Effect of weight loss on operational lung volumes and oxygen cost of breathing in obese women

Post-gastric Sleeve Surgery Chronic Symptoms From a Sample of Patients in Saudi Community

BACKGROUND

A common bariatric procedure known as gastric sleeve surgery can cause significant weight loss and co-morbid condition alleviation. However, patients could experience persistent problems such as gastrointestinal, musculoskeletal/neural, and psychiatric disorders after surgery. This study aims to identify the most prevalent chronic symptoms following sleeve gastrectomy among a sample of Saudi patients and the impact these symptoms have on patients' lives.

METHODOLOGY

Patients who underwent gastric sleeve surgery at the Ensan Clinic, a facility specializing in gastroenterology, were the subjects of this retrospective cohort analysis. The study population consisted of patients who underwent gastric sleeve surgery, showed up for follow-up after the procedure, and met the inclusion and exclusion criteria. The data collection sheet is divided into seven sections. Sociodemographic information was required in the first section, gastric sleeve surgery information in the second, vital signs in the third, lab results in the fourth, past medical history in the fifth, current treatments in the sixth, and postoperative complications and chronic symptoms in the seventh and final sections.

RESULTS

In 117 patients, the study evaluated the effects of gastric sleeve surgery. Participants had an average age of 40.21 years, and 61.5% were female. Regarding persistent symptoms after surgery, a sizable percentage of patients mentioned digestive issues such as GERD (44.4%), dyspepsia (60.7%), vomiting (23.1%), nausea (39.3%), and abdominal distention (45.3%). A total of 34.2% of patients reported experiencing anxiety, compared to 11.1% who said they had depression or 2.6% who said they had social issues. A few patients reported experiencing neurological or musculoskeletal issues, including exhaustion (7.7%), faintness (5.1%), back or joint discomfort (7.7%), and shortness of breath (8.5%).

CONCLUSION

After undergoing gastric sleeve surgery, a sizable proportion of patients complained of various chronic symptoms and nutritional inadequacies, primarily gastrointestinal problems and musculoskeletal/neurological issues. The study's findings show a connection between these symptoms and surgery.

Respiratory complications of obesity: from early changes to respiratory failure

Obesity is a significant and increasingly common cause of respiratory compromise. It causes a decrease in static and dynamic pulmonary volumes. The expiratory reserve volume is one of the first to be affected. Obesity is associated with reduced airflow, increased airway hyperresponsiveness, and an increased risk of developing pulmonary hypertension, pulmonary embolism, respiratory tract infections, obstructive sleep apnoea and obesity hypoventilation syndrome. The physiological changes caused by obesity will eventually lead to hypoxic or hypercapnic respiratory failure. The pathophysiology of these changes includes a physical load of adipose tissue on the respiratory system and a systemic inflammatory state. Weight loss has clear, well-defined benefits in improving respiratory and airway physiology in obese individuals.

Obesity Indices and Ventilatory Function Responses to High-Level Laser Therapy in Subjects with Abdominal Obesity

Objective: The aim of this study is to investigate the effectiveness of pulsed Nd:YAG high-intensity laser therapy (HILT) on body weight (Wt), body-mass index (BMI), waist circumference (WC), forced vital capacity (FVC), and forced expiratory volume in 1 sec (FEV1) in young adults with abdominal obesity (AO). Materials and methods: Thirty-seven young adult males (age 19-25 years) with BMI >30 kg/m² and WC >102 cm participated in this 12-week, randomized controlled study and were randomly allocated into either Group I [received pulsed Nd:YAG HILT plus moderate-intensity aerobic exercise training (AET) program] or Group II (received placebo pulsed Nd:YAG HILT plus the same AET program). The variables were evaluated pre- and poststudy. Results: Poststudy mean values and percentages of changes were calculated for Wt [83.7 ± 6.58 kg (-6.14%) and 88.71 ± 5.09 kg (-4.29%)], BMI [29.27 ± 1.06 kg/m² (-6.14%) and 30.09 ± 1.23 kg/m² (-4.24%)], WC [105.44 ± 5.84 cm (-3.78%) and 109.42 ± 4.9 cm (-1.74%)], FVC [4.79 ± 0.4 L (+13.6%) and 4.39 ± 0.66 L (+5.89%)], and FEV1 [4.04 ± 0.22 L (+16.4%) and 3.82 ± 0.39 L (+8.8%)] for Group I and Group II, respectively. Between groups, there were significant differences in mean values of Wt (p = 0.014), BMI (p = 0.04), WC (p = 0.03), FVC (p = 0.03), and FEV1 (p = 0.04) at the end of the study, but in favor of Group I. Conclusions: Utilizing the pulsed Nd:YAG HILT as an adjunctive therapeutic modality proved to be effective in improving the anthropometric indices and ventilatory functions in subjects with AO.

From Beneath the Skin to the Airway Wall: Understanding the Pathological Role of Adipose Tissue in Comorbid Asthma-Obesity

This article provides a contemporary report on the role of adipose tissue in respiratory dysfunction. Adipose tissue is distributed throughout the body, accumulating beneath the skin (subcutaneous), around organs (visceral), and importantly in the context of respiratory disease, has recently been shown to accumulate within the airway wall: "airway-associated adipose tissue." Excessive adipose tissue deposition compromises respiratory function and increases the severity of diseases such as asthma. The mechanisms of respiratory impairment are inflammatory, structural, and mechanical in nature, vary depending on the anatomical site of deposition and adipose tissue subtype, and likely contribute to different phenotypes of comorbid asthma-obesity. An understanding of adipose tissue-driven pathophysiology provides an opportunity for diagnostic advancement and patient-specific treatment. As an exemplar, the potential impact of airway-associated adipose tissue is highlighted, and how this may change the management of a patient with asthma who is also obese. © 2023 American Physiological Society. Compr Physiol 13:4321-4353, 2023.

A Human Model of the Effects of an Instant Sheer Weight Loss on Cardiopulmonary Parameters during a Treadmill Run

Exercise tolerance is limited in obesity and improves after weight reduction; therefore, we mutually compared the relative changes in exercise capacity variables during cardiopulmonary exercise tests (CPET) in a 12 kg sheer weight reduction model. Twenty healthy male runners underwent two CPETs: CPET1 with the actual body weight, which determined the anaerobic threshold (AT) and respiratory compensation point (RCP); and CPET2 during which the participants wore a +12 kg vest and ran at the AT speed set during the CPET1. Running after body weight reduction shifted the CPET parameters from the high-mixed aerobic-anaerobic (RCP) to the aerobic zone (AT), but these relative changes were not mutually similar. The most beneficial changes were found for breathing mechanics parameters (range 12-28%), followed by cardiovascular function (6-7%), gas exchange (5-6%), and the smallest for the respiratory exchange ratio (5%) representing the energy metabolism during exercise. There was no correlation between the extent of the relative body weight change (median value ~15%) and the changes in CPET parameters. Weight reduction improves exercise capacity and tolerance. However, the observed relative changes are not related to the magnitude of the body change nor comparable between various parameters characterizing the pulmonary and cardiovascular systems and energy metabolism.

Sleep-disordered breathing, sleep apnea, and other obesity-related sleep disorders: An Obesity Medicine Association (OMA) Clinical Practice Statement (CPS) 2022

Background

This Obesity Medicine Association (OMA) Clinical Practice Statement (CPS) provides clinicians an overview of sleep-disordered breathing, (e.g., sleep-related hypopnea, apnea), and other obesity-related sleep disorders.

Methods

The scientific support for this CPS is based upon published citations, clinical perspectives of OMA authors, and peer review by the Obesity Medicine Association leadership.

Results

Obesity contributes to sleep-disordered breathing, with the most prevalent manifestation being obstructive sleep apnea. Obesity is also associated with other sleep disorders such as insomnia, primary snoring, and restless legs syndrome. This CPS outlines the evaluation, diagnosis, and treatment of sleep apnea and other sleep disorders, as well as the clinical implications of altered circadian system.

Conclusions

This Obesity Medicine Association (OMA) Clinical Practice Statement (CPS) on "Sleep-Disordered Breathing, Sleep Apnea, and Other Obesity-Related Sleep Disorders" is one of a series of OMA CPSs designed to assist clinicians in the care of patients with the disease of obesity.

Sex differences in the ventilatory responses to exercise in mild-moderate obesity

NEW FINDINGS

What is the central question of the study? What are the sex differences in ventilatory responses during exercise in adults with obesity. What is the main finding and its importance? Tidal volume and expiratory flows are lower in females when compared with males at higher levels of ventilation despite small increases in end-expiratory lung volumes. Since dyspnea on exertion is a frequent complaint, particularly in females with obesity, careful attention should be paid to unpleasant respiratory symptoms and mechanical ventilatory constraints before prescribing exercise.

ABSTRACT

Obesity is associated with altered ventilatory responses, which may be exacerbated in females due to the functional consequences of sex-related morphological differences in the respiratory system. This study examined sex differences in ventilatory responses during exercise in adults with obesity. Healthy adults with obesity (n = 73; 48 females) underwent pulmonary function testing, underwater weighing, magnetic resonance imaging, a graded exercise test to exhaustion, and two constant work rate exercise tests; one at a fixed work rate (60W for females and 105W for males) and one at a relative intensity (50% of peak oxygen uptake, V̇O_2peak ). Metabolic, respiratory, and perceptual responses were assessed during exercise. Compared with males, females used a smaller proportion of their ventilatory capacity at peak exercise (69.13 ± 14.49 vs. 77.41 ± 17.06 % maximum voluntary ventilation, P = 0.0374). Females also utilized a smaller proportion of their forced vital capacity (FVC) at peak exercise (tidal volume: 48.51±9.29 vs. 54.12±10.43 %FVC, P = 0.0218). End-expiratory lung volumes were 2-4% higher in females compared with males during exercise (P<0.05), while end-inspiratory lung volumes were similar. Since the males were initiating inspiration from a lower lung volume, they experienced greater expiratory flow limitation during exercise. Ratings of perceived breathlessness during exercise were similar between females and males at comparable levels of ventilation. In summary, sex differences in the manifestations of obestity-related mechanical ventilatory constraints were observed. Since dyspnea on exertion is a common complaint in patients with obesity, particularly in females, exercise prescriptions should be tailored with the goal of minimizing unpleasant respiratory sensations. This article is protected by copyright. All rights reserved.

Repeatability of dyspnea measurements during exercise in women with obesity

While the 0-10 Borg scale to rate perceived breathlessness (RPB) is widely used to assess dyspnea on exertion, the repeatability of RPB in women with obesity is unknown. We examined the repeatability of RPB in women with obesity during submaximal constant-load cycling following at least 10 weeks of normal daily life. Seventeen women (37 ± 7 yr; 34.6 ± 4.5 kg/m2) who rated their breathlessness as 3 on the Borg scale (i.e., "moderate") during 60 W submaximal cycling repeated the same test following 19 ± 9 weeks of normal living. Mean body weight (93.8 ± 16.1 vs. 93.6 ± 116.8 kg, p = 0.94) and RPB (3.0 ± 0.0 vs. 3.1 ± 1.4, p = 0.80) did not differ between pre- and post-normal living periods. We demonstrate that subjective ratings of breathlessness are repeatable for the majority of subjects and can be used to accurately assess DOE during submaximal constant-load cycling in women with obesity.

Severity stages of obesity-related breathing disorders - a cross-sectional cohort study

INTRODUCTION

There is a general underappreciation of the spectrum of obesity-related breathing disorders and their consequences. We therefore compared characteristics of obese patients with eucapnic obstructive sleep apnea (OSA), OSA with obesity-related sleep hypoventilation (ORSH) or obesity hypoventilation syndrome (OHS) to identify the major determinants of hypoventilation.

PATIENTS AND METHODS

In this prospective, diagnostic study (NCT04570540), obese patients with OSA, ORSH or OHS were characterized applying polysomnography with transcutaneous capnometry, blood gas analyses, bodyplethysmography and measurement of hypercapnic ventilatory response (HCVR). Pathophysiological variables known to contribute to hypoventilation and differing significantly between the groups were specified as potential independent variables in a multivariable logistic regression to identify major determinants of hypoventilation.

RESULTS

Twenty, 43 and 19 patients were in the OSA, ORSH and OHS group, respectively. BMI was significantly lower in OSA as compared to OHS. The extent of SRBD was significantly higher in OHS as compared to OSA or ORSH. Patients with ORSH or OHS showed a significantly decreased forced expiratory volume in 1 s and forced vital capacity compared to OSA. HCVR was significantly lower in OHS and identified as the major determinant of hypoventilation in a multivariable logistic regression (Nagelkerke R² = 0.346, p = 0.050, odds ratio (95%-confidence interval) 0.129 (0.017-1.004)).

CONCLUSION

Although there were differences in BMI, respiratory mechanics and severity of upper airway obstruction between groups, our data support HCVR as the major determinant of obesity-associated hypoventilation.

Energy cost of walking and body composition changes during a 9-month multidisciplinary weight reduction program and 4-month follow-up in adolescents with obesity

The purpose of the present study was to investigate changes in the energy cost of locomotion during walking (Cw) related to changes in body mass (BM, kg) and body composition in adolescents with obesity. Twenty-six (12 boys and 14 girls) obese adolescents (mean: body mass index, 33.6 ± 3.7 kg·m-2; 42.7 ± 4.5% fat mass (FM)) followed a 9-month multidisciplinary inpatient weight-reduction program consisting of lifestyle education, moderate energy restriction, and regular physical activity in a specialised institution. At baseline (M0), the end of the 9-month program (M9), and after the 4-month follow-up (M13), oxygen consumption and carbon dioxide production of the standardised activity program were assessed by whole-body indirect calorimetry over 24 hours, and body composition was assessed by dual-energy X-ray absorptiometry. At M9, adolescents showed an 18% reduction in BM (p < 0.001) and 40% in total FM, while fat-free mass (kg) remained stable in boys but decreased by ∼6% in girls (p = 0.001). Similarly, the mean Cw decreased by 20% (p < 0.001). At M13, BM, FM, and Cw were slightly higher compared with at M9. In conclusion, moderate energy restriction and regular moderate physical activities improved walking economy, improved exercise tolerance, and induced beneficial changes in the body composition of adolescents with obesity. Novelty: Reduction of FM in the trunk region, and consequently reducing the work carried out by respiratory muscles, contributes to reducing Cw in adolescents with obesity. A lower walking cost can be effective in improving exercise tolerance and quality of life in obese adolescents.

Recruitment and Retention of Healthy Women with Obesity for a Psychophysiological Study before and After Weight Loss: Insights, Challenges, and Suggestions

OBJECTIVE

The objective of this paper is to present data on participant recruitment, retention, and weight loss success during a psychophysiological study in women with obesity.

METHODS

Volunteers were women with obesity, 20 - 45 yr, with a BMI between 30 - 45 kg/m². The study was approximately 20 weeks in duration, including a 12-week weight loss program.

RESULTS

Recruitment was not completed until 8 months past the original projected date of 12 months. The study was not completed until 11 months past the original projected completion date of 14 months. On average 4.4 ± 2.1 (mean ± SD) volunteers were consented per month (N = 99) and 2.5 ± 1.1 participants started the weight loss program per month. 24% of consented volunteers were lost due to exclusion criteria, withdrawals, and unresponsive behavior before starting the weight loss program. Attrition of participants who started the weight loss program was 45%. Only 11% of those who started the program were unable to lose weight (N = 6).

CONCLUSION

Recruiting and/or weight loss success do not always present the most challenging aspects of completing a psychophysiological weight loss intervention. While participant attrition during a weight loss program can occur for a wide range of reasons supportive efforts in the early phases of the intervention may maximize retention.

Effects of obesity on the oxygen cost of breathing in children

The objective of this study was to examine the effects of obesity on the oxygen (O₂) cost of breathing using the eucapnic voluntary hyperpnea (EVH) technique in 10- and 11-year-old children. Seventeen children (8 without and 9 with obesity) underwent EVH trials at two levels of ventilation for assessing the O₂ cost of breathing (slope of oxygen uptake, V˙O₂ vs. minute ventilation) and a dual energy x-ray absorptiometry scan. Resting and EVH V˙O₂ was higher in children with obesity when compared with children without obesity (P = 0.0096). The O₂ cost of breathing did not statistically differ between children without (2.09 ± 0.46 mL/L) and with obesity (2.08 ± 0.64 mL/L, P = 0.99), but the intercept was significantly greater in children with obesity. Chest mass explained 85 % of the variance in resting V˙O₂ in children with obesity. Higher resting energy requirements, attributable to increased chest mass, can increase the absolute metabolic costs of exercise and hyperpnea in children with obesity.

[The impact of obesity on respiratory function]

The respiratory impact of obesity can be both symptomatic (resting and exertional breathlessness) and functional (pulmonary function at rest and on exercise). The prevalence of breathlessness is increased in adult obese individuals, ∼50% at rest and ∼75% on exertion (mMRC score>0). Pulmonary function abnormalities in obese adults include reduced functional residual capacity (FRC) and expiratory residual volume (ERV), and less frequently reduced total lung capacity (a restrictive defect, with TLC below the 5th percentile of predicted is present in around 15% in severe obese adults), with normal residual volume (RV). Airflows are barely affected by obesity, but bronchial hyperresponsiveness (BHR) is very prevalent, which may be due to the loss of bronchoprotective effect of deep inspiration in obesity (mechanical pathophysiology of BHR). In children, the modifications of lung volumes seen are quite different: TLC is normal while FRC and RV are reduced, explaining the increase in FVC. FEV1/FVC is therefore reduced by obesity, without true airflow obstruction (dysanaptic growth). Resting oxygen consumption (V'O₂) is increased due to obesity and normally increases with exercise. Maximum V'O₂ is normal or weakly reduced in obese patients; on the other hand, the increase in respiratory load increases the oxygen cost of ventilation, which tends to be rapid, both at rest and during exertion. Finally, it should be noted that there is only limited statistical correlation between exercise dyspnoea and respiratory function abnormalities in obesity.

Exercise Capacity in Unilateral Diaphragm Paralysis: The Effect of Obesity

Purpose

Healthy patients with unilateral diaphragm paralysis (UDP) are often asymptomatic; those with UDP and comorbidities that increase work of breathing are often dyspneic. We report the effect of obesity on exercise capacity in UDP patients.

Methods

All obese and nonobese patients with UDP undergoing cardiopulmonary exercise testing (CPET) during a 32-month period in the exercise laboratory of an academic hospital were compared to a retrospectively identified cohort of obese and nonobese controls without UDP, matched for key features. CPET used a modified Bruce treadmill protocol with breath-to-breath expired gas analysis. O2 uptake, minute ventilation, exercise time, and work rate were recorded at peak exercise. Static pulmonary functions were measured. Kruskal-Wallis, Wilcoxon rank sum, and Fisher's exact tests were used to compare continuous and categorical variables, respectively. Stratified linear regression was used to quantify the effect of UDP and obesity on CPET variables.

Results

Twenty-two UDP patients and 46 controls were studied. The BMI of obese and nonobese patients was 33.0±4.2 and 25.8±2.4 kg/m2, respectively. UDP subjects with obesity, compared to controls with neither condition, showed significantly reduced peak O2 uptake normalized to actual body weight (1.57±0.64 versus 2.01±0.88 L/min), shorter exercise time (5.7±2.0 versus 8.5±2.9 minutes), and lower peak ventilation. This was not observed in UDP alone or obesity alone. Peak work rate trended lower in the combined UDP-obesity group.

Conclusion

Neither UDP nor obesity alone significantly reduced exercise capacity. Superimposed UDP and obesity interact to create a ventilatory limitation to exercise, with reduced peak-VO2, exercise time, and work rate.

Weight loss reduces dyspnea on exertion and unpleasantness of dyspnea in obese men

We hypothesized that weight loss would ameliorate dyspnea on exertion (DOE) and feelings of unpleasantness related to the DOE in obese men. Eighteen men (34 ± 7yr, 35 ± 4 kg/m2 BMI, mean ± SD) participated in a 12-week weight loss program. Body composition, pulmonary function, cardiorespiratory measures, DOE, and unpleasantness (visual analog scale) were assessed before and after weight loss. Subjects were grouped by Ratings of Perceived Breathlessness (RPB, Borg 0-10 scale) during submaximal cycling: Ten men rated RPB ≥ 4 (+DOE), eight rated RPB ≤ 2 (-DOE). Subjects lost 10.3 ± 5.6 kg (9.2 ± 4.5%) of body weight (n = 18). RPB during submaximal cycling was significantly improved in both groups (+DOE: 4.1 ± 0.3-2.8 ± 1.1; -DOE: 1.3 ± 0.7 to 0.8 ± 0.6, p < 0.001). Several submaximal exercise variables (e.g., V˙O2, V˙E) were decreased similarly in both groups (p < 0.01). Unpleasantness associated with the DOE was reduced (p < 0.05). The improved RPB was not significantly correlated with changes in body weight or cardiopulmonary exercise responses (p > 0.05). Moderate weight loss appears to be an effective option to ameliorate DOE and unpleasantness related to DOE in obese men.

Effects of weight loss on dynamic hyperinflation in obese women asthmatics

Obese adults with asthma are more likely to develop dynamic hyperinflation (DH) and expiratory flow limitation (EFL) than nonobese asthmatics, and weight-loss seems to improve the breathing mechanics during exercise. However, studies evaluating the effect of weight loss on DH in obese adults with asthma have not been performed. We sought to evaluate the effect of a weight loss program on DH in obese adults with asthma. Forty-two asthma patients were enrolled in a weight loss program (diet, psychological support, and exercise) and were subsequently divided into two groups according to the percentage of weight loss: a ≥5% group ( n = 19) and a <5% group ( n = 23). Before and after the intervention, DH and EFL (constant load exercise), health-related quality of life (HRQoL), asthma control, quadriceps muscle strength and endurance, body composition, and lung function were assessed. Both groups exhibited a decrease of ≥10% in inspiratory capacity (DH) before intervention, and only the ≥5% group showed clinical improvement in DH compared with the <5% group postintervention (-9.1 ± 14.5% vs. -12.5 ± 13.5%, respectively). In addition, the ≥5% group displayed a significant delay in the onset of both DH and EFL and a clinically significant improvement in HRQoL and asthma control. Furthermore, a correlation was observed between reduced waist circumference and increased inspiratory capacity ( r = -0.45, P = 0.05) in the ≥5% group. In conclusion, a weight-loss of ≥5% of the body weight improves DH, which is associated with waist circumference in obese adults with asthma. In addition, the group with greater weight-loss showed a delayed onset of DH and EFL during exercise and improved asthma clinical control and HRQoL. NEW & NOTEWORTHY This is the first study to evaluate dynamic hyperinflation (DH) after a weight loss program in obese patients with asthma. Our results demonstrate that moderate weight loss can improve DH in obese patients with asthma that is associated with a decrease in abdominal fat. Moreover, a minimum of 5% in weight loss delays the onset of DH and expiratory flow limitation besides inducing a clinical improvement in asthma quality of life and clinical control.

Verification of Maximal Oxygen Uptake in Obese and Nonobese Children

PURPOSE

The purpose of this study was to examine whether a supramaximal constant-load verification test at 105% of the highest work rate would yield a higher V˙O2max when compared with an incremental test in 10- to 12-yr-old nonobese and obese children.

METHODS

Nine nonobese (body mass index percentile = 57.5 ± 23.2) and nine obese (body mass index percentile = 97.9 ± 1.4) children completed a two-test protocol that included an incremental test followed 15 min later by a supramaximal constant-load verification test.

RESULTS

The V˙O2max achieved in verification testing (nonobese = 1.71 ± 0.31 L·min and obese = 1.94 ± 0.47 L·min) was significantly higher than that achieved during the incremental test (nonobese = 1.57 ± 0.27 L·min and obese = 1.84 ± 0.48 L·min; P < 0.001). There was no significant group (i.e., nonobese vs obese)-test (i.e., incremental vs verification) interaction, suggesting that there was no effect of obesity on the difference between verification and incremental V˙O2max (P = 0.747).

CONCLUSION

A verification test yielded significantly higher values of V˙O2max when compared with the incremental test in obese children. Similar results were observed in nonobese children. Supramaximal constant-load verification is a time-efficient and well-tolerated method for identifying the highest V˙O2 in nonobese and obese children.

Respiratory muscle endurance training reduces the O2 cost of cycling and perceived exertion in obese adolescents

In obesity, the increased O2 cost of breathing negatively affects the O2 cost of exercise and exercise tolerance. The purpose of the study was to determine whether, in obese adolescents, the addition of respiratory muscle endurance training (RMET) (isocapnic hyperpnea) to a standard body mass reduction program decreases the O2 cost of exercise and perceived exertion. Nine male obese adolescents [16.0 ± 1.4 yr ( x ± SD), body mass 114.4 ± 22.3 kg] underwent 3 wk of RMET (5 days/week) in addition to a standard body mass reduction program. Eight age- and sex-matched obese adolescents underwent only the standard program (CTRL). Before and after interventions, patients performed on a cycle ergometer: incremental exercise; 12-min exercises at a constant work rate (CWR) of 65% and 120% at the gas exchange threshold (GET) determined before the intervention. Breath-by-breath pulmonary ventilation (V̇e) and O2 uptake (V̇o2), heart rate (HR), and ratings of perceived exertion for dyspnea/respiratory discomfort (RPER) and leg effort (RPEL) were determined. Body mass decreased (by ~3.0 kg) after both RMET ( P = 0.003) and CTRL ( P = 0.002). Peak V̇o2 was not affected by both interventions. Peak work rate was slightly, but significantly ( P = 0.04), greater after RMET but not after CTRL. During CWR < GET, no changes were observed after both interventions. During CWR > GET, the O2 cost of cycling at the end of exercise ( P = 0.02), the slope of V̇o2 vs. time (3–12 min) ( P = 0.01), RPER ( P = 0.01), and RPEL ( P = 0.01) decreased following RMET, but not following CTRL. HR decreased after both RMET ( P = 0.02) and CTRL ( P = 0.03), whereas V̇e did not change. In obese adolescents RMET, superimposed on a standard body mass reduction program, lowered the O2 cost of cycling and perceived exertion during constant heavy-intensity exercise.

Exertional dyspnoea in obesity

The purpose of cardiopulmonary exercise testing (CPET) in the obese person, as in any cardiopulmonary exercise test, is to determine the patient's exercise tolerance, and to help identify and/or distinguish between the various physiological factors that could contribute to exercise intolerance. Unexplained dyspnoea on exertion is a common reason for CPET, but it is an extremely complex symptom to explain. Sometimes obesity is the simple answer by elimination of other possibilities. Thus, distinguishing among multiple clinical causes for exertional dyspnoea depends on the ability to eliminate possibilities while recognising response patterns that are unique to the obese patient. This includes the otherwise healthy obese patient, as well as the obese patient with potentially multiple cardiopulmonary limitations. Despite obvious limitations in lung function, metabolic disease and/or cardiovascular dysfunction, obesity may be the most likely reason for exertional dyspnoea. In this article, we will review the more common cardiopulmonary responses to exercise in the otherwise healthy obese adult with special emphasis on dyspnoea on exertion.

Short-term modulation of the ventilatory response to exercise is preserved in obstructive sleep apnea

BACKGROUND

The ventilatory response to exercise can be transiently adjusted in response to environmentally (e.g., breathing apparatus) or physiologically altered conditions (e.g., respiratory disease), maintaining constant relative arterial P_CO2 regulation from rest to exercise (Mitchell and Babb, 2006); this augmentation is called short-term modulation (STM) of the exercise ventilatory response. Obesity and/or obstructive sleep apnea could affect the exercise ventilatory response and the capacity for STM due to chronically increased mechanical and/or ventilatory loads on the respiratory system, and/or recurrent (chronic) intermittent hypoxia experienced during sleep. We hypothesized that: (1) the exercise ventilatory response is augmented in obese OSA patients compared with obese non-OSA adults, and (2) the capacity for STM with added dead space is diminished in obese OSA patients.

METHODS

Nine obese adults with OSA (age: 39±6 yr, BMI: 40±5kg/m², AHI: 25±24 events/h [range 6-73], mean±SD) and 8 obese adults without OSA (age: 38±10 yr, BMI: 37±6kg/m², AHI: 1±2) completed three, 20-min bouts of constant-load submaximal cycling exercise (8min rest, 6min at 10 and 30W) with or without added external dead space (200 or 400mL; 20min rest between bouts). Steady-state measurements were made of ventilation (V˙_E)_, oxygen consumption V˙_O2), carbon dioxide production (V˙_CO2), and end-tidal P_CO2 (PET_CO2). The exercise ventilatory response was defined as the slope of the V˙E-V˙_CO2 relationship (ΔV˙E/ΔV˙_CO2).

RESULTS

In control (i.e. no added dead space), the exercise ventilatory response was not significantly different between non-OSA and OSA groups (ΔV˙E/ΔV˙_CO2 slope: 30.5±4.2 vs 30.5±3.8, p>0.05); PET_CO2 regulation from rest to exercise did not differ between groups (p>0.05). In trials with added external dead space, ΔV˙E/ΔV˙_CO2 increased with increased dead space (p < 0.05) and the PET_CO2 change from rest to exercise remained small (<2mmHg) in both groups, demonstrating STM. There were no significant differences between groups.

CONCLUSIONS

Contrary to our hypotheses: (1) the exercise ventilatory response is not increased in obese OSA patients compared with obese non-OSA adults, and (2) the capacity for STM with added dead space is preserved in obese OSA and non-OSA adults.