Unit 5 - Breathing PART H-J Flashcards
Alveolar ventilation
Not all air that enters the respiratory tract during a tidal inspiration goes to the alveoli. Some of it fills the anatomical dead space. As a result, the alveolar ventilation is lower than the pulmonary ventilation.
The TOTAL PULMONARY VENTILATION PER MINUTE (or minute ventilation) is
= tidal volume x respiratory rate
= 500 mL/breath x 12 breaths/min = 6000 mL/min
(the volume of air moved into & out of the lungs each min)
Due to anatomical dead space,…
only ~350 mL of fresh air from each 500 mL tidal breath actually reaches the lungs. So TOTAL ALVEOLAR VENTILATION is
= (tidal volume – dead space volume) x respiratory rate
= (500 mL/breath – 150 mL/breath) x 12 breaths/min = 4200 mL/min
Anatomical dead space
b/c the conducting airways do not exchange gases with the blood, they are known as the anatomic dead space
B/c a sign. portion of inspired air never reaches an exchange surface, a more accurate indicator of ventilation efficiency is…
ALVEOLAR VENTILATION, the volume of fresh air that reaches the alveoli each min
Alveolar ventilation
Steps:
- At end of inspiration, fresh air from the atmosphere (yellow) fills the ~150 mL of the dead space and lung volume is at its maximum for a tidal breath.
- As you expire, the ~150 mL of fresh air in the dead space is expired, along with 350 mL of low oxygen air (blue) from the alveoli. The dead space then fills with ~150 mL of low oxygen air from the alveoli.
- As you inspire , the 150 mL of low oxygen air in the dead-space re-enters the alveolus along with 350 mL of fresh air from the tidal breadth. The other 150 mL of fresh air left from the tidal inspiration now occupies the dead space.
Because the volume of the dead space does not change, depth of breath is…
far more important in increasing alveolar ventilation than respiratory rate
Alveolar ventilation can be drastically affected by changes in the rate or depth of breathing…
MAXIMUM VOLUNTARY VENTILATION, which involves breathing as deeply & quickly as possible, may increase total pulmonary ventilation to as much as 170 L/min
Increasing alveolar ventilation by…
increasing breathing rate and depth (hyperventilation) increases alveolar PO2 and decreases PCO2 within physiological limits.
Decreasing alveolar ventilation by…
decreasing breathing rate and depth (hypoventilation) decreases alveolar PO2 and increases PCO2 within physiological limits.
We find only v. small swings in PO2. Why?
1) the amount of O2 that enters the alveoli with each breath is roughly = to the amount of O2 that enters the blood, &
2) the amount of fresh air that enters the lungs with each breath is only a little more than 10% of the total lung volume at the end of inspiration
Although alveolar gases do not change much with quiet breathing, changes in alveolar ventilation can sign. affect the amount of fresh air & O2 that reach the alveoli
Ventilation patterns
- Eupnea
- Bradypnea
- Tachypnea
- Hypoventilation
- Hyperventilation
- Dyspnea
- Apnea
Eupnea =
breathing is normal quiet (tidal) breathing; 12-20 breaths per minute.
Bradypnea =
decreased respiratory rate compared to normal (<12 breaths/minute)
Tachypnea =
increased respiratory rate and decreased depth compared to normal (panting). (>20 breaths/min)
Hypoventilation =
decreased alveolar ventilation (due to decreased respiratory rate and depth (<12 breaths per minute).
Hyperventilation =
increased alveolar ventilation (due to increased respiratory rate and depth (>20 breaths/minute).
Dyspnea =
shortness of breath and difficulty breathing (a severe symptom of COVID-19, pneumonia and many other diseases).
Apnea =
period of cessation of breathing. May occur in association with some breathing disorders (e.g. sleep apnea).
Hypoventilation when
less fresh air enters the alveoli, alveolar PO2 ↓’s & alveolar PCO2 ↑’s
Hyperventilation as
AV ↑’s, alveolar PO2 ↑’s & alveolar PCO2 falls
Ventilation perfusion coupling
It is important to match the rate of air flow (VENTILATION) into groups of alveoli with the rate of blood flow (PERFUSION) past those alveoli.
- otherwise, blood draining poorly ventilated alveoli will mix with that from well-ventilated alveoli, decreasing the average PO2 of systemic arterial blood
Ventilation/perfusion matching involves…
the local regulation of smooth muscle tone in BOTH the bronchioles and pulmonary arterioles in response to changes in the PCO2 and PO2 of the air, blood, or interstitial fluid (ISF) surrounding these structures.
External respiration:
1) Moving O2 from the atmosphere to the alveolar exchange surface
2) Gas exchange must occur across the alveolar-capillary interface
3) BF (perfusion) past the alveoli must be high enough to pick up the avail. O2
