Ventilation and Its Control during Incremental Exercise in Obesity

Playing around the anaerobic threshold during COVID-19 pandemic: advantages and disadvantages of adding bouts of anaerobic work to aerobic activity in physical treatment of individuals with obesity

INTRODUCTION

Obesity is a condition that generally limits work capacity and predisposes to a number of comorbidities and related diseases, the last being COVID-19 and its complications and sequelae. Physical exercise, together with diet, is a milestone in its management and rehabilitation, although there is still a debate on intensity and duration of training. Anaerobic threshold (AT) is a broad term often used either as ventilatory threshold or as lactate threshold, respectively, detected by respiratory ventilation and/or respiratory gases (VCO₂ and VO₂), and by blood lactic acid.

AIMS AND METHODOLOGY

This review outlines the role of AT and of the different variations of growth hormone and catecholamine, in subjects with obesity vs normal weight individuals below and beyond AT, during a progressive increase in exercise training. We present a re-evaluation of the effects of physical activity on body mass and metabolism of individuals with obesity in light of potential benefits and pitfalls during COVID-19 pandemic. Comparison of a training program at moderate-intensity exercise (< AT) with training performed at moderate intensity (< AT) plus a final bout of high-intensity (> AT) exercise at the end of the aerobic session will be discussed.

RESULTS

Based on our data and considerations, a tailored strategy for individuals with obesity concerning the most appropriate intensity of training in the context of rehabilitation is proposed, with special regard to potential benefits of work program above AT.

CONCLUSION

Adding bouts of exercise above AT may improve lactic acid and H⁺ disposal and improve growth hormone. Long-term aerobic exercise may improve leptin reduction. In this way, the propensity of subjects with obesity to encounter a serious prognosis of COVID-19 may be counteracted and the systemic and cardiorespiratory sequelae that may ensue after COVID-19, can be overcome. Individuals with serious comorbidities associated with obesity should avoid excessive exercise intensity.

Obesity Blunts the Ventilatory Response to Exercise in Men and Women

Rationale: Obesity presents a mechanical load to the thorax, which could perturb the generation of minute ventilation (V̇e) during exercise. Because the respiratory effects of obesity are not homogenous among all individuals with obesity and obesity-related effects could vary depending on the magnitude of obesity, we hypothesized that the exercise ventilatory response (slope of the V̇e and carbon dioxide elimination [V̇co₂] relationship) would manifest itself differently as the magnitude of obesity increases.Objectives: To investigate the V̇e/V̇co₂ slope in an obese population that spanned across a wide body mass index (BMI) range.Methods: A total of 533 patients who presented to a surgical weight loss center for pre-bariatric surgery testing performed an incremental maximal cycling test and were studied retrospectively. The V̇e/V̇co₂ slope was calculated up to the ventilatory threshold. Patients were examined in groups based on BMI (category 1: 30-39.9 kg/m², category 2: 40-49.9 kg/m², and category 3: ≥50 kg/m²). Because the respiratory effects of obesity could be sex and/or age specific, we further examined patients in groups by sex and age (younger: <50 yr and older: ≥50 yr). Differences in the V̇e/V̇co₂ slope were then compared between BMI category, age, and sex using a three-way ANOVA.Results: No significant BMI category by sex by age interactions was detected (P = 0.75). The V̇e/V̇co₂ slope decreased with increases in BMI (category 1, 29.1 ± 4.0; category 2, 28.4 ± 4.1; and category 3, 27.1 ± 3.3) and was elevated in women (28.9 ± 4.1) compared with men (26.7 ± 3.2) (BMI category by sex interaction, P < 0.05). No age-related differences were observed (BMI category by age interaction, P = 0.55). The partial pressure for end-tidal CO₂ was elevated at the ventilatory threshold in BMI category 3 compared with BMI categories 1 and 2 (both P < 0.01).Conclusions: These findings suggest that obesity presents a unique challenge to augmenting ventilatory output relative to CO₂ elimination, such that the increase in the exercise ventilatory response becomes blunted as the magnitude of obesity increases. Further studies are required to investigate the clinical consequences and the mechanisms that may explain the attenuation of exercise ventilatory response with increasing BMI in men and women with obesity.

Ventilatory efficiency in athletes, asthma and obesity

During submaximal exercise, minute ventilation (V' _E) increases in proportion to metabolic rate (i.e. carbon dioxide production (V' _CO2 )) to maintain arterial blood gas homeostasis. The ratio V' _E/V' _CO2 , commonly termed ventilatory efficiency, is a useful tool to evaluate exercise responses in healthy individuals and patients with chronic disease. Emerging research has shown abnormal ventilatory responses to exercise (either elevated or blunted V' _E/V' _CO2 ) in some chronic respiratory and cardiovascular conditions. This review will briefly provide an overview of the physiology of ventilatory efficiency, before describing the ventilatory responses to exercise in healthy trained endurance athletes, patients with asthma, and patients with obesity. During submaximal exercise, the V' _E/V' _CO2 response is generally normal in endurance-trained individuals, patients with asthma and patients with obesity. However, in endurance-trained individuals, asthmatics who demonstrate exercise induced-bronchoconstriction, and morbidly obese individuals, the V' _E/V' _CO2 can be blunted at maximal exercise, likely because of mechanical ventilatory constraint.

Association of weight fluctuation with cardiovascular disease risk among initially obese adults

The association of fluctuations in body mass index with cardiovascular risk in long-term is not well understood. This study aimed to investigate cardiovascular outcomes of weight fluctuation. Total of 67,101 obese adults from the Korean National Health Insurance Service who received health examinations in three separate biennial periods were included. Participants were followed up from January 1, 2008 to the date of cardiovascular disease, death, or December 31, 2015, and categorized into 9 distinctive groups according to the BMI. Continuous weight gain showed an increased risk of overall cardiovascular disease (hazard ratio [HR], 2.36; P = 0.007), whereas weight loss after weight maintenance (HR, 0.91; P = 0.016) and weight maintenance after weight loss (HR, 0.91; P = 0.004) were ameliorative compared to the no weight change group. As for coronary heart disease, weight maintenance after weight gain was unfavorable (HR, 1.25; P = 0.004) while weight loss after weight maintenance (HR, 0.82; P < 0.001), weight cycling (HR, 0.83; P = 0.043), and weight maintenance after weight loss (HR, 0.88; P = 0.012) were beneficial. Weight maintenance after weight loss is beneficial for obese adults in terms of cardiovascular risks. In addition, weight loss is in part related to reduced risk of coronary heart disease despite weight cycling.

Determinants of Cardiorespiratory Fitness After Bariatric Surgery: Insights From a Randomised Controlled Trial of a Supervised Training Program

BACKGROUND

Severely obese patients have decreased cardiorespiratory fitness (CRF) and poor functional capacity. Bariatric surgery-induced weight loss improves CRF, but the determinants of this improvement are not well known. We aimed to assess the determinants of CRF before and after bariatric surgery and the impact of an exercise training program on CRF after bariatric surgery.

METHODS

Fifty-eight severely obese patients (46.1 ± 6.1 kg/m², 78% women) were randomly assigned to either an exercise group (n = 39) or usual care (n = 19). Exercise training was conducted from the 3rd to the 6th months after surgery. Anthropometric measurements, abdominal and mid-thigh computed tomographic scans, resting echocardiography, and maximal cardiopulmonary exercise testing was performed before bariatric surgery and 3 and 6 months after surgery.

RESULTS

Weight, fat mass, and fat-free mass were reduced significantly at 3 and 6 months, without any additive impact of exercise training in the exercise group. From 3 to 6 months, peak aerobic power (V̇O_2peak) increased significantly (P < 0.0001) in both groups but more importantly in the exercise group (exercise group: from 18.6 ± 4.2 to 23.2 ± 5.7 mL/kg/min; control group: from 17.4 ± 2.3 to 19.7 ± 2.4 mL/kg/min; P value, group × time = 0.01). In the exercise group, determinants of absolute V̇O_2peak (L/min) were peak exercise ventilation, oxygen pulse, and heart rate reserve (r² = 0.92; P < 0.0001), whereas determinants of V̇O_2peak indexed to body mass (mL/kg/min) were peak exercise ventilation and early-to-late filling velocity ratio (r² = 0.70; P < 0.0001).

CONCLUSIONS

A 12-week supervised training program has an additive benefit on cardiorespiratory fitness for patients who undergo bariatric surgery.

External dead space explains sex-differences in the ventilatory response to submaximal exercise in children with and without obesity

We compared the exercise ventilatory response (slope of the ventilation, V̇_E and carbon dioxide production, V̇CO₂ relationship) in boys and girls with and without obesity. 46 children with obesity (BMI percentile: 97.7 ± 1.4) and 27 children without obesity (BMI percentile: 55.1 ± 22.2) were included and divided into groups by sex (with obesity: 17 girls and 29 boys; without obesity: 13 girls and 14 boys). A 6 min constant load cycling test at 45 % of peak work rate was performed. The V̇_E/V̇CO₂ slope was similar (p = 0.67) between children with (32.7 ± 4.3) and without (32.2 ± 6.1) obesity; however, it was higher (p = 0.02) in girls (35.4 ± 5.6) than boys (32.6 ± 4.9). We also examined a corrected V̇_E/V̇CO₂ slope for the effects of mechanical dead space (V_DM), by subtracting V̇_DM from V̇_E (V̇_Ecorr/V̇CO₂ slope). The V̇_Ecorr/V̇CO₂ slope remained similar (p = 0.37) between children with (26.8 ± 3.2) and without obesity (26.1 ± 3.1); however, no sex differences were observed (p = 0.13). Therefore, V_DM should be accounted for before evaluating the V̇_E/V̇CO₂ slope, particularly when making between-sex comparisons.

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.

Obesity and Cardiovascular Disease

The prevalence of obesity has increased worldwide over the past few decades. In 2013, the prevalence of obesity exceeded the 50% of the adult population in some countries from Oceania, North Africa, and Middle East. Lower but still alarmingly high prevalence was observed in North America (≈30%) and in Western Europe (≈20%). These figures are of serious concern because of the strong link between obesity and disease. In the present review, we summarize the current evidence on the relationship of obesity with cardiovascular disease (CVD), discussing how both the degree and the duration of obesity affect CVD. Although in the general population, obesity and, especially, severe obesity are consistently and strongly related with higher risk of CVD incidence and mortality, the one-size-fits-all approach should not be used with obesity. There are relevant factors largely affecting the CVD prognosis of obese individuals. In this context, we thoroughly discuss important concepts such as the fat-but-fit paradigm, the metabolically healthy but obese (MHO) phenotype and the obesity paradox in patients with CVD. About the MHO phenotype and its CVD prognosis, available data have provided mixed findings, what could be partially because of the adjustment or not for key confounders such as cardiorespiratory fitness, and to the lack of consensus on the MHO definition. In the present review, we propose a scientifically based harmonized definition of MHO, which will hopefully contribute to more comparable data in the future and a better understanding on the MHO subgroup and its CVD prognosis.

Body Mass Index, the Most Widely Used But Also Widely Criticized Index: Would a Criterion Standard Measure of Total Body Fat Be a Better Predictor of Cardiovascular Disease Mortality?

OBJECTIVES

To examine whether an accurate measure (using a criterion standard method) of total body fat would be a better predictor of cardiovascular disease (CVD) mortality than body mass index (BMI).

PARTICIPANTS AND METHODS

A total of 60,335 participants were examined between January 1, 1979, and December 31, 2003, and then followed-up for a mean follow-up period of 15.2 years. Body mass index was estimated using standard procedures. Body composition indices (ie, body fat percentage [BF%], fat mass index [FMI], fat-free mass [FFM], and FFM index [FFMI]) were derived from either skinfold thicknesses or hydrostatic weighing. For exact comparisons, the indices studied were categorized identically using sex-specific percentiles.

RESULTS

Compared with a medium BMI, a very high BMI was associated with a hazard ratio (HR) of 2.7 (95% CI, 2.1-3.3) for CVD mortality, which was a stronger association than for BF% or FMI (ie, HR, 1.6; 95% CI, 1.3-1.9 and HR, 2.2; 95% CI, 1.8-2.7, respectively). Compared with a medium FFMI, a very high FFMI was associated with an HR of 2.2 (95% CI, 1.7-2.7) for CVD mortality, with these estimates being markedly smaller for FFM (ie, HR, 1.2; 95% CI, 0.9-1.6). When the analyses were restricted only to the sample assessed with hydrostatic weighing (N=29,959, 51.7%), the results were similar, with even slightly larger differences in favor of BMI (ie, HR, 3.0; 95% CI, 2.2-4.0) compared with BF% and FMI (ie, HR, 1.5; 95% CI, 1.2-1.9 and HR, 2.1; 95% CI, 1.6-2.7, respectively). We estimated Harrell's c-index as an indicator of discriminating/predictive ability of these models and observed that the c-index for models including BMI was significantly higher than that for models including BF% or FMI (P<.005 for all).

CONCLUSION

The simple and inexpensive measure of BMI can be as clinically important as, or even more than, total adiposity measures assessed using accurate, complex, and expensive methods. Physiological explanations for these findings are discussed.

Obesity: challenges to ventilatory control during exercise--a brief review

Obesity is a national health issue in the US. Among the many physiological changes induced by obesity, it also presents a unique challenge to ventilatory control during exercise due to increased metabolic demand of moving larger limbs, increased work of breathing due to extra weight on the chest wall, and changes in breathing mechanics. These challenges to ventilatory control in obesity can be inconspicuous or overt among obese adults but for the most part adaptation of ventilatory control during exercise in obesity appears remarkably unnoticed in the majority of obese people. In this brief review, the changes to ventilatory control required for maintaining normal ventilation during exercise will be examined, especially the interaction between respiratory neural drive and ventilation. Also, gaps in our current knowledge will be discussed.

Does obstructive sleep apnea impair the cardiopulmonary response to exercise?

STUDY OBJECTIVES

The aim of this study was to evaluate cardiopulmonary exercise performance in lean and obese patients with obstructive sleep apnea (OSA) compared with controls.

DESIGN

Case-control study.

SETTING

The study was carried out in Sao Paulo Sleep Institute, Sao Paulo, Brazil.

PATIENTS AND PARTICIPANTS

INDIVIDUALS WITH SIMILAR AGES WERE ALLOCATED INTO GROUPS: 22 to the lean OSA group, 36 to the lean control group, 31 to the obese OSA group, and 26 to the obese control group.

INTERVENTIONS

The participants underwent a clinical evaluation, polysomnography, a maximum limited symptom cardiopulmonary exercise test, two-dimensional transthoracic echocardiography, and spirometry.

MEASUREMENTS AND RESULTS

The apnea-hypopnea index, arousal index, lowest arterial oxygen saturation (SaO2) and time of SaO2 < 90% were different among the groups. There were differences in functional capacity based on the following variables: maximal oxygen uptake (VO2max), P < 0.01 and maximal carbon dioxide production (VCO2max), P < 0.01. The obese patients with OSA and obese controls presented significantly lower VO2max and VCO2max values. However, the respiratory exchange ratio (RER) and anaerobic threshold (AT) did not differ between groups. Peak diastolic blood pressure (BP) was higher among the obese patients with OSA but was not accompanied by changes in peak systolic BP and heart rate (HR). When multiple regression was performed, body mass index (P < 0.001) and male sex in conjunction with diabetes (P < 0.001) independently predicted VO2max (mL/kg/min).

CONCLUSIONS

The results of this study suggest that obesity alone and sex, when associated with diabetes but not OSA, influenced exercise cardiorespiratory function.

Effect of arterial carbon dioxide on ventilation during recovery from impulse exercises of various intensities

To determine that whether arterial carbon dioxide (PaCO₂) affects ventilation (VE) during recovery from impulse-like exercises of various intensities, subjects performed four impulse-like tests with different workloads. Each test consisted of a 20-sec impulse-like exercise at 80 rpm and 60-min recovery. Blood samples were collected at rest and during recovery to measure blood ions and gases. VE was measured continuously during rest, exercise and recovery periods. A significant curvilinear relationship was observed between VE and pH during recovery from the 300- and 400-watt tests in all subjects. VE was elevated during recovery from the 100-watt test despite no change in any of the humoral factors. Arterialized carbon dioxide (PaCO₂) kinetics showed fluctuation, being increased at 1 min and decreased at 5 min during recovery, and this fluctuation was more enhanced with increase in exercise intensity. There was a significant relationship between VE and PaCO₂ during recovery from the 300- and 400-watt tests in all subjects. The results of the present study demonstrate that pH and neural factors drive VE during recovery from impulse-like exercise and that fluctuation in PaCO₂ controls VE as a feedback loop and this feedback function is more enhanced as the work intensity increases.

Effects of humoral factors on ventilation kinetics during recovery after impulse-like exercise

To clarify the ventilatory kinetics during recovery after impulse-like exercise, subjects performed one impulse-like exercise test (one-impulse) and a five-times repeated impulse-like exercises test (five-impulse). Duration and intensity of the impulse-like exercise were 20 sec and 400 watts (80 rpm), respectively. Although blood pH during recovery (until 10 min) was significantly lower in the five-impulse test than in the one-impulse test, ventilation (.VE) in the two tests was similar except during the first 30 sec of recovery, in which it was higher in the five-impulse test. In one-impulse, blood CO2 pressure (PCO2) was significantly increased at 1 min during recovery and then returned to the pre-exercise level at 5 min during recovery. In the five-impulse test, PCO2 at 1 min during recovery was similar to the pre-exercise level, and then it decreased to a level lower than the pre-exercise level at 5 min during recovery. Accordingly, PCO2 during recovery (until 30 min) was significantly lower in the five-impulse than in one-impulse test..VE and pH during recovery showed a curvilinear relationship, and at the same pH, ventilation was higher in the one-impulse test. These results suggest that ventilatory kinetics during recovery after impulse-like exercise is attributed partly to pH, but the stimulatory effect of lower pH is diminished by the inhibitory effect of lower PCO2.

Lifestyle and the Respiratory Health of Children

This article offers a review of the potential influences of personal lifestyle on respiratory health in children, looking at both healthy individuals and those with respiratory disorders. As with many aspects of health, regular physical activity, an appropriate diet, and avoidance of obesity and cigarette smoke all contribute to optimal development of the healthy child. An active lifestyle is associated with greater static and dynamic lung volumes, greater efficiency of the ventilatory process, and an optimization of breathing patterns. The risk of upper respiratory infections is also reduced in those maintaining a moderate level of physical activity. Maternal smoking during pregnancy, as well as active and passive smoking, all have an adverse influence on lung function in the child, the largest effects being on dynamic lung volumes. The risk of developing asthma seems reduced in children who maintain a normal body mass and are physically active. A program of graded physical activity is of therapeutic value in a number of established respiratory conditions, including asthma, cystic fibrosis, and ventilatory impairment from neuromuscular disorders. Exercise carries a slight risk of fatalities from asthma and anaphylactic reactions. In designing an optimal physical activity program, it is also important to guard against the hazards of deep oronasal breathing, including the precipitation of bronchospasm by the inhalation of cold, dry air and pollens; an increased exposure to atmospheric pollutants (reducing and oxidant smog, fine and ultra-fine particulates, and carbon monoxide); and possible long-term dangers from chlorine derivatives in the atmosphere of indoor swimming pools.