 weeks and 3.5 months postoperatively.

RESULTS

Pre- and postoperative PFTs were inversely related to severity of preoperative symptoms. Forced vital capacity (FVC) dropped from 98% of predicted preoperatively, to 63% (P < 0.00001) and 75% (P < 0.00001) 3 weeks and 3.5 months postoperatively, respectively. Expiratory volume in the first 1 s of forced expiration (FEV1.0) decreased from 95% to 61% (P < 0.00001) and 70% (P < 0.00001), respectively. Forced expiratory flow at 50% of vital capacity (FEF50) decreased from 85% to 56% (P < 0.00001) and 59% (P < 0.00001). Forced expiratory flow at 75% of vital capacity (FEF75) decreased from 77% to 47% and 47% (P < 0.00001). Peak expiratory flow rate (PEFR) declined from 101% to 66% (P < 0.00001) and 86% (P < 0.003). Maximal voluntary ventilation declined from 103% to 68% (P < 0.00001) and 77% (P < 0.00001). Only FVC (P < 0.0003), FEV1.0 (P < 0.02) and PEFR (P < 0.0001) partially recovered postoperatively. Smoking history did not affect perioperative PFTs. Pre-, but not postoperative FVC, FEV1.0, FEF50 and FEF75 were worse in valve than in CABG patients.

CONCLUSIONS

Pulmonary functions deteriorate significantly for at least 3.5 months after cardiac surgery. Preoperative cardiac ischaemic and failure symptoms are inversely related to perioperative PFTs.

Breathlessness and exercise capacity in heart failure: the role of bronchial obstruction and responsiveness

The cause of the breathlessness and reduced exercise capacity that occur in patients with chronic heart failure remains obscure. We examined the hypothesis that airway obstruction and bronchial hyper-responsiveness, which are recognised features of chronic heart failure, might contribute to the breathlessness and reduced exercise capacity in this condition. We studied 37 patients (7 female) with chronic heart failure, of mean age 61 years. Each patient underwent: (i) lung function testing with spirometry and expiratory flow volume loops. (ii) Measurement of bronchial responsiveness to methacholine. (iii) Symptom-limited treadmill exercise capacity using both incremental and fixed workload protocols, with measurement of Borg scores for breathlessness. Lung function was not significantly related to either exercise time, or Borg symptom scores in either exercise protocol. Bronchial hyper-responsiveness to methacholine was demonstrated in 12 patients. Exercise time did not correlate with the degree of bronchial hyper-responsiveness in these 12 patients. Group mean exercise time and Borg scores were not significantly different in these 12 patients when compared to the 25 patients in whom bronchial hyper-responsiveness was not found. We conclude that airway obstruction and bronchial hyper-responsiveness are not likely to be important determinants of reduced exercise capacity and breathlessness in chronic heart failure.

The effect of transfusion on pulmonary function in patients with thalassemia major

Pulmonary involvement has been documented in thalassemia major (TM). We studied 12 patients with TM before and 24 hr after transfusion to evaluate the effect of transfusion on baseline lung function. Personal and family histories of respiratory illnesses were obtained by a questionnaire. Spirometry and carbon monoxide diffusion capacity (KCO) measurements were made. Blood gases (PO2 and SO2) were determined on arterialized samples. Baseline expiratory volumes and flows were within normal range in all patients. Transfusion resulted in a significant reduction of forced expiratory volume in 1 sec (FEV1) and forced expiratory flow between 25 and 75% vital capacity (FEF25-75%). In two subgroups of patients identified by the questionnaire, those with no history of airway disease had normal baseline flows and no posttransfusion changes; those with history of airway obstruction had lower pretransfusion flows and significantly decreased posttransfusion FEV1 and FEF25-75%. The mean pretransfusion KCO value of 80% predicted for the whole group, significantly increased after transfusion (P < 0.05). Blood gases also significantly increased after transfusion (P < 0.05). When tested for the spirometric response to albuterol, patients with a history of asthma had a slightly greater increase in FEV1 and FEF25-75% than those who had never had asthma. We conclude that in our small study group, transfusion resulted in improved gas exchange and lung perfusion. The effect on flow limitation evident in some patients could, in part, be related to a preexisting bronchial hyperreactivity. Accurate evaluation of pulmonary function and of bronchial reactivity is advisable for patients with TM.

Frequency of chronic obstructive airways disease and pulmonary hypertension in patients with acute inferior myocardial infarction with or without right ventricular infarction

OBJECTIVE

Factors influencing the incidence of right ventricular infarction among patients with acute inferior myocardial infarction have not yet been fully established. Chronic obstructive airways disease and right ventricular hypertrophy were suggested as possible predisposing factors but no definite evidence was shown. This study analyses the frequency of chronic obstructive airway disease and of Doppler assessed pulmonary hypertension among patients with acute inferior myocardial infarction with or without right ventricular infarction.

DESIGN AND PATIENTS

Sixty consecutive patients with acute inferior myocardial infarction were prospectively enrolled into the study.

MEASUREMENTS

Standard 12-lead ECG with right precordial leads (V3-6R) were recorded on admission to the Coronary Care Unit and on days 2 and 3. Doppler echocardiography was performed within 48 h after the onset of myocardial infarction and repeated 6 weeks later together with a pulmonary function test. Routine biochemical and clinical data were collected.

RESULTS

Right ventricular infarction occurred in 35% of patients with acute inferior myocardial infarction. No differences in respiratory indices of chronic obstructive airways disease or in Doppler echocardiography parameters of pulmonary hypertension were revealed among patients with and without right ventricular infarction. Peak total creatine kinase level and creatine kinase myocardial isoenzyme levels were higher in patients with right ventricular infarction than in those without (2925 +/- 1321 vs. 1682 +/- 1216 U/l; P < 0.001 and 207 +/- 108 vs. 127 +/- 102 U/l; P < 0.05, respectively).

CONCLUSIONS

In the course of acute inferior myocardial infarction, the frequencies of chronic obstructive airways disease and/or pulmonary hypertension were not higher among patients with right ventricular infarction than among those without right ventricular infarction. Thus, history of chronic obstructive airways disease and/or pulmonary hypertension do not necessitate specific precautions in respect of right ventricular infarction.

Abnormal pulmonary function specifically related to congestive heart failure: comparison of patients before and after cardiac transplantation

PURPOSE

A variety of abnormalities in pulmonary function have been attributed to, or are believed to be, exacerbated by congestive heart failure. Separating out specific contributions from cardiac versus pulmonary disease is difficult. In order to investigate the impact of cardiac disease on pulmonary function, we performed spirometry on patients immediately before and after cardiac transplantation.

PATIENTS AND METHODS

Seventeen patients (13 men, 4 women) with a mean age of 44 years (range: 20 to 62 years) were studied before and 15 +/- 10 (mean +/- SD) months after cardiac transplantation. Eleven patients had a significant smoking history.

RESULTS

In comparing pre- and post-transplant spirometric results, forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1) increased substantially after transplant (3.34 +/- 0.96 L versus 3.89 +/- 1.00 L, p = 0.0054, and 2.63 +/- 0.80 L versus 2.95 +/- 0.83 L, p = 0.042, respectively). FEV1/FVC was not significantly different between study states in the entire group (0.78 +/- 0.10 versus 0.76 +/- 0.10, p = NS), nor was it different in those patients with and without a smoking history (0.76 +/- 0.11 versus 0.72 +/- 0.10, p = NS, and 0.87 +/- 0.06 versus 0.84 +/- 0.02, p = NS, respectively). Furthermore, normal lung volumes were obtained after transplant in those patients without a smoking history in contrast to those with a smoking history. Finally, the increase in FVC after cardiac transplantation directly correlated with the decrease in cardiac volume with cardiac replacement (r = 0.83, p less than 0.0001).

CONCLUSION

We conclude that in patients selected as cardiac transplant candidates (those without severe obstructive lung disease), restrictive but not obstructive pulmonary physiology can be attributed in part to congestive heart failure, and a major part of the reduction in lung volumes is secondary to the space occupied by a large heart. Other factors, such as accompanying pleural effusions and interstitial edema, likely contribute to the reduction in lung volumes. Abnormal pulmonary function secondary to chronic congestive heart failure in this selected population is completely reversible with normalization of cardiovascular physiology and anatomy.

Bronchial hyperresponsiveness in patients with chronic congestive heart failure

To investigate the relationship between pulmonary congestion and bronchial responsiveness, we measured bronchial responsiveness to acetylcholine in 51 patients with left heart disorders. The measurement of bronchial responsiveness was performed by inhaling doses of acetylcholine chloride (0.08 to 20 mg/ml) and calculating the PC20-FEV1. The median value for PC20-FEV1 was above 20 mg/ml in the subjects without history of congestive heart failure (n = 18), was 5.29 mg/ml in the subjects with clinical evidence of congestive heart failure in the past days (n = 18; p less than 0.01), and was 5.74 mg/ml in the subjects with clinical evidence of congestive heart failure at the time of study (n = 15; p less than 0.01). The hemodynamic variables by cardiac catheterization and the clinical symptoms were not correlated with the grade of bronchial responsiveness. These results suggest that the bronchial responsiveness was increased in most of the patients with chronic congestive heart failure. We concluded that continuous pulmonary congestion may contribute to the pathogenesis of bronchial hyperresponsiveness.

Bronchial hyperresponsiveness to inhaled methacholine in subjects with chronic left heart failure at a time of exacerbation and after increasing diuretic therapy

Cough and wheezing are common findings in left heart failure. However, it is still questionable whether nonallergic bronchial hyperresponsiveness, the hallmark of asthma, is also associated with this condition. In 12 subjects with acute decompensation of chronic postischemic LV failure, we assessed the PC20 methacholine during an episode of acute LV failure and after five to 15 days of intensive diuretic therapy. Weight, arterial blood gases, plethysmographic lung volumes, and expiratory flows were also measured on both visits. Extravascular lung water was estimated indirectly with a radiologic score. During acute decompensation, six subjects had significant airway obstruction and eight had a PC20 less than or equal to 16 mg/ml (significant bronchial hyperresponsiveness). After diuretic therapy, subjects improved significantly, losing an average of 2.2 kg, but they still had chronic LV failure and evidence of an obstructive breathing defect. Although mean PC20 was unchanged, three subjects had significantly improved PC20 after treatment. We conclude that: (1) left ventricular failure is often associated with mild bronchial hyperresponsiveness, although it is not excluded that smoking and the resulting possibility of bronchial obstruction can also play some role; and (2) acute treatment does not generally alter bronchial responsiveness to methacholine, suggesting that chronic LV failure can cause chronic changes to the airways.

Right ventricular hypertrophy is an important determinant of right ventricular infarction complicating acute inferior left ventricular infarction

To explore the role of right ventricular hypertrophy and chronic obstructive pulmonary disease in the pathogenesis of right ventricular infarction, 27 consecutive patients with a first inferior left ventricular infarction were prospectively studied. Right ventricular infarction was diagnosed using established hemodynamic criteria. Right ventricular hypertrophy was defined as right ventricular free wall thickness greater than or equal to 5 mm. Patients were classified into two groups: Group I patients with right ventricular infarction (n = 15), and Group II patients without right ventricular infarction (n = 12). The ratio of forced expiratory volume over forced vital capacity (FEV1/FVC) and forced expiratory flow between 25 and 75% expired volume (FEF) as a percent of predicted values were significantly reduced in Group I versus Group II (90 +/- 5 versus 105 +/- 6% and 63 +/- 13 versus 103 +/- 15%, respectively; p less than 0.05). This was associated with increased right ventricular wall thickness (Group I 5.5 +/- 0.3 mm versus Group II 3.9 +/- 0.2 mm, p less than 0.001). Multiple logistic regression analysis demonstrated that right ventricular wall thickness was the strongest predictor of right ventricular infarction (p less than 0.0005). No significant difference was found in the site of right coronary occlusion, collateral blood supply or extent of coronary artery disease between the two groups. These findings suggest that right ventricular hypertrophy predisposes patients with acute inferior myocardial infarction to right ventricular infarction independent of the site or extent of coronary artery disease.

Heart failure and airway obstruction

We investigated 60 patients with severe left-sided heart failure before and after cardiac recompensation. We observed that the cardiac insufficiency had a marked effect on dynamic ventilatory parameters. The "effort independent part" of the flow-volume curve was changed significantly by means of cardiac therapy.

Closing volume after inspiratory resistive loading to fatigue

Closing volume was measured by the single breath nitrogen washout test in six normal subjects both before and after inspiratory resistive loading to fatigue. Subjects breathed through an inspiratory resistance until they could no longer maintain the required mouth pressure throughout inspiration. There was electromyographic evidence of diaphragmatic fatigue in all experiments. Closing volume (expressed as a percentage of vital capacity) after resistive loading to fatigue (10.1 +/- 1.9%) was not significantly different from that before resistive loading (10.5 +/- 1.7%). Because pulmonary edema increases closing volume, this study suggests that the very negative intrathoracic pressures generated during resistive loading do not cause pulmonary edema. Therefore, the rapid shallow breathing following inspiratory resistive loading to fatigue is not due to pulmonary edema but is probably a direct consequence of fatigue.

Effects of nifedipine on arterial oxygenation at rest and during exercise in patients with stable angina

The effects of nifedipine on arterial oxygenation and hemodynamics were studied at rest and during bicycle exercise in 12 men (mean age 55 years, range 41 to 67) with stable exertional angina. The study was conducted double-blind on 2 days, 1 week apart, using a placebo-controlled crossover design. On each day, measurements at rest were made before and 20 minutes after 20 mg sublingual nifedipine or placebo and were followed by measurements made during exercise. Compared with placebo, nifedipine reduced mean arterial pressure, systemic vascular resistance and pulmonary vascular resistance, and increased heart rate and cardiac output at rest and during exercise. It did not alter mean pulmonary artery or pulmonary artery wedge pressures at rest, but decreased them during exercise. Nifedipine decreased arterial oxygen tension (PaO2) from 96 +/- 10 to 90 +/- 13 mm Hg (p less than 0.05) at rest and from 99 +/- 11 to 92 +/- 12 mm Hg (p less than 0.005) at submaximal exercise (33 +/- 21 W), but did not alter it (100 +/- 12 versus 100 +/- 16 mm Hg, p = NS) at maximal exercise (68 +/- 30 W). The reduction in PaO2 was not due to alveolar hypoventilation, because nifedipine did not alter arterial carbon dioxide tension, or to changes in mixed venous oxygen tension, which nifedipine increased at rest (39 +/- 2 versus 43 +/- 3 mm Hg, p less than 0.001) and during submaximal exercise (31 +/- 4 versus 33 +/- 4 mm Hg, p less than 0.03) and maximal exercise (27 +/- 3 versus 31 +/- 3 mm Hg, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Interpretation of changes in DLCO and pulmonary function after running five miles

The purpose of this study was to evaluate changes in pulmonary function after running five miles. Of particular interest was the reaffirmation of the previously reported 'uncoupling' or dissociation of pulmonary diffusing capacity (DLCO) and cardiac output (Q) after moderate or strenuous exercise. Cardiopulmonary assessments were made on eight runners before and after completing three separate five mile runs. There were significant reductions in vital capacity (5.7%) and volume at closing with increases in residual volume (22.5%) and closing capacity post-run. Although DLCO did not change, significant change in cardiac output occurred during the DLCO 10 sec breathhold maneuver. The pre-run DLCO maneuver produced a fall in stroke volume (SV) with an increase in HR while maintaining Q. The post-run Q fell during the DLCO maneuver due to a fall in SV with HR remaining constant. The primary basis for previous speculation of the development of a transient pulmonary edema during exercise has been the failure of DLCO to increase immediately after exercise when HR and presumably Q is elevated. To avoid any misinterpretation of changes in DLCO produced by exercise, Q should be measured at the time of the DLCO determination. Our findings suggest that values for DLCO post-exercise are entirely appropriate for the pulmonary blood flow at the time of the DLCO maneuver.

Respiratory system impedance in patients with acute left ventricular failure: pathophysiology and clinical interest

To investigate the relationship between alterations in lung mechanics and acute pulmonary vascular congestion, repeated measurements of the respiratory system impedance (Zrs) were performed in 11 patients with and in seven without acute left ventricular failure. Indexes of Zrs were obtained by calculating the average and slope of the resistance and reactance in low (10 to 20 Hz) and high (20 to 50 Hz) frequency intervals. Zrs indexes in patients with ventricular failure differ significantly from those in patients without failure. Pulmonary vascular congestion is regularly associated with an abnormal frequency dependence of resistance at low frequencies and with an increased resonant frequency. Discriminant analysis of Zrs indexes allows 92% correct classification of pulmonary capillary wedge pressures lower than and those equal to or higher than 18 mm Hg. Zrs differences between patients with and without left ventricular failure are consistent with the presence of a small airways obstruction even in patients with mild left ventricular failure. Furthermore, use of Zrs indexes permits moderate and severe pulmonary vascular congestion to be distinguished from one another and this is probably due to a significant narrowing of the large airways during severe left ventricular failure.

Pulmonary ventilation in long-term beta-adrenergic blockade after myocardial infarction

In a double-blind, randomized study, the long-term effects of timolol and placebo on FEV1, PEFR, FVC, VC, respiratory rate and heart rate were compared in 32 patients surviving acute myocardial infarction, 17 on timolol and 15 on placebo. The patients were assessed before and after 1, 3 and 6 months of medication, and then every 6 months for up to 2 years; the mean observation period was 17.4 months. Timolol decreased FEV1 significantly (9-17%) throughout the study. PEFR and FVC fell by 4-13% and 9-11%, respectively, on timolol; the reductions were significant at 3, 6 and 24 months, and at 1, 3 and 6 months, respectively. VC showed only small changes and respiratory rate did not change. In only one patient were the changes in pulmonary function of clinical relevance. Thus, significant, persisting airways dysfunction was induced by long-term beta-adrenergic blockade in patients surviving myocardial infarction.

Circulatory and ventilatory effects of hypervolaemia in artificially ventilated piglets

The influence of hypervolaemia upon circulation and pulmonary ventilation was studied in six piglets (body weights 8.5-10.5 kg). A new functional principle for artificial ventilation was used. The alveolar ventilation was unchanged at normovolaemia and hypervolaemia. Arterial blood gases were sampled and end-tidal carbon dioxide concentrations were measured continuously. Central circulation was followed by pressure recordings and an electromagnetic flow meter for cardiac output measurements. Mean values +/- SEM of end-inspiratory tracheal pressures increased from 0.98 +/- 0.06 kPa at normovolaemia to 1.57 +/- 0.06 kPa at hypervolaemia (p less than 0.02). In all animals total compliance decreased (p less than 0.02). Simultaneously the insufflation time for the tidal volume decreased by 13 per cent (p less than 0.05). Arterial oxygen tensions decreased from 8.5 +/- 0.48 kPa to 7.0 +/- 0.77 kPa (p less than 0.05). During hypervolaemia aortic pressures increased from 13.1 +/- 1.3 kPa to 14.9 +/- 0.8 kPa (p less than 0.05), pulmonary artery pressures from 2.8 +/- 0.33 kPa to 5.0 +/- 0.53 kPa (p less than 0.02) and cardiac output from 1.07 +/- 0.17 1 . min-1 to 1.5 +/- 0.19 1 . min-1 (p less than 0.02). The stroke work for the right heart increased by 74 per cent (p less than 0.02) and for the left heart by 62 per cent (p less than 0.02). Pulmonary vascular resistance was unchanged, while systemic vascular resistance was significantly decreased (p less than 0.05). The positive effect upon systemic circulation gained by the use of excessive fluid therapy resulted in an overcirculation within the lungs which reduced pulmonary ventilation. This reduction could most probably be related to a closure of terminal airways secondary to lung hyperperfusion, increasing the pulmonary shunt.

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.

Lung mechanics after cardiac valve replacement

Fourteen patients undergoing single aortic or mitral valve replacement had measurements made of lung volumes, static pressure-volume (P-V) relationships, and conductance-pressure relationships during deflation before operation and again between one and two years later. At follow-up, total lung capacity (TLC), functional residual capacity (FRC), residual volume (RV), and static tidal compliance (slope of static P-V deflation line for one litre above FRC) had increased significantly, in association with a decrease in heart size. There was a change in the shape and position of some P-V curves both in the aortic and mitral patients. In the patients with aortic disease P-V deflation curves shifted to the left after operation. In the patients with mitral disease the P-V deflation curves before operation crossed those measured after operation, so that at high lung volumes recoil became less after operation, but at low lung volumes recoil increased. Conductance had increased at high lung volumes. The data suggest that in longstanding pulmonary congestion, airways are more rigid making them less distensible at high and less compressible at low transpulmonary pressures than after operation when congestion has been at least partly relieved.

Alterations in lung volume and pulmonary function in relation to hemodynamic changes in acute myocardial infarction

To characterize the changes in lung volumes after acute myocardial infarction (AMI), and the relationship of these changes to other alterations in lung function which correlate with the severity of pulmonary vascular congestion, we made measurements of pulmonary hemodynamics, lung volume, closing volume, frequency dependence of total pulmonary resistance to forced oscillation, and arterial PO2 in 18 subjects with AMI. The most consistent finding was reduced lung volume which correlated with the severity of pulmonary diastolic hypertension. Frequency dependence of resistance showed a small but significant correlation with pulmonary hemodynamics. Closing volume measurements by the resident gas method in nine subjects was not related to hemodynamics. Follow-up studies at the time of hospital discharge revealed a significant return toward normal for arterial PO2, all lung volumes, and total pulmonary resistance at 9 Hz. Based on measurements in healthy subjects, the reduced lung volume after AMI may explain the changes in resistance. In acute and follow-up studies the degree of lung volume reduction and the severity of hypoxemia were strongly correlated.

Hypoxemia following the administration of sublingual nitroglycerin

Nitroglycerin, 0.6 mg sublingually, was given to 27 nonasthmatic subjects with varying degrees of airways dysfunction to determine the effect on arterial oxygenation. In six normal subjects, the partial pressure of oxygen in arterial blood (Pao2) transiently decreased by 9 mm Hg (p less than 0.05) and in eight subjects with only small airways dysfunction, the Pa02 decreased by 14 mm Hg (p less than 0.0001). The alveolar-arterial oxygen gradient on oxygen increased by only 11 mm Hg indicating that the decrease in room air Pao2 was primarily due to worsening ventilation-perfusion mismatch and not to an increase in shunt. Thirteen subjects with advanced obstructive or restrictive lung disease experienced a much lesser decrease in Pao2 of 4 mm Hg. Data are presented on xenon perfusion studies of a dog model of unilateral alveolar hypoxia that suggest the worsening ventilation-perfusion ratio seen in the human subjects after the administration of nitroglycerin could be due to loss of the lung's ability to vasoconstrict in regions of alveolar hypoxia and shift perfusion to better ventilated regions of the lung.

New tests for the detection of obstructive pulmonary disease

Abnormalities in small airways appear to be important in the evolution of chronic obstructive pulmonary disease. Patients with these pathologic lesions may have normal values for airway resistance and forced expiratory volume in one second. Two new tests, the closing volume (CV) and the dependence of maximal flow on density, are believed to be sensitive to abnormalities in the peripheral airways. The CV test detects an increased nonuniformity of changes in volume of pulmonary units. Reduced dependence of flow on density is believed to result from an increase in the peripheral component of the losses of driving pressure which determine maximal expiratory flow. Both tests differentiate smokers with normal conventional spirometric data from age-matched nonsmokers. Although this evidence suggests that these tests can be used to detect abnormalities in small airways, there is very little pathologic confirmation of this belief. The clinical significance of abnormalities in the results of either of these tests in an otherwise normal person has not yet been determined.

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.

The influence of clinically undetectable pulmonary edema on small airway closure in the dog

The relationship between elevated pulmonary extravascular water volume(PEWV)and small airway closure was examined. The slow accumulation of lung water was achieved by a combination of pulmonary venous hypertension and mild hemodilution. PEWV was measured using a double indicator method based on the differential right to left transit time for simultaneously injected Evans blue dye and tritiated water. Trapped gas volume (VTG) was measured by the helium equilibration technique. Clinically undetectable levels of pulmonary engorgement and edema were reproducibly associated with an increase in gas trapping. Positive end expiratory pressure reduced, but did not abolish, edema formation. Evaluation of airway closure, with consequent gas trapping and pulmonary shunting, is currently non-invasive, simple and safe. Determination of gas trapping or closing volume should be incorporated into the rountine pre-operative evaluation of patients prior to major surgery.

Pulmonary parenchymal tissue volume measurements in graded degrees of pulmonary edema in dogs

We investigated the accuracy and the sensitivity of a modification of the acetylene inhalation technique for the determination of lung tissue volume (Vt) during various grades of hemodynamic pulmonary edema in 23 dogs. After base-line acetylene measurements were obtained, intravascular driving force (pulmonary wedge pressure minus intravascular colloid osmotic pressure) was varied between -8 and +71 mm Hg by the inflation of an intra-aortic ballon and the infusion of isotonic saline. After 30 minutes at this new driving force, four timed acetylene samples were again collected. Vt (when factored by alveolar volume, VA) increased from base line to 0.23 plus or minus 0.07 ml/ml between a driving force of 0 and + 17 mm Hg. This same change in Vt/VA was accompanied by an increase in the lung wet weight-dry weight ratio from 3.84 plus or minus 0.31 to 5.2 plus or minus 0.25. Vt was 271 plus or minus ml compared with an actual lung wet weight of 288 plus or minus 57 g; Vt tended to overestimate lung wet weight in severe pulmonary edema. Alloxan-induced pulmonary edema (6 dogs) tended to parallel these data. We conclude that the acetylene method may ve a relatively accurate noninvasive method for the determination of increasing lung water in pulmonary edema.