Oxygen cost for cycling as related to leg mass in males and females, aged 20 to 80

Clinical Interpretation of Cardiopulmonary Exercise Testing: Current Pitfalls and Limitations

Several shortcomings on cardiopulmonary exercise testing (CPET) interpretation have shed a negative light on the test as a clinically useful tool. For instance, the reader should recognize patterns of dysfunction based on clusters of variables rather than relying on rigid interpretative algorithms. Correct display of key graphical data is of foremost relevance: prolixity and redundancy should be avoided. Submaximal dyspnea ratings should be plotted as a function of work rate (WR) and ventilatory demand. Increased work of breathing and/or obesity may normalize peak oxygen uptake (V̇O₂) despite a low peak WR. Among the determinants of V̇O₂, only heart rate is measured during non-invasive CPET. It follows that in the absence of findings suggestive of severe impairment in O₂ delivery, the boundaries between inactivity and early cardiovascular disease are blurred in individual subjects. A preserved breathing reserve should not be viewed as evidence that "the lungs" are not limiting the subject. In this context, measurements of dynamic inspiratory capacity are key to uncover abnormalities germane to exertional dyspnea. A low end-tidal partial pressure for carbon dioxide may indicate either increased "wasted" ventilation or alveolar hyperventilation; thus, direct measurements of arterial (or arterialized) PO₂ might be warranted. Differentiating a chaotic breathing pattern from the normal breath-by-breath noise might be complex if the plotted data are not adequately smoothed. A sober recognition of these limitations, associated with an interpretation report free from technicalities and convoluted terminology, is crucial to enhance the credibility of CPET in the eyes of the practicing physician.

The Obesity Factor: How Cardiorespiratory Fitness is Estimated More Accurately in People with Obesity

OBJECTIVE

Cardiopulmonary exercise testing is clinically used to estimate cardiorespiratory fitness (CRF). The relation to total body mass (TBM) leads to an underestimation of CRF in people with obesity and to inappropriate prognostic and therapeutic decisions. This study aimed to determine body composition-derived bias in the estimation of CRF in people with obesity.

METHODS

Two hundred eleven participants (58.8% women; mean BMI 35.7 kg/m² [± 6.94; 20.7-58.6]) were clinically examined, and body composition (InBody720; InBody Co., Ltd., Seoul, South Korea) and spiroergometrical peak oxygen consumption (VO₂ peak) were assessed. The impacts of TBM, lean body mass (LBM), and skeletal muscle mass (SMM) on CRF estimates were analyzed by the application of respective weight models. Linear regression and plotting of residuals against BMI were performed on the whole study population and two subgroups (BMI < 30 kg/m² and BMI ≥ 30 kg/m² ).

RESULTS

For every weight model, Δmean VO₂ peak (expected - measured) was positive. LBM and SMM had a considerable impact on VO₂ peak demand (P = 0.001; ΔR²  = 2.3%; adjusted R²  = 56% and P = 0.001; ΔR² = 2.7%; adjusted R²  = 56%), whereas TBM did not. Confounding of body composition on VO₂ peak did not differ in LBM and SMM.

CONCLUSIONS

TBM-adjusted overestimation of relative VO₂ demand is much higher in people with obesity than in those without. LBM or SMM adjustment may be superior alternatives, although small residual body composition-derived bias remains.

Systemic vascular dysfunction is associated with emphysema burden in mild COPD

BACKGROUND

Cardiovascular diseases play a major role in morbidity and mortality in the earlier stages of COPD. We hypothesized that systemic vascular dysfunction would be present even in patients who are currently considered at "low-risk" for negative cardiovascular outcomes, i.e., those with largely preserved FEV₁, few exacerbations and only mild burden of respiratory symptoms (GOLD spirometric grade 1, clinical group A).

METHODS

16 patients (FEV₁ = 86 ± 13%) and 16 age- and gender-matched controls underwent measurements of: a) central arterial stiffness by pulse wave velocity, b) brachial flow-mediated dilation and c) forearm muscle oxygenation by near-infrared spectroscopy. Computed tomography quantified emphysema (% of low attenuation areas (LAA)) and airway disease.

RESULTS

Patients and controls were well matched for key clinical variables including co-morbidities burden. Thirteen patients presented with more than 5% LAA: emphysema extension was negatively related to transfer factor for carbon monoxide (TL_CO) (r = -0.63; p = .01). Compared to controls, patients had higher central arterial stiffness, lower normalized (to shear stress) flow-mediated dilation, delayed time to peak flow-mediated dilation and poorer muscle oxygenation (p < .05). TL_CO and emphysema, but not airway disease, were significantly related to each of these functional abnormalities (r values ranging from 0.51 to 0.66; p < .05).

CONCLUSION

Systemic vascular dysfunction is present in the earlier stages of COPD, particularly in patients with greater emphysema burden and low TL_CO. Regardless FEV₁, patients showing those structural and functional abnormalities might be at higher risk of negative events thereby deserving closer follow-up for early detection of cardiovascular disease.

When obesity and chronic obstructive pulmonary disease collide. Physiological and clinical consequences

In many parts of the world, the prevalence of both chronic obstructive pulmonary disease (COPD) and obesity is increasing at an alarming rate. Such patients tend to have greater respiratory symptoms, more severe restriction of daily activities, poorer health-related quality of life, and greater health care use than their nonobese counterparts. Physiologically, increasing weight gain is associated with lung volume reduction effects in both health and disease, and this should be considered when interpreting common pulmonary function tests where lung volume is the denominator, such as FEV1/FVC and the ratio of diffusing capacity of carbon monoxide to alveolar volume, or indeed when evaluating the physiological consequences of emphysema in obese individuals. Contrary to expectation, the presence of mild to moderate obesity in COPD appears to have little deleterious effect on respiratory mechanics and muscle function, exertional dyspnea, and peak symptom-limited oxygen uptake during cardiopulmonary exercise testing. Thus, in evaluating obese patients with COPD reporting activity restriction, additional nonpulmonary factors, such as increased metabolic loading, cardiocirculatory impairment, and musculoskeletal abnormalities, should be considered. Care should be taken to recognize the presence of obstructive sleep apnea in obese patients with COPD, as effective treatment of the former condition likely conveys an important survival advantage. Finally, morbid obesity in COPD presents significant challenges to effective management, given the combined effects of erosion of the ventilatory reserve and serious metabolic and cardiovascular comorbidities that collectively predispose to an increased risk of death from respiratory failure.

Feasibility and reproducibility of measurement of whole muscle blood flow, oxygen extraction, and VO2 with dynamic exercise using MRI

PURPOSE

Develop an MRI method to estimate skeletal muscle oxygen consumption (VO2 ) with dynamic exercise using simultaneous measurement of venous blood flow (VBF) and venous oxygen saturation (SvO2 ).

METHODS

Real-time imaging of femoral VBF using a complex-difference method was interleaved with imaging of venous hemoglobin oxygen saturation (SvO2 ) using magnetic susceptometry to estimate muscle VO2 (Fick principle). Nine healthy subjects performed repeated 5-watt knee-extension (quadriceps) exercise within the bore of a 1.5 Tesla MRI scanner, for test/re-test comparison. VBF, SvO2 , and derived VO2 were estimated at baseline and immediately (<1 s) postexercise and every 2.4 s for 4 min.

RESULTS

Quadriceps muscle mass was 2.43 ± 0.31 kg. Mean baseline values were VBF = 0.13 ± 0.06 L/min/kg, SvO2 = 69.4 ± 10.1%, and VO2 = 6.8 ± 4.1 mL/min/kg. VBF, SvO2 , and VO2 values from peak exercise had good agreement between trials (VBF = 0.9 ± 0.1 versus 1.0 ± 0.1 L/min/kg, R(2) = 0.83, CV = 7.6%; SvO2 = 43.2 ± 13.5 versus 40.9 ± 13.1%, R(2) = 0.88, CV = 15.6%; VO2 = 95.7 ± 18.0 versus 108.9 ± 17.3 mL/min/kg, R(2) = 0.88, CV = 12.3%), as did the VO2 recovery time constant (26.1 ± 3.5 versus 26.0 ± 4.0 s, R(2) = 0.85, CV = 6.0%). CV = coefficient of variation.

CONCLUSION

Rapid imaging of VBF and SvO2 for the estimation of whole muscle VO2 is compatible with dynamic exercise for the estimation of peak values and recovery dynamics following exercise with good reproducibility.

Noncontrast skeletal muscle oximetry

PURPOSE

The objective of this study was to develop a new noncontrast method to directly quantify regional skeletal muscle oxygenation.

METHODS

The feasibility of the method was examined in five healthy volunteers using a 3 T clinical MRI scanner, at rest and during a sustained isometric contraction. The perfusion of skeletal muscle of the calf was measured using an arterial spin labeling method, whereas the oxygen extraction fraction of the muscle was measured using a susceptibility-based MRI technique.

RESULTS

In all volunteers, the perfusion in soleus muscle increased significantly from 6.5 ± 2.0 mL (100 g min)(-1) at rest to 47.9 ± 7.7 mL (100 g min)(-1) during exercise (P < 0.05). Although the corresponding oxygen extraction fraction did not change significantly, the rate of oxygen consumption increased from 0.43 ± 0.13 to 4.2 ± 1.5 mL (100 g min)(-1) (P < 0.05). Similar results were observed in gastrocnemius muscle but with greater oxygen extraction fraction increase than the soleus muscle.

CONCLUSION

This is the first MR oximetry developed for quantification of regional skeletal muscle oxygenation. A broad range of medical conditions could benefit from these techniques, including cardiology, gerontology, kinesiology, and physical therapy.

Oxygen uptake for cycling in relation to body composition: a pilot study

The purpose of this study was to investigate the relationship between oxygen uptake (VO2) for cycle ergometry and body composition in untrained healthy young men. Fifty-six men underwent body composition measurements and ramp work rate tests at 60 revolutions/minute on a cycle ergometer. Cell mass (CM), fat mass (FM), lean body mass (LMB) and total body mass (TBM) were assessed by multifrequency and segmental bioelectric impedance analysis. Resting, unloaded, and peak VO2 were determined by a gas analyzer, and their relationships with CM, FM, LBM, and TBM were analyzed. Values of VO2/TBM were positively related to the increasing CM/TBM ratios (p < 0.05-0.01). However, VO2/CM did not change with anthropometric characteristics (p > 0.05). Resting, unloaded and peak VO2 were more strongly related to CM (p < 0.005-0.001) than to FM, LBM or TBM. Our findings revealed that FM, LBM and TBM least affected the relationship between VO2 and CM. These data suggest that CM actually provides the preferred frame of reference for estimating the VO2 for cycle ergometry at 60 revolutions/minute in untrained healthy young men.

The energy cost of cycling and aerobic performance of obese adolescent girls

In order to assess the energy cost of cycling and aerobic capacity in juvenile obesity, responses to cycle ergometer exercise were studied in 10 pubertal obese (OB) [body mass index (BMI) SD score (SDS): 3.40+/-0.58 SD] adolescent girls (age: 16.0+/-1.2 yr) and in 10 normal-weight (NW, BMI SDS: -0.30+/-0.54) girls of the same age (15.1+/-1.9). To this aim, gas exchange, heart rate (HR), and energy expenditure (EE) were studied during graded cycle ergometer test at 40, 60, 80, 100, and 120 W. The energy cost of cycling was higher in OB, being oxygen uptake (VO2) higher (about 20%) in OB than in NW girls at all workloads (p<0.01-0.001). Estimated maximal VO2 and VO2 at anaerobic threshold were significantly (p<0.05) higher in OB girls [although lower per unit body mass (p<0.01) and similar for unit fat-free mass], and explained the higher oxygen pulse and lower HR for any EE observed during submaximal exercise in OB. While net mechanical efficiency (ME) was significantly lower in OB (p<0.01), delta ME was similar in both groups, indicating no substantial derangement of muscle intrinsic efficiency. It is concluded that, despite a higher cost of cycling, OB girls can rely on a larger aerobic capacity which makes them able to sustain this kind of exercise within a wide range of work loads, with relevant implications when planning protocols of physical activity in the context of interventions for the reduction of juvenile obesity.

Clinical Relevance of Inter-Method Differences in Fat-Free Mass Estimation in Chronic Obstructive Pulmonary Disease

BACKGROUND

Evaluation of fat-free mass (FFM) is becoming recognised as an important component in the assessment of clinical status and formulation of prognosis in patients with chronic obstructive pulmonary disease (COPD).

OBJECTIVE

The aim of this study was to determine whether potential differences in FFM estimation performed by air displacement plethysmography (ADP), bioelectrical impedance (BIE) and anthropometry (ANTHRO) would assume clinical significance.

METHODS

Twenty-eight patients with moderate-to-severe COPD were submitted to FFM estimation by ADP, BIE and ANTHRO. FFM was then allometrically related to peak oxygen uptake (peak VO2) as determined by symptom-limited incremental cycle ergometry.

RESULTS

We found that ANTHRO classified fewer patients as 'FFM-depleted' than the other two techniques (p < 0.05). Although mean biases of the BIE-ADP differences were close to zero, their 95% confidence limits extended as high as 5.9 kg (16%). The ANTHRO-based allometric exponents for peak VO2 correction of FFM, therefore, were typically higher than those obtained by the other two methods in both depleted and non-depleted patients (ANTHRO: 1.45-1.41, BIE: 0.97-1.18, ADP: 1.08-1.14, respectively).

CONCLUSION

We conclude that between-method differences in FFM estimation can be sufficiently large to have practical implications in patients with moderate-to-severe COPD. A single method of body composition assessment, therefore, should be used for FFM estimation in these patients.

Peak VO2 correction for fat-free mass estimated by anthropometry and DEXA

PURPOSE

Anthropometric (ANTHRO) and dual-energy x-ray absorptiometric (DEXA) estimates of total body and leg fat-free masses (FFM) were obtained in 77 randomly selected sedentary men and women, aged 20-80: intermethod limits of agreement and their clinical significance, as inferred from the differences on peak VO2 corrected for FFMANTHRO and FFMDEXA, were determined.

METHODS

Limits of agreement were calculated as mean bias +/- 95% confidence intervals: peak VO2 at maximum cycle ergometry was related to FFMANTHRO and FFMDEXA by using both standard (y x x(-1)) and power function ratios (allometry).

RESULTS

Data distribution of the ANTHRO-DEXA differences presented significant heteroscedasticity in both sexes, i.e., differences were proportional to the mean (P < 0.05). After logarithmic transformation, the mean bias +/- 95% limits of agreement were expressed as ratios (ANTHRO x DEXA(-1) x// error ratio): these corresponded to 0.95 x// 1.11 or 0.99 x// 1.15 for total body FFM and 0.90 x// 1.10 or 1.02 x// 1.07 for leg FFM in men and women, respectively. In addition, we found different allometric exponents for FFMANTHRO and FFMDEXA: the intermethod differences, therefore, increased after power function expression (P < 0.05).

CONCLUSION

Discrepancies between ANTHRO and DEXA measurements of FFM depend on the magnitude of the estimate: differences are typically within 10 to 15%. Importantly, FFM-corrected peak VO2 values can vary according to the method chosen for body composition assessment, especially when allometry is used for peak VO2 correction. These results demonstrate that ANTHRO-DEXA differences in FFM estimation do have relevant practical consequences for the analysis of maximum aerobic capacity in nontrained humans.

Reference values for dynamic responses to incremental cycle ergometry in males and females aged 20 to 80

Interpretation of incremental cardiopulmonary exercise tests (CPET) might be enhanced by considering the simultaneous rates of change of certain key variables, e.g., Delta oxygen uptake/Delta work rate (Delta VO(2)/Delta WR), Delta heart rate/Delta VO(2) (Delta HR/Delta VO(2)), Delta ventilation/Delta carbon dioxide production (Delta VE/Delta VCO(2)), and the linearized Delta tidal volume/Delta VE (Delta VT/Delta lnVE) relationships. However, there are no published age- and sex-dependent reference values for these relationships that were appropriately obtained in randomly selected subjects. We therefore prospectively evaluated 120 sedentary individuals (60 male, 60 female, age 20 to 80 yr) who were randomly selected from more than 8,000 subjects, and submitted to standard ramp-incremental CPET on an electronically braked cycle ergometer. We found that sex and age significantly influenced several of the dynamic relationships, in addition to anthropometric attributes (p < 0.05). A comprehensive set of linear prediction equations is provided; the limits of normality (at the 95% confidence level) differed substantially from previous recommendations based on single discrete values. These data therefore provide a frame of reference for assessing the normalcy of the response profiles of four standard indices of metabolic, cardiovascular, and ventilatory function during rapidly incremental cycle ergometry in sedentary males and females up to 80 yr of age.