Mechanics of Breathing and Ventilation Flashcards
What muscles are active during forced inspiration?
Sternocleidomastoid
Scalenes
What is transpulmonary pressure?
The difference between the alveolar pressure and the pleural pressure. Larger during inspiration and lower during expiration.
During inspiration, the volume of the lungs increases. What effect does this have on airway resistance?
Decreases resistance
The smaller an alveoli is, the […] likely it is to collapse.
More
What is the effect on airway resistance of stimulation of beta 2 adrenergic receptors (activated by sympathetic NS)?
Airway dilation –> decreased resistance
How does the anatomy of the lungs help overcome airway resistance?
The airways are arranged in parallel to reduce resistance (just like electrical circuit)
Laminar flow of air occurs in […] airways
Small
What is compliance?
The ability of the lung to be stretched (change in volume) allowing for a change in pressure
What is the compliance of the:
- Lungs
- Chest wall
- Respiratory Sytem
- 200 mL / cm H2O
- 200 mL / cm H2O
- 1/200 + 1/200 = 2/200 = 1/100 –> 100 mL / cm H2O
- Total lung compliance is less than individual compliance of the lungs or chest wall
- Alveolar pressure is […] during inspiration and […] during expiration
- Intrapleural pressure is always […]
- Transpulmonary pressure is always […]
- Negative; Positive
- Negative
- Positive
The flow of air in the trachea is […]
Turbulent
Airway resistance is directly proportional to the length of the airway and inversely proportional to the r4 of the airway. Thus, as radius decreases, resistance increases. What is the clinical signficance of this statement?
Diseases like asthma and bronchitis more heavily affect airways that have high resistance
With respect to lung capacity:
- What is the tidal volume?
- What is the expiratory reserve volume?
- What is the residual volume
- What is functional residual capacity?
- The baseline volume of air that is inspired and expired with each cycle of normal breathing
- The extra volume of air that you could force out with effort that exceeds that of normal breathing
- The extra volume of air that you cannot force out of your lungs no matter how hard you try
- FRC = ERV + RV
What effect does kyphosis and pulmonary fibrosis have on respiratory compliance?
Kyphosis: decrease chest wall compliance
Pulmonary fibrosis: decrease lung compliance
What muscles are active during normal expiration?
TRICK QUESTION - normal expiration is passive
What muscles are active during forced expiration?
Internal intercoastals
External oblique
Internal oblique
Transverse abdominis
Rectus abdominis
What are the forces that need to be overcome during inspiration?
Recoil of lungs
Airway resistance
Compliance
Nitrogen is not normally soluble in blood. Why does scuba diving put someone at increased risk for caisson disease, or nitrogen bubbles in the blood?
Atmospheric pressure increases below sea level, which increases the solubility of nitrogen leading to increased nitrogen in the blood and the potential for nitrogen bubbles in the blood upon return to atmospheric pressure.
What muscles are active during quiet, baseline breathing?
Diaphragm
External intercostals
Why does a compliance curve (change in pressure on x and change in volume on y) display hysteresis for the lungs?
Compliance is defined as the change in volume for a given change in pressure. Lung compliance for inspiration and expiration are different. This is called hysteresis and is probably related to the different effects of surface tension on resistance during inspiration and expiration. Compliance is higher during expiration. As the lungs expand, as alveoli become filled more, the lungs becomes stiffer and compliance decreases.
What effect does emphysema have on ventilation?
In emphysema, there is a reduction in the surface area of the lungs available to participate in gas exchange. As such, patients with this condition have to expand their lungs beyond a normal baseline capacity to obtain enough oxygen. This requires muscles for forced inspiration (SCM and scalenes) so these muscles are enlarged. Breathing is less efficient so there is greater caloric demand during breathing.
Describe what is happening to alveolar and intrapleural pressure during ventilation.
- Alveolar pressure: the difference between alveolar and atmospheric pressure. To produce inspiration, the diagphragm flatens and the ribs rise and spread apart leading to an increase in volume in the chest cavity and a decrease in pressure in the chest wall. Pressure is just a force/area, so this is a force that expands the lungs past their baseline expansion.
- Intrapleural pressure: the lungs naturally want to recoil inward, however the reason they don’t collapse on themselves is because of the pleural space which maintains a negative pressure relative to the lungs at all times. This allows the lungs to remain inflated to some baseline extent at all times. Inspiration is expansion above this baseline, expiration is return to this baseline.
Unlike inhalation, exhalation is a […] process.
Passive –> inhalation requires muscle activation where as exhalation is purely driven by recoiling forces that naturally oppose the movements generated during inhalation
What is the driving force for air to enter the lungs so that pulmonary ventilation can occur?
The body makes the volume of the thoracic cavity larger, creating a decrease in relative pressure compared to the atmosphere which is going to drive air into the lungs. The opposite occurs on expiration.
What function does surfactant serve in the lungs?
Reduce surface tension
Increase compliance
Increase lung stability
Decrease alveolar edema
Prevents collapse of lung at end of expiration
From a mechanical perspective, what does the functional residual capacity represent?
The point at which the inward recoiling forces of the lungs (due to elastic fibers covering the lungs) is in equal opposition to the outward expansion force of the chest wall (wanting to expand the lungs)
What causes the lungs to recoil?
Elastic properties of lung tissue (elastic fibers surrounding lung tissue)
Surface tension at alveolar wall surface
