Study Question Lab 4

Question 1

1. Exercise 1 n 2: Are the systolic + diastolic BP from Ex 1 and 2 identical? What are the possible sources of variation?

Answer 1

• Not identical
• Possible sources of variation: changes in posture, emotional state, releasing cuff at diff rates, errors in analysis, poor hearing acuity, the experience of the measurer, incorrect placement of the cuff and excessive outside noise

Question 2

2. Exercise 1 n 2: Since the pressures are determined using changes in the pulse amplitude, would slowing the rate at which pressure is released form cuff make ur readings more accurate?

Answer 2

• Yes slowing the rate at which pressure is released form cuff make ur readings more accurate, allows for u to detect small changes btwn trials more easily (f you release the pressure too quickly then you may not catch the SP in time)

Question 3

3. Exercise 3: Are the values the same as those obtained from left arm? Explain any differences

Answer 3

• No the values obtained in Ex 3 (measurement from right arm) are lower for both SBP and DBP. This is because measurement is taken from a further distance from left ventricle which generates the large pressure waves… the blood must go from the left side to right side of body

Question 4

4. Exercise 4: Are the values from forearm the same as those obtained w/cuff on upper arm? Explain any variations u see

Answer 4

• No the values obtained in Ex 4 (measurement of forearm) are lower than those obtained w/cuff on upper arm. This is because is measurement is taken from a further distance from left ventricle which generates the large pressure waves. Also there is branching into brachial and ulnar artery so changes pressure.

Question 5

5. Exercise 5: What is effect of raising each hand on the BP in left arm? Explain results

Answer 5

• If put right arm up (and measuring from left arm), inc pressure due to inc blood volume
• If put left arm up, dec BP cause dec BV (since measuring from the arm that has dec circulation)

Question 6

6. Exercise 6: Are the BP values from the leg the same as those obtained from arms? Explain any differences

Answer 6

• No leg values are higher cause subject is sitting and blood pools in his leg due to the effects of gravity; more blood volume means more pressure.

Question 7

7. Exercise 6: What would happen to BPs in subjects left leg when they stand

Answer 7

• Inc in pressure, estimate 20mmHg higher. This is due to gravity effect, causing the blood to pool into the legs.

Question 8

8. Exercise 6: Would u expect the BP to change after subject has been standing for 5 mins? Why would there be change?

Answer 8

• Yes slow and steady drop in BP (orthostatic hypotension). This is caused by venous pooling of blood in legs due to no muscle pump action. Which in turn leads to lower low venous return, lower CO, and lower BP.

Question 9

9. Exercise 7: Compare the BPs before n after exercise. How long does it take ur subjects blood pressure to return to resting lvls

Answer 9

• BPs increase after exercise. It takes subject 2 minutes to return to resting levels
  During dynamic exercise, the SP will raise while the SP remains ~constant. The raise in SP is due to the increase in HR and contractility of the heart, increased SV and CO which is needed to deliver more oxygen to the working muscles. We have increased vasodilatory response in skeletal muscles and vasoconstriction of the splanchnic circulation and non-working muscles. DP remains ~same due to the net decrease in TPR

Question 10

10. Exercise 8: What effect does apnea have on subjects BP?

Answer 10

Holding one’s breath will show an initial INC in SP and DP due to transmission of intrathoracic pressure to the left heart and aorta. The baroreceptors may sense the increase in blood pressure and the HR may decrease to compensate, but this isn’t always observed. EVENTUALLY there is an overall DEC in BP as the amount O2 oxygen in the body decreases, and CO2 levels increase, causing vasodilation.

Question 11

11. Exercise 8: How does the subjects BP change when subject resumes breathing after apnea?

Answer 11

When resume breathing after apnea, the intrathoracic pressure will suddenly drop so there is much less pressure exerted on the left ventricle and aorta. Consequently there will be a further drop in BP. From that drop in intrathoracic pressure there is also a large increase in VR (reversal of the collapse of thoracic veins) which consequently increases SV and CO. What happens here with the large increase in VR, SV and thus CO but existing peripheral vasoconstriction is an arterial pressure overshoot that last about 4-8 seconds. After this the baroreceptor reflex kicks in to reduce BP by slowing HR and reducing peripheral vasoconstriction.

Question 12

12. Give detailed explanation of how HR and BP change w/time in normal subject who performs valsalva maneuver. Explain these expected results in physiological terms.

Answer 12

Valsalva Maneuver is the forced expiration against the closed glottis. The forceful expiration causes changes in the intrathoracic pressure that dramatically affects the VR, CO, arterial pressure and HR.

Phase I: The onset of strain
There is an abrupt elevation of SP and DP due to transmission of intrathoracic pressure to left heart and aorta. The baroreceptors MAY sense inc in BP and HR may dec to compensate.

Phase IIa: the continued strain
The inc in SP and DP rapidly reversed and falls below normal resting values due to dec VR caused by collapse of thoracic veins due to inc intrathoracic pressure.

Phase IIb: the baroreceptor response
Resulting decreases in BP are sensed by baroreceptors, there is a reflex mediated inc in HR, and peripheral vasoconstriction which prevents further dec in BP, and may cause rise in BP towards end of strain phase.

Phase III: the release of strain
Occurs immediately after release of the strain. Further dec in BPs as the pressure surrounding left heart and aorta is suddenly decreased. May be additional inc in HR during this phase caused by additional stimulation of baroreceptors.

Phase IV: the arterial pressure overshoot
After the intrathoracic pressure is suddenly reduced there is a large inc in VR which results in large inc in SV. This, along with still-existing peripheral vasoconstriction, causes an arterial pressure overshoot that lasts 4-8 secs. The baroreceptor reflex is then activated resulting in a dec in BP and slowing of HR back towards normal

Question 13

13. Give detailed explanation of how HR and BP change w/time in normal subject who is rapidly moved from supine to 70 degree head up tilt position

Answer 13

1. This will result in orthostatic stress, caused by a transition to a upright position after extended positions in supine. Orthostatic hypotension is defined as reduction in SBP of at least 20mmHg, or reduction in DBP of at least 10mmHg, during first 3 mins of standing of HUP to at least 60 degrees on tilt table.
2. Results in pooling of 500-1000mL of blood in lower extremities and splanchnic circulation.
3. BP decreases in a linear fashion with increasing tilt (up to 90 degrees). This effect is especially pronounced in early transition phase and is associated with significant change in perfusion pressure across the body.
4. On initial transition to HUP there’s venous pooling effect seen in legs as MABP significantly drops due to orthostatic stress being placed upon vasculature. The result is hypovolemia (low venous return) induced from venous pooling in the legs.
5. HUP ~80 degrees necessary to elicit this central hypovelemia effect, however HUP at smaller angles from horizontal are still able to produce orthostatic stress upon body, to less degree
6. When orthostatic hypotension exhibited, 2 mechanisms may occur that inhibit BF back to heart and brain.
7. 1st: failure of regulatory system (e.g. baroreceptors) to elicit changes in vasculature and HR to counter a fall in MABP. One implication is that the TPR does not increase as a consequence of an increase in the sympathetic activation of the muscle arteries causing vasocontraction.
   10: 2nd: reduction in CBV, which leads to central hypovolemia (associated with high venous compliance, peripheral vasodilation, and muscle atrophy).