Exercise physiology in healthy individuals Flashcards
Describe the RQ values for the metabolism of different substrates
Fats- 0.70
Carbohydrates- 1.0
Protein- 0.82
How do we calculate RQ
CO2 production/oxygen consumption - usually = 1
What is most of our energy at rest produced by
Aerobic metabolism
How many molecules of ATP are produced per molecule of glucose
37
What is a consequence of respiring more fat
less CO2 produced
lungs don’t have to work as hard to get rid of CO2
Summarise the RQ
§ The ratio of CO2: O2
§ 1 is the theoretical maximum.
§ Lowest for fat, intermediate for protein and highest for glucose.
§ O2 requirement at rest = 3.5mlmin-1kg-1.
Compare oxygen requirements for different activities
Oxygen requirements: sat at rest - O2 consumption roughly 3.5ml/min/kg - equal to 1 metabolic equivalent
Metabolic equivalents: standing = 1.5, walking = 2, running > 7
Describe the ventilation response to exercise
At the onset of exercise, there is a O2 deficit and post-exercise, there is an O2 debt (to refill the myoglobin stores).
O2 increases linearly with workload
What does the plateau of O2 consumption define
Max O2 consumption (VO2 max) and therefore max workload
Describe the muscular response to exercise
stored energy (ATP, PCr) used to generate muscular contraction; inorganic phosphates, ADP and creatine drive oxidative phosphorylation while Krebs/glycolysis increases; oxygen consumption at muscle increases, and initially CO2 production rises slowly (as buffered), but then rises to match O2
Describe how SV, Q and HR respond to exercise
Stroke volume initially increases but then decreases past a peak of 160mls while the CO and HR continue to rise.
Why does SV decrease
Q increases linearly with intensity until plateaus as maximum reached, alongside HR and oxygen consumption - exercise limited by cardiac output; when HR too fast, filling time in diastole reduced, which reduces SV after a peak
Describe the response of the lungs to exercise
TV increases with ventilation up to a peak where plateaus, and breathing frequency increases - will breathe at half vital capacity in exercise (increase further not as efficient); VQ matching at rest not ideal, but in exercise increases
How does the human body perform exercise
Gas exchange, O2, CO2
The muscle
The circulatory system
The lungs
Anaerobic metabolism/Acidosis
What is the purpose of gas exchange
Transport of oxygen to tissues
Removal of waste products (namely CO2)
Summarise the flow of oxygen and carbon dioxide
Negative pressure is generated within the chest cavity
Air travels from the mouth down the airways and into the alveoli of the lungs.
Assuming normal atmospheric concentrations of O2 (21%) it will diffuse down a concentration gradient across the alveolar surface to the pulmonary capillaries (venous O2 content 16%)
Binds to haemoglobin, raising blood oxygen levels
Blood travels through the heart, to target organs
Here capillaries, get smaller and densely infiltrate the tissue to allow easy diffusion of oxygen, again down a concentration gradient, into metabolising cells
Carbon dioxide diffuses in the opposite direction (largely dissolves into plasma) and returns to the lungs via the venous system
Carbon dioxide diffuses from the high concentration venous blood (approx 4%) to the low concentration alveolar air (0.04%)
Positive intrathoracic pressures cause expiration
What do we breathe out
FEO2 ~16%
FECO2 ~4%
What do we breathe in
FIO2 21%
FICO2 0.0%
Summarise the response of the muscle to exercise
Onset of exercise
Stored energy muscular contraction
Inorganic phosphates, ADP and creatine drive oxidative phosphorylation
Kreb’s cycle and glycolysis increase
Oxygen consumption at the muscle (QO2) increases
Initially CO2 production only slightly increases (buffered as HCO3-) but then rises, matching O2
How does oxygen consumption change during exercise
Cardiac Output rises 4-7 fold
Oxygen consumption rises 10-15 fold
Mixed venous sats typically ~75-80% at rest dropping to 15-20% at peak exercise
Up to 85% of oxygen can be extracted during exercise
Recall Fick’s equations
Cardiac Output = Oxygen Consumption/
(a-v) O2 Content
VO2= Cardiac Output x (a-v) O2 Content
What is the response of the lungs to exercise
TV increases with ventilation up to a peak where plateaus, and breathing frequency increases - will breathe at half vital capacity in exercise (increase further not as efficient); VQ matching at rest not ideal, but in exercise increase
Compare VQ at rest and during exercise
At rest VQ matching not ideal
PAO2 = 102mmHg
PaO2 = 92mmHg
P(A-a)O2 = 10mmHg
Early exercise
VQ matching improves
PaO2
Close coupling of VE to VCO2 Decreasing P(A-a)
Describe incremental aerobic metabolism in exercise
Aerobic metabolism - oxygen flow matches demand
Total body RQ rises towards 1 as glucose becomes the predominant fuel source
Ventilation increases to match CO2 production and attempts to maintain steady-state
Describe anaerobic metabolism
Central to human exercise physiology is the anaerobic production of energy
Probable evolutionary role in flight or fight
Highly inefficient but short-term solution when greater energy is required
Describe the bohr effect
as pH increases, Bohr shift of ODC to right so at given PO2 Hb has less affinity to oxygen so offload more to acidotic muscles
why oxygen consumption quadruples as o2 delivery doubles
How does the body deal with acidosis
lactate converted to protons, and is buffered by bicarbonate to increase CO2, increased ventilation allows pH to remain relatively stable; when [H+] exceeds HCO3- cannot buffer and begin hyperventilation
lactic acid is handled by increased ventilation- we see an increase in ventilation above the aerobic threshold
Describe the phases of exercise
VE increases until anaerobic threshold and in isocapnic buffering
Increases further in respiratory compensation (H+ exceeds buffering)
PCO2 increases until anaerobic threshold, same in isocapnic buffering, increases in respiratory compensation
VO2 increases throughout- not as much as the other two
How does ventilation change through the anaerobic threshold and ventilation compensation point
Exponentially- see graph
How does PaCO2 change through the anaerobic threshold and ventilation compensation point
Decreases after ventilation compensation point- constant before
How does VO2 change through the anaerobic threshold and ventilation compensation point
DELAY THEN INCREASES LINEARLY THROUGH BOTH
Summarise exercise terminology
QO2/CO2 - At muscle VO2/CO2 - At mouth VE - Minute ventilation PAO2/CO2 - Alveolar partial pressure PaO2/CO2 - Arterial partial pressure PETO2/CO2 - End-tidal partial pressures
What is seen in fit people
max heart rate and FEV at the same time
Peak Q limits you
How do we calibrate
volume - blow fix amount of volume
bike- apply known force
calibrate with biological control- who repeats the test in the same conditions each time
Describe a cardiopulmonary exercise test
patient on a bike has continuous ECG and gas exchange monitoring and the power is slowly increased to put cardiopulmonary strain on the patient - can be used to detect heart/lung conditions/restrictions on exercise etc.
Describe the Nurse’s health study
Nurses health study – followed up for 18 years (ages 30-55 yrs)
Starts to rise from a BMI 21
Risk of type 2 DM rises by 8 fold at BMI 25
CHD rises 2 fold at BMI 25 and 4 fold at BMI 30
Describe the Forsyth report
Mapped which factors affected one’s intake
societal changes
jigsaw of factors- just one bit doesn’t do anything- but public health focusses on one change
Does BMI on its own determine risk
Subject A: BMI 26.5 kg/m2, 1.3 litres visceral adipose tissue
Subject B: BMI 26.8 kg/m2, 5.5 litres visceral adipose tissue
visceral fat dictates metabolism- as it has a blood supply from G.I tract- increased risk of CHD and T2DM-
blood has to go through adipose tissue and the inflammatory cells- inflammatory mediators reduce liver function
Describe the consequences of increased visceral adiposity
Deteriorated lipid profile Impaired insulin sensitivity Increased susceptibility to thrombosis Increased inflammation markers Impaired endothelial function
How do we measure waist circumference
Mid point between the lowest rib and ileac crest.
~1 cm above navel
Accuracy difficult if BMI>35
Describe action level 1 in waist circumference
Action level 1
Women ≥80cm / 31.5 in Health risk increasing
Men ≥ 94cm / 37 in Take personal action to
avoid weight gain
Describe action level 2
Action level 2
Women ≥ 88 cm /34.5 in Multiple health problems
Men ≥ 102 cm / 40 in Professional help needed
Lower for south asians
Describe the impact of a 10% decrease in weight loss
Improves all aspects of the metabolic syndrome, including: 50% fall in FBS 10% decrease in total cholesterol 15% reduction in LDL 30% fall in triglycerides 8% rise in HDL Ave improvement of BP by 10/20mmHg
Overall relates to:
20-25% reduction in all mortality
30-40% reduction in diabetes related mortality
40-50% reduction in certain cancers
What are NICE recommendations for obese patients
Recommends: Diet Exercise Behavioural therapy Drug treatment Surgery (if BMI >40)
Essentially, what leads to T2DM
Genetic defect in pancreas + obesity (adipotoxicity)- insulin resistance
Do we have targets for waist circumference
No- only weight
diet or liposuction- no reduction in risk- only weight provides benefit
Describe the issue with perception
Patients want to be thin
But health professionals want reductions in complications
Describe the issue with lifestyle advice
Short half-life
loses a lot of weight initially- but will put it back on
Compare weight loss outcomes with different managements
§ With lifestyle changes, there was a 58% improvement (in the study on the left) in diabetic patients.
§ With lifestyle changes, it’s much harder to keep the weight off in this environment (without constant monitoring).
§ Using Orlistat (vs. placebo) and lifestyle changes, the same pattern is observed but Orlistat provides a much greater loss of weight.
o There is a GREAT reduction in weight over the first year which is gradually put back on and then plateaus.
Describe the different types of bariatric surgery
There are 3 main procedures:
o Adjustable band.
§ A fluid can be injected into the sub-cutaneous bag to increase or decrease to food into the stomach.
o Sleeve gastrectomy.
o Gastric bypass (GBP) – Gold-standard.
§ The duodenum and part of the ileum only see bile and no food – may play a role in success of procedure.
How can we make lifestyle advice more effective
Messages are simple
They are individualised
There is frequent follow-up
What are the criteria for bariatric surgery
o BMI > 40, no co-morbidities.
o BMI > 35, co-morbidities.
o BMI 30-35, short duration of T2DM.
Describe the benefits of bariatric surgery
§ GBP surgery was also found to be the most effective in patients with diabetes at glycaemic control.
o This could be due to a number of hypothesised reasons – as the effect occurs immediately after GBP:
§ Change in insulin resistance.
§ Change in insulin secretion.
§ Changes in the gut microbiota.
§ Changes in bile salt secretion.
o GBP also found to reduce mortality and to reduce occurrence of long-term CVD events.
§ Health benefits of bariatric surgery include; resolution/improvement of T2DM and hypertension, reduced cardiac risk, resolution of obstructive sleep apnoea, resolution of PCOS (improved fertility), reduction in cancer-related deaths, regression of non-alcoholic fatty liver disease, reduced MORTALITY.
Describe the duodenal-jejunal sleeve
Duodenal-Jejunal Sleeve – Metabolic/Endocrinological control for diabetes and obesity.
o This results in less food digested and thus can improve glycaemic control.
Describe the pharmacological control
§ Victoza – Liraglutide injection, patients with diabetes AND obesity.
o Oral GLP-1 – Oral version of liraglutide.
§ Saxenda – Liraglutide injection at a higher dose for obese patients.
§ Belviq – Lorcaserin pills, serotonin agonist that supresses appetite, results in a ~5% weight loss.
§ Qsymia – Phenteremine to supress appetite and topiramate (unknown method of action, acts as a pain killer), results in ~7-8% weight loss.
§ Contrave – Naltrexone to supress appetite, results in a ~5% weight loss, side effects on the heart and depression.
Describe the use of sibutarmine
serotonin appetite system- effects on depression and hypertension
Describe ghrelin
makes you hungry as you lose weight
losing weight is not easy
sees it as a state of starvation
tries to drive you back to your previous state
Describe peptide gamma
Produced by colon
makes you hungry
physiologically works against you
Describe energy intake as a cause of obesity
Energy Intake:
a. The energy per person of food sold has been fairly constant BUT there has been a shift in the content of the foods from carbohydrates to fats – i.e. percentage of CHO has dropped while fats has risen.
i. Autoregulation of fats in the body is bad – the body preferentially stores fat instead (unlike CHO and protein which the body has little ability to store).
ii. When we ingest fat we don’t feel as full as when we ingest CHO and protein (endocrine).
b. There has been an increase in fast food outlets.
Describe energy usage as a cause of obesity
a. Reduction in energy expenditure – we now use cars, trains, laptops etc.
i. Quantified using Amish community studies
Describe genes as a cause of obesity
a. While most obesity is NOT monogenic, the amount a person gains and WHERE they gain it is genetic.
i. One example of a variant gene contributing to obesity = FTO gene.
ii. Encode for hormones – e.g. Ghrelin, PYY, Leptin, Insulin.
Which factors can lead to obesity
Societal influence Food production Biology Food consumption Individual physiology Individual activity Activity environment
Describe the issue with obesity in the UK
At the present time obesity is fuelling much of the ill health in the UK
On a primary prevention level we have no answer to this
There is urgent need for be better treatment algorithms
