Pulmonary Mechanics: Compliance Flashcards
when does positive pressure inflate the lungs?
when pressure is applied externally as in the case of a respirator
what is eupnea?
normal quiet breathing
how does air leave the lungs?
it is either forced out by muscular contraction or it is passively expelled by the elasticity of the lungs and rib cage
what exerts the force to inspire during normal breathing?
contraction of the diaphragm increases the volume of the intrapleural space which decreases the pressure and causes the lung to inflate
what kind of pump is the lung?
a negative pressure pump
what is the difference of pressure between the atmosphere and intrapleural space during relaxation?
pulmonary is less by 5 cm H2O
when is a pulmonary pressure negative? is it actually negative?
when it is less than atmospheric pressure
it is not actually negative but the negative number is the difference from atmospheric pressure
why does the lung collapse in the event of a puncture wound to the thoracic cavity? what is this called?
because the pressure inside the cavity equilibrates with the atmosphere and puts positive pressure outside the lung. called a pneumothorax
what is the only respiratory muscle that must contract to breathe?
the diaphragm
how far down can the diaphragm move in inspiration?
up to 10 cm
what is hyperpnea?
active breathing
what muscles are involved with inspiration during hyperpnea?
external intercostals
what are the role of the sternocleidomastoid and scalene muscles during inspiration?
to reduce resistance to airflow during strenuous exercise
at what point is expiration aided?
when ventilation exceeds 40 L/min
which muscles aid in expiration?
internal intercostals , rectus abdominus, external obliques, internal obliques and the transversus abdominus
what is tachypnea?
more rapid breathing than normal
what is the ventilation during eupnea and hyperpnea?
7.5 L/min in eupnea
<120 L/min in hyperpnea
what leads to respiratory acidemia and respiratory alkalosis?
acidemia- hypoventilation
alkalosis- hyperventilation
what are the three important pressures when talking about respiration?
atmospheric pressure, intrapleural pressure and alveolar pressure
how does alveolar pressure vary along the breathing cycle?
it is less than atmospheric pressure during inspiration and greater during expiration
how thick is the intrapleural space and how much liquid does it hold?
it is 10 microns thick and holds a few mL of volume
how is intrapleural pressure estimated?
by swallowing a balloon into the intrathoracic esophagus. the pressure on the balloon represents the intrapleural pressure
when is the external pressure on the chest wall greater than the atmospheric pressure?
when there is a weight placed on the chest
what are the transmural pressures involved in breathing?
chest wall pressure (P intrapleural-P atm) lung pressure (P alveoli- P intrapleural) total transmural pressure (P alveoli- P atm)
what do the transmural pressures do?
set the degree of inflation of the first term in the equation
what are outwardly directed transmural pressures regarded as?
positive
what is the total transmural pressure pressure at rest?
0
what is the lung pressure and chest wall pressure at rest?
lung- positive
chest wall- negative
why is the lung pressure always positive/
to maintain inflation
what is static compliance of the lung?
determines what particular volume the lung and chest wall will assume for a given transmural pressure
what two things must be measured to determine lung compliance in a patient? how is this done?
volume- a spirometer is used during the inhale to determine lung volume
pressure- at a certain lung volume, the respiratory muscles are relaxed and the pressure is measured with a esophageal balloon
how is lung volume maintained in the relaxed state when measuring pressure to determine compliance?
a weight is placed on the spirometer to prevent the air from escaping the lungs when the glottis is open
what is the compliance near the resting position of the lung?
about 0.1 L/cm H2O
what pressure must be used to calculate lung compliance?
alveolar pressure
how do the compliances of the lungs add up? what implication does this have when describing the compliance of both lungs?
1/Ct=1/C1 + 1/C2
the compliance of both lungs is 1/2 of an individual lung
how is compliance calculated?
as a change in volume over a change pressure (need to take multiple data points)
how do the elastic forces of the lung and the chest differ?
the lung only has elastic force inwards but the chest has elastic force directed in both directions
when the lungs and chest are in the relaxed position, what are the elasticity forces?
the elastic recoil of the lung equals the elastic recoil of the chest wall
how does the compliance of the lungs change with volume?
it is lower at larger lung volumes
what is the lung volume when Pt equals zero?
the functional residual capacity
what force acts on the lungs to return the volume to functional residual capacity after forced expiration?
recoil of the chest wall only (lungs have no contribution)
what happens to intrapleural pressure when the muscles are relaxed and a weight is placed onto the spirometer?
it becomes positive
what happens to intrapleural pressure with a weighted spirometer when more air is inspired?
it becomes more positive
give an example of disease with increased lung compliance and one where it decreases?
increased-emphysema
decreased-pneumoconiosies (fibrosis)
what changes when compliance of the lung changes?
total lung capacity and functional residual capacity
why does compliance increase in emphysema?
neutrophils that are attracted to the lung secret proteases. the inhibitors for these proteases are inactivated by cigarette smoke
what is the effect of surfactant on lung surface tension and compliance?
it lowers surface tension and increases compliance
how does a the compliance of a saline filled lung compare to an air filled lung?
there is an increase in compliance
what forces are eliminated when filling the lung with saline?
eliminates recoil pressure due to surface tension and only leaves the component due to elastic fibers
how does the compliance of a lung without surfactant compare to one with surfactant?
no surfactant reduces compliance
what is respiratory distress syndrome?
lung immaturity in newborns causing collapse due to a deficiency in pulmonary surfactan
if there are two bubbles of varying sizes with the same surface tension, which will have a larger internal pressure?
the smaller bubble
what happens when there are two alveoli of different sizes next to each other without surfactant? with surfactant?
without- the smaller alveolus empties into the larter
with-the larger alveolus has pressure equal to the smaller
why does surface tension increase with radius when involving surfactant?
becuase the larger area dilutes the surfactant
