Week 10: Hunyady's Respiratory Physio 4 (Ben) Flashcards
What is the systolic, diastolic and mean pressure in the pulmonary arteries?
Sys - 24 mmHg
Dias - 9 mmHg
Mean - 14 mmHg
What is the pressure in the pulmonary capillaries?
And veins?
capillaries - 10 mmHg
veins - 9 mmHg
What is the pressure difference which drives pulmonary circulation?
(Think mean pulmonary arterial minus left atrial pressures)
14 - 8 = 6 mmHg pressure driving pulm. circulation
How does the flow (Q) compare in the pulmonary and systemic circulation?
Why?
Considering the different perfusion pressures in each system, what does this mean for resistance?
- Flow is the same because two systems are in series (~5.5 L/min)
- Resistance is much lower in pulmonary circulation
(Q = ΔP/R)
What is the reason for the low resistance in pulmonary circulation?
high compliance of the pulmonary vessels
- they distend easily with increased pressure
How is pulmonary circulatory pressure passively regulated?
vessels passively dilate due to their high compliance
What are the dilators and constrictors of pulmonary vascular smooth muscle?
- Dilator - NO
- Constrictors - Angiotensin II + NE
What is the most important constrictor of pulmonary vessel smooth muscle?
Why is this important?
Hypoxia
- important homeostatic mechanism to shift blood flow to parts of the lung which are better ventilated and thus can better oxygenate the blood
How does chronic respiratory insufficiency (low PO2, high PCO2) affect pulmonary circulation?
it causes pulmonary hypertension (> 14 mmHg pulmonary MAP)
- because hypoxia is a pulmonary vasoconstrictor
- this can also result in right ventricular hypertrophy as the right ventricle works harder to overcome this increased resistance
What is the equation for diffusion of a gas across the alveolar wall into the capillary?
VO2 = (A·D·ΔP)/T
- A = surface area
- D = diffusion coefficient
- ΔP = partial pressure difference
- T = barrier thickness
How does the diffusion of O2 compare to that of CO2?
its diffusion coefficient is 20x smaller
- meaning CO2 is 20x more soluble in water than O2
How does exercise affect diffusing capacity?
it increases diffusing capacity, because…
more alveolar capillaries are recruited so surface area for diffusion increases
About how long is blood in pulmonary capillaries for?
0.75 seconds
What is the average concentration of hemoglobin in the blood?
2.3 mmol/liter
What are the 4 factors affecting O2 affinity of hemoglobin?
- increased blood PCO2
- increased blood [H+] (acidity)
- increased [2,3-BPG]
- increased temperature
