The Oxygen Cascade During Exercise in Health and Disease

Abstract

The oxygen transport cascade describes the physiological steps that bring atmospheric oxygen into the body where it is delivered and consumed by metabolically active tissue. As such, the oxygen cascade is fundamental to our understanding of exercise in health and disease. Our narrative review will highlight each step of the oxygen transport cascade from inspiration of atmospheric oxygen down to mitochondrial consumption in both healthy active males and females along with clinical conditions. We will focus on how different steps interact along with principles of homeostasis, physiological redundancies, and adaptation. In particular, we highlight some of the parallels between elite athletes and clinical conditions in terms of the oxygen cascade.

Figure 1.

Schematic of the oxygen cascade during exercise.

Figure 2.

The respiratory, cardiovascular and metabolic response to aerobic exercise. Each x-axis represents progressive exercise starting at rest and ending at maximal intensity. The y-axis are unitless and are intended to show the relative change. Abbreviations: PAO₂, alveolar oxygen tension; A-aDO₂, alveolar-to-arterial oxygen gradient; PaO₂, arterial oxygen tension; PaCO₂, arterial carbon dioxide tension; SaO₂, oxyhemoglobin saturation; V̇_E, minute ventilation; V_A, alveolar ventilation; V_T, tidal volume; Fb, breathing frequency; TPR, total peripheral resistance; SBP, systolic blood pressure; MAP, mean arterial pressure; DBP, diastolic blood pressure; MSNA, muscle sympathetic nerve activity; Q, cardiac output; SV, stroke volume; HR, heart rate; PvO₂, mixed venous oxygen tension; HCO₃⁻, arterial bicarbonate; K⁺, arterial potassium ion concentration; A-vDO₂, arterial-to-venous oxygen difference; V̇CO₂, carbon dioxide production; V̇O₂, oxygen uptake; Lac, arterial lactate concentration.

Figure 3.

Typical maximal ventilations in different populations of males and females. Rowers (males) and cross-country skiers (females) represent highly trained individuals with very high ventilations. V̇_E, minute ventilation

Figure 4.

Ventilatory response to exercise in terms of lung volumes and flow. Leftmost side represents a spirogram showing the change in lung volumes and flows during progressive exercise in a young healthy female (solid black), an aerobically trained young female (solid blue) and a healthy older female (solid red). The dotted lines represent the change in lung volumes. The rightmost side shows a maximal flow-volume curve along with maximal flow-volume loops for the same color coordinated subjects.

Figure 5.

The relationship between maximal oxygen uptake and cardiac output and red blood cell volume. V̇O_2max, maximal oxygen uptake; Q_max, maximal cardiac output; RBCV, red blood cell volume