Effect of circulatory congestion on the components of pulmonary diffusing capacity in morbid obesity

Obesity-related Changes in Diffusing Capacity and Transfer Coefficient of the Lung for Carbon Monoxide and Resulting Patterns of Abnormality across Reference Equations

Rationale: In 2017, an American Thoracic Society/European Respiratory Society Task Force report recommended further research on the effects that body mass index (BMI) has on diffusing capacity of the lung for carbon monoxide (DlCO), the transfer coefficient (Kco), and the alveolar volume (VA). Objectives: Our goals were to 1) quantify the magnitude and direction of change to measured and predicted DlCO values as BMI increases in patients free of cardiopulmonary disease and 2) identify how BMI and obesity-related changes differ by reference set. Methods: Using data from a prospective cohort study of service members free of cardiopulmonary disease, we modeled the effect that BMI has on measured values of DlCO, Kco, and VA, after adjusting for age, sex, hemoglobin (Hgb), and height. We then referenced DlCO, Kco, and VA to normal values using four different reference equations. Results: There were 380 patients with data available for analysis, and 130 had a BMI ⩾ 30 kg/m2 (87.7% class I obesity). After controlling for age, sex, Hgb, and height, increased BMI was significantly associated with Kco (β = 0.09, P < 0.01) and VA (β = -0.15, P < 0.01) but not DlCO. After adjustment for Hgb, for every 5-kg/m2 increase in BMI, the mean increase in percent predicted (PPD) values ranged from 4.2% to 6.5% and from 5.0% to 7.5% for DlCO and Kco, respectively; and the mean decrease in VA PPD was 3.2-4.0%. In the presence of obesity (BMI ⩾ 30 kg/m2), the prevalence of DlCO and Kco abnormalities dropped by 4.1-12.1% and 0.4-16.3%, respectively, across equations, whereas VA abnormalities increased from 7.7% to 9.9%. Eliminating 163 patients with abnormal trans-thoracic echocardiogram (TEE), high-resolution computed tomographic (HRCT) scan, or Hgb altered the magnitude of relationships, but significance was preserved. Conclusions: In an otherwise healthy population with predominantly class I obesity and normal TTE, HRCT scan, and Hgb, we found that Kco and VA were more affected by BMI than DlCO. Increases in PPD values varied across equations and were modest but significant and could change clinical decision making by reducing sensitivity for detecting gas-exchange abnormalities. BMI and obesity had the smallest effect on Global Lung Function Initiative PPD values.

The association between transfer coefficient of the lung and the risk of exacerbation in asthma-COPD overlap: an observational cohort study

BACKGROUND

Asthma-chronic obstructive pulmonary disease (COPD) overlap (ACO) patients experience exacerbations more frequently than those with asthma or COPD alone. Since low diffusing capacity of the lung for carbon monoxide (DLCO) is known as a strong risk factor for severe exacerbation in COPD, DLCO or a transfer coefficient of the lung for carbon monoxide (KCO) is speculated to also be associated with the risk of exacerbations in ACO.

METHODS

This study was conducted as an observational cohort survey at the National Hospital Organization Fukuoka National Hospital. DLCO and KCO were measured in 94 patients aged ≥ 40 years with a confirmed diagnosis of ACO. Multivariable-adjusted hazard ratios (HRs) for the exacerbation-free rate over one year were estimated and compared across the levels of DLCO and KCO.

RESULTS

Within one year, 33.3% of the cohort experienced exacerbations. After adjustment for potential confounders, low KCO (< 80% per predicted) was positively associated with the incidence of exacerbation (multivariable-adjusted HR = 3.71 (95% confidence interval 1.32-10.4)). The association between low DLCO (< 80% per predicted) and exacerbations showed similar trends, although it failed to reach statistical significance (multivariable-adjusted HR = 1.31 (95% confidence interval 0.55-3.11)).

CONCLUSIONS

Low KCO was a significant risk factor for exacerbations among patients with ACO. Clinicians should be aware that ACO patients with impaired KCO are at increased risk of exacerbations and that careful management in such a population is mandatory.

Impact of obesity on pulmonary function: current understanding and knowledge gaps

PURPOSE OF REVIEW

Obesity is an increasing world-wide public health concern. Obesity both causes respiratory symptoms and contributes to many cardiorespiratory diseases. The effects of obesity on commonly used lung function tests are reviewed.

RECENT FINDINGS

The effects of obesity on lung function are attributed both to mechanical factors and to complex metabolic effects that contribute to a pro-inflammatory state. The effects of obesity on lung function correlate with BMI and correlate even better when the distribution of excess adipose tissue is taken into account, with central obesity associated with more prominent abnormalities. Obesity is associated with marked decreases in expiratory reserve volume and functional residual capacity. Total lung capacity, residual volume, and spirometry are less affected by obesity and are generally within the normal range except with severe obesity. Obesity decreases total respiratory system compliance primarily because of decreased lung compliance, with only mild effects on chest wall compliance. Obesity is associated with impaired gas transfer with decreases in oxygenation and varied but usually mild effects on diffusing capacity for carbon monoxide, while the carbon monoxide transfer coefficient is often increased.

SUMMARY

Obesity has significant effects on lung function. The relative contribution of the mechanical effects of obesity and the production of inflammatory cytokines by adipose tissue on lung function needs further study.

Bariatric Surgery as a Bridge to Heart Transplantation in Morbidly Obese Patients: a Systematic Review and Meta-Analysis

Class 2 obesity or greater (body mass index [BMI] >35 kg/m) is a relative contraindication for heart transplant due to its associated perioperative risks and mortality. Whether bariatric surgery can act as a potential bridging procedure to heart transplantation is unknown. The aim of this systematic review and meta-analysis is to investigate the role of bariatric surgery on improving transplant candidacy in patients with end-stage heart failure (ESHF). MEDLINE, EMBASE, CENTRAL, and PubMed databases were searched up to September 2019 for studies that performed bariatric surgery on patients with severe obesity and ESHF. Outcomes of interest included incidence of patients listed for heart transplantation after bariatric surgery, proportion of patients that successfully received transplant, the change in BMI after bariatric surgery, and 30-day complications. Pooled estimates were calculated using a random effects meta-analysis of proportions. Eleven studies with 98 patients were included. Mean preoperative BMI was 44.9 (2.1) kg/m and BMI after surgery was 33.2 (2.3) kg/m with an absolute BMI reduction of 26.1%. After bariatric surgery, 71% (95% confidence interval [CI], 55%-86%) of patients with ESHF were listed for transplantation. The mean time from bariatric surgery to receiving a heart transplant was 14.9 (4.0) months. Of the listed patients, 57% (95% CI, 39-74%) successfully received heart transplant. The rate of 30-day mortality after bariatric surgery was 0%, and the 30-day major and minor complications after bariatric surgery was 28% (95% CI, 10%-49%). Bariatric surgery can facilitate sustained weight loss in obese patients with ESHF, improving heart transplant candidacy and the incidence of transplantation.

Simultaneous measurement of pulmonary diffusing capacity for carbon monoxide and nitric oxide

In Europe and America, the newly-developed, simultaneous measurement of diffusing capacity for CO (D_LCO) and NO (D_LNO) has replaced the classic D_LCO measurement for detecting the pathophysiological abnormalities in the acinar regions. However, simultaneous measurement of D_LCO and D_LNO is currently not used by Japanese physicians. To encourage the use of D_LNO in Japan, the authors reviewed aspects of simultaneously-estimated D_LCO and D_LNO from previously published manuscripts. The simultaneous D_LCO-D_LNO technique identifies the alveolocapillary membrane-related diffusing capacity (membrane component, D_M) and the blood volume in pulmonary microcirculation (V_C); V_C is the principal factor constituting the blood component of diffusing capacity (D_B,D_B=θ·V_C where θ is the specific gas conductance for CO or NO in the blood). As the association velocity of NO with hemoglobin (Hb) is fast and the affinity of NO with Hb is high in comparison with those of CO, θ_NO can be taken as an invariable simply determined by diffusion limitation inside the erythrocyte. This means that θ_NO is independent of the partial pressure of oxygen (PO₂). However, θ_CO involves the limitations by diffusion and chemical reaction elicited by the erythrocyte, resulting in θ_CO to be a PO₂-dependent variable. Furthermore, D_LCO is determined primarily by D_B (∼77%), while D_LNO is determined equally by D_M (∼55%) and D_B (∼45%). This suggests that D_LCO is more sensitive for detecting microvascular diseases, while D_LNO can equally identify alveolocapillary membrane and microcirculatory abnormalities.

The relationship between body fat and respiratory function in young adults

The relationship between adiposity and respiratory function is poorly understood. Most studies investigating this have used indirect measures of body fat and few have assessed how changes in adiposity influence lung function.Body fat measured by bio-electrical impedance analysis, body mass index, waist circumference, spirometry, body plethysmography and transfer factor were measured at ages 32 and 38 years in 361 non-smoking, non-asthmatic participants from a population-based birth cohort.Higher percentage body fat was associated with lower spirometric and plethysmographic lung volumes, but not with airflow obstruction, or transfer factor at 32 years. Changes in adiposity between ages 32 and 38 years were inversely associated with changes in lung volumes. These associations were generally stronger in men than women, but an association between increasing adiposity and lower airway function (forced expiratory volume in 1 s/forced vital capacity) was only found in women. Similar associations were found for body mass index and waist circumference.Higher percentage body fat is associated with lower lung volumes. Direct and indirect measures of adiposity had similar associations with lung function. Adiposity had a greater effect on lung volumes in men than women but was associated with airway function only in women. There was little evidence that adiposity influenced transfer factor.

Pulmonary Vascular Congestion: A Mechanism for Distal Lung Unit Dysfunction in Obesity

RATIONALE

Obesity is characterized by increased systemic and pulmonary blood volumes (pulmonary vascular congestion). Concomitant abnormal alveolar membrane diffusion suggests subclinical interstitial edema. In this setting, functional abnormalities should encompass the entire distal lung including the airways.

OBJECTIVES

We hypothesize that in obesity: 1) pulmonary vascular congestion will affect the distal lung unit with concordant alveolar membrane and distal airway abnormalities; and 2) the degree of pulmonary congestion and membrane dysfunction will relate to the cardiac response.

METHODS

54 non-smoking obese subjects underwent spirometry, impulse oscillometry (IOS), diffusion capacity (DLCO) with partition into membrane diffusion (DM) and capillary blood volume (VC), and cardiac MRI (n = 24). Alveolar-capillary membrane efficiency was assessed by calculation of DM/VC.

MEASUREMENTS AND MAIN RESULTS

Mean age was 45±12 years; mean BMI was 44.8±7 kg/m2. Vital capacity was 88±13% predicted with reduction in functional residual capacity (58±12% predicted). Despite normal DLCO (98±18% predicted), VC was elevated (135±31% predicted) while DM averaged 94±22% predicted. DM/VC varied from 0.4 to 1.4 with high values reflecting recruitment of alveolar membrane and low values indicating alveolar membrane dysfunction. The most abnormal IOS (R5 and X5) occurred in subjects with lowest DM/VC (r2 = 0.31, p<0.001; r2 = 0.34, p<0.001). Cardiac output and index (cardiac output / body surface area) were directly related to DM/VC (r2 = 0.41, p<0.001; r2 = 0.19, p = 0.03). Subjects with lower DM/VC demonstrated a cardiac output that remained in the normal range despite presence of obesity.

CONCLUSIONS

Global dysfunction of the distal lung (alveolar membrane and distal airway) is associated with pulmonary vascular congestion and failure to achieve the high output state of obesity. Pulmonary vascular congestion and consequent fluid transudation and/or alterations in the structure of the alveolar capillary membrane may be considered often unrecognized causes of airway dysfunction in obesity.

Obesity hypoventilation syndrome in Japan and independent determinants of arterial carbon dioxide levels

BACKGROUND AND OBJECTIVE

Obesity hypoventilation syndrome (OHS) prevalence was previously estimated at 9% in patients with obstructive sleep apnoea (OSA) in Japan. However, the definition of OSA in that study was based on an apnoea-hypopnoea index (AHI) of ≥ 20/h rather than ≥ 5/h. Therefore, the prevalence of OHS in OSA was not measured in the same way as for Western countries. Our study objectives were to investigate the characteristics of Japanese patients with OHS.

METHODS

Nine hundred eighty-one consecutive patients investigated for suspected OSA were enrolled. At least 90% of them were from urban areas, including 162 with obese OSA (body mass index (BMI) ≥ 30 kg/m(2) and AHI ≥ 5/h).

RESULTS

The prevalence of OHS (BMI 36.7 ± 4.9 kg/m(2) ) in OSA and that in obese OSA were 2.3% and 12.3%, respectively. Multiple regression analysis revealed that independent of age and BMI, arterial oxygen pressure (contribution rate (R(2) ) = 7.7%), 4% oxygen desaturation index (R(2)  = 8.9%), carbon monoxide diffusing capacity/alveolar volume (R(2)  = 8.3%), haemoglobin concentration (R(2)  = 4.9%) and waist circumference (R(2)  = 4.9%) were independently associated with arterial carbon dioxide pressure. After 12.3 ± 4.6 months of CPAP treatment, more than 60% of OHS patients no longer had hypercapnia.

CONCLUSIONS

The prevalence of OHS in OSA in Japan was 2.3%. The mean BMI of patients with OHS in Japan was lower than that in Western countries (36.7 kg/m(2) vs 44.0 kg/m(2) ).

Airway dysfunction in obesity: response to voluntary restoration of end expiratory lung volume

Introduction

Abnormality in distal lung function may occur in obesity due to reduction in resting lung volume; however, airway inflammation, vascular congestion and/or concomitant intrinsic airway disease may also be present. The goal of this study is to 1) describe the phenotype of lung function in obese subjects utilizing spirometry, plethysmography and oscillometry; and 2) evaluate residual abnormality when the effect of mass loading is removed by voluntary elevation of end expiratory lung volume (EELV) to predicted FRC.

Methods

100 non-smoking obese subjects without cardio-pulmonary disease and with normal airflow on spirometry underwent impulse oscillometry (IOS) at baseline and at the elevated EELV.

Results

FRC and ERV were reduced (44±22, 62±14% predicted) with normal RV/TLC (29±9%). IOS demonstrated elevated resistance at 20 Hz (R₂₀, 4.65±1.07 cmH₂O/L/s); however, specific conductance was normal (0.14±0.04). Resistance at 5–20 Hz (R₅₋₂₀, 1.86±1.11 cmH₂O/L/s) and reactance at 5 Hz (X₅, −2.70±1.44 cmH₂O/L/s) were abnormal. During elevation of EELV, IOS abnormalities reversed to or towards normal. Residual abnormality in R₅₋₂₀ was observed in some subjects despite elevation of EELV (1.16±0.8 cmH₂O/L/s). R₅₋₂₀ responded to bronchodilator at baseline but not during elevation of EELV.

Conclusions

This study describes the phenotype of lung dysfunction in obesity as reduction in FRC with airway narrowing, distal respiratory dysfunction and bronchodilator responsiveness. When R₅₋₂₀ normalized during voluntary inflation, mass loading was considered the predominant mechanism. In contrast, when residual abnormality in R₅₋₂₀ was demonstrable despite return of EELV to predicted FRC, mechanisms for airway dysfunction in addition to mass loading could be invoked.

Respiratory Consequences of Mild-to-Moderate Obesity: Impact on Exercise Performance in Health and in Chronic Obstructive Pulmonary Disease

In many parts of the world, the prevalence of obesity is increasing at an alarming rate. The association between obesity, multiple comorbidities, and increased mortality is now firmly established in many epidemiological studies. However, the link between obesity and exercise intolerance is less well studied and is the focus of this paper. Although exercise limitation is likely to be multifactorial in obesity, it is widely believed that the respiratory mechanical constraints and the attendant dyspnea are important contributors. In this paper, we examined the evidence that critical ventilatory constraint is a proximate source of exercise limitation in individuals with mild-to-moderate obesity. We first reviewed existing information on exercise performance, including ventilatory and perceptual response patterns, in obese individuals who are otherwise healthy. We then considered the impact of obesity in patients with preexisting respiratory mechanical abnormalities due to chronic obstructive pulmonary disease (COPD), with particular reference to the effect on dyspnea and exercise performance. Our main conclusion, based on the existing and rather sparse literature on the subject, is that abnormalities of dynamic respiratory mechanics are not likely to be the dominant source of dyspnea and exercise intolerance in otherwise healthy individuals or in patients with COPD with mild-to-moderate obesity.

Model of functional performance in obese elderly people with chronic obstructive pulmonary disease

PURPOSE

To test a theoretically and empirically supported model of the relationships among percent truncal fat (truncal obesity); disease severity (carbon monoxide diffusing capacity [DLCO]); symptoms (dyspnea); functional capacity (6-min walk test distance); and functional performance (functional performance index) of elderly people with chronic obstructive pulmonary disease (COPD).

DESIGN AND METHOD

A model of functional performance was proposed using a multidimensional framework as expounded by Leidy, and incorporating Wilson and Cleary's model for the relationship between symptoms and functional status. Path analysis was used to examine the relationships among variables. The researchers used a descriptive, cross-sectional design. Subjects were phone screened and completed electrocardiography, physical examination, spirometry testing, and a 4-min walk test as part of initial screening. Enrolled subjects completed a whole-body dual-energy x-ray absorptiometry scan to measure truncal obesity, 6-min walk test, upper body functional performance test, and questionnaires. Subjects were grouped into normal weight, overweight, or obese according to body mass index.

RESULTS

The sample consisted of 76 people 55 years of age and older with mild to severe COPD. Percent truncal fat (truncal obesity) did not affect functional performance directly, but did affect it indirectly through dyspnea. The 6-min walk test distance, dyspnea, and DLCO accounted for 29% of the variability in functional performance.

CONCLUSIONS

We believe that the effectiveness of pulmonary rehabilitation will be enhanced when nurses consider weight loss as a controllable factor for overweight and obese clients. The increasing prevalence of obesity in this population may dictate collaboration between dieticians and pulmonary rehabilitation nurses for effective rehabilitation programs.

CLINICAL RELEVANCE

These findings suggest that percent truncal fat (truncal obesity) may be an indirect factor in the performance of daily activities of people with COPD. We anticipate that clinicians will use knowledge derived from this study to develop interventions to reduce or minimize truncal fat (truncal obesity) and its effects on people with COPD.

Examination of the carbon monoxide diffusing capacity (DL(CO)) in relation to its KCO and VA components

The single-breath carbon monoxide diffusing capacity (DL(CO)) is the product of two measurements during breath holding at full inflation: (1) the rate constant for carbon monoxide uptake from alveolar gas (kco [minute(-1)]) and (2) the "accessible" alveolar volume (Va). kco expressed per mm Hg alveolar dry gas pressure (Pb*) as kco/Pb*, and then multiplied by Va, equals Dl(CO); thus, Dl(CO) divided by Va (DL(CO)/Va, also called Kco) is only kco/Pb* in different units, remaining, essentially, a rate constant. The notion that DL(CO)/Va "corrects" DL(CO) for reduced Va is physiologically incorrect, because DL(CO)/Va is not constant as Va changes; thus, the term Kco reflects the physiology more appropriately. Crucially, the same DL(CO) may occur with various combinations of Kco and Va, each suggesting different pathologies. Decreased Kco occurs in alveolar-capillary damage, microvascular pathology, or anemia. Increased Kco occurs with (1) failure to expand normal lungs to predicted full inflation (extrapulmonary restriction); or (2) increased capillary volume and flow, either globally (left-to-right intracardiac shunting) or from flow and volume diversion from lost or damaged units to surviving normal units (e.g., pneumonectomy). Decreased Va occurs in (1) reduced alveolar expansion, (2) alveolar damage or loss, or (3) maldistribution of inspired gases with airflow obstruction. Kco will be greater than 120% predicted in case 1, 100-120% in case 2, and 40-120% in case 3, depending on pathology. Kco and Va values should be available to clinicians, as fundamental to understanding the clinical implications of DL(CO). The diffusing capacity for nitric oxide (DL(NO)), and the DL(NO)/DL(CO) ratio, provide additional insights.

Lung physiology and obesity: anesthetic implications for thoracic procedures

Obesity is a worldwide health problem affecting 34% of the American population. As a result, more patients requiring anesthesia for thoracic surgery will be overweight or obese. Changes in static and dynamic respiratory mechanics, upper airway anatomy, as well as multiple preoperative comorbidities and altered drug metabolism, characterize obese patients and affect the anesthetic plan at multiple levels. During the preoperative evaluation, patients should be assessed to identify who is at risk for difficult ventilation and intubation, and postoperative complications. The analgesia plan should be executed starting in the preoperative area, to increase the success of extubation at the end of the case and prevent reintubation. Intraoperative ventilatory settings should be customized to the changes in respiratory mechanics for the specific patient and procedure, to minimize the risk of lung damage. Several non invasive ventilatory modalities are available to increase the success rate of extubation at the end of the case and to prevent reintubation. The goal of this review is to evaluate the physiological and anatomical changes associated with obesity and how they affect the multiple components of the anesthetic management for thoracic procedures.

Paradoxical clearance of natriuretic peptide between pulmonary and systemic circulation: a pulmonary mechanism of maintaining natriuretic peptide plasma concentration in obese individuals

CONTEXT

Although it has been reported that obese patients have low levels of natriuretic peptide, the metabolism of natriuretic peptide in this population remains unclear.

OBJECTIVES

This study aimed to examine the effects of body mass index on the natriuretic peptide clearance rate from the pulmonary and systemic circulation.

DESIGN

We conducted a prospective observational cohort study.

SETTING/PATIENTS

Thirty patients with atrial fibrillation undergoing pulmonary vein isolation in single center participated in the study.

MAIN OUTCOMES AND MEASURES

We measured pulmonary and systemic atrial/brain natriuretic peptide clearance and clinical parameters including body mass index and pulmonary oxygen levels.

RESULTS

Significantly lower atrial natriuretic peptide levels were found in all pulmonary veins when compared with the pulmonary artery. The pulmonary atrial natriuretic peptide clearance rate was negatively correlated with body mass index. In contrast, the systemic atrial natriuretic peptide clearance rate was positively correlated with the body mass index. A reciprocal relationship therefore exists between pulmonary and systemic atrial natriuretic peptide clearance. Regional pulmonary atrial natriuretic peptide clearances in the inferior lung were significantly negatively correlated to oxygen pressure in the inferior pulmonary veins. There was a similar tendency for brain natriuretic peptide, but the differences between the pulmonary artery and each pulmonary vein were not significant.

CONCLUSIONS

Overweight patients have higher systemic atrial natriuretic peptide clearance, whereas they show a lower pulmonary atrial natriuretic peptide clearance, which might be related to pulmonary tissue hypoxia.

Orthopedic trauma-induced pulmonary injury in the obese Zucker rat

OBJECTIVE

Obese subjects with orthopedic trauma exhibit increased inflammation and an increased risk of pulmonary edema. Prostaglandin E(2) (PGE(2) ) production is elevated during inflammation and associated with increased vascular permeability. We hypothesize that pulmonary edema in obesity following orthopedic trauma is due to elevated PGE(2) and resultant increases in pulmonary permeability.

METHODS

Orthopedic trauma was induced in both hindlimbs in lean (LZ) and obese Zucker rats (OZ). On the following day, plasma interleukin-6 (IL-6) and PGE(2) levels, pulmonary edema, and pulmonary gas exchange capability were compared between groups: LZ, OZ, LZ with trauma (LZT), and OZ with trauma (OZT). Vascular permeability in isolated lungs was measured in LZ and OZ before and after application of PGE(2) .

RESULTS

As compared with the other groups, the OZT exhibited elevated plasma IL-6 and PGE(2) levels, increased lung wet/dry weight ratio and bronchoalveolar protein concentration, and an impaired pulmonary gas exchange. Indomethacin treatment normalized plasma PGE(2) levels and pulmonary edema. Basal pulmonary permeability in isolated lungs was higher in OZ than LZ, with a further increase in permeability following treatment with PGE(2) .

CONCLUSIONS

These results suggest that pulmonary edema in OZ following orthopedic trauma is due to an elevated PGE(2) and resultant increases in pulmonary permeability.

Impact of altered alveolar volume on the diffusing capacity of the lung for carbon monoxide in obesity

BACKGROUND

Studies on the diffusing capacity of the lung for carbon monoxide (DL(CO)) in obese patients are conflicting, some studies showing increased DL(CO) and others unaltered or reduced values in these subjects.

OBJECTIVES

To compare obese patients to controls, examine the contribution of alveolar volume (VA) and CO transfer coefficient (K(CO)) to DL(CO), and calculate DL(CO) values adjusted for VA.

METHODS

We measured body mass index (BMI), waist circumference (WC), spirometry and DL(CO) in 98 adult obese patients without cardiopulmonary or smoking history and 48 healthy subjects. All tests were performed in the same laboratory.

RESULTS

Using conventional reference values, mean DL(CO) and VA were lower (-6%, p < 0.05, and -13%, p < 0.001, respectively), and K(CO) was higher (+9%, p < 0.05) in obese patients than in controls. VA decreased whereas K(CO) increased with increasing BMI and WC in the obese group. Patients with lower DL(CO) had low K(CO) in addition to decreased VA. In contrast, some obese patients maintained normal VA, which, coupled with high K(CO), resulted in higher DL(CO). The main result is that diffusion capacity differences between obese patients and controls disappeared using reference equations adjusting DL(CO) for VA.

CONCLUSIONS

Using conventional reference equations, our obese patients show slightly lower mean DL(CO,) lower mean VA and higher mean K(CO) than controls, but with a large range of DL(CO) values and patterns. Adjusting DL(CO) for VA suggests that low lung volumes are the main cause of low DL(CO) and high K(CO) values in obese patients.

Pulmonary diffusing capacity for nitric oxide during exercise in morbid obesity

Morbidly obese individuals may have altered pulmonary diffusion during exercise. The purpose of this study was to examine pulmonary diffusing capacity for nitric oxide (DLNO) and carbon monoxide (DLCO) during exercise in these subjects. Ten morbidly obese subjects (age = 38 +/- 9 years, BMI = 47 +/- 7 kg/m(2), peak oxygen consumption or VO(2peak) = 2.4 +/- 0.4 l/min) and nine nonobese controls (age = 41 +/- 9 years, BMI = 23 +/- 2 kg/m(2), VO(2peak) = 2.6 +/- 0.9 l/min) participated in two sessions: the first measured resting O(2) and VO(2peak) for determination of wattage equating to 40, 75, and 90% oxygen uptake reserve (VO(2)R). The second session measured pulmonary diffusion from single-breath maneuvers of 5 s each, as well as heart rate (HR) and VO(2) over three workloads. DLNO, DLCO, and pulmonary capillary blood volume were larger in obese compared to nonobese groups (P <or= 0.06) only when expressed relative to alveolar volume (VA). The slope between VO(2) and all measures of pulmonary diffusion, whether or not expressed to VA, were not different between groups (P > 0.10). The morbidly obese have increased pulmonary diffusion per unit increase in VA compared with nonobese controls which may be due to a lower rise in VA per unit increase in VO(2) in the obese during exercise.

Physiological models of body composition and human obesity

Background

The body mass index (BMI) is the standard parameter for predicting body fat fraction and for classifying degrees of obesity. Currently available regression equations between BMI and fat are based on 2 or 3 parameter empirical fits and have not been validated for highly obese subjects. We attempt to develop regression relations that are based on realistic models of body composition changes in obesity. These models, if valid, can then be extrapolated to the high fat fraction of the morbidly obese.

Methods

The analysis was applied to 3 compartment (density and total body water) measurements of body fat. The data was collected at the New York Obesity Research Center, Body Composition Unit, as part of ongoing studies. A total of 1356 subjects were included, with a BMI range of 17 to 50 for males and 17 to 65 for females. The body composition model assumes that obese subjects can be represented by the sum of a standard lean reference subject plus an extra weight that has a constant adipose, bone and muscle fraction.

Results

There is marked age and sex dependence in the relationship between BMI and fat fraction. There was no significant difference among Caucasians, Blacks and Hispanics while Asians had significantly greater fat fraction for the same BMI. A linear relationship between BMI and fat fraction provides a good description for men but overestimates the fat fraction in morbidly obese women for whom a non-linear regression should be used. New regression relations for predicting body fat just from experimental measurements of body density are described that are more accurate then those currently used. From the fits to the experimental BMI and density data, a quantitative description of the bone, adipose and muscle body composition of lean and obese subjects is derived.

Conclusion

Physiologically realistic models of body composition provide both accurate regression relations and new insights about changes in body composition in obesity.