Exam 2- Lecture 7 Flashcards
Primary functions of the respiratory response to exercise
- increase oxygen uptake to support accelerated cellular metabolism
- remove carbon dioxide produced as a result of accelerated cellular metabolism and as a result of buffering metabolic acids (lactic acid)
What components of the respiratory response to exercise should you consider?
- mechanics of ventilatory response
- gas exchange at the alveolus
- oxygen transport in the blood
- oxygen extraction at the muscle capillary/tissue interface
- regulation of the ventilatory response
- does Ve limit max aerobic capacity?
Inspiration during exercise
- diaphragm flattens
- active contraction of external intercostals and scaleni to move rib case upward
- net effect is to increase volume of thoracic cavity, “sucking” air into lungs
expiration during rest and light exercise
passive recoil and relaxation of inspiratory muscles
expiration during increased intensity of exercise
active expiration
internal intercostals and abdominal muscles contribute to expiration by reducing thoracic volume
airway resistance during exercise
- resistance in the airways affects the rate of airflow
- with exercise, airway resistance decreases due to bronchodilation
what is a very important determinant of airway resistance?
airway diameter
how does bronchodilation occur during exercise?
sympathetic NS –> release NE and circulating E from adrenals –> these catacholemines relax bronchial smooth muscle via beta-2 receptors
3 phases of exercise hyperpnea
- there is a step increase in Ve at the onset of exercise (phase I; 0-15 s)
- Phase I is followed by a slower, exponential rise in Ve (phase II, about 3 mins for submaximal exercise)
- phase III occurs after 3 mins
- if submaximal exercise is being performed, Ve will stabilize
ventilatory response to a graded exercise test
- ventilation will continue to rise as workload increases
- response is linear up to a point called the ventilatory threshold, at which point further increases in workload are accompanied by a disproportional increase in Ve
Components of Ve response
Ve=Vt x f
At rest, ventilation = 500 ml x 12 = 6 L/m
With maximal exercise, Vt is about 2 L or greater; f= 35-45 breaths/min or higher
maximal exercise Ve
about 100-120 L/min
17-20x resting
does exercise Vt ever exceed 60% of FVC?
rarely
at moderate levels of exercise, what causes most of the rise in Ve?
increase in Vt
some smaller contribution from f
what occurs once Vt = 50-60% of FVC?
Ve can only increase further by f
what regulates the combination of Vt and f necessary for a given Ve?
the brainstem
Why does tidal volume increase at the expense of IRV and ERV?
during exercise, you are inspiring to a greater volume and expiring to a small lung volume so that tidal volume increases
there is a greater dependence on changes in inspiratory volume
Ve = ?
Ve= Vd + Va
What is alveolar ventilation?
the portion of the insured air (Ve) that participated in gas exchange
at the same Ve, what provides more effective alveolar ventilation?
deeper breathing and lower f
what does deeper breath cause?
a larger portion of the tidal volume to enter and mix with alveolar air
FEV1% =
% of FVC expelled in 1 second
inversely related to airway resistance
what can FEV1% be used to detect?
exercise-induced bronchospasm
10-15% fall in FEV1% suggests airway obstruction due to bronchospasm
Gas exchange in the alveolus
- Diffusion of O2 and CO2 across alveolar membrane and capillary walls is a function of the partial pressure differential, surface area for exchange, and thickness of membranes
- Most healthy individuals maintain adequate gas exchange during heavy exercise
What occurs to PaO2, even in heavy exercise?
it is well-maintained
what occurs to PaCO2 as intensity increases past moderate exercise?
decreases
Diffusion of CO2 across alveolar membrane and capillary walls are a function of what?
pressure differential
membrane thickness
surface area
Why is there a fall in PaCO2 at higher intensities of exercise?
look up recording
why does mixed venous PCO2 increase with increasing intensity?
look up recording
What is exercise-induced arterial hypoxemia associated with?
- Increased ventilation/perfusion (V/Q) mismatch
- Diffusion limitation: the high pulmonary blood flow decreases time available for gas transfer (AKA diffusion disequilibrium)
Mild EIAH
SaO2: 93-95%
Moderate EIAH
SaO2: 88-93%
Severe EIAH
SaO2 < 88%
when is supplemental O2 during exercise indicated?
in patients with pulmonary disease who have a rising SaO2 < 88%
why might elite endurance athletes may experience arterial desaturation during maximal exercise
- Most likely due to diffusion limitation due to an exceptionally fast transit-time of red blood cells through the pulmonary capillaries (incomplete gas exchange), secondary to extremely high cardiac output
- Other factors: mechanical constraints on airflow and a less than maximal ventilatory response
When is VO2 measurably affected?
- When SaO2 reaches 3% below resting levels (1.5-2% decrease in VO2max for every 1% reduction in SaO2)
how much can EIAH decrease VO2 max?
up to 15%
What is the relevance of EIAH?
- It can limit VO2max in healthy, active individuals, and this effect will be magnified in hypoxic environments, like altitude
Who is most affected by altitude?
Those with higher VO2max
When do person with pulmonary disease show EIAH?
- At low work rates
- They require supplemental O2 during exercise
What occurs to PO2 during exercise?
it is well maintained
when does PaCO2 decrease?
when the lactate or ventilatory threshold is reached because ventilation increases out of proportion to the CO2 production
when might arterial O2 desaturation occur?
At high work rates in some well-trained persons (especially at high altitudes) and at lower work rates in persons with pulmonary disease
How is oxygen transported in the blood?
Hemoglobin
O2 content =
(Hb concentration x 1.34 ml O2/g Hb x SaO2) + 0.003 PaO2
a-v O2 difference =
CaO2 - CvO2
What is the difference of Hb concentration between men and women?
- Hb concentration is 5-10% lower in women
- This lower Hb contributes to lower aerobic capacity in women
What does alterations in Hb concentration affect?
O2 content (iron-deficiency anemia)
What does interference of binding of O2 to Hb affect?
O2 content
smoking–carbon dioxide
what drives unloading of O2 from Hb?
Low tissue PO2
what is the a-v O2 difference at rest?
4-5 ml O2/100ml at rest
what does exercise do to a-v O2 difference?
increases it up to 15-16 ml/100 ml
What does decrease in tissue PO2 from 40 at rest to 15 mmhm during exercise do?
increases the pressure gradient, favoring release of oxygen from Hb
What factor facilitate unloading of oxygen/shift O2 dissociation curve to the right?
- lower pH
- increase body temperature
- increase carbon dioxide concentration
what is 2,3 DPG and what does it do?
it is produced in red blood cells during glycolysis and facilitates unloading of oxygen from Hb (reduces affinity of Hb for O2)
what results in chronically increased levels of 2,3 DPG?
altitude or chronic cardiopulmonary disease
do males or females have a higher level of 2,3- DPG?
females
What is myoglobin?
an oxygen-binding protein found in skeletal and cardiac muscle
where is there more myoglobin?
in the “red” muscles
does training enhance the cell store of myoglobin?
it is not clear
When does myoglobin release the O2 that it is storing?
At very low O2 tensions
Ex: at very start of exercise and during intense exercise
Thought to help shutting O2 to mitochondria
