Flashcards in Bergdahl- Chapter 16 and 17 Deck (60):
what is the formula to calculate the volume of flow ?
F= (P1-P2) / R
so flow is directly proportional to the pressure gradient between the two ends of the vessels
and indirectly proportional to the resistance encountered to fluid flow
how does resistance come about ?
from the friction between blood flow and the internal vascular wall
what are the three factors that determine resistance ?
- blood thickness/ viscosity
- length of the conducting tube
- blood vessel radius
what does Poiseuille's Law express ?
the general relationship among pressure difference, resistance, and flow
Q= (pressure gradient x vessel radius ^4)
/ (vessel length x fluid viscosity)
in Poiseuille's law, which variables remain constant ? which are the most impactful ?
vessel length won't change much
blood viscosity too
the radius affects the blood flow the most because it's ^4
how is flow related to resistance ?
resistance = 1/flow
during exercise, how does the body adjust its blood flow ?
local arterioles of active muscles dilate
non-active tissues will constrict
what 2 factors contribute to reduced blood flow to non-active muscles ?
1) increased SNS outflow which will inhibit blood flow to non-essential organs
2) local metabolites that directly stimulate vasoconstriction or enhance the effect of other vasoconstrictors
how does skeletal muscle couple to metabolic demands ?
at rest, 1 out of 30-40 capillaries stay open
so the opening of dormant capillaries have a tremendous effect
the opening of dormant capillaries in active skeletal muscle serves three purposes
1) increase total muscle blood flow
2) deliver a large blood volume with only a minimal increase in blood flow velocity
3) increase the effective surface for gas and nutrient exchange between blood and muscle fibers
what increases or decreases act as stimuli for vasodilation within the active muscle ?
decreased tissue oxygen
increase in blood flow, temperature, Co2, acidity, adenosine, magnesium, potassium, nitric oxide
where is the nitric oxide produced ?
in endothelial cells lining the blood vessels
what can happen with endothelial dysfunction, for example in diabetes or CHD?
not enough nitric oxide produced
how does nitric oxide regulate blood flow ?
endothelial cells lining the blood release NO
this reduces SNS vasoconstriction, induces vasodilation to increase blood flow
when does vasodilation occur as related to NO ?
when NO penetrates smooth muscle cells
how is NO released ?
released from endothelial cells by autonomic neurons, or drugs like Viagra that stimulate its release
what is the definition of cardiac output ?
the amount of blood pumped by the heart during a 1 minute period
what variable reflects the functional capacity of the cardiovascular system ?
cardiac output (Q)
what are three methods to assess cardiac output ?
1) direct fick
2) indicator dilution
3) CO2 rebreathing
in what environment is the Direct Fick usually done ?
in a hospital
how do you measure the different variables in the Direct Fick Method?
Q= VO2 / a-vO2 (mixed venous) difference
VO2 with open-circuit spirometry during 1 min
a-vO2 (mixed venous) difference- sampling from pulmonary artery, or RA
which method to assess cardiac output is the standard but is invasive ?
what is the Indicator Dilution method to measure cardiac output ?
known quantity of inert dye on venous side mixes with blood, goes to lungs and returns to heart
photosensitive device assesses arterial blood samples
what is cardiac output at rest ?
can vary with different emotional conditions
however, 5L approx for males, 4L for females
what are the average values for HR and SV in endurance athletes at rest ?
HR 50 bpm
SV 100 mL
what two factors can explain the large SV and low HR of endurance-trained athletes ?
for HR: increased vagal tone and decreased sympathetic drive
for SV: increased blood volume, myocardial contractility, and compliance of LV, which augment SV
how does cardiac output increase during exercise ?
increase rapidly during transition from rest to steady state and then rides gradually until it plateaus when blood flow meets the exercise metabolic requirements
how is cardiac output different in exercise for endurance athletes ?
they achieve a large maximal CO solely through a larger stroke volume
what are three mechanisms that increase the heart's SV during exercise ?
1) enhanced cardiac filling in diastole followed by a more forceful systolic contraction
2) normal ventricular filling followed by a subsequent forceful ejections and emptying during systole
3) training adaptations that expand blood volume and reduce resistance to blood flow in peripheral tissues
explain the enhanced diastolic filling which increases the heart's SV during exercise ?
any factor that increases venous return or slows the heart produces greater preload during diastolic phase
increase in EDV which produces a more powerful ejection stroke
ejects normal SV + additional blood
explain the Frank-Starling law of the heart
the force of contraction of the cardiac muscle remains proportional to its initial resting length
this means that when the ventricles are stretched more due to a higher preload (EDV) the ejection is then more forceful proportionally
when SV increases during exercise, will ESV be higher or lower ?
lower. the ventricles will more forcefully eject blood leaving less since systolic emptying is facilitated
what is cardiovascular drift ?
the phenomenon in which, with time (usually 15 min submax) some responses decrease
eg SV decrease with a concomitant HR increase
what should a person do during cardiovascular drift ?
work out at a lower intensity
in a cardiovascular drift, SV decreases. what happens ?
compensatory heart rate increase to maintain a nearly constant cardiac output
what is the cardiac output distribution during rest ?
5L output with
1L to muscle
4/5 L to digestive tract, liver, spleen, brain, etc
what is the cardiac output distribution during exercise ?
most of exercise cardiac output goes to ACTIVE muscles
more precisely to oxidative portions of muscles at the expense of those with high glycolytic capacity
what is the difference in blood (CO) redistribution during exercise between trained and untrained individuals ?
for trained begins in the anticipatory period
which two tissues cannot tolerate a compromised blood supply ?
heart and brain
at rest, the myocardium uses what percentage of the oxygen flowing in coronary circulation ?
during exercise, what changes in the coronary circulation ?
it has a 4-5 fold increase
during exercise, what changes in the cerebral blood flow ?
it increases during exercise by 25-30% compared with the resting flow
arterial blood carries how much mL of O2 / L ? how do we calculate mL of O2 available to body from that ?
200 mL O2/ L (or 20 mL/dL)
if SV is 5 L, that means that per minute, 1000 mL of oxygen is available to the body
what happens to extra oxygen circulating above the resting requirement ?
it's in reserve
what is the amount of oxygen circulating each minute in exercise ?
CO increases 4-5 fold to 16 L/ min
therefore since there is 200 mL O2/L, this gives us 3200 mL O2 available to body during exercise
what is the association between cardiac output an VO2 max ?
a close one.
(it's a direct proportion on graph)
how does a lower Hb change CO ?
women and children have a 5-10% larger CO in submax exercise due to lower levels of Hn
kids have a smaller CO in exercise. why ?
they have a smaller stroke volume for which a higher HR does not fully compensate.
it's the a-v (mixed) O2 difference that expands to meet the oxygen requirements
during rest what is the a-v O2 difference in tissues ?
20 mL/ dL blood
this means that 15 mL of O2 (75% of blood's O2) still remains bound to Hb
exercise oxygen consumption increases due to two things:
Q= VO2 / (a-v mixed O2 difference)
so VO2= Q x a-v O2 difference
in this manner, VO2 will increase with an increase in Q (cardiac output)
and with an increase in a-v O2 difference (Hb releases a considerable quantity of reserve O2)
how does arterial blood oxygen content vary during exercise ?
it doesn't. throughout the whole exercise range it's about 20 mL/ dL blood or 200 mL/ L blood
how does mixed venous blood oxygen content vary during exercise ?
between 12-15 mL/dL during rest to 2-4 mL/dL during maximal exercise
what does progressive expansion of the a-v O2 difference result from ?
a reduced venous oxygen content
what is hemoconcentration ?
increased concentration in RBC
results from the progressive mvmt of fluid from the plasma to the interstitial space
basically the capacity of arterial blood to carry oxygen increases due to hemoconcentration
how do central and peripheral factors ensure increased oxygen extraction in active tissue during exercise ? (4)
- by diverting CO to active muscle
- augmenting aerobic enzyme activity
- increased capillary to fiber ratio
- increase in size and number of mitochondria
how does O2 consumption and MHR differ in MAXIMAL upper body and lower body exercise ?
arm exercise max consumption still 20-30% lower than leg and smaller MHR values
due to relatively smaller muscle activated in upper body
how does arm exercise compare to leg exercise in terms of oxygen consumption SUBMAXIMALLY ? why ?
higher levels during arm exercises submaximally
because UB uses O2 that doesn't directly help mvmt since it needs stabilizing muscles and such
SUBMAX: does arm or leg exercise produce the greatest physiologic strain ? why ?
arm produces higher HR, pulmonary ventilation, effort, BP
elevated HR because of greater feed-forward stimulation from brain's central command to medullary control center
and increased feedback stim to medulla from peripheral receptors in active tissue
what will produce greater metabolic and physiologic strain- arm or leg exercise, submaximally ?