Flashcards in Lab Review Deck (39):
What does an increase in metabolic rate require?
Increase in oxygen supply and carbon dioxide removal
What is the requirement of metabolic rate being met by?
Increasing both the volume of gas moved in and out of the lungs per minute and the rate of the blood flow (cardiac output) through the systemic circulation
What is the highest rate of aerobic muscular work a healthy person?
Depends on the highest rate at which oxygen can be delivered to the active muscle fibres
What is the limit of the highest cardiac output which a person can attain?
Ventilation can increase sufficiently to keep arterial blood fully oxygenated, whatever the rate of uptake of oxygen
What is Cardiac output?
CO= SV x HR
When are increased requirements of gas exchange needed?
How can VO2 be expressed?
In relative and absolute terms
What is Pulse pressure?
Pulse pressure= SBP-DBP
What is mean arterial BP?
Mean arterial BP= Diastolic BP + 1/3 Pulse pressure
What happens when the aortic valve opens?
The ventricular ejection begins, aortic pressure increases rapidly to a peak value, and then decreases
How is part of the energy from the left ventricular contraction stored?
By stretching the elastic components of the aortic walls
What is the definition of pulse pressure?
The difference between the maximum (systolic blood pressure, SBP) and minimum (diastolic blood pressure, DBP) blood pressure
What is 'mean pressure'?
Constant pressure which would result in the same total blood flow as arterial pressure waveform actually observed
What does the temporary storage of part of the stroke volume serve to do?
During ejection period serves to smooth out the flow of blood in the circulation, so that flow continues during diastole
What does the extent of the pressure increase in the arterial system depend on?
Stroke volume which the arteries have to store
The arterial compliance
What does compliance mean?
Compliance is a measure of the change in volume for a given change in pressure: the more compliant the arteries are, the more easily are they distended
What does arterial compliance depend on?
Physical properties of the arterial wall
Value of the mean arterial pressure
What happens to the arterial wall at a higher pressure?
Arterial wall becomes less compliant as it is stretched more
What happens to the arteries when the ventricle relaxes and ejection ceases?
The pressure in the arteries is maintained by elastic recoil
What happens to the arterial walls in old age?
Lose elasticity and are less compliant
What is a given stroke volume likely to produce?
(hence larger pulse pressure in a subject aged 70 compared to age 20)
What is a classical sphygmomanometer comprised of?
Inflatable cuff connected to a manometer by flexible tubing
What is the standard manometer?
Glass U-tube containing mercury
What does a sphygmomanometer measure?
How is blood pressure measured using a sphygmomanometer?
The cuff is wrapped around the upper arm and inflated to a pressure sufficient to squeeze shut the brachial artery, detected by the absence of the brachial pulse
Pressure is then reduced until the pulse reappears; the manometer reading is taken to equal SBP
What else is used along side a sphygmomanometer?
By listening with a stethoscope to the sounds produced in the brachial artery during the gradual reduction of cuff pressure, it is possible to identify not only the SBP but also the DBP
What are the possible variations between individual BP?
Nervous subjects (sympathetic discharge)
HR and BP could be higher than normal
Seeing own reading may increase sympathetic drive
Resistance peripheral resistance
Fitting of cuff
How much oxygen is in the air room?
What is mixed expired gas collected in?
What does a Douglas bag help measure?
Collected over a known period of time and the volume of gas measured to obtain the volume expired per minute and the oxygen content (% volume) in the gas
What is heart rate measured by?
Heart rate monitor positioned on the chest wall of subject
How is blood pressure measured using an electronic cuff?
At rest with the subject sitting on the bike in the exercising position
Immediately on cessation of the exercise period
After 10 minutes recovery period
What does watts equate to?
e.g. 100 watts = 100 J/sec = 6000 J/min = 6kJ/min
What is found indirectly by measuring the oxygen consumption?
The rate of total energy output during exercise
What does increase Ventilation cause?
Increased alveolar PO2, therefore oxygen consumption rises
What is the H+ buffered by in the blood?
Bicarbonate forming carbonic acid
What are two main drawbacks of the linear extrapolation method?
Assumption that HR and VO2 relationship remains linear as exercise intensifies
What is VO2?
Measure of the maximum volume of oxygen that an athlete can use