Pulmonary function in obese persons

The Impact of Obesity on Critical Illnesses

ABSTRACT

In the last few decades, obesity became one of the world's greatest health challenges reaching a size of global epidemic in virtually all socioeconomic statuses and all age groups. Obesity is a risk factor for many health problems and as its prevalence gradually increases is becoming a significant economic and health burden. In this manuscript we describe how normal respiratory and cardiovascular physiology is altered by obesity. We review past and current literature to describe how obesity affects outcomes of patients facing critical illnesses and discuss some controversies related to this topic.

Causal relationships between obesity and the leading causes of death in women and men

Obesity traits are causally implicated with risk of cardiometabolic diseases. It remains unclear whether there are similar causal effects of obesity traits on other non-communicable diseases. Also, it is largely unexplored whether there are any sex-specific differences in the causal effects of obesity traits on cardiometabolic diseases and other leading causes of death. We constructed sex-specific genetic risk scores (GRS) for three obesity traits; body mass index (BMI), waist-hip ratio (WHR), and WHR adjusted for BMI, including 565, 324, and 337 genetic variants, respectively. These GRSs were then used as instrumental variables to assess associations between the obesity traits and leading causes of mortality in the UK Biobank using Mendelian randomization. We also investigated associations with potential mediators, including smoking, glycemic and blood pressure traits. Sex-differences were subsequently assessed by Cochran's Q-test (Phet). A Mendelian randomization analysis of 228,466 women and 195,041 men showed that obesity causes coronary artery disease, stroke (particularly ischemic), chronic obstructive pulmonary disease, lung cancer, type 2 and 1 diabetes mellitus, non-alcoholic fatty liver disease, chronic liver disease, and acute and chronic renal failure. Higher BMI led to higher risk of type 2 diabetes in women than in men (Phet = 1.4×10-5). Waist-hip-ratio led to a higher risk of chronic obstructive pulmonary disease (Phet = 3.7×10-6) and higher risk of chronic renal failure (Phet = 1.0×10-4) in men than women. Obesity traits have an etiological role in the majority of the leading global causes of death. Sex differences exist in the effects of obesity traits on risk of type 2 diabetes, chronic obstructive pulmonary disease, and renal failure, which may have downstream implications for public health.

Identification of significant obstructive sleep apnoea in the obese patient: development of the novel DX-OSA score

BACKGROUND AND OBJECTIVES

There is a high prevalence of undiagnosed obstructive sleep apnoea (OSA) in obese surgical patients. We investigated the extent to which anthropometric measurements can be used to identify the presence of significant OSA (Apnoea/Hypopnoea Index (AHI) ≥ 20) in adult patients.

MATERIALS AND METHODS

We prospectively studied 1357 adult patients scheduled for elective laparoscopic bariatric surgery. Prior to surgery, body mass index (BMI), gender, neck circumference, STOP-Bang score, SpO₂, neck and trunk fat (by dual X-ray absorptiometry) were recorded. All patients with a STOP-Bang score ≥ 5 underwent polysomnography. Auto-titrated Positive Airway Pressure (APAP) therapy was instituted when AHI ≥ 20/h. Predictors of OSA were identified and their cut-off values determined.

RESULTS

In total, 1357 patients were screened; 345 patients underwent preoperative polysomnography; 190 had AHI ≥ 20/h and received APAP treatment. The novel Dual X-Ray-Obstructive Sleep Apnoea (DX-OSA) score was derived from the data. The score included 6 items: the STOP-Bang score, BMI, neck fat, trunk fat, baseline SpO₂, and Expiratory Reserve Volume (ERV), and its sensitivity, specificity, positive-predictive values, negative-predictive values, likelihood ratios, and post-test probabilities determined. At a cut-off of 3, the DX-OSA score had the same sensitivity as the STOP-bang score, but better specificity. The lowest likelihood ratio was found for STOP-Bang and the highest for the DX-OSA score (OSA probability > 83%).

CONCLUSION

The DX-OSA score may be useful for identifying obese patients with significant OSA who require CPAP (continuous positive airway pressure) treatment, and CPAP could be commenced without the need for polysomnography, therefore, without delaying surgery.

Emerging Comorbidities in Adult Asthma: Risks, Clinical Associations, and Mechanisms

Asthma is a heterogeneous disease with many phenotypes, and age at disease onset is an important factor in separating the phenotypes. Most studies with asthma have been performed in patients being otherwise healthy. However, in real life, comorbid diseases are very common in adult patients. We review here the emerging comorbid conditions to asthma such as obesity, metabolic syndrome, diabetes mellitus type 2 (DM2), and cardiac and psychiatric diseases. Their role as risk factors for incident asthma and whether they affect clinical asthma are evaluated. Obesity, independently or as a part of metabolic syndrome, DM2, and depression are risk factors for incident asthma. In contrast, the effects of comorbidities on clinical asthma are less well-known and mostly studies are lacking. Cross-sectional studies in obese asthmatics suggest that they may have less well controlled asthma and worse lung function. However, no long-term clinical follow-up studies with these comorbidities and asthma were identified. These emerging comorbidities often occur in the same multimorbid adult patient and may have in common metabolic pathways and inflammatory or other alterations such as early life exposures, systemic inflammation, inflammasome, adipokines, hyperglycemia, hyperinsulinemia, lung mechanics, mitochondrial dysfunction, disturbed nitric oxide metabolism, and leukotrienes.

Weight loss predictability by plasma metabolic signatures in adults with obesity and morbid obesity of the DiOGenes study

OBJECTIVE

Aim is to predict successful weight loss by metabolic signatures at baseline and to identify which differences in metabolic status may underlie variations in weight loss success.

METHODS

In DiOGenes, a randomized, controlled trial, weight loss was induced using a low-calorie diet (800 kcal) for 8 weeks. Men (N = 236) and women (N = 431) as well as groups with overweight/obesity and morbid obesity were studied separately. The relation between the metabolic status before weight loss and weight loss was assessed by stepwise regression on multiple data sets, including anthropometric parameters, NMR-based plasma metabolites, and LC-MS-based plasma lipid species.

RESULTS

Maximally, 57% of the variation in weight loss success can be predicted by baseline parameters. The most powerful predictive models were obtained in subjects with morbid obesity. In these models, the metabolites most predictive for weight loss were acetoacetate, triacylglycerols, phosphatidylcholines, specific amino acids, and creatine and creatinine. This metabolic profile suggests that high energy metabolism activity results in higher amounts of weight loss.

CONCLUSIONS

Possible predictive (pre-diet) markers were found for amount of weight loss for specific subgroups.

Association between different indexations of extravascular lung water (EVLW) and PaO2/FiO2: a two-center study in 231 patients

Background

Variability of body weight (BW) and height calls for indexation of volumetric hemodynamic parameters. Extravascular lung water (EVLW) has formerly been indexed to actual BW (BW_act) termed EVLW-index (EVLWI). In overweight patients indexation to BW_act might inappropriately lower indexed EVLWI_act. Several studies suggest indexation of EVLWI to predicted BW (EVLWI_pred). However, data regarding association of EVLWI_act and EVLW_pred to mortality and PaO₂/FiO₂ are inconsistent. Two recent studies based on biometric database-analyses suggest indexation of EVLWI to height (EVLWI_height). Therefore, our study compared the association of un-indexed EVLW, EVLWI_height, EVLW_pred and EVLWI_act to PaO₂/FiO₂ and Oxygenation index (OI = mean airway pressure*FiO₂*/PaO₂).

Methods

A total of 2119 triplicate transpulmonary thermodilutions (TPTDs; PiCCO; Pulsion Medical-Systems, Germany) were performed in 50 patients from the evaluation, and 181 patients from the validation groups. Correlations of EVLW and EVLWI to PaO₂/FiO₂, OI and ROC-AUC-analyses regarding PaO₂/FiO₂<200 mmHg (primary endpoint) and OI>10 were performed.

Results

In the evaluation group, un-indexed EVLW (AUC 0.758; 95%-CI: 0.637-0.880) and EVLWI_height (AUC 0.746; 95%-CI: 0.622-0.869) provided the largest ROC-AUCs regarding PaO₂/FiO₂<200 mmHg. The AUC for EVLWI_pred was smaller (0.713). EVLWI_act provided the smallest AUC (0.685). This was confirmed in the validation group: EVLWI_height provided the largest AUC (0.735), EVLWI_act (0.710) the smallest. In the merged data-pool, AUC was significantly greater for EVLWI_height (0.729; 95%-CI: 0.674–0.784) compared to all other indexations including EVLWI_act (ROC-AUC 0.683, p = 0.007) and EVLWI_pred (ROC-AUC 0.707, p = 0.015). The association of EVLW(I) was even stronger to OI compared to PaO₂/FiO₂. In the merged data-pool, EVLWI_height provided the largest AUC regarding “OI>10” (0.778; 95%-CI: 0.713–0.842) compared to 0.739 (95%-CI: 0.669–0.810) for EVLWI_act and 0.756 (95%-CI: 0.688–0.824) for EVLWI_pred.

Conclusions

Indexation of EVLW to height (EVLWI_height) improves the association of EVLW(I) to PaO₂/FiO₂ and OI compared to all other indexations including EVLWI_pred and EVLWI_act. Also considering two recent biometric database analyses, EVLWI should be indexed to height.

Linking obesity and asthma

A growing body of literature suggests that obesity has a significant impact on asthma risk, phenotype, and prognosis. Epidemiological studies have clearly demonstrated that asthma is more likely to occur in obese patients, and health status is impaired in obese individuals with asthma, with obese asthmatics experiencing more symptoms, worse quality of life, increased healthcare use, and increased asthma severity. However, obesity has well-described effects on lung function and mechanics that can lead to symptoms of dyspnea without causing the pathophysiologic changes of asthma. Adding to the challenges of evaluating this association, some studies have failed to demonstrate a robust relationship between obesity and traditional biomarkers of airway inflammation in adult asthmatics, leading to the conclusion that obesity does not necessarily worsen airway inflammation in asthma. In this regard, emerging data suggest that nonatopic mechanisms may be relevant in obese asthmatics, and that these mechanisms may have a direct impact on the response of obese asthmatics to asthma therapies, most notably inhaled glucocorticoids. This article will review selected aspects of the contributions of obesity-related airway and systemic inflammation to asthma, with a focus on the impact of obesity as a modifier of risk, prognosis, and therapeutic response in asthma.

Environmental perturbations: Obesity

Obesity currently affects about one-third of the U.S. population, while another one-third is overweight. The importance of obesity for certain conditions such as heart disease and type 2 diabetes is well appreciated. The effects of obesity on the respiratory system have received less attention and are the subject of this article. Obesity alters the static mechanical properties of the respiratory system leading to a reduction in the functional residual capacity (FRC) and the expiratory reserve volume (ERV). There is substantial variability in the effects of obesity on FRC and ERV, at least some of which is related to the location rather than the total mass of adipose tissue. Obesity also results in airflow obstruction, which is only partially attributable to breathing at low lung volume, and can also promote airway hyperresponsiveness and asthma. Hypoxemia is common is obesity and correlates well with FRC, as well as with measures of abdominal obesity. However, obese subjects are usually eucapnic, indicating that hypoventilation is not a common cause of their hypoxemia. Instead, hypoxemia results from ventilation-perfusion mismatch caused by closure of dependent airways at FRC. Many obese subjects complain of dyspnea either at rest or during exertion, and the dyspnea score also correlates with reductions in FRC and ERV. Weight reduction should be encouraged in any symptomatic obese individual, since virtually all of the respiratory complications of obesity improve with even moderate weight loss.

Obesity and obstructive sleep apnoea: mechanisms for increased collapsibility of the passive pharyngeal airway

Epidemiological evidence suggests there are significant links between obesity and obstructive sleep apnoea (OSA), with a particular emphasis on the importance of fat distribution in the development of OSA. In patients with OSA, the structure of the pharyngeal airway collapses. A collapsible tube within a rigid box collapses either due to decreased intraluminal pressure or increased external tissue pressure (i.e. reduction in transmural pressure), or due to reduction in the longitudinal tension of the tube. Accordingly, obesity should structurally increase the collapsibility of the pharyngeal airway due to excessive fat deposition at two distinct locations. In the pharyngeal airway region, excessive soft tissue for a given maxillomandibular enclosure size (upper airway anatomical imbalance) can increase tissue pressure surrounding the pharyngeal airway, thereby narrowing the airway. Even mild obesity may cause anatomical imbalance in individuals with a small maxilla and mandible. Lung volume reduction due to excessive central fat deposition may decrease longitudinal tracheal traction forces and pharyngeal wall tension, changing the 'tube law' in the pharyngeal airway (lung volume dependence of the upper airway). The lung volume dependence of pharyngeal airway patency appears to contribute more significantly to the development of OSA in morbidly obese, apnoeic patients. Neurostructural interactions required for stable breathing may be influenced by obesity-related hormones and cytokines. Accumulating evidence strongly supports these speculations, but further intensive research is needed.

Função pulmonar de obesos mórbidos submetidos à cirurgia bariátrica

OBJETIVO: Comparar a função pulmonar de indivíduos obesos mórbidos submetidos à gastroplastia. MÉTODOS: Participaram da pesquisa 25 indivíduos, divididos em grupo experimental com 15 sujeitos (feminino = 13 e masculino = 2) e grupo controle com 10 sujeitos (feminino = 8 e masculino = 2). Foram mensurados os valores espirométricos na fase pré-operatória e na fase pós-operatória, três meses após a cirurgia. RESULTADOS: Verificou-se diferença significante intragrupo na análise inicial e após os três meses de acompanhamento de peso, índice de massa corporal (IMC), Capacidade Vital forçada (CVF), Volume de Reserva Expiratório (VRE), Capacidade Inspiratória (CI) e do Fluxo Expiratório Forçado (FEF25-75%), nos indivíduos que foram submetidos à cirurgia. Para os resultados obtidos da análise de diferença entre os grupos experimental e controle na análise de grupo e tempo, foram considerados significativos a CVF e o VRE. Verificou-se que aqueles que apresentavam distúrbios inespecíficos na fase pré-operatória passaram a ter função pulmonar normal na fase pós-operatória. Não foram verificadas diferenças significativas entre as características de proporções da espirometria entre os grupos e na avaliação intragrupo experimental. CONCLUSÃO: A cirurgia bariátrica influencia na melhora da função pulmonar, observando que um tempo maior de acompanhamento desses indivíduos pode nos mostrar resultados ainda mais confirmatórios sobre a importância da perda de peso para a função pulmonar.

Asthma and Sleep

Asthma significantly affects quality of sleep. Asthma physiology follows a diurnal pattern with peak flow at its lowest during early morning hours. The type and timing of release of inflammatory mediators also varies during the day and nighttime. Nocturnal symptoms are common in poorly controlled asthma. Hence, these nighttime symptoms play a significant role in the assessment of asthmatic patients as demonstrated in validated asthma control and quality of life questionnaires. Comorbid conditions may include allergic rhinitis, obesity, obstructive sleep apnea, and gastroesophageal reflux, all of which may worsen asthma symptoms, especially during sleep. In addition, exposure to greater loads of allergens in susceptible individuals during sleep is a significant problem and must be addressed to break the cycle of poor asthma control. Thus, asthma education for better symptom control should address these particular issues surrounding sleep.

Impaired response to deep inspiration in obesity

Deep inspirations modulate airway caliber and airway closure and their effects are impaired in asthma. The association between asthma and obesity raises the question whether the deep inspiration (DI) effect is also impaired in the latter condition. We assessed the DI effects in obese and nonobese nonasthmatics. Thirty-six subjects (17 obese, 19 nonobese) underwent routine methacholine (Mch) challenge and 30 of them also had a modified bronchoprovocation in the absence of DIs. Lung function was monitored with spirometry and forced oscillation (FO) [resistance (R) at 5 Hz (R5), at 20 Hz (R20), R5-R20 and the integrated area of low-frequency reactance (AX)]. The response to Mch, assessed with area under the dose-response curves (AUC), was consistently greater in the routine challenge in the obese (mean ± SE, obese vs. nonobese AUC: R5: 15.7 ± 2.3 vs. 2.4 ± 2.0, P < 0.0005; R20: 5.6 ± 1.4 vs. 1.4 ± 1.2, P = 0.027; R5-R20: 10.2 ± 1.6 vs. 0.9 ± 0.1.4, P < 0.0005; AX: 115.6 ± 22.0 vs. 1.5 ± 18.9, P < 0.0005), but differences between groups in the modified challenge were smaller, indicating reduced DI effects in obesity. Given that DI has bronchodilatory and bronchoprotective effects, we further assessed these components separately. In the obese subjects, DI prior to Mch enhanced Mch-induced bronchoconstriction, but DI after Mch resulted in bronchodilation that was of similar magnitude as in the nonobese. We conclude that obesity is characterized by increased Mch responsiveness, predominantly of the small airways, due to a DI effect that renders the airways more sensitive to the stimulus.

Do Patients with Obstructive Sleep Apnea have an Increased Risk of Desaturation During Induction of Anesthesia for Weight Loss Surgery?

Background:

Obstructive sleep apnea (OSA) is an independent risk factor to develop perioperative complications during weight loss surgery, but the mechanisms are unclear. It is possible, that patients with OSA have a higher incidence of desaturation during induction of anesthesia.

Methods:

We enrolled 100 morbidly obese (body mass index: 53±10) adult patients undergoing open bariatric surgery in a prospective study. At least 1 h before induction of anesthesia, peripheral oxygen saturation (SpO₂) was measured by an oximetry finger probe in the sitting and supine positions, and Mallampati score was taken. Oxygen saturation was recorded also during induction of anesthesia, and nadir values were analyzed, and the STOP-BANG questionnaire was applied.

Results:

Thirty-six patients presented with clinical suspicion of OSA. Body weight predicted oxygen saturation in the supine and sitting position, prior to induction of anesthesia. Nadir oxygen saturation during induction of anesthesia was considerably higher in patients with clinical suspicion of OSA, a significant finding that persisted as a trend after correction for age, gender and BMI. The Mallampati score was an independent predictor of OSA, even in morbidly obese patients scheduled for weight loss surgery.

Conclusions:

Morbidly obese patients presenting for weight loss surgery have a significant risk to desaturate during induction of anesthesia. A history of OSA does not independently increase the risk of desaturation during induction of anesthesia, if the appropriate precautions are being taken.

Obesity and acute lung injury

Acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS) are common indications for ICU admission and mechanical ventilation. ALI/ARDS also consumes significant health care resources and is a common cause of death in ICU patients. Obesity produces changes in respiratory system physiology that could affect outcomes for ALI/ARDS patients and their response to treatment. Additionally, the biochemical alterations seen in obese patients, such as increased inflammation and altered metabolism, could affect the risk of developing ALI/ARDS in patients with another risk factor (eg, sepsis). The few studies that have examined the influence of obesity on the outcomes from ALI/ARDS are inconclusive. Furthermore, observed results could be biased by disparities in provided care.

Altered resting and exercise respiratory physiology in obesity

Obesity, particularly severe obesity, affects resting and exercise-related respiratory physiology. Severe obesity classically produces a restrictive ventilatory abnormality characterized by reduced expiratory reserve volume. Obstructive ventilatory abnormality may also be associated with abdominal obesity. Decreased peak work rates are usually seen among obese subjects in a setting of normal or decreased ventilatory reserve and normal cardiovascular response to exercise. Weight loss may reverse many adverse physiologic consequences of severe obesity on the respiratory system.

Obesity and asthma

Population-based studies have defined a significant, bidirectional, dose-dependent association between obesity and asthma. Obesity does not cause airflow obstruction, but can result in pulmonary restriction and a reduction in airway diameter, and that could contribute to airway hyper-responsiveness. Mouse models of asthma have demonstrated that obesity and adipokines can enhance airway hyper-responsiveness, airway inflammation, and allergic responses, but it is unclear whether obesity-associated inflammatory mechanisms are relevant in human asthma. Shared environmental and genetic factors are incompletely understood, but very likely to be relevant. Obese asthma appears to be a distinct and novel phenotype of asthma, associated with a reduction in lung volumes, lack of eosinophilic inflammation, altered response to asthma controller therapy, glucocorticoid resistance, and poor asthma control.

Imitators of exercise-induced bronchoconstriction

Exercise-induced bronchoconstriction (EIB) is described by transient narrowing of the airways after exercise. It occurs in approximately 10% of the general population, while athletes may show a higher prevalence, especially in cold weather and ice rink athletes. Diagnosis of EIB is often made on the basis of self-reported symptoms without objective lung function tests, however, the presence of EIB can not be accurately determined on the basis of symptoms and may be under-, over-, or misdiagnosed. The goal of this review is to describe other clinical entities that mimic asthma or EIB symptoms and can be confused with EIB.

Obesity and asthma

Over the last two decades, the convergence of secular trends indicating increases in the prevalence of obesity and asthma has led to a hypothesis that these two disorders might be related. Although the mechanisms underlying a putative relationship between obesity and asthma have not been fully described, a relatively mature body of literature suggests that obesity increases the risk of incident asthma. This article addresses studies that could be interpreted as supporting the hypothesis that obesity leads to asthma. We evaluate animal studies that provide biological underpinnings to an association between the two disorders and clinical and epidemiologic studies that suggest that the relationship between these two disorders is clinically important.

Obesity and asthma: a specific phenotype?

BACKGROUND

Obesity is associated with an increased prevalence of asthma, especially in women, and appears to be more severe in the obese. This study aimed to determine if obese subjects have a specific asthma phenotype.

METHODS

Forty-four consecutive obese subjects (body mass index [BMI] > or = 30 kg/m(2)) and 44 consecutive nonobese subjects (BMI < 25 kg/m(2)), all with asthma, completed an asthma control questionnaire, and underwent methacholine challenge with symptom perception scores, and sputum induction for differential cell count. BMI, waist circumference, and waist-to-hip ratio also were measured.

RESULTS

Despite similar expiratory flows, bronchodilator response, airway responsiveness to methacholine, and symptom perception scores, asthma control was poorer in obese subjects than in nonobese subjects (p = 0.005). Total lung capacity (p = 0.01), expiratory reserve volume (p < 0.0001), functional residual capacity (p < 0.0001), and residual volume (p = 0.006) were lower in obese subjects than in nonobese subjects. Induced-sputum eosinophil and neutrophil counts were similar in both groups, although there was an inverse correlation between sputum eosinophils and waist circumference and a trend for a similar relationship for BMI. Blood serum C-reactive protein (p = 0.009) and fibrinogen (p = 0.0004) levels were higher in obese subjects than in nonobese subjects.

CONCLUSION

Obese people with asthma had poorer asthma control than nonobese asthmatics despite similar symptoms perception. Bronchial and systemic inflammatory characteristics and the specific pattern of pulmonary function changes suggest a different phenotype of asthma in these subjects.

TRIAL REGISTRATION

Clinicaltrials.gov Identifier: NCT00532363 and NCT00532831.

Pulmonary gas exchange in the morbidly obese

The literature on pulmonary gas exchange at rest, during exercise, and with weight loss in the morbidly obese (body mass index or BMI > or = 40 kg m(-2)) is reviewed. Forty-one studies were found (768 subjects weighted mean = 40 years old, BMI = 48 kg m(-2)). The alveolar-to-arterial oxygen partial pressure difference (AaDO2) was large at rest in upright subjects at sea level (23, range 5-38 mmHg) while the arterial pressure of oxygen (PaO2) was low (81, range 50-95 mmHg). Arterial pressure of carbon dioxide (PaCO2) was normal. At peak exercise (162 W), gas exchange improves. Weight loss of 45 kg (BMI = -13 kg m(-2)) over 18 months is associated with an improvement in PaO2 (by 10 mmHg, range 1-23 mmHg), a reduction in AaDO2 (by 8 mmHg, range -3 to -16 mmHg), and PaCO2 (by -3 mmHg, range 3 to -14 mmHg) at rest. Every 5-6 kg reduction in weight increases PaO2 by 1 and reduces AaDO2 by 1 mmHg, respectively. Morbidly obese women have better gas exchange at rest compared with morbidly obese men which is likely due to lower waist-to-hip ratios in women than from differences in weight or BMI.

Challenges in pulmonary risk assessment and perioperative management in bariatric surgery patients

Bariatric surgery has serious associated medical comorbidity and procedure-related risks and is, thus, considered an intermediate-to-high-risk non-cardiac surgery. Altered respiratory mechanics, obstructive sleep apnea (OSA), and less often, pulmonary hypertension and postoperative pulmonary embolism are the major contributors to poor pulmonary outcomes in obese patients. Attention to posture and positioning is critical in patients with OSA. Suspected OSA patients requiring intravenous narcotics should be kept in a monitored setting with frequent assessments and naloxone kept at the bedside. Use of reverse Tredelenburg position, preinduction, maintenance of positive end-expiratory pressure, and use of continuous positive airway pressure can help improve oxygenation in the perioperative period.

Decline in lung function and mortality: implications for medical monitoring

AIM

To investigate the risk of death associated with selected cut-off points for rate of decline of forced expiratory volume in one second (FEV(1)).

METHODS

Mortality rates of a cohort of 1730 coal miners who had performed two pulmonary function tests 12.8 years apart were followed up for an additional 12 years. Based on previous studies, cut-off points for FEV(1) rate of decline (ml/year) were selected as 30, 60 and 90 ml/year. Cox proportional hazard regression was used to estimate multivariate risk ratio of death in each category.

RESULTS

The risk ratios (compared to "below 30 ml/year") were 1.39 (95% CI 0.99 to 1.97) in the "60 to less than 90 ml/year" category and 1.90 (95% CI 1.32 to 2.76) in the "90 ml/year and above" category. Rates of decline above 90 ml/year were consistently related to excess mortality. In non-smokers and those with neither restrictive nor obstructive patterns at the first survey, rates of decline above 60 ml/year were significantly associated with increased mortality.

CONCLUSIONS

Risk of death increases in individuals with rates of decline above about 60 ml/year and is statistically significant with declines of 90 ml/year or more. These results should be useful to healthcare providers in assessing lung function declines observed in individuals.

The effects of body mass index on lung volumes

BACKGROUND

Obesity is a major health issue in North America, and the trend is for obesity to be a more important medical issue in the future. Since obesity can cause respiratory symptoms, many obese people are referred for pulmonary function tests (PFTs). It is well known that obesity causes decreases in lung volumes, but there has never been a large study showing the correlation between body mass index (BMI) and the various lung volumes.

DESIGN

We collected PFT results from 373 patients sent for lung function testing who had normal values for airway function but a wide range of BMIs.

SETTING

The PFTs were done in two accredited outpatient laboratories.

RESULTS

There were significant linear relationships between BMI and vital capacity and total lung capacity, but the group mean values remained within the normal ranges even for morbidly obese patients. However, functional residual capacity (FRC) and expiratory reserve volume (ERV) decreased exponentially with increasing BMI, such that morbid obesity resulted in patients breathing near their residual volume. An important finding was that the greatest rates of change in FRC and ERV occurred in the overweight condition and in mild obesity. At a BMI of 30 kg/m2, FRC and ERV were only 75% and 47%, respectively, of the values for a lean person with a BMI of 20 kg/m2.

CONCLUSIONS

We showed that BMI has significant effects on all of the lung volumes, and the greatest effects were on FRC and ERV, which occurred at BMI values < 30 kg/m2. Our results will assist clinicians when interpreting PFT results in patients with normal airway function.

Physiologic correlates of dyspnea in patients with morbid obesity

OBJECTIVE

Mechanisms of dyspnea in obesity remain unclear. This study was undertaken to determine the relationships between dyspnea and pulmonary function including inspiratory muscle endurance (IME) in morbidly obese patients before bariatric surgery.

RESEARCH METHODS AND PROCEDURES

Fifty-five patients with a mean+/-s.d. body mass index (BMI) of 49.4+/-7.0 kg/m(2) were included. Dyspnea was evaluated by the Baseline Dyspnea Index (BDI; 0-12, 0=maximal dyspnea). Pulmonary function tests included a plethysmography, maximal inspiratory pressure (PImax) and IME was assessed by the incremental threshold loading test, determining the maximal pressure sustained for 2 min (Plim(2)) and Plim(2)/PImax ratio. Patients were classified according to their BMI in two groups: BMI < or =49 (n=27) and >49 kg/m(2) (n=28).

RESULTS

Breathlessness was higher in the BMI >49 kg/m(2) group compared to the BMI < or =49 kg/m(2) group (BDI score at 6.9+/-2.2 in the BMI >49 kg/m(2) group vs 8.9+/-2.5 in the BMI < or =49 kg/m(2) group, P<0.01). Patients with BMI >49 kg/m(2) had significantly higher PaCO(2) level and significantly lower vital capacity, inspiratory capacity and PImax values compared with the BMI < or =49 kg/m(2) group. Correlations between BDI and lung function were moderate: forced expiratory volume in 1 s (FEV(1))% pred: Rho=0.27; P=0.05; vital capacity % pred: Rho=0.40; P=0.004; and Plim(2)/PImax: Rho=0.40; P=0.003. Higher correlations with dyspnea were found in the BMI < or =49 kg/m(2) group: FEV(1)% pred: Rho=0.38; P=0.05; and Plim(2)/PImax: Rho=0.49; P=0.01.

DISCUSSION

Inspiratory muscle performance is moderately reduced in morbid obesity. Dyspnea in these patients remains moderately related to lung function and inspiratory muscle performance. However, inspiratory muscles performance correlates more significantly with dyspnea in patients with a BMI < or =49 kg/m(2).

Obesity and asthma

Asthma and obesity are prevalent disorders, each with a significant public health impact, and a large and growing body of literature suggests an association between the two. The systemic inflammatory milieu in obesity leads to metabolic and cardiovascular complications, but whether this environment alters asthma risk or phenotype is not yet known. Animal experiments have evaluated the effects of leptin and obesity on airway inflammation in response to both allergic and nonallergic exposures and suggest that airway inflammatory response is enhanced by both endogenous and exogenous leptin. Cross-sectional and prospective cohort studies of humans have shown a modest overall increase in asthma incidence and prevalence in the obese, although body mass index does not appear be a significant modifier of asthma severity. Studying the obesity-asthma relationship in large cohorts, in which self-reports are frequently used to ascertain the diagnosis of asthma, has been complicated by alterations in pulmonary physiology caused by obesity, which may lead to dyspnea or other respiratory symptoms but do not fulfill accepted physiologic criteria for asthma. Recent investigations toward elucidating a shared genetic basis for these two disorders have identified polymorphisms in specific regions of chromosomes 5q, 6p, 11q13, and 12q, each of which contains one or more genes encoding receptors relevant to asthma, inflammation, and metabolic disorders, including the beta(2)-adrenergic receptor gene ADRB2 and the glucocorticoid receptor gene NR3C1. Further research is warranted to synthesize these disparate observations into a cohesive understanding of the relationship between obesity and asthma.

Avaliação da função pulmonar na obesidade graus I e II

INTRODUÇÃO: A obesidade pode afetar o tórax, diafragma e músculos abdominais, determinando alterações na função respiratória. OBJETIVO: Avaliar os efeitos da obesidade e correlacionar o índice de massa corporal (IMC) e a circunferência abdominal com os valores espirométricos em individuos obesos. MÉTODO: Foram estudados 48 indivíduos não obesos e 48 indivíduos com obesidade graus I e II, não fumantes, ambos os sexos, idade variando entre 18 e 75 anos, IMC entre 30 e 40kg/m² e ausência de história progressa de morbidade. Foram realizadas espirometria e medidas da circunferência abdominal. RESULTADOS: Não houve diferenças significativas quando se comparou valores espirométricos de homens com obesidade graus I e II com de não obesos. Nas mulheres obesas, a capacidade vital forçada e o volume expirado forçado no primeiro segundo foram significativamente menores que nas não obesas. Homens e mulheres obesos apresentaram volumes de reserva expiratório significativamente menores que não obesos. Embora a capacidade inspiratória tenha sido maior em homens e mulheres obesos, esse aumento foi significativo apenas em homens. Em homens obesos houve correlação negativa e significativa entre o IMC e circunferência abdominal e o volume de reserva expiratório, e também correlação negativa e significativa entre a circunferência abdominal e o volume expirado forçado no primeiro segundo, o que não ocorreu entre as mulheres. CONCLUSÃO: Mulheres com obesidade graus I e II apresentaram alterações na função pulmonar. Esta não é influenciada pelo IMC em homens obesos. No entanto, observou-se que eles apresentaram correlação negativa e significativa entre o IMC e o volume de reserva expiratório. A função pulmonar é influenciada pelos valores da circunferência abdominal em homens com obesidade graus I e II.

Postural changes in lung volumes and respiratory resistance in subjects with obesity

Reduced functional residual capacity (FRC) is consistently found in obese subjects. In 10 obese subjects (mean +/- SE age 49.0 +/- 6 yr, weight 128.4 +/- 8 kg, body mass index 44 +/- 3 kg/m2) without respiratory disease, we examined 1) supine changes in total lung capacity (TLC) and subdivisions, 2) whether values of total respiratory resistance (Rrs) are appropriate for mid-tidal lung volume (MTLV), and 3) estimated resistance of the nasopharyngeal airway (Rnp) in both sitting and supine postures. The results were compared with those of 13 control subjects with body mass indexes of <27 kg/m2. Rrs at 6 Hz was measured by applying forced oscillation at the mouth (Rrs,mo) or the nose (Rrs,na); Rnp was estimated from the difference between sequential measurements of Rrs,mo and Rrs,na. All measurements were made when subjects were seated and when supine. Obese subjects when seated had a restrictive defect with low TLC and FRC-to-TLC ratio; when supine, TLC fell 80 ml and FRC fell only 70 ml compared with a mean supine fall of FRC of 730 ml in control subjects. Values of Rrs,mo and Rrs,na at resting MTLV in obese subjects were about twice those in control subjects in both postures. Relating total respiratory conductance (1/Rrs) to MTLV, the increase in Rrs,mo in obese subjects was only partly explained by their reduced MTLV. Rnp was increased in some obese subjects in both postures. Despite the increased extrapulmonary mass load in obese subjects, further falls in TLC and FRC when supine were negligible. Rrs,mo at isovolume was increased. Further studies are needed to examine the causes of reduced TLC and increases in Rrs,mo and sometimes in Rnp in obese subjects.

A Management Guideline for Obesity-Hypoventilation Syndromes

A survey of our pulmonary service revealed little consensus as to the definition, work-up, and management of hypoventilation, more often encountered in the presence of obesity. If hypoventilation is defined by an arterial carbon dioxide level above 45mmHg, 22% of artrial blood gas samples over a 5-month period met this criterium, suggesting a high Oany-causeO prevalence. This article presents the rationale and explanation for a management protocol for obesity-hypoventilation that is currently being assessed in the VA Medical Center and Case Western Reserve University training program in Pulmonary and Critical Care Medicine.

Pulmonary function testing in obesity, pregnancy, and extremes of body habitus

Knowing the effect body habitus can have on pulmonary function is important when there is a concern of an underlying respiratory impairment. The pattern of PFT abnormaLities can help distinguish an underlying ventilatory defect as deriving from the body habitus or from a second process. There are limitations, however. Individuals who are obese and have the same weight will likely have different degrees of impairment, for instance. It then becomes difficult to predict the effect body habitus will have in each patient. It therefore is vitally important to evaluate these patients using other clinical data to decide whether the ventilatory defect can be explained by body habitus alone. It also should be noted that some of the more subtle physiologic changes that occur in these conditions are still not fully understood. Hopefully, further insight into these changes can be obtained with further investigation. Certainly, better predictors of the impact of the patient's weight, abdominal girth, and other anthropomorphic data on PFT results would be extremely helpful in the evaluation of these individuals.

Expiratory Flow Limitation and Orthopnea in Massively Obese Subjects

BACKGROUND

Morbidly obese subjects, who often complain about breathlessness when lying down, breathe at low lung volume with a reduced expiratory reserve volume (ERV). Therefore, during tidal breathing the expiratory flow reserve is decreased, promoting expiratory flow limitation (EFL), which is more likely to occur in the supine position, when the relaxation volume of the respiratory system, and hence the functional residual capacity (FRC), decrease because of the gravitational effect of the abdominal contents.

PURPOSE

The aim of the study was to assess EFL and orthopnea in massively obese subjects and to evaluate whether orthopnea was associated with the development of supine EFL.

METHODS

In 46 healthy obese subjects (18 men) with a mean (+/- SD) age of 44 +/- 11 years and a mean body mass index (BMI) of 51 +/- 9 kg/m(2), we assessed EFL in both the seated and the supine positions by the negative expiratory pressure method and assessed postural changes in FRC by measuring the variations in the inspiratory capacity (IC) with recumbency. Simultaneously, dyspnea was evaluated in either position using the Borg scale dyspnea index (BSDI) to determine the presence of orthopnea, which was defined as any increase of the BSDI in the supine position.

RESULTS

Partial EFL was detected in 22% and 59%, respectively, of the overall population in seated and supine position. The mean increase in the supine IC amounted to 120 +/- 200 mL (4.1 +/- 6.4%), indicating a limited decrease in FRC with recumbency in these subjects. Orthopnea, although mild (mean BSDI, 1.7 +/- 1.3), was claimed by 20 subjects, and in 15 of them EFL occurred or worsened in the supine position. Orthopnea was associated with lower values of seated ERV (p < 0.05) and was marginally related to supine EFL values (p = 0.07). No significant effect of age, BMI, obstructive sleep apnea-hypopnea syndrome, FEV(1), and forced expiratory flow at 75% of vital capacity was found on either orthopnea or EFL.

CONCLUSION

In morbidly obese subjects, EFL and dyspnea frequently occur with the subject in the supine position, and both supine EFL and low-seated ERV values are related to orthopnea, suggesting that dynamic pulmonary hyperinflation and intrinsic positive end-expiratory pressure may be partly responsible for orthopnea in massively obese subjects.

Chest mechanics in morbidly obese non-hypoventilated patients

Seventy-seven patients with morbid obesity, body mass index (BMI) 40-69.9 kg m(-2), who were candidates for gastroplasty, were studied in our laboratory as part of a pre-operative survey. They had no complaints other than obesity and were not cyanotic. A group of 28 lean subjects (BMI 20-29.8 kg m(-2)) who were candidates for abdominal surgery, without any respiratory complaint, were included as controls. For each patient a pulmonary function test was performed, measuring slow vital capacity with expiratory residual volume (ERV), forced vital capacity (flow/volume) and maximal voluntary ventilation (MVV). In obese patients the MVV is reduced as BMI increases. This results in the reduction of expiratory flows and volumes. Forced expiratory volume in 1 sec (FEV1) is reduced in proportion to the FVC reduction and is related to MVV. It is suggested that the main consequence of the burden of the chest wall by increased adipose mass is a reduction in its compliance, making inspiration increasingly difficult, and resulting in lower static volumes and flows.

Ventilatory responses to hypercapnia and hypoxia in relatives of patients with the obesity hypoventilation syndrome

BACKGROUND

It is unclear why some morbidly obese individuals have waking alveolar hypoventilation while others with similar obesity do not. Some evidence suggests that patients with the obesity hypoventilation syndrome (OHS) may have a measurable premorbid impairment of ventilatory chemoresponsiveness. Such an impairment of ventilatory chemoresponsiveness in OHS, however, may be an acquired and reversible consequence of severe obstructive sleep apnoea (OSA). We hypothesised that, in patients with OHS who do not have coincident severe OSA, there may be a familial impairment in ventilatory responses to hypoxia and hypercapnia.

METHODS

Sixteen first degree relatives of seven patients with OHS without severe OSA (mean (SD) age 40 (16) years, body mass index (BMI) 30 (6) kg/m(2)) and 16 subjects matched for age and BMI without OHS or OSA were studied. Selection criteria included normal arterial blood gas tensions and lung function tests and absence of sleep apnoea on overnight polysomnography. Ventilatory responses to isocapnic hypoxia and to hyperoxic hypercapnia were compared between the two groups.

RESULTS

The slope of the ventilatory response to hypercapnia was similar in the relatives (mean 2.33 l/min/mm Hg) and in the control subjects (2.12 l/min/mm Hg), mean difference 0.2 l/min/mm Hg, 95% confidence interval (CI) for the difference -0.5 to 0.9 l/min/mm Hg, p=0.5. The hypoxic ventilatory response was also similar between the two groups (slope factor A: 379.1 l/min * mm Hg for relatives and 373.4 l/min * mm Hg for controls; mean difference 5.7 l/min * mm Hg; 95% CI -282 to 293 l/min * mm Hg, p=0.7; slope of the linear regression line of the fall in oxygen saturation and increase in minute ventilation: 2.01 l/min/% desaturation in relatives, 1.15 l/min/% desaturation in controls; mean difference 0. 5 l/min/% desaturation; 95% CI -1.7 to 0.7 l/min/% desaturation, p=0. 8).

CONCLUSION

There is no evidence of impaired ventilatory chemoresponsiveness in first degree relatives of patients with OHS compared with age and BMI matched control subjects.

Lung volume and its correlation to nocturnal apnoea and desaturation

The cross-sectional area of the upper airway is known to be lung volume dependent. If, and to what extent, lung volume variables correlate to nocturnal obstructive apnoeas and oxygen desaturations independently of other factors known to affect lung volumes and sleep disordered breathing is still unclear. A total of 92 subjects were examined by ambulatory recording of nocturnal obstructive apnoeas and desaturations. Sixty-nine of the subjects had a history of snoring and 23 were healthy subjects without complaints of snoring and daytime sleepiness. All subjects performed static and dynamic spirometry for measurements of lung volumes. To evaluate the correlation between lung volume variables and apnoea index (AI) and oxygen desaturation index (ODI), simple and multiple regression analysis was performed. Expiratory reserve volume (ERV) was found to be lower in subjects with snoring and apnoeas (ERV = 1.0 l) than in non-snoring subjects (ERV = 1.7 l), (P<0.001). Forced expiratory volume in 1 sec (FEV1)/vital capacity (VC) was slightly, but significantly (P = 0.031), lower in subjects with snoring and nocturnal apnoeas and desaturations. In the multiple regression analysis ERV was found to be independently correlated to both AI (R2=0.13; P=0.001) and ODI (R2 = 0.11; P = 0.002). Multiple regression analysis also revealed that ERV, body mass index (BMI) and habitual smoking together accounted for 43% of the variation in AI and 48% of the variation in ODI. We find a significant independent association between ERV and nocturnal obstructive apnoea and oxygen desaturation frequency. Our results indicate that ERV is correlated to these events to a similar extent, as is obesity.

Pulmonary physiologic changes of morbid obesity

OBJECTIVE

Our objective was to study the effects of extreme obesity on pulmonary function tests and the effects of smoking on these variables in a population group larger than has previously been reported.

DESIGN

Retrospective data analysis.

SETTING

Academic medical center.

PATIENTS

Forty-three patients with extreme obesity [ratio of weight in kilograms to height in centimeters greater than 0.9 (W/H)] who underwent pulmonary function testing at Cedars-Sinai on an out-patient or in-patient basis during the period of 1979 to 1 997.

MEASUREMENTS AND RESULTS

Patients underwent standard pulmonary function testing. The patients were divided into 2 groups based on the W/H ratio: group A (0.9-0.99) and group B (greater than 1.0). Chart review was performed to identify pertinent history/co-morbidities. The independent effects of smoking between each group's patients were assessed. Forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), expiratory reserve volume (ERV), functional residual capacity (FRC), maximum voluntary ventilation (MVV), and forced expiratory flow during midexpiratory phase (FEF25-75%,) were significantly reduced in both groups. Single-breath diffusing capacity for carbon monoxide (DLCO) and the volume of gas into which the single-breath of carbon monoxide and helium was diluted were not elevated. Smoking did not account for the results in group A but did seem to partially explain the decrease in FVC, FEV1, and FEF25-75% in group B.

CONCLUSIONS

Extreme obesity is associated with a reduction in ERV, FVC, FEV1, FRC, FEF25-75%, and MVV. However, contrary to prior reports, D(LCO) is not elevated. These effects are only partially explained by smoking.

Dyspnea in obese healthy men

STUDY OBJECTIVES

To determine whether obese, apparently healthy individuals experience dyspnea at rest and, if so, whether their pulmonary function test (PFT) profile and maximal respiratory pressures are different from obese, healthy subjects without dyspnea.

DESIGN

Prospective, open.

SETTING

Pulmonary function test laboratory, Veterans Administration Medical Center.

PATIENTS

Twenty-three obese male subjects (each with a body mass index [BMI] of > 28 kg/m2) with an FEV1 level and an FEV1/FVC ratio > or = 80% of predicted and no coexisting conditions. Fifteen complained of dyspnea, where eight denied having it, at rest.

MEASUREMENTS AND RESULTS

Standard PFT parameters and maximum static inspiratory (P(Imax)) and expiratory (P(Emax)) mouth pressures were determined. Subjects with dyspnea had similar age and height but larger body weight (113.9+/-5.0 vs 97.4+/-2.6 kg, p = 0.03) and BMI (37.4+/-1.6 vs 31.8+/-0.7 kg/m2, p = 0.02) than subjects without dyspnea, and a greater number of them were current or previous smokers. Forced expiratory flow at 75% vital capacity (54.9+/-6 vs 75.5+/-7% predicted, p = 0.05), maximum voluntary ventilation (MVV; 90.2+/-3.8 vs 107.8+/-9.3% predicted, p = 0.05), and P(Emax) (77+/-2 vs 97.8% predicted, p = 0.007) were significantly reduced in the group of subjects with dyspnea. Large airway function (FVC, FEV1, and FEV1/FVC ratio), lung volumes, and gas exchange parameters were similar between the two groups.

CONCLUSIONS

Some obese, but otherwise healthy, individuals experience dyspnea at rest. Reduced P(Emax) and MVV combined with greater body mass and peripheral airway disease are most likely responsible for the sensation of dyspnea in these individuals.

Influence of excessive weight loss after gastroplasty for morbid obesity on respiratory muscle performance

BACKGROUND

Morbidly obese subjects are known to have impaired respiratory function and inefficient respiratory muscles. A study was undertaken to investigate the influence of excessive weight loss on pulmonary and respiratory muscle function in morbidly obese individuals who underwent gastroplasty to induce weight loss.

METHODS

Twenty one obese individuals with mean (SE) body mass index (BMI) 41.5 (4.5) kg/m2 without overt obstructive airways disease (FEV1/FVC ratio > 80%) were studied before and six months after vertical banded gastroplasty. Only patients who had lost at least 20% of baseline BMI were included in the study. Standard pulmonary function tests and respiratory muscle strength and endurance were measured.

RESULTS

Before operation the predominant abnormalities in respiratory function were significant reductions in lung volumes and respiratory muscle endurance and, to a lesser degree, reductions in respiratory muscle strength. All parameters increased towards normal values after weight loss with significant increases in functional residual capacity (FRC) from 84.0 (2.2) to 91.3 (2.5)% of predicted normal values (mean difference 7.3, 95% confidence interval of difference (CI) 4.2 to 10.5), total lung capacity (TLC) from 85.6 (3.0) to 93.5 (3.7)% of predicted normal values (mean difference 7.9, 95% CI 4.5 to 11.5), residual volume (RV) from 86.7 (3.1) to 96.4 (3.0) of predicted normal values (mean difference 9.7, 95% CI 5.2 to 14.1), expiratory reserve volume (ERV) from 76.6 (3.0) to 89.0 (3.4)% of predicted normal values (mean difference 12.4, 95%, CI 6.3 to 18.9), respiratory muscle strength: PImax from 92 (4.4) to 113 (4.6) cm H2O (mean difference 21, 95% CI 12.2 to 31.6), PEmax from 144 (5.6) to 166 (4.3) cm H2O (mean difference 22, 95% CI 12.9 to 32.0), and endurance: PmPeak/PImax from 56 (1.4) to 69 (2.0)% (mean difference 13, 95% CI 9.7 to 16.9). The strongest correlation was between weight loss and the improvement in respiratory muscle endurance.

CONCLUSIONS

Lung volumes and respiratory muscle performance are decreased in obese individuals. Weight loss following gastroplasty is associated with improvement in lung volumes and respiratory muscle function.

Weight gain and longitudinal changes in lung function in steel workers

Associations among dust exposure, smoking habits, and demographic factors and longitudinal changes of lung function were assessed among male steel workers. Cohort descriptive data analysis was conducted in 541 steel workers who had performed spirometry at least twice between 1982 and 1991 (mean follow-up, 6.1 years). The annual change (slope) in FVC, FEV1, FEV1/FVC%, and in body weight was determined by simple linear regression. The Pearson correlation coefficient between weight change and spirometry changes was calculated. Comparisons were also done in 75 pairs of steel workers matched by age, height, initial FEV1, and smoking status, but whose FEV1 declines differed by > or = 60 mL/yr. The FEV1 and FVC declined an average of 44 and 50 mL/yr, respectively, for the cohort as a whole. The FEV1 and FVC declined 52 and 54 mL/yr for current smokers, 43 and 53 mL/yr for ex-smokers, and 36 and 43 mL/yr for nonsmokers, respectively. Increasing weight was highly correlated with accelerated decline in lung function (p<0.0001). In the matched pairs, mean slopes for FVC, FEV1, and FEV1/FVC ratio were -96 mL/yr, -95 mL/yr, and -0.40%/yr for the rapid decliners; and +5 mL/yr, +10 mL/yr, and +0.10%/yr for their partners (p<0.0001). Matched pair comparisons showed that the rapid decliners averaged a 4.313 kg weight gain, while their partners gained 1.044 kg during the follow-up period. The slope of weight gain was 0.708 kg/yr for rapid decliners and 0.191 kg/yr for comparison workers (p<0.0036). Weight gain, in addition to aging and cigarette smoking, was found to be associated with the longitudinal rate of decline in FVC, FEV1, and FEV1/FVC ratio.

Pulmonary function in obese subjects with a normal FEV1/FVC ratio

STUDY OBJECTIVE

To determine pulmonary function test (PFT) profile and respiratory muscle strength (RMS) of a group of obese individuals who did not have evidence of obstructive airway disease or other underlying diseases affecting their respiratory system.

DESIGN

Prospective, open.

SETTING

PFT laboratory, VA Medical Center.

PARTICIPANTS

Sixty-three consecutive obese (body mass index greater than 27.8 kg/m2) male subjects without overt obstructive airway disease (FEV1/FVC ratio greater than 80%).

MEASUREMENTS AND RESULTS

Standard PFTs and maximum static inspiratory (PImax) and expiratory (PEmax) mouth pressures were determined. RMS was calculated from the following formula: (PImax+PEmax):2. Two distinct groups were identified, those with normal maximum voluntary ventilation (MVV) (> 80% predicted) and those with low MVV. Both inspiratory and expiratory flow rates (FVC, FEV1, forced expiratory flow at 50% vital capacity [V50], maximum inspiratory flow rate [MIFR]), lung volumes (vital capacity [VC], inspiratory capacity [IC], expiratory reserve volume), PImax, and RMS were significantly lower, and residual volume/total lung capacity (RV/TLC) ratio was significantly higher in obese subjects with low MVV compared with those in whom MVV was normal. MVV correlated significantly with FVC, FEV1, V50, MIFR, TLC, VC, IC, RV/TLC, and RMS; the strongest correlation was with MIFR (r = 0.76, p < 0.0001).

CONCLUSIONS

Standard PFTs allow recognition of a subgroup of obese subjects without overt obstructive airway disease who have more severe lung dysfunction, the marker of which is a low MVV. Peripheral airway abnormalities may be responsible for these observations.

Effects of lumbar puncture position on arterial blood gases

We observed the changes in partial pressure of arterial oxygen (PaO ₂) and carbon dioxide (PaCO ₂) before and during assumption of the lateral position prior to lumbar puncture in 81 patients to investigate whether lung volume decreased and ventilation was suppressed. PaO ₂ significantly decreased while the patients were in the lateral position, while PaCO ₂ remained unchanged. There was a negative correlation between the change in PaO ₂ and age [change in PaO ₂ (mmHg)=-0.13×age (years)+4.28,P<0.01]. The fact that closing volume increases with age implies that the decrease in functional residual capacity in the lateral position could have caused the decrease in PaO ₂. It is therefore advisable to continuously monitor arterial oxygenation using a noninvasive monitor, such as a pulse oximeter, while performing spinal or epidural block, especially in elderly patients.

Effect of obesity on pulmonary function in children

The effect of obesity on pulmonary function was studied in 13 children, aged 8-15 years, with 147-300% ideal body weight (IBW). Measurements included lung volumes, airflow rates pre- and post-bronchodilator nebulization, diffusing capacity (DLCO), maximal voluntary ventilation (MVV), minute ventilation VE), and resting energy expenditure (REE). When compared with predicted normal values for sex, height, and body surface area (BSA), decreases (mean % predicted, +/- SE) were observed in expiratory reserve volume (ERV, 36 +/- 5); forced expiratory volume in 1 second (FEV1, 73 +/- 5); forced expiratory flow between 25% and 75% of vital capacity (FEF25-75%, 70 +/- 6); DLCO, absolute (52 +/- 3) and corrected (DLCO/VA, 71 +/- 5); and MVV (62 +/- 5). Residual volume (RV), RV/total lung capacity (TLC), VE, and REE were elevated. Other lung volumes were normal. Thus, obese children have altered pulmonary function, which is characterized by reductions in DLCO and ventilatory muscle endurance and airway narrowing. These alterations may reflect extrinsic mechanical compression on the lung and thorax, and/or intrinsic changes within the lung. The reduced DLCO may result from decreases in alveolar surface area relative to lung volume.

Effects of obesity on respiratory resistance

To assess the effects of obesity on pulmonary function, 46 healthy subjects exhibiting various degrees of obesity underwent lung function tests. Subjects were divided into three groups according to body mass index (BMI): 13 had minimal obesity (BMI, 25 to 29 kg/m2, group 1); 24 had a BMI in the 30 to 40 range (group 2); and 9 displayed to morbid obesity (BMI > 40, group 3). Respiratory resistance was estimated by the forced random noise oscillation technique and airway resistance was determined by body plethysmography. Lung volumes and expiratory flows were also determined and significant negative correlations with BMI were found. Expiratory flows diminished in proportion to lung volumes, and the ratio of forced expiratory volume in 1 s to forced vital capacity was within normal limits. Although expiratory flows did not suggest bronchial obstruction, both respiratory resistance and airway resistance rose significantly with the level of obesity (p < 0.005 and p < 0.025, respectively), from 3.2 (+/- 0.02) and 3.2 (+/- 0.02) cm H2O.s.L-1, respectively, in group 1, to 5.5 (+/- 0.06) and 5.0 (+/- 0.05), respectively, in group 3. Evaluation of the factors responsible for this increased resistance disclosed a significant linear correlation between airway conductance and functional residual capacity (r = 0.70, p < 10(-4)), but specific airway conductance was found to be independent of the degree of obesity. The difference between respiratory resistance and airway resistance did not widen significantly according to the level of obesity, suggesting that chest wall resistance was not a factor enhancing these resistances. Taken together, these findings suggest that in addition to the elastic load, obese subjects have to overcome increased respiratory resistance resulting from the reduction in lung volumes related to being overweight.

Body weight and weight gain related to pulmonary function decline in adults: a six year follow up study

BACKGROUND

Obesity increases the risk of cardiovascular disease, hypertension, diabetes, digestive diseases, and some cancers. Several studies have shown that excess weight or weight gain is related to pulmonary dysfunction, but this issue needs to be further clarified.

METHODS

The analysis was based on data of the Humboldt cohort study which was conducted in the town of Humboldt, Saskatchewan, Canada. The baseline survey in 1977 included 1202 adults, comprising 94% of all residents aged 25-59 years. Of these, 709 (59%) were followed up in 1983. Pulmonary function (forced vital capacity (FVC), forced expiratory volume in one second (FEV1) and maximal mid expiratory flow rate (MMFR) and weight were measured in both surveys. Weight gain was determined by subtracting weight at baseline from weight at follow up. A residual analysis was used to examine the relationship between body mass index (BMI) at baseline, weight gain, and pulmonary function decline.

RESULTS

Both BMI at baseline and weight gain were significantly related to pulmonary function at follow up. The effect of weight gain during the study period, however, was more prominent. The results showed that both mean residual FVC and FEV1 were highest in the group that gained < 1.0 kg, lowest in the group that gained > or = 4.0 kg, and intermediate in the group that gained 1.0-3.9 kg in both men and women after taking age, BMI at baseline, and smoking into account. The effect of weight gain on pulmonary function was greater in men than in women. Multiple regression analysis showed that each kilogram of weight gain was associated with an excess loss of 26 ml in FVC and 23 ml in FEV1 in men, and 14 ml and 9 ml respectively in women.

CONCLUSIONS

Weight gain is significantly related to lung dysfunction. The effect of weight gain on pulmonary function is greater in men than in women.

Anesthetic management of a morbidly obese woman with a massive ovarian cyst

Morbid obesity affects 3% to 5% of the U.S. population and poses challenging problems to the anesthesiologist during the perioperative period. We present a unique case of the management of a morbidly obese woman complicated by a massive ovarian cyst. The major cardiopulmonary, metabolic, and technical features special to this patient population are discussed.