Attenuated relationship between cardiac output and oxygen uptake during high-intensity exercise

AIM

Recent findings have challenged the belief that the cardiac output (CO) and oxygen consumption (VO(2) ) relationship is linear from rest to maximal exercise. The purpose of this study was to determine the CO and stroke volume (SV) response to a range of exercise intensities, 40-100% of VO(2max), during cycling.

METHODS

Ten well-trained cyclists performed a series of discontinuous exercise bouts to determine the CO and SV vs. VO(2) responses.

RESULTS

The rate of increase in CO, relative to VO(2) , during exercise from 40 to 70% of VO(2max) was 4.4 ± 1.4 L L(-1). During exercise at 70-100% of VO(2max) , the rate of increase in CO was reduced to 2.1 ± 0.9 L L(-1) (P = 0.01). Stroke volume during exercise at 80-100% of VO(2max) was reduced by 7% when compared to exercise at 50-70% of VO(2max) (134 ± 5 vs. 143 ± 5 mL per beat, P = 0.02). Whole body arterial-venous O(2) difference increased significantly as intensity increased.

CONCLUSION

The observation that the rate of increase in CO is reduced as exercise intensity increases suggests that cardiovascular performance displays signs of compromised function before maximal VO(2) is reached.

Pulmonary function in patients with reduced left ventricular function: influence of smoking and cardiac surgery

STUDY OBJECTIVE

The impact of stable, chronic heart failure on baseline pulmonary function remains controversial. Confounding influences include previous coronary artery bypass or valve surgery (CABG), history of obesity, stability of disease, and smoking history.

DESIGN

To control for some of the variables affecting pulmonary function in patients with chronic heart failure, we analyzed data in four patient groups, all with left ventricular (LV) dysfunction (LV ejection fraction [LVEF] < or =35%): (1) chronic heart failure, nonsmokers, no CABG (n = 78); (2) chronic heart failure, nonsmokers, CABG (n = 46); (3) chronic heart failure, smokers, no CABG (n = 40); and (4) chronic heart failure, smokers, CABG (n = 48). Comparisons were made with age- and gender-matched patients with a history of coronary disease but no LV dysfunction or smoking history (control subjects, n = 112) and to age-predicted norms.

RESULTS

Relative to control subjects and percent-predicted values, all groups with chronic heart failure had reduced lung volumes (total lung capacity [TLC] and vital capacity [VC]) and expiratory flows (p < 0.05). CABG had no influence on lung volumes and expiratory flows in smokers, but resulted in a tendency toward a reduced TLC and VC in nonsmokers. Smokers with chronic heart failure had reduced expiratory flows compared to nonsmokers (p < 0.05), indicating an additive effect of smoking. Diffusion capacity of the lung for carbon monoxide (DLCO) was reduced in smokers and in subjects who underwent CABG, but not in patients with chronic heart failure alone. There was no relationship between LV size and pulmonary function in this population, although LV function (cardiac index and stroke volume) was weakly associated with lung volumes and DLCO.

CONCLUSIONS

We conclude that patients with chronic heart failure have primarily restrictive lung changes with smoking causing a further reduction in expiratory flows.

Variance of ventilation during exercise

Expired gas concentrations were measured during a multibreath washin of He in one female and seven male subjects at rest (seated) and during cycle exercise at work rates of 70-210 W. In a computational model, the ventilation distribution was represented as a log-normal distribution with standard deviation (sigmaV); values of sigmaV were obtained by fitting the output of the model to the data. At rest, sigmaV was 0.89 +/- 0.18; during exercise, sigmaV was 0.60 +/- 0.13, independent of the level of exercise. These values for the width of the functional ventilation distribution at the scale of the acinus are approximately two times larger than those obtained from anatomic measurements in animals at a scale of 1 cm3. The values for sigmaV, together with data from the literature on the width of the functional ventilation-perfusion distribution, show that ventilation and perfusion are highly correlated at rest, in agreement with anatomic data. The structural sources of nonuniform ventilation and perfusion and of the correlation between them are unknown.

Predictors of oxygen desaturation during submaximal exercise in 8,000 patients

STUDY OBJECTIVES

To determine predictors of oxygen desaturation during submaximal exercise in patients with various lung diseases.

DESIGN AND SETTING

This retrospective case series used pulmonary function laboratory results from all patients referred to a major tertiary-care center.

PATIENTS AND MEASUREMENTS

All patients > or = 35 years old who underwent spirometry, diffusing capacity of the lung for carbon monoxide (DLCO), lung volumes, and pulse oximetry during 3-min submaximal step-test exercise during 1996 were included (4,545 men and 3,472 women). Logistic regression models, correcting for gender, age, and weight, determined the odds ratios (ORs) for oxygen desaturation of > or = 4% during exercise for each category of lung function abnormality (compared to those with entirely normal lung function).

RESULTS

Approximately 74% of the patients had airways obstruction, while only 5.6% had restriction of lung volumes. One third of those with obstruction had a low DLCO, compared to 56% with restriction, while 2.7% had a low DLCO without obstruction or restriction. The risk of oxygen desaturation during submaximal exercise was very high (OR, 34) in patients with restriction and low DLCO (as in interstitial lung disease) and in patients with obstruction and low DLCO (as in COPD; OR, 18), intermediate (OR, 9) in patients with only a low DLCO, and lowest in those with a normal DLCO (OR, 4 if restricted; OR, 2 if obstructed). A cut point of DLCO < 62% predicted resulted in 75% sensitivity and specificity for exercise desaturation. No untoward cardiac events occurred in any patients during or following the submaximal exercise tests.

CONCLUSIONS

The risk of oxygen desaturation during submaximal exercise is very high in patients with a low DLCO. Submaximal exercise tests are safe, even in elderly patients with heart and lung diseases.

Role of nitric oxide during hyperventilation-induced bronchoconstriction in the guinea pig

Airway function is largely preserved during exercise or isocapnic hyperventilation in humans and guinea pigs despite likely changes in airway milieu during hyperpnea. It is only on cessation of a hyperpneic challenge that airway function deteriorates significantly. We tested the hypothesis that nitric oxide, a known bronchodilator that is produced in the lungs and bronchi, might be responsible for the relative bronchodilation observed during hyperventilation (HV) in guinea pigs. Three groups of anesthetized guinea pigs were given saline and three groups given 50 mg/kg N(G)-monomethyl-L-arginine (L-NMMA), a potent nitric oxide synthase inhibitor. Three isocapnic ventilation groups included normal ventilation [40 breaths/min, 6 ml/kg tidal volume (VT)], increased respiratory rate only (150 breaths/min, 6 ml/kg VT), and increased respiratory rate and increased volume (100 breaths/min, 8 ml/kg VT). L-NMMA reduced expired nitric oxide in all groups. Expired nitric oxide was slightly but significantly increased by HV in the saline groups. However, inhibition of nitric oxide production had no significant effect on rate of rise of respiratory system resistance (Rrs) during HV or on the larger rise in Rrs seen 6 min after HV. We conclude that nitric oxide synthase inhibition has no effect on changes in Rrs, either during or after HV in guinea pigs.

Airway function after cyclooxygenase inhibition during hyperpnea-induced bronchoconstriction in guinea pigs

Airway function deteriorates significantly on cessation of exercise or isocapnic hyperventilation challenges but is largely preserved during the challenge in humans and guinea pigs. PGE(2), an endogenous bronchodilator, might be responsible for the preservation of lung function during hyperventilation (HV). We hypothesized that PGE(2) might have a protective effect during HV, partially explaining the minimal changes in respiratory system resistance (Rrs) usually seen during HV in humans and guinea pigs. Therefore, changes in Rrs were measured during and after HV in anesthetized, mechanically ventilated guinea pigs treated with flurbiprofen (FBN) or placebo. With HV, there was an initial bronchodilation that was unaffected by FBN. Rrs then increased with time during HV, an effect that was blocked by FBN. After HV, Rrs increased further in all groups, but the increase in Rrs was less in the FBN-treated groups. FBN treatment reduced the PGE(2) concentration slightly in lung lavage fluid compared with placebo. We found no enhancement or refractoriness of the Rrs response to repeat bouts of HV and no effect of FBN treatment on the response of Rrs to repeat HV. These results suggest that a constrictor PG is released during and possibly after HV and that the post-HV increase in Rrs is the sum of effects of the PG released during HV and a second constrictor mechanism operating after HV. We found no evidence for bronchodilator PG during or after HV in the guinea pig.

Cardiac output during exercise by the open circuit acetylene washin method: comparison with direct Fick

An open-circuit (OpCirc) acetylene uptake cardiac output (QT) method was modified for use during exercise. Two computational techniques were used. OpCirc1 was based on the integrated uptake vs. end-tidal change in acetylene, and OpCirc2 was based on an iterative finite difference modeling method. Six subjects [28-44 yr, peak oxygen consumption (VO(2)) = 120% predicted] performed cycle ergometry exercise to compare QT using OpCirc and direct Fick methods. An incremental protocol was repeated twice, separated by a 10-min rest, and subsequently subjects exercised at 85-90% of their peak work rate. Coefficient of variation of the OpCirc methods and Fick were highest at rest (OpCirc1, 7%, OpCirc2, 12%, Fick, 10%) but were lower at moderate to high exercise intensities (OpCirc1, 3%, OpCirc2, 3%, Fick, 5%). OpCirc1 and OpCirc2 QT correlated highly with Fick QT (R(2) = 0.90 and 0.89, respectively). There were minimal differences between OpCirc1 and OpCirc2 compared with Fick up to moderate-intensity exercise (<70% peak VO(2)); however, both techniques tended to underestimate Fick at >70% peak VO(2). These differences became significant for OpCirc1 only. Part of the differences between Fick and OpCirc methods at the higher exercise intensities are likely related to inhomogeneities in ventilation and perfusion matching (R(2) = 0.36 for Fick - OpCirc1 vs. alveolar-to-arterial oxygen tension difference). In conclusion, both OpCirc methods provided reproducible, reliable measurements of QT during mild to moderate exercise. However, only OpCirc2 appeared to approximate Fick QT at the higher work intensities.

Ventilatory constraints during exercise in patients with chronic heart failure

We examined the degree of ventilatory constraint in patients with a history of chronic heart failure (CHF; n = 11; mean +/- SE age, 62 +/- 4 years; cardiac index [CI], 2.0 +/- 0.1; and ejection fraction [EF], 24 +/- 2%) and in control subjects (CTLS; n = 8; age, 61 +/- 5 years; CI, 2.6 +/- 0.3) by plotting the tidal flow-volume responses to graded exercise in relationship to the maximal flow-volume envelope (MFVL). Inspiratory capacity (IC) maneuvers were performed to follow changes in end-expiratory lung volume (EELV) during exercise, and the degree of expiratory flow limitation was assessed as the percent of the tidal volume (VT) that met or exceeded the expiratory boundary of the MFVL. CHF patients had significantly (p < 0.05) reduced baseline pulmonary function (FVC, 76 +/- 4%; FEV(1), 78 +/- 4% predicted) relative to CTLS (FVC, 99 +/- 4%; FEV(1), 102 +/- 4% predicted). At peak exercise, oxygen consumption (VO(2)) and minute ventilation (V(E)) were lower in CHF patients than in CTLS (VO(2), 17 +/- 2 vs 32 +/- 2 mL/kg/min; VE, 56 +/- 4 vs 82 +/- 6 L/min, respectively), whereas VE/carbon dioxide output was higher (42 +/- 4 vs 29 +/- 5). In CTLS, EELV initially decreased with light exercise, but increased as VE and expiratory flow limitation increased. In contrast, the EELV in patients with CHF remained near residual volume (RV) throughout exercise, despite increasing flow limitation. At peak exercise, IC averaged 91 +/- 3% and 79 +/- 4% (p < 0.05) of the FVC in CHF patients and CTLS, respectively, and flow limitation was present over > 45% of the VT in CHF patients vs < 25% in CTLS (despite the higher VE in CTLS). The least fit and most symptomatic CHF patients demonstrated the lowest EELV, the greatest degree of flow limitation, and a limited response to increased inspired carbon dioxide during exercise, all consistent with VE constraint. We conclude that patients with CHF commonly breathe near RV during exertion and experience expiratory flow limitation. This results in VE constraint and may contribute to exertional intolerance.

Advances in pulmonary laboratory testing

This review examines emerging technologies that are of potential use in the routine clinical pulmonary laboratory. These technologies include the following: the measurement of exercise tidal flow-volume (FV) loops plotted within the maximal FV envelope for assessment of ventilatory constraint during exercise; the use of negative expiratory pressures to asses expiratory flow limitation in various populations and under various conditions; the potential use of expired nitric oxide for assessing airway inflammation; and the use of forced oscillation for assessment of airway resistance. These methodologies have been used extensively in the research setting and are gaining increasing popularity and clinical application due to the availability of commercially available, simplified, and automated systems. An overview of each technique, its potential advantages and limitations will be discussed, along with suggestions for further investigation that is considered necessary prior to extensive clinical use.

Airway obstruction during exercise and isocapnic hyperventilation in asthmatic subjects

We compared pulmonary mechanics measured during long-term exercise (LTX = 20 min) with long-term isocapnic hyperventilation (LTIH = 20 min) in the same asthmatic individuals (n = 6). Peak expiratory flow (PEF) and forced expiratory volume in 1 s (FEV(1)) decreased during LTX (-19.7 and -22.0%, respectively) and during LTIH (-6.66 and 10. 9%, respectively). In contrast, inspiratory pulmonary resistance (RL(I)) was elevated during LTX (57.6%) but not during LTIH (9.62%). As expected, airway function deteriorated post-LTX and post-LTIH (FEV(1) = -30.2 and -21.2%; RL(I) = 111.8 and 86.5%, respectively). We conclude that the degree of airway obstruction observed during LTX is of a greater magnitude than that observed during LTIH. Both modes of hyperpnea induced similar levels of airway obstruction in the posthyperpnea period. However, the greater airway obstruction during LTX suggests that a different process may be responsible for the changes in airway function during and after the two modes of hyperpnea. This finding raises questions about the equivalency of LTIH and LTX in the study of airway function during exercise-induced asthma.

Emerging concepts in the evaluation of ventilatory limitation during exercise: the exercise tidal flow-volume loop

Traditionally, ventilatory limitation (constraint) during exercise has been determined by measuring the ventilatory reserve or how close the minute ventilation (VE) achieved during exercise (i.e., ventilatory demand) approaches the maximal voluntary ventilation (MVV) or some estimate of the MVV (i.e., ventilatory capacity). More recently, it has become clear that rarely is the MVV breathing pattern adopted during exercise and that the VE/MVV relationship tells little about the specific reason(s) for ventilatory constraint. Although it is not a new concept, by measuring the tidal exercise flow-volume (FV) loops (extFVLs) obtained during exercise and plotting them according to a measured end-expiratory lung volume (EELV) within the maximal FV envelope (MFVL), more specific information is provided on the sources (and degree) of ventilatory constraint. This includes the extent of expiratory flow limitation, inspiratory flow reserve, alterations in the regulation of EELV (dynamic hyperinflation), end-inspiratory lung volume relative to total lung capacity (or tidal volume/inspiratory capacity), and a proposed estimate of ventilatory capacity based on the shape of the MFVL and the breathing pattern adopted during exercise. By assessing these types of changes, the degree of ventilatory constraint can be quantified and a more thorough interpretation of the cardiopulmonary exercise response is possible. This review will focus on the potential role of plotting the extFVL within the MFVL for determination of ventilatory constraint during exercise in the clinical setting. Important physiologic concepts, measurements, and limitations obtained from this type of analysis will be defined and discussed.

Evaluation of pulmonary resistance and maximal expiratory flow measurements during exercise in humans

To evaluate methods used to document changes in airway function during and after exercise, we studied nine subjects with exercise-induced asthma and five subjects without asthma. Airway function was assessed from measurements of pulmonary resistance (RL) and forced expiratory vital capacity maneuvers. In the asthmatic subjects, forced expiratory volume in 1 s (FEV1) fell 24 +/- 14% and RL increased 176 +/- 153% after exercise, whereas normal subjects experienced no change in airway function (RL -3 +/- 8% and FEV1 -4 +/- 5%). During exercise, there was a tendency for FEV1 to increase in the asthmatic subjects but not in the normal subjects. RL, however, showed a slight increase during exercise in both groups. Changes in lung volumes encountered during exercise were small and had no consistent effect on RL. The small increases in RL during exercise could be explained by the nonlinearity of the pressure-flow relationship and the increased tidal breathing flows associated with exercise. In the asthmatic subjects, a deep inspiration (DI) caused a small, significant, transient decrease in RL 15 min after exercise. There was no change in RL in response to DI during exercise in either asthmatic or nonasthmatic subjects. When percent changes in RL and FEV1 during and after exercise were compared, there was close agreement between the two measurements of change in airway function. In the groups of normal and mildly asthmatic subjects, we conclude that changes in lung volume and DIs had no influence on RL during exercise. Increases in tidal breathing flows had only minor influence on measurements of RL during exercise. Furthermore, changes in RL and in FEV1 produce equivalent indexes of the variations in airway function during and after exercise.

Control of airway function during and after exercise in asthmatics

Control of airway function during and after exercise in asthmatics. Med. Sci. Sports Exerc., Vol. 31, No. 1 (Suppl.), pp. S4-S11, 1999. In asthmatics, airway function can be quite variable during exercise depending on the level of exercise intensity, the duration of exercise, and whether the exercise is at constant load or variable in intensity. Airway diameter can be affected by activity of parasympathetic and sympathetic nerves, by systemic mediators such as catecholamines, and by local mediators such as histamine or leukotrienes. Asthmatic airways are populated with more inflammatory cells than normal airways, and bronchoconstrictor mediator release from these cells is probably caused by drying of the mucosa during and after periods of increased ventilation. There are a few bronchodilating mediators present in both asthmatic and normal airways that could protect against this bronchoconstriction, including prostaglandin PGE2 and nitric oxide. Although it is clear that many of the inflammatory mediators play a role in causing bronchoconstriction after exercise, the role of either bronchoconstrictor or bronchodilator mediators in controlling airway function during exercise has yet to be resolved. In addition, the mechanical interaction between lung parenchyma and airways may provide a bronchodilating influence. In conclusion, the variability in airway function during exercise in asthmatics could be caused by balance among various bronchodilator and bronchoconstrictor mediators, but it may also reflect a mechanical effect of varying levels of ventilation.

Lung volumes in 4,774 patients with obstructive lung disease

STUDY OBJECTIVES

To determine the correlates of static lung volumes in patients with airways obstruction, and to determine if static lung volumes differ between asthma and COPD.

PATIENTS AND METHODS

We examined the data from all of the adult patients (mean age of 69) who were referred to a pulmonary function laboratory from January 1990 through July 1994 with an FEV1/FVC ratio of < 0.70 and tested using a body plethysmograph. Correlates were determined using regression analysis.

MEASUREMENTS AND RESULTS

Of the 4,774 patients observed with evidence of airways obstruction, 61% were men. Self-reported diagnoses included asthma, 19%; emphysema or COPD, 23%; chronic bronchitis, 1.5%; and alpha1-antiprotease deficiency, 0.6%. Fifty-six percent of the patients did not report a respiratory disease. The degree of hyperinflation, as determined by the residual volume (RV)/total lung capacity (TLC) ratio, or the RV % predicted (but not the TLC % predicted), was strongly associated with the degree of airways obstruction (the FEV1 % predicted). Patients with moderate to severe airways obstruction and high RV and TLC levels were more likely to have COPD than asthma. Of the 1,872 patients with a reduced vital capacity determined by spirometry testing, 87% had hyperinflation as defined by the RV/TLC, and 9.5% had a low TLC (with less severe airways obstruction).

CONCLUSION

In patients found to have airways obstruction by spirometry, the additional measurement of static lung volumes added little to the clinical interpretation.

Influence of age and gender on cardiac output-VO2 relationships during submaximal cycle ergometry

It is presently unclear how gender, aging, and physical activity status interact to determine the magnitude of the rise in cardiac output (Qc) during dynamic exercise. To clarify this issue, the present study examined the Qc-O2 uptake (Vo2) relationship during graded leg cycle ergometry in 30 chronically endurance-trained subjects from four groups (n = 6-8/group): younger men (20-30 yr), older men (56-72 yr), younger women (24-31 yr), and older women (51-72 yr). Qc (acetylene rebreathing), stroke volume (Qc/heart rate), and whole body Vo2 were measured at rest and during submaximal exercise intensities (40, 70, and approximately 90% of peak Vo2). Baseline resting levels of Qc were 0.6-1.2 l/min less in the older groups. However, the slopes of the Qc-Vo2 relationship across submaximal levels of cycling were similar among all four groups (5.4-5.9 l/l). The absolute Qc associated with a given Vo2 (1.0-2.0 l/min) was also similar among groups. Resting and exercise stroke volumes (ml/beat) were lower in women than in men but did not differ among age groups. However, older men and women showed a reduced ability, relative to their younger counterparts, to maintain stroke volume at exercise intensities above 70% of peak Vo2. This latter effect was most prominent in the oldest women. These findings suggest that neither age nor gender has a significant impact on the Qc-Vo2 relationships during submaximal cycle ergometry among chronically endurance-trained individuals.

Posttransplantation physiologic features of the lung and obliterative bronchiolitis

Obliterative bronchiolitis remains the major obstacle to long-term survival after lung transplantation. Herein we provide a brief review of the key literature as well as our own experience with this condition. Obliterative bronchiolitis has occurred in up to two-thirds of all lung transplant recipients. The characteristic physiologic changes include declines in (1) forced expiratory volume in 1 second, (2) forced vital capacity, and (3) diffusing capacity of the lungs for carbon monoxide. Lung biopsy in patients with obliterative bronchiolitis reveals occlusion of bronchioles in a patchy but extensive distribution. Mucous plugging and bronchiectasis may also be seen. Furthermore, intimal thickening of pulmonary vessels together with mild arteriosclerotic changes of the muscular and elastic pulmonary arterioles may be observed. To date, the main risk factor for the development of obliterative bronchiolitis is recurrent, severe, and persistent acute lung rejection. The recommended management is prevention because the established fibrotic condition may necessitate retransplantation.

Delay time adjustments to minimize errors in breath-by-breath measurement of Vo2 during exercise

If the delay time between gas concentration and flow signals is not adequately corrected during breath-by-breath analysis of expired gas, an error in calculation of oxygen consumption (Vo2) will result. To examine the frequency and delay time dependences of errors in Vo2 measurement, six healthy men exercised at 100, 200, and 250 W on a cycle ergometer while breath-by-breath assessment of Vo2 was made simultaneously with collection of expired air. Subjects breathed first at normal rates (15-30 breaths/min) and then at 70 breaths/min. Each subject performed each level of exercise twice by using erroneous values for the delay time between gas concentration and flow signals. At normal breathing frequencies, errors in Vo2 measurement were +/- 10% over the full range of delay times used, and the errors were not tightly correlated with variations in delay times from optimum. However, at 70 breaths/min, errors approached +/- 30% as the variations in delay times deviated +/- 0.1 s from the optimal, and the errors were highly correlated with the variations in delay times. We conclude that there is greater potential for errors in Vo2 measurement with incorrect delay time at higher breathing frequencies. These findings suggest that the optimal delay time for breath-by-breath systems should be adjusted by using high breathing frequencies.

Frequency and clinical implications of increased pulmonary artery pressures in liver transplant patients

OBJECTIVE

To characterize the pulmonary hemodynamics and identify predictors of pulmonary hypertension in a group of patients before liver transplantation and to determine whether pulmonary hypertension in these patients is related to survival.

MATERIAL AND METHODS

In 362 patients before their first liver transplantation (between 1985 and 1993), the clinical history, laboratory data, and results of pulmonary function tests were recorded. Pulmonary artery (PA) catheterization was performed after induction of anesthesia at the time of transplantation. Monthly follow-up was maintained.

RESULTS

A hyperdynamic circulation was often present -- an increased mean cardiac output (7.6 L/min), increased mean PA pressure (20.9 mm Hg), correlation of mean PA pressure with cardiac output (r = 0.25; P<0.001), and decreased mean pulmonary vascular resistance (60 dynes times s/cm5). Mean PA pressures were more than 25 mm Hg in 72 patients (20%). Pulmonary hypertension (defined as mean PA pressure of more than 25 mm Hg and pulmonary vascular resistance in excess of 120 dynes times s/cm5) occurred in 15 patients (4%). Pulmonary function tests revealed obstruction in 7%, restriction in 18%, and low diffusing capacity in 46%. By univariate analysis, lower forced expiratory volume in 1 second, forced vital capacity, and total lung capacity were the only preoperative factors associated with pulmonary hypertension (P<0.05). Survival was significantly lower in patients with acute fulminant hepatitis (P<0.001), the group with the highest mean PA pressure, than in those with other diagnoses. Increased PA pressures or mild to moderate pulmonary hypertension was not found to be associated with a worse survival by univariate or multivariate analysis.

CONCLUSION

Increased PA pressure is common in liver transplant patients (20%). "True" pulmonary hypertension occurred in only 4% of our patients and was not associated with an adverse outcome.

Experimental emphysema

This animal model of emphysema exhibits the same abnormalities in respiratory mechanics as those seen in human emphysema. The histologic and radiographic findings also closely resemble changes of panacinar disease. Moreover, the progressive hypoxemia preceding hypercarbia also parallels the clinical course seen in human disease. Drawbacks of this model include the long time period required to develop significant changes and the cost of maintaining the animals for such a time period. Large cystic areas were not noted in our animals and one would have to turn to another model to address the problem of giant bullous emphysema. There is no ideal animal model of pulmonary emphysema, and the usefulness of an experimental model should be judged on how well it answers the specific questions. Significant information has been obtained using various animal models of emphysema in lung transplantation, diaphragmatic function, pulmonary hemodynamics, and in several other areas. The dog appears to be a suitable model for thoracic surgical research on emphysema.

Regulation of ventilatory capacity during exercise in asthmatics

In asthmatic and control subjects, we examined the changes in ventilatory capacity (VECap), end-expiratory lung volume (EELV), and degree of flow limitation during three types of exercise: 1) incremental, 2) constant load (50% of maximal exercise capacity; 36 min), and 3) interval (alternating between 60 and 40% of maximal exercise capacity; 6-min workloads for 36 min). The VECap and degree of flow limitation at rest and during the various stages of exercise were estimated by aligning the tidal breathing flow-volume (F-V) loops within the maximal expiratory F-V (MEFV) envelope using the measured EELV. In contrast to more usual estimates of VECap (i.e., maximal voluntary ventilation and forced expiratory volume in 1 s x 40), the calculated VECap depended on the existing bronchomotor tone, the lung volume at which the subjects breathed (i.e., EELV), and the tidal volume. During interval and constant-load exercise, asthmatic subjects experienced reduced ventilatory reserve, higher degrees of flow limitation, and had higher EELVs compared with nonasthmatic subjects. During interval exercise, the VECap of the asthmatic subjects increased and decreased with variations in minute ventilation, due in part to alterations in their MEFV curve as exercise intensity varied between 60 and 49% of maximal capacity. In conclusion, asthmatic subjects have a more variable VECap and reduced ventilatory reserve during exercise compared with nonasthmatic subjects. The variations in VECap are due in part to a more labile MEFV curve secondary to changes in bronchomotor tone. Asthmatics defend VECap and minimize flow limitation by increasing EELV.

Access to medical care and health-related quality of life for low-income persons with symptomatic human immunodeficiency virus

Despite growing interest in the accessibility of medical care and health-related quality of life for persons infected with human immunodeficiency virus, an association between these variables has not been documented. The authors conducted a cross-sectional study of access to care and its association with health-related quality of life among 205 persons of low income infected with the human immunodeficiency virus with constitutional symptoms and/or diarrhea at one public and one Veterans Administration hospital, using a 9-item measure of perceived access and a 55-item health-related quality of life instrument. Problems with access were widespread: 55% traveled for longer than 30 minutes to their usual source of care (compared with 9% to 12% of general populations in national surveys), 49% had problems meeting costs of care, and 48% had problems with clinic hours (compared with 23% in national surveys). In multivariate analyses, uninsured patients reported worse access than patients with Medicaid or Veterans Administration insurance, particularly for meeting the cost of care (P < 0.01). Adjusted health-related quality of life scores in this sample were far lower (by about 1 SD) than those of subjects in a large national acquired immune deficiency syndrome clinical trial. For 8 of 11 health-related quality of life subscales, worse perceived access was significantly (P < 0.05) associated with poorer health-related quality of life, even after controlling for T-4 lymphocyte count, symptoms and other factors. Access and health-related quality of life measures similar to those used in this study may prove useful in future evaluations of medical care systems serving poor, clinically ill populations infected with human immunodeficiency virus.

Reduced work of breathing after single lung transplantation for emphysema

BACKGROUND

Pulmonary emphysema, with or without chronic bronchitis, has emerged as the most common indication for successful single lung transplantation. Although gas exchange can be expected to improve after successful transplantation, such changes do not adequately explain the improvement in dyspnea experienced by these patients and resulting in improved quality of life.

METHODS

We prospectively studied the respiratory mechanics of 14 single lung transplantation recipients with pulmonary emphysema, of whom 10 have been followed up beyond 1 year. The mean age of the group was 48.8 years (range, 42 to 60 years) for the seven men and seven women. Average donor-predicted total lung capacity was 0.6 L (+0.2 [standard error]) greater than recipient-predicted total lung capacity. Comparison of pulmonary resistance, dynamic lung compliance, and static lung compliance were taken to examine the possible role of reduced airways resistance and of improved elastic recoil in the reduced work of breathing. Results were analyzed by means of a one-tailed paired Student t test and linear regression analysis (both stepwise and multivariate); results are tabulated by mean (+/- 1 [standard error]).

RESULTS

Between preoperative measurements and 12 months postoperatively, maximum lung elastic recoil increased from 8.1 (+/- 0.7) to 11.3 (+/- 1.0) cm H2O, p < 0.01; pulmonary resistance fell from 8.3 (+/- 0.8) to 5.4 (+/- 0.7) cm H2O sec/L, p < 0.01. Dynamic lung compliance fell from 0.23 (+/- 0.04) to 0.12 (+/- 0.02) L/cm H2O, p < 0.02, and static lung compliance fell from 0.66 (+/- 0.13) to 0.22 (+/- 0.05) L/cm H2O, p < 0.001.

CONCLUSIONS

The decline in lung compliance after single lung transplantation reflects the importance of improvement in elastic recoil and reduced chest wall distention, improving the work of breathing. The 67% decline in static lung compliance (300% increase in elastic recoil) is probably the single most important mechanical factor leading to reduced dyspnea after single lung transplantation for emphysema.

Bronchoconstriction occurring during exercise in asthmatic subjects

To demonstrate physiologic changes associated with asthma symptoms that many patients with asthma develop during exercise, we used sustained constant-load and interval exercise protocols with subjects breathing dry room temperature air. In constant-load exercise, subjects pedaled a stationary bicycle at 50% of their maximal power capacity for 36 min. In interval protocols, subjects pedaled at 60% of maximal capacity for 6 min and then 40% of maximal for 6 min; the 12-min cycle was repeated three times for a total exercise time of 36 min. Maximal expiratory flow versus volume maneuvers (MEFV) were obtained before, at 6-min intervals during, and at 5-min intervals after exercise. Changes in peak expiratory flow (PEF), forced expiratory volume in 1 s (FEV1), and forced expiratory flow at 50% of pre-exercise vital capacity (FEF50) were compared with pre-exercise values. Within 15 min after a maximal 1-min incremental exercise protocol, mean flows decreased compared with pre-exercise (PEF, mean -22%, range -46 to 5%; FEV1, mean -21%, range -42 to -3%; FEF50, mean -41%, range -80 to 3%; all p < 0.05). There were no significant changes in MEFV flows until 18 min of constant-load exercise, when FEV1 and FEF50 fell (FEV1, mean -6%, range -15 to 2%; FEF50, mean -14%, range -32 to 6%; both p < 0.05), although changes in PEF were minimal and were not significantly different compared with pre-exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of four methods for calculating diffusing capacity by the single breath method

In 283 patients referred for testing in an outpatient pulmonary function laboratory, we studied the single-breath diffusing capacity of the lungs for carbon monoxide (Dco) using the Ogilvie (Og), Jones-Meade (JM), Epidemiological Standardization Project (ESP), and three-phase iterative methods (3PIT, similar to the three equation method). The Dco maneuvers were performed using automated equipment and American Thoracic Society (ATS) recommended procedures. There were small but significant differences in mean Dco, the ESP method yielding the largest, followed in order by JM, 3PIT, and Og methods. The 3PIT and JM Dcos were in close agreement in all degrees and patterns of pulmonary function abnormality. The Og Dco method was 6 percent less than JM in patients with normal pulmonary function, although the difference was less in patients with expiratory flow limitation, restriction, or reduced Dco. There were no differences in the reproducibility of Dco measurements among the methods. Based on these results and a review of the literature, we conclude the following: (1) when measuring single-breath Dco using automated equipment that follows ATS recommended procedures for collecting a single expired gas sample of 500-ml volume, calculated Dco is largest using ESP method, following by JM, 3PIT, and Og methods; (2) in patients with reduced Dco associated with obstructive or restrictive abnormalities, the Og, 3PIT, and JM timing methods are nearly equivalent; and (3) reproducibility of Dco is the same by all methods.

Contributions of ventilation and perfusion inhomogeneities to the VA/Q distribution

The anatomic distributions of ventilation (VA) and perfusion (Q) in prone and supine dogs have been described in the literature. These data also provide frequency distributions, i.e., the distribution of lung units as a function of VA or Q. A comprehensive distribution that encompasses these two distributions is described, and the properties of the comprehensive distribution that determine the width of the VA/Q distribution are identified. Using data on the VA and Q distributions taken from various sources in the literature, we estimated the widths of the VA/Q distributions. The widths estimated from the independent data on the VA and Q distributions agree well with the widths obtained from gas exchange data. The analysis provides information about the relative contributions of the VA and Q distributions to the width of the VA/Q distribution. In the prone dog, the VA and Q distributions, as described by the available data, have different length scales, and we argue that these distributions are therefore not highly correlated. As a result, the variance of the VA/Q distributions is approximately the sum of the variances of the VA and Q distributions. Two-thirds of the variance in VA/Q is a result of nonuniform Q, and one-third is a result of nonuniform VA. In the supine dog, the variance of VA is larger than in the prone dog because of a vertical gradient and the variance of Q is larger, in part, because of a vertical gradient. Because the magnitudes of the vertical gradients of VA and Q are about equal, the vertical gradient of VA/Q is small, and these components of the VA and Q inhomogeneities contribute little to the width of the VA/Q distribution. The other components of Q inhomogeneity cause the additional variance of VA/Q in the supine dog.

Gas exchange in dogs in the prone and supine positions

To determine the cause of the difference in gas exchange between the prone and supine postures in dogs, gas exchange was assessed by the multiple inert gas elimination technique (MIGET) and distribution of pulmonary blood flow was determined using radioactively labeled microspheres in seven anesthetized paralyzed dogs. Each animal was studied in the prone and supine positions in random order while tidal volume and respiratory frequency were kept constant with mechanical ventilation. Mean arterial PO2 was significantly lower (P less than 0.01) in the supine [96 +/- 10 (SD) Torr] than in the prone (107 +/- 6 Torr) position, whereas arterial PCO2 was constant (38 Torr). The distribution of blood flow (Q) vs. ventilation-to-perfusion ratio obtained from MIGET was significantly wider (P less than 0.01) in the supine [ln SD(Q) = 0.75 +/- 0.26] than in the prone position [ln SD (Q) = 0.34 +/- 0.05]. Right-to-left pulmonary shunting was not significantly altered. The distribution of microspheres was more heterogeneous in the supine than in the prone position. The larger heterogeneity was due in part to dorsal-to-ventral gradients in Q in the supine position that were not present in the prone position (P less than 0.01). The decreased efficiency of oxygenation in the supine posture is caused by an increased ventilation-to-perfusion mismatch that accompanies an increase in the heterogeneity of Q distribution.

Body plethysmography in the evaluation of intrathoracic airway abnormalities

A patient with a previously unsuspected intrathoracic tracheal malignancy presented with symptoms suggestive of asthma and an unusual pattern seen by conventional PFTs. Reduced expiratory flows with a large difference between FVC and SVC, normal inspiratory flows and high MVV/FEV1 were found. Body plethysmography using normal and panting efforts with increasing tidal volume and flow helped define the lesion as a variable intrathoracic obstruction and document its regression after palliative therapy.

Exercise limitation and pulmonary rehabilitation in chronic obstructive pulmonary disease

Impairment of exercise tolerance is a common problem in patients with severe chronic obstructive pulmonary disease. The cause of exercise intolerance in patients with severe chronic obstructive pulmonary disease is multifactorial and includes impaired lung mechanics, fatigue of inspiratory muscles, impaired gas exchange, right ventricular dysfunction, malnutrition, occult cardiac disease, deconditioning, and psychologic problems; however, impaired lung mechanics and gas exchange abnormalities seem to be the major limiting factors. Recently, the approach to management of pulmonary rehabilitation in patients with chronic obstructive pulmonary disease has changed because improvement in exercise tolerance has been demonstrated after pulmonary rehabilitation. Other adjunctive measures that have been shown to contribute to the observed improvement in exercise tolerance include administration of oxygen, nutritional support, cessation of smoking, and psychosocial support. The roles of ventilatory muscle endurance training, respiratory muscle rest therapy, nasally administered continuous positive airway pressure, and training of the muscles of the upper extremities are less clearly defined.

Influence of vascular distending pressure on regional flows in isolated perfused dog lungs

To confirm the regional differences in vascular pressure vs. flow properties of lung regions that have been documented in zone 2 conditions [pulmonary venous pressure (Ppv) less than alveolar pressure], regional distending pressure vs. flow curves in zone 3 were generated by use of isolated blood-perfused dog lungs (3 right and 5 left lungs). Each lung was kept inflated at constant inflation pressure (approximately 50% of full inflation volume) while radioactively labeled microspheres were injected at different settings of Ppv. To achieve maximal vascular distension, Ppv was increased to approximately 30 cmH2O above alveolar pressure for the first injection. Subsequent injections were made at successively lower Ppv's. The difference between pulmonary arterial pressure and Ppv was kept constant for all injections. As was found in zone 2 conditions, there were differences in the regional distending pressure vs. flow curves among lung regions. To document the regional variability in the curves, the distribution of flow at a regional Ppv of 30 cmH2O above alveolar pressure was analyzed. There was a statistically significant linear gradient in this flow distribution from dorsal to ventral regions of the lungs but no consistent gradient in the caudad to cephalad direction. These results indicate that, even in near-maximally distended vessels, the dorsal regions of isolated perfused dog lungs have lower intrinsic vascular resistance compared with ventral regions.

Partitioning of pulmonary resistance in dogs: effect of tidal volume and frequency

To determine the sensitivity of pulmonary resistance (RL) to changes in breathing frequency and tidal volume, we measured RL in intact anesthetized dogs over a range of breathing frequencies and tidal volumes centering around those encountered during quiet breathing. To investigate mechanisms responsible for changes in RL, the relative contribution of airway resistance (Raw) and tissue resistance (Rti) to RL at similar breathing frequencies and tidal volumes was studied in six excised, exsanguinated canine left lungs. Lung volume was sinusoidally varied, with tidal volumes of 10, 20, and 40% of vital capacity. Pressures were measured at three alveolar sites (PA) with alveolar capsules and at the airway opening (Pao). Measurements were made during oscillation at five frequencies between 5 and 45 min-1 at each tidal volume. Resistances were calculated by assuming a linear equation of motion and submitting lung volume, flow, Pao, and PA to a multiple linear regression. RL decreased with increasing frequency and decreased with increasing tidal volume in both isolated and intact lungs. In isolated lungs, Rti decreased with increasing frequency but was independent of tidal volume. Raw was independent of frequency but decreased with tidal volume. The contribution of Rti to RL ranged from 93 +/- 4% (SD) with low frequency and large tidal volume to 41 +/- 24% at high frequency and small tidal volume. We conclude that the RL is highly dependent on breathing frequency and less dependent on tidal volume during conditions similar to quiet breathing and that these findings are explained by changes in the relative contributions of Raw and Rti to RL.

Carbon monoxide diffusing capacity of the lungs determined by single-breath and steady-state exercise methods

We measured carbon monoxide diffusing capacity of the lungs (DL,CO) by both the resting single-breath (SB) and steady-state (SS) exercise methods in 95 patients referred for pulmonary function testing. A 10-second breath-holding method was used for the SB test. DL,CO (SS) was measured during the last minute of a 3-minute exercise test on a 9-inch step. Results of the two methods showed good agreement, the SB-SS difference averaging -0.70 (SD, 3.39) ml/min per mm Hg. The difference between the two methods was not correlated with other measurements of pulmonary function except minute ventilation during the exercise performed in the DL,CO (SS) procedure. In a separate study of laboratory personnel, the day-to-day variabilities of the two tests were similar (SD, 1.4 ml/min per mm Hg). Alveolar volume obtained by helium dilution during the SB test was comparable to total lung capacity (TLC) estimated by multiple-breath nitrogen washout in patients without severe airway obstruction. In severe airway obstruction, the mean SB alveolar volume was 13.8% less than the TLC by nitrogen washout, a difference that may be useful as an indicator of inefficiency of gas mixing in the lungs. We conclude that the SB and SS exercise methods provide similar estimates of DL,CO in patients referred to a pulmonary function laboratory.

Actions of enflurane, isoflurane, vecuronium, atracurium, and pancuronium on pulmonary resistance in dogs

The effects of enflurane, isoflurane, vecuronium, atracurium, and pancuronium on pulmonary resistance and heart rate were studied in 30 vagotomized dogs lying supine and anesthetized with chloralose-urethane. None of the five drugs affected pulmonary resistance when the airway was unstimulated. Enflurane and isoflurane significantly attenuated the increase in pulmonary resistance induced by electrical stimulation of the vagus nerves. This effect was dose-dependent and similar for both anesthetics at equivalent multiples of their minimum alveolar concentration. Atracurium significantly (P less than 0.05) enhanced the increase in pulmonary resistance induced by vagus nerve stimulation; vecuronium had no significant effect. Pancuronium, up to a cumulative dose of 0.14 mg/kg, also significantly (P less than 0.05) enhanced the increase in pulmonary resistance induced by vagus nerve stimulation; but this effect was reversed by further increasing the dose. Pancuronium also attenuated the cardiodecelerator response to vagus nerve stimulation in a dose-dependent fashion. The underlying mechanisms for the attenuation of responses to vagus nerve stimulation by enflurane or isoflurane or for the increase in response with atracurium are unknown. Pancuronium at lower doses increases the response most likely by blocking prejunctional muscarinic receptors (M2) that physiologically inhibit vagally mediated increases in pulmonary resistance.

Muscarinic M1 receptors mediate the increase in pulmonary resistance during vagus nerve stimulation in dogs

The physiologic roles of the 2 muscarinic receptors (M1 and M2) in the vagal control of pulmonary resistance were studied by comparing the effects of pirenzepine (PZ, M1-blocker), gallamine (GAL, M2-blocker), and atropine (AT, M1- and M2-blocker) on the increase in pulmonary resistance (RL) and on the reduction in heart rate (HR) during bilateral cervical vagus nerve stimulation in 18 anesthetized (chloralose and urethane) and paralyzed (vecuronium) dogs. PZ, AT, and GAL all inhibited the reduction in HR during vagus nerve stimulation, although the inhibition required relatively high doses of PZ and GAL. AT and PZ inhibited the increase in RL during vagus nerve stimulation. The ratio of the dose needed to inhibit by 50% the HR response to the dose needed to inhibit by 50% the RL response was approximately 45:1 for PZ, 12:1 for AT, and less than 0.4:1 for GAL. Thus, compared with AT, PZ is a more selective blocker of vagally induced increases in RL, indicating that M1 receptors are present in the airway smooth muscle of intact anesthetized dogs. In the same dose range as that which caused the inhibition of the HR response, GAL had no consistent effect on the increase in RL during vagus nerve stimulation, indicating that M2 receptors do not mediate the increase in RL in intact anesthetized dogs.

Regional trapping of microspheres in the lung compares well with regional blood flow

Microspheres (MS) are often used to measure the distribution of pulmonary blood flow in the assumption that the number of MS trapped in a region is proportional to blood flow. However, regional distribution of trapped MS has not been directly compared with regional blood flow in the lung. Regional trapping of MS was compared with regional flow of erythrocytes (RBC's) in isolated, perfused left lungs of dogs. Radioactivity from labeled MS and RBC's was measured by external detection using a gamma camera. We defined six regions of interest in the image of the left lateral surface of the lung: a dorsocaudal, a caudal, two ventral, an apical, and a central region. In each lung, regional trapping of MS was measured from the image of radioactivity obtained after slow injection of a suspension of MS into the arterial perfusion tubing. A radioactive bolus of labeled RBC's was injected during rapid imaging of the lung to obtain radioactivity vs. time curves from each region. The peaks of the regional radioactivity vs. time curves were used to estimate regional flows, though compensation had to be made for overlap of the washout and washin phases of the bolus of labeled RBC's. The results indicated that there were no differences in the regional distribution of MS compared with the regional distribution of RBC flow in isolated, perfused dog lungs.

Quantification of thoracic volumes by three-dimensional imaging

End-expiratory thoracic cavity volume (Vthx) was measured in eight volunteers lying supine by three-dimensional X-ray computed tomography using the Dynamic Spatial Reconstructor. Untrapped end-expiratory pulmonary gas volume at functional residual capacity (FRC) was determined by nitrogen clearance. Both measurements were done before and after induction of anesthesia-paralysis. After induction of anesthesia-paralysis, Vthx and FRC were consistently and significantly (P less than 0.01) reduced by 0.28 +/- 0.22 (SD) and 0.59 +/- 0.24 liter, respectively. The reduction of FRC was larger than the reduction of Vthx (delta Vthx) in six of the eight subjects, a finding suggesting that intrathoracic fluid (blood) plus trapped gas volume (Vtt) increased. Changes in Vthx were partitioned into volume changes from the thoracic rib cage (delta Vrc) and from shape and/or position changes of the diaphragm (delta Vdi). delta Vrc contributed significantly (0.17 +/- 0.15 liter, P less than 0.02) to delta Vthx, whereas delta Vdi contributed only in four of the eight subjects. We conclude that delta Vrc, delta Vdi, and delta Vtt contribute to the reduction of FRC after induction of anesthesia-paralysis in humans; the relative contribution of them varies among subjects.

Differences in regional vascular conductances in isolated dog lungs

The distribution of pulmonary blood flow is influenced by gravity, regional lung expansion, and hypoxic pulmonary vasoconstriction. However, these factors cannot completely explain the three-dimensional distribution of blood flow in the lung. The present study was designed to see whether anatomically related factors could contribute. Regional blood pressure vs. flow curves were determined in 100-230 small parenchymal samples (0.3-0.4 ml) from 12 isolated perfused dog lungs held at constant inflation pressure. In each region four blood flows were measured using radioactively labeled microspheres, and the four corresponding regional perfusion pressures were determined by correcting the measured perfusion pressure for hydrostatic effects. There were considerable differences in the slopes of the pressure vs. flow curves among lung regions. Dorso-caudal regions of the lung had higher vascular conductances than ventrocephalad regions, independent of the vertical orientation of the lung or the inflation volume during injections of microspheres. Thus the distributions of regional vascular conductances were related to the anatomic location and were not related to gravity, nor were they caused by nonuniformities in regional lung expansion or by hypoxic vasoconstriction or edema.

Resonant amplification of delivered volume during high-frequency ventilation

The volume of gas delivered from a high-frequency ventilation (HFV) circuit was measured with an ultrasonic flowmeter. The measurements were done in vitro (20-liter air-filled glass bottle) and in vivo (9 anesthetized dogs lying supine) at oscillation frequencies ranging from 4 to 23 Hz and stroke volumes of the pump ranging from 36 to 150 ml. We varied the length and diameter of the tube connecting the pump with the endotracheal tube, the length and diameter of the bias outflow tube, the diameter of the endotracheal tube, and the stroke volume of the pump. Both in vitro and in vivo, there was resonant amplification of the delivered gas volume; i.e., the delivered gas volume exceeded the stroke volume at certain frequencies. Altering the dimensions of connecting tube, endotracheal tube, bias outflow tube, or stroke volume, i.e., changing the resistance to gas flow, gas compliance, and/or gas inertance in these elements, altered the ratio of gas delivered to stroke volume that could be predicted by an electric analog. These data indicate that the delivered gas volume during HFV depends critically on the configuration of the HFV circuit, the size of the endotracheal tube, the oscillation frequency, and the pump stroke volume. Knowledge of the delivered gas volume during HFV and appreciation of the phenomenon of resonant amplification of the delivered gas volume will permit a more accurate description of factors contributing to gas transport during HFV.

Pulmonary blood flow vs. gas volume at various perfusion pressures in rabbit lung

To obtain a detailed description of the dependence of pulmonary blood flow on changes in lung volume, we perfused isolated rabbit lungs with homologous blood at 37 degrees C while controlling vascular pressures during lung deflation. We set pulmonary arterial pressure (Ppa) and pulmonary venous pressure (Ppv) to constant values relative to alveolar pressure (Palv) to keep the effective driving pressure for flow constant during lung deflation from total lung capacity (TLC) to 25% TLC. The shapes of the flow vs. lung volume curves were dependent on the levels of Ppa-Palv and Ppv-Palv at which they were obtained. When Ppv greater than Palv throughout the lung (zone 3 conditions), flow increased as the lungs were deflated from TLC, independent of the level of Ppa-Palv. When Ppv less than Palv (zone 2 conditions) and Ppa-Palv was moderately high, flow increased as the lungs were deflated from 100 to approximately 50% TLC, then decreased at lower lung volumes. When Ppa - Palv was less than 10 cmH2O in zone 2 conditions, flow decreased monotonically during deflation from TLC. We concluded that the dependence of blood flow on lung volume is complex, which may be a reflection of the nonlinear pressure-diameter properties of pulmonary vessels.

Direct and indirect blood pressure during exercise

In 27 subjects, we compared rest and exercise blood pressure (BP) measurements determined directly by catheterization of the radial artery with simultaneous values obtained indirectly by auscultation of the brachial artery. As work increased, the systolic BP increased, whereas the diastolic BP did not change. Considering all comparisons, direct BP was greater than indirect BP by a mean of 29.0 mm Hg for systolic BP and 12.3 mm Hg for diastolic BP. As exercise level increased, the difference between direct and indirect systolic BP decreased whereas the difference between direct and indirect diastolic BP did not change. Both methods have advantages for assessment of BP response to exercise: normality of BP response is best assessed by auscultation, whereas beat-by-beat trends in BP are more accurately defined by the direct method.

Pleural liquid pressure measured by micropipettes in rabbits

Pleural liquid pressure (Ppl) was measured by the micropipette servo-nulling method. In anesthetized, paralyzed, and mechanically ventilated rabbits, windows were made by dissecting away the intercostal muscle layers, exposing the parietal pleura over the right caudal lung lobe. Repeated measurements of Ppl were made at the windows by puncturing the parietal pleura with micropipettes during apnea at functional residual capacity. In five supine rabbits, Ppl relative to atmospheric pressure averaged -3.32 +/- 1.22 (SD) cmH2O at a distance of 5.64 +/- 0.34 (SD) cm above the lung base and -1.64 +/- 0.79 cmH2O at a distance of 2.35 +/- 0.64 cm above the lung base; the vertical Ppl gradient was 0.51 cmH2O/cm height. Ppl interpolated to midlung height was equal in absolute magnitude to mean lung static recoil (Pst) of 2.00 cmH2O. In prone rabbits, Ppl measured near the dorsal surface, 3.9 cm above the lung base, averaged -1.32 +/- 0.46 cmH2O on the costal surface, not statistically different in magnitude from mean Pst of 1.59 +/- 0.09. In contrast, Ppl measured at the same vertical height off the edge of the caudal lung in the costo-diaphragmatic recess was -4.64 +/- 0.65 cmH2O. We concluded from these data that Ppl was equal to pleural surface pressure over the costal surface and that the vertical gradient in Ppl was not hydrostatic, except in large fluid spaces off the sharp edges of the lung.

Effect of edema and height on bronchial diameter and shape in excised dog lung

Mechanical interactions among the artery, bronchus, and lung parenchyma cause the bronchus to be pulled from a circular cross-section in such a way that the largest diameter of the bronchus ( Db2 ) lies along a line joining the centers of bronchus and artery. To effect these interactions, the peribronchovascular interstitial space must transmit stresses from the lung parenchyma to the artery and bronchus. To test how interstitial edema affects the interdependence between the artery and the bronchus, we measured orthogonal diameters ( Db2 , Db1 ) from tantulum bronchograms as a function of edema formation at a fixed transpulmonary pressure (Ptp). As lobe weight increased to three times normal, Db2 / Db1 decreased from 1.08 to 1.0 at a Ptp of 6 and 25 cm H2O. Cross-sectional area decreased only at a Ptp of 6 cm H2O. We conclude (1) that peribronchovascular interstitial (Pi) pressure became more uniform with edema present, causing the bronchus to assume a more circular shape, and (2) that it increased, causing bronchial cross-sectional area to decrease at a Ptp of 6 cm H2O. To determine whether Pi is uniform with height, in a separate group of lungs we measured Db1 as a function of height in two configurations: hilus-dependent, Db1 (d) and then inverted or hilus-nondependent, Db1 (nd). Db1 was unaffected by lobe inversion at 25, 10, 6 and 4 cm H2O Ptp. At a Ptp of 2 cm H2O, the difference Db1 (d) - Db1 (nd) was positive near the hilus, decreased to zero in the lung periphery, and increased with edema. This bronchial distortion due to lobe inversion was consistent with the effect of gravitational forces on lung parenchyma as modeled by a finite-element analysis, as was opposite to that predicted by a vertical hydrostatic gradient in Pi.

Alveolar liquid pressure in excised edematous dog lung with increased static recoil

Alveolar liquid pressure (Pliq) was measured by micropipettes in conjunction with a servo-nulling pressure measuring system in isolated air-inflated edematous dog lungs. Pliq was measured in lungs either washed with a detergent (0.01% Triton X-100) or subjected to refrigeration for 2-3 days followed by ventilation for 3 h. At 55% of total lung capacity (TLC, the volume at a transpulmonary pressure (Ptp) of 25 cmH2O before treatment), in both the Triton-washed and the ventilated lung, Ptp increased from 5 to 11 cmH2O, whereas Pliq, decreased from -3 to -11 cmH2O relative to alveolar air pressure. Similar increases in Ptp and decreases in Pliq were obtained at higher lung volumes. Alveolar surface tension (T) was estimated from the Laplace equation for a spherical air-liquid interface, assuming that the radius of curvature varies as (volume)n, for -1/3 less than n less than 1/3. For uniform expansion of alveoli (n = 1/3), estimated T was 6 and 18 dyn/cm at 55 and 85% TLC, respectively, before treatment and increased to 23 and 40 dyn/cm following either Triton washing or ventilation. If pericapillary interstitial fluid pressure (Pi) equaled Pliq in edematous lungs, increases in T might reduce Pi and increase extravascular fluid accumulation in lungs made stiff by either Triton washing or cooling and ventilation using large tidal volumes.

Adaptation of vascular pressure-flow-volume hysteresis in isolated rabbit lungs

Hysteresis within two pairs of variables describing the state of the lung vascular system [pulmonary arterial pressure (Ppa) and flow (Q) and Ppa and change in vascular volume (delta Vvasc)] was investigated in isolated plasma-perfused rabbit lungs. Q was increased and decreased stepwise, in series of five cycles each, while pulmonary venous pressure (Ppv) and lung volume were held constant. Changes in Vvasc were estimated from changes in fluid volume of the venous reservoir. The relationships within pairs of variables over each complete cycle were described by loops whose areas and widths were used to quantify the hysteresis. In successive cycles, these parameters decreased toward constant values (limit cycles), most of the change occurring by the second cycle. Areas of Ppa-delta Vvasc loops correlated closely with areas of Ppa-Q loops over all five cycles of a series. For Ppa-Q loops, the ratio of average pressure-width to total pressure excursion decreased from 0.15 initially to around 0.05 in the fifth cycle. It was concluded that the relationships between Ppa and Q and Ppa and delta Vvasc are markedly sensitive to vascular pressure or flow history.