JTA: D, KSA: m slide set

Maximal Oxygen Uptake (VO2 max)

• VO2 max = maximal volume of oxygen consumed per unit time
• typically expressed clinically as relative or absolute
• relative - mL/kg/min
• absolute - mL/min
• it is the product of maximal cardiac output and arterial-venous oxygen difference
• can be calculated or measured through multiple means

Open Circuit Spirometry

• used to measure VO2 max during graded incremental or ramp exercise tests to the point of exhaustion; indirect calorimetry
• subject breathes through a valve with his or her nose occluded while pulmonary ventilation and expired fractions of oxygen and carbon dioxide are measured
• this direct measurement of VO2 max is not often used due to the costs associated with the equipment, space needed to conduct the tests, and personnel needed to carry out the tests

Estimating VO2 max

• to estimate VO2 max, there are a variety of maximal and submaximal tests that could be conducted
• these tests are validated by examining one of two correlations:
• ​​​​​​​correlation between directly measured VO2 max and the VO2 max estimated from physiologic responses to submaximal exercise
• correlation between directly measured VO2 max and field test performance or time to volitional (client's judgement) fatigue using a standard graded exercise test protocol

Calculating VO2 max

• Fick Principle - a mathematical equation representing the oxygen needs during exercise; this allows for the determination of VO2 max
• VO2 max = (HR max) x (SV max) x (a-v02 diff max)
• VO2 = mL/kg/min (relative)
• SV = stroke volume (volume of blood pumped per beat)
• a-vO2 difference = arteriovenous oxygen difference