Dynamic Interactions of Gas Exchange, Body Mass, and Progressive Exercise in Children

Abstract

Purpose Cardiopulmonary exercise testing (CPET) is increasingly used as a biomarker of fitness in children. Maximal or peak values remain the most common variables obtained in CPET, but these physiologically challenging high-intensity work rates are often not achieved. We hypothesized that interactions of gas exchange, heart rate (HR), and work rate (WR) CPET variables (slopes) could yield useful mechanistic and clinical insights that might enhance the clinical utility of CPET in children. We further hypothesized that the dependence of the slope on body mass could be predicted by first-principle analysis of body size and physiological response. Methods One hundred sixty-nine healthy participants (8–18 years old, BMI<95th percentile, 82 females) underwent dual X-ray absorptiometry scan to estimate lean body mass (LBM) and performed a ramp-type progressive cycle ergometry exercise protocol with breath-by-breath measurement of gas exchange. Linear regression was used to calculate the slopes among V•O2,V•normalCO2,normalV•E, HR, and WR. Results ΔWR/ΔHR (r=0.87) and normalΔV•O2/normalΔnormalHnormalRfalse(normalr=0.96false) were strongly correlated with peak V•O2, while normalΔV•O2/normalΔnormalWnormalRfalse(normalr=0.42false) and normalΔnormalV•E/normalΔV•normalCO2false(normalr=−0.51false) were mildly correlated with peak values. LBM was more highly correlated than was total body mass with those slopes predicted to be body size dependent (p<0.0001). Conclusion The data largely supported our original hypotheses. Unlike peak or maximal values, which are derived from no more than a few data points at the end of a progressive exercise test, the CPET slopes were calculated from a much larger data set obtained throughout the test. Analysis of these slopes might ultimately prove useful clinically and in research studies when peak values are not achieved.

Cardiopulmonary Exercise Testing in Children and Adolescents with High Body Mass Index

“…The ΔWR/ΔHR and ΔVO 2 /ΔHR slopes reflect a useful physiological response supplying the clinician with insights (albeit, indirect) into cardiac function and muscle perfusion (9). Resting VO 2 and VO 2 at unloaded (0-W) pedaling are elevated in obese subjects because of their greater body mass and the work associated with it (5).…”

“…We used the CPET and body composition data from 142 children and adolescents whose BMI was ≤ 85th percentile as described previously (9). The normal-BMI group participants had participated in 5 UC Irvine IRB approved pediatric exercise research studies, 3 of which were the same as the high-BMI participants, in the same laboratory using identical protocols.…”

“…In typical CPET, gas exchange measured at the mouth (i.e., oxygen uptake [VO 2 ], carbon dioxide production [VCO 2 ], and ventilation [VE]) increases as the workload progresses and reflects gas exchange in the skeletal muscle (44). Not surprisingly, muscle mass is a major determinant of peak exercise gas exchange (9). …”

“…Consequently, in the current study, in addition to the VO 2max or peak VO 2 , we used variables obtained from the submaximal portions of CPET (Figure 1; such as dynamic slopes of gas exchange and HR during progressive exercise) which we recently demonstrated might prove useful when peak VO 2 or VO 2max values were questionable (9). Unlike peak VO 2 , which is derived from no more than a few data points at the end of a progressive exercise test, the CPET slopes were calculated from a response continuum of gas exchange, WR, and HR variables throughout a large portion of the progressive exercise test.…”

The Common Fund Initiative and Its Implication for Advancing Exercise and Physical Activity Research in Child Health

“…Ongoing promising activities include novel ways in which we can more fully use the data obtained from exercise testing in children (8) and employing ubiquitous computing to assess physical activity in the real lives of children (5). Finally, tied to any successful intervention will be innovative use of behavioral science in understanding how best to motivate children and adolescents to participate in exercise training programs with optimal fidelity (10).…”