Eighteen Flashcards
What is VO2 max? Explain it using the Fick equation. What are its units?
Recall that V˙o2
always is equal to the product of the amount of blood delivered to all body tissue, that is, the cardiac output, multiplied
by the amount of oxygen extracted from the blood during
each passage through the tissues, that is, its arterial-venous oxygen content difference. Mathematically this relationship is
expressed by the Fick equation:
V˙o2 = Q˙ · (Cao2 – C _v o2)
And thus: V˙o2max = ˙Qmax · (Cao2 – C _v o2)max
When evaluating aerobic capacity using weightbearing
exercises like running, walking, or climbing stairs, the V˙o2max is expressed in mL/kg/min or L/kg/min to correct
for differences in a subject’s body weight (and from which can
be calculated their body mass index, BMI). When evaluating
aerobic capacity using non-weight-bearing exercises like swimming,
rowing, or biking, then V˙o2max is expressed in mL/min or
L/min to exclude infl uences of a subject’s body weight.
Explain the concept of METs .
A useful alternative is to express V˙o2max in METs, with
one MET being the average for a subject’s resting V˙o2. Historically,
1 MET = 3.5 mL/kg/min, although recent research indicates
that a truer estimate over a wider range of body weights
is 2.6 mL/kg/min. Thus, a subject with V˙o2max of 8 METs has
an aerobic capacity approximately seven-fold above their resting
metabolic rate. This subject would also be described as
having a metabolic reserve of 7 METs. Tables 12.1 and 12.2
provide normative data for weight-adjusted aerobic capacity
(mL/kg/min) for subjects sorted by age and sex. The verbal
classifi cation rankings in each table are useful in distinguishing
among patients from a range of lifestyles, and have been
validated using the ACSM Guidelines Handbook.
Explain the relationship between aerobic capacity and mortality risk.
Aerobic capacity is a more powerful predictor of mortality than
any other established risk factor for cardiovascular disease.
Indeed, as reported in the New England Journal of Medicine
in 2002 by Myers and colleagues, a high aerobic capacity is
protective even in the presence of other known risk factors
(Fig. 12.1). When subjects are defi ned according to other
known risk factors like diabetes, the risk of death from any
cause in subjects whose exercise capacity is 8 METs.
Because physical fi tness is a modifi able risk factor,
improving it enhances patient prognoses: Each MET of increased aerobic capacity yields ~12% improvement in
survival. As shown in Fig. 12.2, mortality rates differ strikingly
just between the least-fi t quintile (lowest 20% of the
population) and the next-least fi t quintile (the second-lowest
20% of the population). Regardless of whether patients have
cardiovascular disease, survival declines as aerobic capacity
decreases. In this multicenter study, fewer than 50% of patients
with an aerobic capacity 75% of patients with an aerobic
capacity >8 METs.
What things will effect the maximum cardiac output and thus aerobic capacity? What about maximum arterial O2 concentration? What about maximum delivery of O2 to tissues (CvO2max)?
Qmax Heart rate, SV, SVR, PVR
CaO2max PIO2, PAO2, Pc′O2, [Hb], P50, shunt
CvO2max Tissue blood flow, Mb, capillarity, [lactate], fiber types, et al.
What effect does traning have on Qmax? Aging? What is the HR max for a given age? How specifically do training and aging affect Qmax?
Qmax increases with aerobic training but decreases with age in both men and women.
For both genders:
HRmax 220 – (age in years)
Changes in SVmax account for most increases in Qmax due to aerobic training, as well as most decreases in Qmax that occur with bed rest and normal aging.
How does heat affect Qmax? Explain. What is cardiovascular drift?
VO2max declines during 45 min of exercise at 36°C (Heat) because blood diverted to skin for evaporative cooling depletes plasma volume, SV, and ventricular preload. The slow rise in HR to maintain any VO2 in the heat is termed cardiovascular drift.
What happens to oxygen consumption during increasing exercise during low FiO2 and high FiO2 ? What happens to SaO2 in the same situation?
In high FiO2, you only get a slight increase in O2 consumption b/c Hb is already saturated and therefore you only slightly increase dissolved O2. However, in low FiO2, you get a more severe decrease in O2 consumption b/c you start to get desaturation of Hb.
In high FiO2, the SaO2 stays relatively constant, the normal FiO2 slowly desaturates, and the low FiO2 greatly and quickly desaturates.
How do you know when a person is about to give out due to exercise? How are these things measured?
Oxygen in the arteries will greatly decrease when a person is about to give out .
Using oximetry to measure yields:
Mild EIAH: SaO2 93.0%, 94.9%
Moderate EIAH: SaO2 = 88.0 – 92.9%
Severe EIAH: SaO2 88.0%
Also, you can measure the amt. of CO2 being exhaled b/c during exercise, lactic acid builds up causing CO2 to be breathed out to combat the acidosis.
What things affect O2 extraction? How?
O2 extraction (CaO2 – CvO2) shows training and age-related effects during progressively greater VO2’s. We cannot determine from these graphs whether extraction increases due to higher values for CaO2 or lower values for CvO2.
What happens to VO2 max during detraining? How long does it take? What causes that? What causes that cause?
VO2max declines significantly within 2 – 3 weeks of ceasing aerobic training.
Detraining significantly reduces Qmax within 2 – 3 weeks of ceasing aerobic training.
Detraining significantly reduces Qmax mostly because of decreased plasma volume that reduces preload and thus SVmax.
A 3-week period of enforced bed rest on 20-year-old elite athletes has a greater impact on their VO2max and Qmax than 30 years of aging, primarily due to bed rest-induced reductions in SVmax.
What are the genetics of VO2 max?
In ten pairs of identical twins, 67% of total variance in % improvements in VO2max was inherited [(0.82)2 = 0.67].
Great genetic component.
What exercise advice should be given to patients? What muscle strenghtening advice should be given?
18-65 yo
5 days a week 30 minutes of moderate exercise OR
3 days a week 20 minutes of vigorous exercise
at least two non consecutive days a week; 8-10 exercises, 8-12 reps, all major muscle groups.
What effects does going to altitude have? Explain. What limits VO2 max at altitude?
PAO2 is the 1st casualty of altitude, caused by PIO2
PaO2 is the 2nd casualty of altitude, due to PAO2
The VO2max of every subject decreases at altitude
CaO2 is maintained at altitude by [Hb] but viscosity suffers; lower limits on CVO2 are poorly understood
The lungs limit VO2max in hypoxic hypoxia
