Is the Lung Built for Exercise? Advances and Unresolved Questions

Cardiac output limits maximal oxygen consumption, but what limits maximal cardiac output?

Maximal oxygen uptake/consumption is an important variable determining exercise performance. It is generally considered to be limited largely, but not exclusively, by maximal cardiac output (CO), which limits the ability of heart to pump oxygen-rich arterial blood to working muscles. Cardiac output is a product of heart rate and stroke volume, which is the amount of blood ejected from the heart by one heart beat. Exercise training, especially of the endurance type, can increase maximal CO substantially. A straightforward way for the heart to increase maximal CO would be to increase maximal heart rate, but this does not happen; instead, maximal heart rate tends to be reduced after training. This is because heart rate is the most important determinant of myocardial oxygen consumption, and ventricular filling and myocardial blood flow (MBF) would be compromised by further increases in heart rate, given that MBF is blunted by contractions and occurs principally during diastole. Myocardial oxygen extraction is already high at rest and is increased further in endurance-trained athletes, making their hearts even more dependent on increases in MBF. The trained heart therefore also shows reduced MBF, enhanced blood mean transit time and higher myocardial vascular resistance at rest and during submaximal exercise, although MBF reserve is not improved. It follows logically that MBF is an important determinant of myocardial performance, and it is proposed in this review that cardiac afferent sensory nerves might contribute to controlling and limiting heart rate, hence maximal CO, in order to protect the heart from ischaemia.

Modeling the marathon and human endurance performances: some thoughts and what's new?

In 1991, I published a physiological model of marathon running performance. My model predicted that it might be possible for a human to run the marathon in less than 2 hours. In this article, I review the genesis of my thinking at that time, share my perspective about what has changed over the last 30 plus years, and speculate about what the future might hold.

Test-retest reliability of cardiopulmonary exercise test-derived metrics in individuals with COPD versus healthy controls

BACKGROUND

Cardiopulmonary exercise testing (CPET) is usually considered the gold standard for assessing maximal oxygen consumption (V̇O2max), a health and performance marker in patients with chronic obstructive pulmonary disease (COPD). Despite the widespread application of CPET, the absolute and relative test-retest reliability of CPET-derived metrics remains unexamined.

OBJECTIVE

To examine and compare test-retest reliability of CPET derived metrics in individuals with COPD and healthy matched controls.

METHODS

12 individuals with COPD and 12 healthy age- and sex-matched controls were included in this case-control study. Each participant completed two CPET on a bicycle ergometer on two different days. Absolute reliability was reported as smallest real difference (SRD) and relative reliability as coefficient of variance (CV) and intraclass correlation coefficients (ICC).

MAIN RESULTS

SRD for peak oxygen uptake was 451.6 (267.4;1006.4) mL/min and CV was 7.8 (4.7;11.0)% in patients with COPD, whereas SRD was 244.2 (151.4;491.5) mL/min and CV was 3.0 (1.8;4.2)% in healthy controls but with no significant between group difference for SRD. CV values for all CPET derived metrics were found to be below 10%. Apart from peak workload achieved and peak minute ventilation, SRD and CV were significantly higher in COPD than in controls for all other CPET-derived metrics.

CONCLUSION

This study provides test-retest reliability estimates of the most widely used CPET derived metrics in individuals with COPD and healthy matched controls. Test-retest reliability for most metrics derived from CPET were found to be lower in individuals with COPD when compared to healthy controls.

Born high, born fast: Does highland birth confer a pulmonary advantage for sea level endurance?

Less than 7% of the world's population live at an altitude above 1500 m. Yet, as many as 67% of medalists in the 2020 men's and women's Olympic marathon, and 100% of medalists in the 2020 men's and women's Olympic 5000 m track race may have been born or raised above this otherwise rare threshold. As a possible explanation, research spanning nearly a quarter of a century demonstrates that indigenous highlanders exhibit pulmonary adaptations distinct from their lowland counterparts. These adaptations may then promote endurance performance. Indeed, healthy indigenous highlanders often exhibit a larger aerobic exercise capacity compared to sea-level residents who travel to high altitude. However, questions remain on whether high-altitude birth is advantageous for sea-level competitions. In this review, we ask whether being born at a high altitude generates an ergogenic advantage for endurance performance in the Summer Olympics-a venue that is generally held at sea level. In so doing, we distinguish between three groups of high-altitude residents: (i) the indigenous highlander, (ii) the highland newcomer, and (iii) the highland sojourner. Concentrating specifically on altitude-induced alterations to pulmonary physiology beginning in the perinatal period, we propose that if altitude-related maladaptations are avoided, genomic and developmental alterations accompanying highland birth may present benefits for endurance competitions at sea level.

Assessing the repeatability of expiratory flow limitation during incremental exercise in healthy adults

We sought to determine the repeatability of EFL in healthy adults during incremental cycle exercise. We hypothesized that the repeatability of EFL would be "strong" when assessed as a binary variable (i.e., absent or present) but "poor" when assessed as a continuous variable (i.e., % tidal volume overlap). Thirty-two healthy adults performed spirometry and an incremental cycle exercise test to exhaustion on two occasions. Standard cardiorespiratory variables were measured at rest and throughout exercise, and EFL was assessed by overlaying tidal expiratory flow-volume and maximal expiratory flow-volume curves. The repeatability of EFL was determined using Cohen's κ for binary assessments of EFL and intraclass correlation (ICC) for continuous measures of EFL. During exercise, n = 12 participants (38%) experienced EFL. At peak exercise, the repeatability of EFL was "minimal" (κ = 0.337, p = 0.145) when assessed as a binary variable and "poor" when measured as a continuous variable (ICC = 0.338, p = 0.025). At matched levels of minute ventilation during high-intensity exercise (i.e., >75% of peak oxygen uptake), the repeatability of EFL was "weak" when measured as a binary variable (κ = 0.474, p = 0.001) and "moderate" when measured as a continuous variable (ICC = 0.603, p < 0.001). Our results highlight the day-to-day variability associated with assessing EFL during exercise in healthy adults.

Cardiopulmonary exercise testing criteria for advanced therapies in patients with heart failure

Many cardiology associations endorse the role of the cardiopulmonary exercise test (CPET) to define the severity of impairment of functional capacity in individuals with heart failure with reduced ejection fraction (HFrEF) and when evaluating the need for advanced therapies for these patients. The focus of the CPET within the cardiology community has been on peak volume of oxygen uptake (VO2). However, several CPET variables are associated with outcomes in individuals with and without chronic disease and can inform clinical decisions in individuals with HFrEF. In this manuscript, we will review the normal cardiopulmonary response to a graded exercise test and review current guideline recommendations relative to CPET in patients with HFrEF.