5. The respiratory Cycle Flashcards
What does the little ‘a’ and big ‘A’ stand for in PaO2 measurements?
a: arterial
A: alveoli
What is the diaphragm innervated by and what does it do when it contracts during inspiration?
Innervated by the phrenic N., it flattens/moves down into the abdomen, increasing the volume of the thorax
What is the main function of the external intercostal muscles between ribs during inspiration?
They raise the ribs during contraction, increasing the anteroposterior diameter of the thorax (bucket handle motion)
What are some extra muscles used during inspiration under conditions such as exercise?
Anterior scalene M: raise 1st and 2nd ribs
Sternomastoids: raise the sternum
What are the main ‘pros’ of the respiratory muscles being skeletal muscle, meaning they need to be activated by the brain? (2)
- Rapid and uniform
2. Ability to respond rapidly to different conditions
What are the main ‘cons’ of the respiratory muscles being skeletal muscle? (2)
- Brain/Spinal cord damage= cannot breath
- Length-tension curve; if the lungs get too big it stretches the muscle. (Myofilaments are too close/too far away= muscles loose tension)
What is the first step of inspiration?
Contraction of the inspiratory muscles, which increases the thoracic volume and decreases the intrapleural pressure
What is located between the visceral and parietal pleura?
There is fluid that effectively connects the two pleura together
What is the intrapleural pressure at rest?
It is near -5cm H2O, meaning it is 5cm H2O less than outside of the body.
When parietal and visceral pleura are pulled away from eachother, it creates intrapleural space
As the thorax increases in volume, what decreases to about -8cm H2O?
the intrapleural pressure (remember V and P are inversely related)
Because of the coupling of the lungs and the chest wall, the lungs expand as thorax expands As the lungs increase in size, the alveolar pressure (pressure inside alveoli) does what? Why?
Aveolar pressure decreases due to the increase in volume and size of the alveolar.
Resting is 0cm, will got to -1cm H2O
What occurs when the aveolar pressure drops below the atomospheric pressure of 0cm H2O?
Air will flow into the lungs
What do we see halway through respiration regarding volume change, alveolar pressure, intrapleural pressure, and air flow?
Volume: Starts at 0L, increases
Aveolar: Starts at 0cm h2o, decreases
Intrapleural: Starts at -5cm h2o, decreases
Airflow: Starts at 0 h2o, decreases (ALWAYS FOLLOWS ALVEOLAR CHART)
As inspiration continues, intrapleural pressure will reach its lowest at ________cm H2O at the end of inspiration and airflow into the lungs will decrease along with alveolar pressure.
-8cm H2O
What is tidal volume and what is the average measurement?
tidal volume (Vt) is the amount of air inhaled in a given breath, typically 500mL
What are the values of Volume, Aveolar/Intrapleural pressure, and air flow at the end of inspriation?
Volume: +0.5mL
Alveolar & Air Flow: 0cm H2O
Intrapleural Pressure: -8cm H2O
What are the main expiratory muscles and what do they do?
Abdominal muscles: push into abdomen to move diaphragm upwards
Internal intercostal M: perpendicular to external intercostal M, decrease AP diameter of the thorax
What is important to remember about expiration during a normal breath?
Expiration is passive because the lungs want to be smaller and have elastic recoil! So expiration muscles are not used during normal breath
What are the values of volume, alveolar/intrapleural pressure, and air flow halfway through expiration?
Volume: from +0.5 to +0.25L
Alveolar pressure/Air flow: from 0 to +1cm H2O
Intrapleural Pressure: from -8cmH2O to -6.5
What are then ending values volume, alveolar/intrapleural pressure, and air flow at the end of expiration, before inspiration?
Volume: 0L
Alveolar Pressure/Air flow: 0cm h2o
Intrapleural: -5cm h2o
Why does the intrapleural pressure not return to resting value until the end of the respiratory cycle?
Remember: when alveolar pressure drops below atmospheric pressure, air flows into the lungs (negative value)
Because air enters the aveoli (more molecules take up the added space) but nothing should enter the intrapleural space, so the number of molecules are spread out over a bigger volume
What is minute ventilation and how is it calculated?
Minute ventilation is how much air is inhaled every minute (Vdot) = Vt (tidal volume) x frequency of respiratory rate
To calculate the CORRECT amount of air actually inhaled we have to include the airways that do not have aveoli, so cannot actually intake air. What is anatomic dead space and how do you ‘calculate’ it?
Anatomic dead space is representative of the airways that donot have aveoli, so do not partake in gas exchange. Anatomic dead space is estimated to be how much you weight
How do you calculate minute aveolar ventilation? (includes anatomic dead space)
Subtract dead space (weight in lbs) from tidal volume, and multiply by respiratory rate
How do you calculate transpulomary pressure?
Palv (alveolar pressure) - Pip (intrapleural pressure)
What is residual volume (RV)?
Volume of air that cannot be forced out, no matter how hard one tries
What is inspiratory reserve volume (IRV)?
volume of air breathed above tidal volume (Vt)
What is expiratory reserve volume (ERV)?
volume of air that can be forced out in addition to tidal volume (Vt), requires muscles and does not include residual volume
What is vital capacity (VC)?
Amount of air that can be maximally inspired following a maximal expiration
VC= IRV + Vt + ERV
What is inspritation capacity (IC)?
capacity of air that can be maximally inspired follow a normal exhale
IC= Vt+ IRV
What is the functional residual capacity (FRC)?
amount of air that remains in the lungs following a normal expiration
FRC= ERV + RV
What is the total lung capacity (TLC)?
maximal volume to which lungs can be expanded with greatest effort
TLC= IC + FRC = VC+RV = ERV+RV+IRV+Vt
Which respiratory capacities cannot be determined by spirometry?
FCR, TLC, (maybe VC)
What does the nitrogen-washout technique determine and how?
Determines FCR; Pt breaths 100% O2 through one-way valve, all expired gas is collected and monitored until N2 reaches zero
Total volume of all gas expired is determined and multiplied by % of N2 in mixed expired air (80%)
How does Helium (He) dilution work to measure residual volume?
Inhalation of a know concentration of He (C1) from a known volume (V1)… change in concentration C2 allows for determination of V2= FRC
FRC=V2=V1 x (C1-C2)/C2
How is body plethysmography used to measure residual volume?
Patient is enclosed in rigid box and breaths against shutter. Pressure in lung changes, pressure in box changes proportionally in opposite direction
BOYLES LAW= P1V1=P2V2
Fraction of oxygen in the inspired air (FlO2) is the percentage of air that is oxygen… What is the room air?
21% of normal/atmospheric air is oxygen (0.21). this would only change is someone was breathing in oxygen as well
What cannot be measured by spirometry?
TLC FRC and RV
What occurs or must occur when the abdominal msucles are activated during the respiratory cycle?
Activated abdominal muscles means that it is an active expiration, meaning that the Aveolar pressure will be more positive than its usual +1cmH2O
What is the main generator of airflow in the respiratory cycle?
Alveolar pressure is! it has to change to either positive or negative in order for air to flow out or in
