Ventilation and gas exchange during exercise in sickle cell anemia

Aerobic physical capacity and health-related quality of life in children with sickle cell disease

BACKGROUND

Aerobic fitness is a predictor of cardiovascular health which correlates with health-related quality of life in the general population. The aim is to evaluate the aerobic capacity by cardiopulmonary exercise test (CPET) in children with sickle cell disease in comparison with healthy matched controls.

METHODS

Controlled cross-sectional study.

RESULTS

A total of 72 children (24 with sickle cell disease and 48 healthy controls), aged 6-17 years old were enrolled. Children with sickle cell disease had a poor aerobic capacity, with median VO2max Z-score values significantly lower than matched controls (-3.55[-4.68; -2.02] vs. 0.25[-0.22; 0.66], P < 0.01, respectively), and a high proportion of 92% children affected by an impaired aerobic capacity (VO2max Z-score < -1.64). The VO2max decrease was associated with the level of anemia, the existence of a homozygote HbS/S mutation, restrictive lung disease and health-related quality of life.

CONCLUSION

Aerobic capacity is poor in children with sickle cell disease. VO2max decrease is associated with the level of anemia, the existence of a homozygote HbS/S mutation, lung function, and health-related quality of life. These results represent a signal in favor of early initiation of cardiac rehabilitation in patients with sickle cell disease.

CLINICAL TRIALS

NCT05995743.

IMPACT

Aerobic fitness is a predictor of cardiovascular health which correlates with health-related quality of life in the general population. Aerobic capacity (VO2max) is poor in children with sickle cell disease, despite the absence of any pattern of heart failure. VO2max decrease was associated with the level of anemia, the existence of a homozygote HbS/S mutation, restrictive lung disease, and health-related quality of life. These results are in favor of early initiation of cardiac rehabilitation in children with sickle cell disease.

Safety of maximal cardiopulmonary exercise testing in individuals with sickle cell disease: a systematic review

OBJECTIVE

We evaluated the safety of maximal cardiopulmonary exercise testing (CPET) in individuals with sickle cell disease (SCD). Maximal CPET using gas exchange analysis is the gold standard for measuring cardiopulmonary fitness in the laboratory, yet its safety in the SCD population is unclear.

DESIGN

Systematic review.

DATA SOURCES

Systematic search of Medline (PubMed), EMBASE, Cochrane, ClinicalTrials.gov and professional society websites for all published studies and abstracts through December 2020.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Two reviewers independently extracted data of interest from studies that assessed safety outcomes of maximal CPET in children and adults with SCD. A modified version of the Newcastle-Ottawa Scale was used to assess for risk of bias in studies included.

RESULTS

In total, 24 studies met inclusion/exclusion criteria. Adverse events were reported separately or as part of study results in 36 (3.8%) of 939 participants with SCD undergoing maximal CPET in studies included. Most adverse events were related to transient ischaemic changes on ECG monitoring or oxygen desaturation during testing, which did not result in arrhythmias or other complications. Only 4 (0.43%) of 939 participants experienced pain events due to maximal CPET.

CONCLUSION

Maximal CPET appears to be a safe testing modality in children and adults with SCD and can be used to better understand the physiological basis of reduced exercise capacity and guide exercise prescription in this population. Some studies did not focus on reporting adverse events related to exercise testing or failed to mention safety monitoring, which contributed to risk of bias.

Salbutamol Worsens the Autonomic Nervous System Dysfunction of Children With Sickle Cell Disease

Background

Sickle cell disease (SCD) patients with asthma have an increased rate of vaso-occlusive crisis (VOC) and acute chest syndrome (ACS) episodes when compared to those without asthma. We hypothesized that either asthma diagnosis or bronchodilator treatment might aggravate SCD via their modulating effect on the autonomic nervous system (ANS).

Methods

Cross-sectional evaluation of heart rate variability (HRV) during pulmonary function tests, including salbutamol administration, in children with SCD receiving asthma treatment or not when compared to asthmatic children without SCD matched for ethnicity.

Results

SCD children with asthma (n = 30, median age of 12.9 years old) were characterized by a reduced FEV₁/FVC ratio, an increased bronchodilator response, and a greater incidence of VOC and ACS when compared to SCD children without asthma (n = 30, 12.7 years). Children with asthma without SCD (n = 29, 11.4 years) were characterized by a higher exhaled NO fraction than SCD children. SCD children when compared to non-SCD children showed reduced HRV [total power, low (LF) and high (HF, vagal tone) frequencies], which was further worsened by salbutamol administration in all the groups: reduction in total power and HF with an increase in LF/HF ratio. After salbutamol, the LF/HF ratio of the SCD children was higher than that of the non-SCD children. The two groups of SCD children were similar, suggesting that asthma diagnosis per se did not modify ANS functions.

Conclusion

SCD children are characterized by impaired parasympathetic control and sympathetic overactivity that is worsened by salbutamol administration.

Clinical Trial Registration

www.ClinicalTrials.gov, identifier NCT04062409.

Veterans with Gulf War Illness exhibit distinct respiratory patterns during maximal cardiopulmonary exercise

INTRODUCTION

The components of minute ventilation, respiratory frequency and tidal volume, appear differentially regulated and thereby afford unique insight into the ventilatory response to exercise. However, respiratory frequency and tidal volume are infrequently reported, and have not previously been considered among military veterans with Gulf War Illness. Our purpose was to evaluate respiratory frequency and tidal volume in response to a maximal cardiopulmonary exercise test in individuals with and without Gulf War Illness.

MATERIALS AND METHODS

20 cases with Gulf War Illness and 14 controls participated in this study and performed maximal cardiopulmonary exercise test on a cycle ergometer. Ventilatory variables (minute ventilation, respiratory frequency and tidal volume) were obtained and normalized to peak exercise capacity. Using mixed-design analysis of variance models, with group and time as factors, we analyzed exercise ventilatory patterns for the entire sample and for 11 subjects from each group matched for race, age, sex, and height.

RESULTS

Despite similar minute ventilation (p = 0.57, η2p = 0.01), tidal volume was greater (p = 0.02, η2p = 0.16) and respiratory frequency was lower (p = 0.004, η2p = 0.24) in Veterans with Gulf War Illness than controls. The findings for respiratory frequency remained significant in the matched subgroup (p = 0.004, η2p = 0.35).

CONCLUSION

In our sample, veterans with Gulf War Illness adopt a unique exercise ventilatory pattern characterized by reduced respiratory frequency, despite similar ventilation relative to controls. Although the mechanism(s) by which this pattern is achieved remains unresolved, our findings suggest that the components of ventilation should be considered when evaluating clinical conditions with unexplained exertional symptoms.

Muscle Strength, Power, and Torque Deficits in Children With Type SS Sickle Cell Disease

In African-American children aged 5 to 17 years with and without type SS sickle cell disease (SCD-SS), dominant hand maximal handgrip strength, peak power, and plantar flexion isometric maximal voluntary contraction (MVC) torque were compared with adjustments for body size and composition. Children with SCD-SS (n=21; age, 11±1 y) compared with healthy control children (n=23; 10±1 y) did not differ by age, sex, or maturation stage, but had significantly lower Z scores for height, weight, body mass index, arm circumference, upper arm muscle area, and lean mass-for-height. Children with SCD-SS had significantly lower unadjusted handgrip strength (16±2 vs. 23±2 kg, P<0.01), peak power (1054±107 vs. 1488±169 W, P<0.04) and MVC torques at 2 angles (10 degrees: 27±3 vs. 42±5 Nm; 20 degrees: 21±3 vs. 34±4 Nm; all P<0.05). Performance decrements persisted when handgrip strength was adjusted for lean body mass and fat mass explaining 66% of the variance; peak power adjusted for age, lean body mass, fat mass, and height explaining 91% of the variance; and the highest MVC torque (10-degree angle) adjusted for left leg length, lean mass-for-height, and fat mass-for-height Z scores explaining 65% of the variance. This suggests additional factors contribute to the attenuated anaerobic performance.

A review of the experimental evidence on the toxicokinetics of carbon monoxide: the potential role of pathophysiology among susceptible groups

BACKGROUND

Acute high level carbon monoxide (CO) exposure can cause immediate cardio-respiratory arrest in anyone, but the effects of lower level exposures in susceptible persons are less well known. The percentage of CO-bound hemoglobin in blood (carboxyhemoglobin; COHb) is a marker of exposure and potential health outcomes. Indoor air quality guidelines developed by the World Health Organization and Health Canada, among others, are set so that CO exposure does not lead to COHb levels above 2.0%, a target based on experimental evidence on toxicodynamic relationships between COHb and cardiac performance among persons with cardiovascular disease (CVD). The guidelines do not consider the role of pathophysiological influences on toxicokinetic relationships. Physiological deficits that contribute to increased CO uptake, decreased CO elimination, and increased COHb formation can alter relationships between CO exposures and resulting COHb levels, and consequently, the severity of outcomes. Following three fatalities attributed to CO in a long-term care facility (LTCF), we queried whether pathologies other than CVD could alter CO-COHb relationships. Our primary objective was to inform susceptibility-specific modeling that accounts for physiological deficits that may alter CO-COHb relationships, ultimately to better inform CO management in LTCFs.

METHODS

We reviewed experimental studies investigating relationships between CO, COHb, and outcomes related to health or physiological outcomes among healthy persons, persons with CVD, and six additional physiologically susceptible groups considered relevant to LTCF residents: persons with chronic obstructive pulmonary disease (COPD), anemia, cerebrovascular disease (CBD), heart failure, multiple co-morbidities, and persons of older age (≥ 60 years).

RESULTS

We identified 54 studies published since 1946. Six studies investigated toxicokinetics among healthy persons, and the remaining investigated toxicodynamics, mainly among healthy persons and persons with CVD. We identified one study each of CO dynamics in persons with COPD, anemia and persons of older age, and no studies of persons with CBD, heart failure, or multiple co-morbidities. Considerable heterogeneity existed for exposure scenarios and outcomes investigated.

CONCLUSIONS

Limited experimental human evidence on the effects of physiological deficits relevant to CO kinetics exists to support indoor air CO guidelines. Both experimentation and modeling are needed to assess how physiological deficits influence the CO-COHb relationship, particularly at sub-acute exposures relevant to indoor environments. Such evidence would better inform indoor air quality guidelines and CO management in indoor settings where susceptible groups are housed.

Pediatric Exercise Testing: Value and Implications of Peak Oxygen Uptake

Peak oxygen uptake (peakV˙O2) measured by clinical exercise testing is the benchmark for aerobic fitness. Aerobic fitness, estimated from maximal treadmill exercise, is a predictor of mortality in adults. PeakV˙O2 was shown to predict longevity in patients aged 7–35 years with cystic fibrosis over 25 years ago. A surge of exercise studies in young adults with congenital heart disease over the past decade has revealed significant prognostic information. Three years ago, the first clinical trial in children with pulmonary arterial hypertension used peakV˙O2 as an endpoint that likewise delivered clinically relevant data. Cardiopulmonary exercise testing provides clinicians with biomarkers and clinical outcomes, and researchers with novel insights into fundamental biological mechanisms reflecting an integrated physiological response hidden at rest. Momentum from these pioneering observations in multiple disease states should impel clinicians to employ similar methods in other patient populations; e.g., sickle cell disease. Advances in pediatric exercise science will elucidate new pathways that may identify novel biomarkers. Our initial aim of this essay is to highlight the clinical relevance of exercise testing to determine peakV˙O2, and thereby convince clinicians of its merit, stimulating future clinical investigators to broaden the application of exercise testing in pediatrics.

Ventilatory Efficiency in Children and Adolescents: A Systematic Review

Introduction. The index of ventilatory efficiency (VE/VCO₂) obtained by the progressive exercise test has been considered the gold standard in the prognosis of adults with heart failure, but few studies have evaluated this approach in children. Objective. To verify the scientific evidence about the VE/VCO₂ in pediatric and adolescents patients. Methods. A systematic literature review was carried out using the key words VE/VCO₂, children, and adolescents using the PEDro and PubMed/MedLine databases. Clinical trials published from 1987 to 2014, including children, adolescents, and young adults up to 25 years, addressing the VE/VCO₂ index as a method of evaluation, monitoring, and prognosis were considered. Results. Initially, 95 articles were found; 12 were excluded as the title/abstract did not contain the VE/VCO₂ index or because they included patients greater than 25 years of age. From the remaining 83, 58 were repeated between the databases. The final sample consisted of 32 studies including healthy children and children with respiratory and other diseases. Conclusion. There are few studies involving cardiorespiratory assessment by ventilatory efficiency. The studies highlight the fact that high VE/VCO₂ values are associated with a worse prognosis of patients due to the relationship with the decrease in pulmonary perfusion and cardiac output.

Reduced fitness and abnormal cardiopulmonary responses to maximal exercise testing in children and young adults with sickle cell anemia

Physiologic contributors to reduced exercise capacity in individuals with sickle cell anemia (SCA) are not well understood. The objective of this study was to characterize the cardiopulmonary response to maximal cardiopulmonary exercise testing (CPET) and determine factors associated with reduced exercise capacity among children and young adults with SCA. A cross-sectional cohort of 60 children and young adults (mean 15.1 ± 3.4 years) with hemoglobin SS or S/β⁰ thalassemia and 30 matched controls (mean 14.6 ± 3.5 years) without SCA or sickle cell trait underwent maximal CPET by a graded, symptom-limited cycle ergometry protocol with breath-by-breath, gas exchange analysis. Compared to controls without SCA, subjects with SCA demonstrated significantly lower peak VO₂ (26.9 ± 6.9 vs. 37.0 ± 9.2 mL/kg/min, P < 0.001). Subjects demonstrated slower oxygen uptake (ΔVO₂/ΔWR, 9 ± 2 vs. 12 ± 2 mL/min/watt, P < 0.001) and lower oxygen pulse (ΔVO₂/ΔHR, 12 ± 4 vs. 20 ± 7 mL/beat, P < 0.001) as well as reduced oxygen uptake efficiency (ΔV_E/ΔVO₂, 42 ± 8 vs. 32 ± 5, P < 0.001) and ventilation efficiency (ΔV_E/ΔVCO₂, 30.3 ± 3.7 vs. 27.3 ± 2.5, P < 0.001) during CPET. Peak VO₂ remained significantly lower in subjects with SCA after adjusting for age, sex, body mass index (BMI), and hemoglobin, which were independent predictors of peak VO₂ for subjects with SCA. In the largest study to date using maximal CPET in SCA, we demonstrate that children and young adults with SCA have reduced exercise capacity attributable to factors independent of anemia. Complex derangements in gas exchange and oxygen uptake during maximal exercise are common in this population.

Longitudinal differences in aerobic capacity between children with sickle cell anemia and matched controls

BACKGROUND

The purpose of this study was to compare longitudinal trajectories of maximal aerobic capacity in children with sickle cell anemia (SCA) and matched healthy controls, and explore whether these trajectories were associated with selected physiologic variables.

PROCEDURE

Children with SCA (n = 33) and healthy controls (n = 30) matched at baseline for race, sex, Tanner stage, height, and weight completed three consecutive annual fitness assessments (VO2peak ). Data were compared between the groups at each time point and within groups over time. Change in VO2peak between the two groups over time was assessed using a linear mixed model with age, sex, fat-free mass (FFM), Tanner stage, and hemoglobin (Hgb) concentration as covariates.

RESULTS

At baseline, children with SCA had significantly lower Hgb concentration (8.9 vs. 13.7 g/dL, P < 0.001) and relative VO2peak (24.2 vs. 27.9 ml/kg/min, P = 0.006) than healthy controls. Over time, children with SCA had smaller increases than healthy controls in VO2peak (-0.1 and +4.9 ml/kg/min, P < 0.001), Tanner stage at year 2 (15% and 66% Tanner 4, P < 0.001), and FFM (+4.0 and +6.8 kg, P = 0.02). Changes in Hgb concentration did not differ between groups (+0.03 and +0.09 g/dL, P = 1.0). After adjusting for age, sex, Tanner stage, FFM, and Hgb concentration the differences in change in VO2peak over time remained significant (P < 0.001).

CONCLUSION

Children with SCA demonstrate lower relative VO2peak compared to healthy children and the difference increases over time. The difference in VO2peak trajectories between the two groups during puberty remains significant after adjusting for age, sex, FFM, Tanner stage, and Hgb concentration.

Exercise tolerance, lung function abnormalities, anemia, and cardiothoracic ratio in sickle cell patients

Many patients with sickle cell disease (SCD) have a reduced exercise capacity and abnormal lung function. Cardiopulmonary exercise testing (CPET) can identify causes of exercise limitation. Forty-four consecutive SCD patients (27 HbSS, 11 HbSC, and 6 HbS-beta thalassemia) with a median age (interquartile range) of 26 (21-41) years underwent pulmonary function tests, CPET, chest x-ray, and echocardiography to further characterize exercise limitation in SCD. Peak oxygen uptake (V'O2 -peak), expressing maximum exercise capacity, was decreased in 83% of the studied patients. V'O2 -peak correlated with hemoglobin levels (R = 0.440, P = 0.005), forced vital capacity (FVC) (R = 0.717, P < 0.0001). Cardiothoracic ratio on chest x-ray inversely correlated with FVC (R = -0.637, P < 0.001). According to criteria for exercise limitation, the patients were limited in exercise capacity due to anemia (n = 17), cardiovascular dysfunction (n = 2), musculoskeletal function (n = 10), pulmonary ventilatory abnormalities (n = 1), pulmonary vascular exercise limitation (n = 1), and poor effort (n = 3). In the present study we demonstrate that anemia is the most important determinant of reduced exercise tolerance observed in SCD patients without signs of pulmonary hypertension. We found a strong correlation between various parameters of lung volume and cardiothoracic ratio and we hypothesize that cardiomegaly and relative small chest size may be important causes of the impairment in pulmonary function, that is, reduced long volumes and diffusion capacity, in SCD. Taking into account anthropomorphic differences between SCD patients and controls could help to interpret lung function studies in SCD better.

Functional capacity in children and young adults with sickle cell disease undergoing evaluation for cardiopulmonary disease

Although cardiopulmonary disease is associated with decreased functional capacity among adults with sickle cell disease (SCD), its impact on functional capacity in children with SCD is unknown. We evaluated 6-min walk (6MW) distance in 77 children and young adults with SCD undergoing screening for cardiopulmonary disease. Of 30 subjects who also underwent cardiopulmonary exercise testing, we found evidence for decreased exercise capacity in a significant proportion. Exercise capacity was related to baseline degree of anemia and was significantly lower in subjects with a history of recurrent acute chest syndrome. We found that 6MW distance adjusted for weight and body surface area was shorter in subjects with restrictive lung disease but that only 6MW adjusted for weight remained significantly shorter when we controlled for baseline hemoglobin. Exercise capacity was not significantly different in subjects with and without cardiopulmonary disease. We conclude that restrictive lung disease is associated with shorter 6MW distances in children and young adults with SCD, but that variables associated with decreased exercise capacity, other than anemia, remain unclear. Our study underscores the importance of further delineating the direct pathophysiologic processes that contribute to decreased exercise capacity observed among individuals with SCD and cardiopulmonary disease.

Cardiovascular function and dysfunction in sickle cell anemia

The 100th anniversary of the discovery of sickle cell anemia (SCA) as a distinct clinical entity by James B. Herrick in 1910 will soon be a reality. SCA continues to present opportunities for elemental observations of basic science and pathophysiologic clinical mechanisms-in particular, those associated with cardiopulmonary and circulatory disorders. Data indicate that cardiomegaly results from increased work caused by the anemia and that myocardial ischemia may result from the combined effects of severe anemia, microthrombi, and increased blood viscosity producing myocardial dysfunction, scarring, and elevated filling pressures. Sudden death has resulted from frank myocardial infarction and ischemia-induced rhythm disturbances. Myocardial injury may also be associated with bone marrow embolism. Mortality risk factors include systemic hypertension, pulmonary hypertension, and possibly subclinical electrical instability.

Airway hyperresponsiveness and acute chest syndrome in children with sickle cell anemia

To determine the occurrence and magnitude of airway hyperresponsiveness (AHR) in children with sickle cell anemia (SCA) who had or had not had acute chest syndrome (ACS) episodes. A subsidiary aim was to determine whether cold air and exercise challenge testing gave similar results in children with SCA. AHR would be greater in SCA children who had had an ACS episode compared to those who had not. Prospective observational study. Forty-two SCA children (median age of 11.5 [range 6.1-16.8] years); 12 children had been previously hospitalized for an ACS episode. AHR was assessed by the change in forced expiratory volume in 1 sec (FEV1) to a cold air challenge and in a subset of the children to an exercise challenge. A positive result to either challenge was deemed to have occurred if the FEV1 fell by at least 10% from the pre-challenge baseline. The magnitude of change in FEV1 following the cold air challenge was similar in children who had or had not had an ACS episode. Six children had a positive response to the cold air challenge (AHR); none had had an ACS hospitalization. Similar proportions of children responded to the cold air and exercise challenge and the magnitude of response to the two tests was similar. Some children, however, responded only to a cold air challenge and others only to an exercise challenge. SCA children who had had an ACS hospitalization episode compared to those who had not were not more likely to respond to a cold air challenge. Importantly, if AHR is to be correctly diagnosed, some SCA children will require to undergo both cold air and exercise challenge testing.

Factors associated with dyspnea in adult patients with sickle cell disease

OBJECTIVE

The aim of this prospective study was to determine the cardiorespiratory factors associated with dyspnea in patients with sickle cell SS-hemoglobin disease, with a specific interest in lung vascular involvement.

MEASUREMENTS

Forty-nine patients (29 women and 20 men; mean [+/- SD] age: women, 29 +/- 6 years; men, 31 +/- 11 years) underwent direct evaluations (Borg scale evaluation during a 6-min walk test) and indirect evaluations (modified Medical Research Council [MRC]score) of their dyspnea, pulmonary function tests (PFTs) [spirometry, volumes, diffusing capacity of the lung for carbon monoxide (Dlco), diffusing capacity of the alveolar-capillary membrane, and pulmonary capillary blood volume measurements], echocardiography, and biological evaluation.

RESULTS

Thirty-four patients complained of significant breathlessness (MRC score, > 1). Indirect and direct evaluations of dyspnea were correlated. PFT results depicted a very mild restrictive pattern (mean total pulmonary capacity, 86 +/- 11% predicted) and an impairment of Dlco (mean Dlco corrected for the degree of anemia, 69 +/- 13% predicted). The statistical analysis demonstrated that dyspnea and exercise performance were closely linked to indexes of Dlco but not with any echocardiographic or biological measure including anemia. Nevertheless, only approximately 25% of the variability was explained by these associations. Despite having a similar history of vasoocclusive crisis events, women had more severe anemia, dyspnea, decreases in Dlco (corrected for the degree of anemia), and a higher capillary blood volume (corrected for alveolar volume) than men.

CONCLUSION

Lung vascular disease contributes to dyspnea and the exercise limitation of patients with sickle cell disease. A sequential assessment of Dlco would therefore constitute one of the objective functional end points for follow-up studies of these patients.

Exercise in sickle cell anemia: effect on inflammatory and vasoactive mediators

The aim of this study was to determine the response of inflammatory and vasoactive mediators to 3 consecutive days of exercise in African-American women with and without sickle cell anemia (SCA). Circulating inflammatory mediators [C-reactive protein (CRP), interleukin-6 (IL-6), tumor necrosis factor alpha (TNFalpha)] were measured before, and vasoactive mediators [endothelin-1 (ET-1), nitric oxide metabolites (NOx)] before and after each exercise bout in ten subjects with SCA and ten controls. Exercise did not affect ET-1, IL-6 or CRP concentrations (p >.05). TNFalpha was higher in SCA than controls (p < or = .0005) at all times; however, the response pattern was similar for the groups: no change from day 1 to day 2, but a decrease from day 2 to day 3 (p < or = .05). NOx increased significantly after exercise (p < or = .0001) but returned to baseline by 24 h afterward. On the 3rd day, NOx increased after exercise in SCA but not in the controls (p < or = .05). In conclusion, exercise did not cause a harmful inflammatory response in these individuals with SCA. However, NOx increased after exercise on all 3 days in SCA but appeared attenuated after 2 days in controls.

Human airway epithelial cells stimulate T-lymphocyte lck and fyn tyrosine kinase

Previous studies have shown that human airway epithelial cells (AEC) can stimulate allogeneic peripheral blood T-lymphocyte (PBT) proliferation. We now sought to determine which AEC surface molecule/T-cell coreceptors are involved in this process. AEC-induced PBT proliferation was inhibited by 25 microM genestein or herbamycin A (0.9 and 1.8 microM), both tyrosine kinase inhibitors. Anti-phosphotyrosine immunoblots performed on PBT lysates after coculture with AEC demonstrated phosphorylation of 56kD and 60kD bands. To determine whether CD3 associated p59fyn, or CD4 and CD8 associated p56lck phosphotyrosine kinases (PTK) were involved, we assayed kinase activity in lymphocyte lysates immunoprecipitated with anti-p56lck and p59fyn mAbs. PBT cells or murine T-cell line transfectants expressing human CD4 (3G4) or human CD8alpha (3G8) were cocultured with AEC or A549, an alveolar-like cell line lacking class II Ag expression. After A549 or AEC coculture, p56lck activity in PB T-cells peaked at 2 min whereas p59fyn kinase activity continued to rise at 8 min. AEC (expressing class II Ags) stimulate PTK activity in both 3G8 and 3G4 cells. A549 stimulated p56lck in 3G8, but not in 3G4 cells. This activation of p56lck was not blocked by preincubation of A549 with anti-class I or anti-CD1d mAbs. An antibody generated in our laboratory, which recognizes an epithelial specific surface molecule (mAb L12) and which blocks AEC driven PBT proliferation, was shown to block PTK activity of peripheral blood T-cell lysates, though not of 3G8 lysates. These studies suggest that AEC are capable of stimulating CD4 and CD8 associated lck and CD3 associated fyn kinases through class II dependent and independent pathways.

Inaccuracy of noninvasive estimates of VD/VT in clinical exercise testing

To evaluate the accuracy of noninvasive estimates of VD/VT in clinical exercise testing, we compared measurements of standard VD/VT with estimates based either on end-tidal CO2 (VD/VTET) or a published estimate of arterial PCO2 (VD/VTest) at peak exercise in 68 patients. Using regression analysis, we identified highly significant differences (p < 0.001) between each method and VD/VTstand across a broad range of observed VD/VT. Assuming a normal exercise VD/VT < or = 0.30, estimate methods were specific but were insensitive (50 percent for VD/VTET and 57 percent for VD/VTest) for identifying patients with abnormal gas exchange during exercise. Separate analysis of subgroups based on resting pulmonary function did not identify any group for which either method was acceptable. Our analysis showed that errors in estimating PaCO2, which are amplified by the Bohr equation when calculating VD/VT, are responsible for the inaccuracies of each noninvasive method. We conclude that noninvasive estimates of PaCO2 cannot replace measured arterial PCO2 for calculation of VD/VT during exercise.

Pulmonary function abnormalities in childhood sickle cell disease

Pulmonary function tests in adults with sickle cell disease have shown a restrictive pattern that has been attributed to the sequelae of acute chest syndrome (ACS). We compared pulmonary function test results in 37 children with sickle cell anemia (20 with SS hemoglobin (HbSS), 14 with SC hemoglobin, and 3 with S beta hemoglobin) with those in 22 control subjects matched for sex, race, and height and compared pulmonary function in patients with and without a history of ACS. Of the 10 patients with a history of ACS, all but one had HbSS. Pulmonary function tests measured forced vital capacity (FVC), the diffusion capacity of carbon monoxide, and the plethysmographic determination of lung volumes. The FVC and forced expiratory volume in 1 second (FEV1), expressed as the percentage of the predicted value, were significantly less for those with HbSS with or without a history of ACS than for control subjects (p < 0.05), but the FEV1/FVC ratio, an index of airway obstruction, was normal in all groups. Total lung capacity was also significantly lower in patients with HbSS with or without a history of ACS than in control subjects (p < 0.05), but the ratio of residual volume to total lung capacity, another index of airway obstruction, was normal. We conclude that children with sickle cell disease, particularly those with HbSS, may have abnormally small lungs that function normally relative to their size; clustering of ACS episodes is not specifically associated with the observed abnormality.