pulmonary Flashcards
What muscles control expiration?
Expiration is largely passive.
Simply by relaxing, the chest springs back into shape, and expiration can occur without any muscle action.
One can, however, voluntarily exhale forcefully using: external and internal intercostal muscles, the transversus thoracis and innermost intercostal muscles, external oblique, internal oblique and transversus abdominis muscles.
What is the main muscle that controls inspiration? And what are the accessory muscles?
The main muscle is the diaphragm. Contraction and downward motion of the diaphragm causes a (-) pressure in the chest, which draws in air.
The accessory muscles of inspiration: pectoralis major and minor, serratus anterior, sternocleidomastoid, scalene muscles, levatores costarum, serratus posterior superior
How doe Hgb affect gas exchange?
Oxygen is not very soluble in plasma. Most oxygen (about 97% of it) is transported via hemoglobin, which has special oxygen-binding capabilities. It binds to significant quantities of O2 at the alveolar level, even when O2 conc in the alveoli is relatively low. It also releases O2 easily at the tissue level, but in just the right amounts, since too much can cause oxygen toxicity, and too little will not provide enough for the respiratory needs of the tissue. It also releases large quantities of O2 when the tissues really need it.
But how can hemoglobin bind well to oxygen in the alveoli, yet release it easily at the peripheral tissue level?
Oxygen dissociation curve for hemoglobin.
Hgb maintains near saturation (above 90% saturated) even when alveolar O2 decreases from the normal 104mm Hg to 60mm Hg. However, when Hgb encounters the low tissue p02 of the body tissues (normally about 40 mm Hg in interstitial fluid), it readily gives up the oxygen.
How does CO2 leaves the body?
CO2 combines with H2O in RBC forming H2CO3.
The H ion from H2CO3 binds with Hgb forming HCO3.
HCO3 leaves the cell, float around the bld until it reaches the lungs.
Hgb releases the H, it combines with HCO3 to form back to H2O and CO2.
CO2 then is expelled by the lungs.
Some CO2 does combine directly to Hgb forming CARBINOHEMOGLOBIN, which releases its CO2 in the lungs
There is greater release of oxygen by Hgb when..
In terms of pO2, pCO2, pH, temp
<60mm Hg pO2, high pCO2, low pH, and high temp.
What is the rate limiting step in the cell’s oxygen utilization?
Level of ADP.
What neural factors control respiration?
Phrenic nerves (C3,4,5) innervates diaphragm and receives voluntary and involuntary message from respiratory centers (medulla and pons)
CO2 and Water forms what pH in blood?
Weak acids
A slight increase of this pressure potential stimulates the respiration.
PCO2
A moderate increase of pCO2 stimulates respiration much more than does a moderate decrease in p02. So why do we need the O2 response mechanism? Wouldn’t it suffice to just have the pCO2 control mechanism?
In severe pulmonary disease, in which there is poor exchange in both O2 and CO2, the CO2 effect is not enough. The large drop in pO2 then comes into play, having a marked effect in increasing the rate of respiration when the pO2 falls to the 30-60 mm Hg range.
Then why do we need the CO2 control mechanism? Why does it not suffice to just control respiration according to the O2 level? After all, isn’t it really the O2 that the body needs? Shouldn’t 02 levels alone provide the best feedback control?
CO2 control mechanism is actually needed more for the control of blood pH than for control of respiration. Subtle changes in the pC02 can significantly affect pH, so the body needs the fine CO2 control mechanism to control CO2 levels and thus control pH.
Breathing high-pressure oxygen (above atmospheric pressure) can markedly increase the saturation of O2 in the blood, even to toxic levels, not by increased uptake by hemoglobin, but by…
dissolving more of oxygen in plasma.
What do you need to do if you want to increase tissue oxygenation?
Increase the O2 conc in the air being breathed, the Hgb conc, or the blood flow ( as by increasing the CO). Hyperventilation is not good enough.
In diving, the alveolar pressure rises to meet the increasing atmospheric pressure that results with greater depth. The higher pressure causes more N2 to be dissolved, which may cause N2 toxicity. O2 toxicity may also occur.
On rising from a dive, it is important that the diver gradually let out air. otherwise, the lungs will continue to expand against the decreasing outside envi. pressure, thereby causing lung injury.
Normal air outside the body consists about how many percent of 02, N2, CO2 and water?
20% O2
79% N2
0.04% CO2
<1% water
At high altitude, as in low altitudes, the alveolar pressure in normal breathing cannot be more than the atmospheric pressure.
The body’s long range compensation to high altitude may occur initially through hyperventilation, and over weeks to months, through increased tissue vascularity and increased numbers of RBC.
Between CO2 and O2, which of these is more soluble in air and blood?
CO2
What is the normal arterial pO2 level?
95mm Hg
What is the normal arterial pCO2?
40mm Hg
Normal pO2 in peripheral intracellular level
23mm Hg. But not to worry, the cell needs a pO2 of only about 2mm Hg for adequate functioning
It is the amt of air normally inhaled or exhaled with each average breath like the steady tides going in and out.
Tidal volume
What is normal amt of TV?
500 ml
It is the extra amt you could have inhaled after breathing in normally.
Inspiratory reserve volume.
It is the extra amt you could have exhaled after exhaling normally.
Expiratory reserve volume
It is the residual left in the lungs after the strongest expiration.
Residual volume.
If you didn’t have a RV, there would be marked fluctuations in CO2 and O2 content of blood passing thru the lungs during respirations.
It is the amt of air exchanged from the maximal intake to the most forceful expiration.
Vital capacity
VC = ERV + TV + IRV
It is the increase in chest volume with each degree of increase of alveolar pressure.
Compliance.
The greater the increase in lung volume with a given increase in alveolar pressure, the greater the compliance
It refers to the tendency of the respiratory system to spring back to its original shape after expansion. It it simple the reciprocal of compliance.
Elastance.
The greater the elastance, the greater tendency to rebound, the greater the rise in pressure that results from an increase in lung volume.
Functional residual capacity (FRC) = RV + ERV
Inspiratory capacity (IC) = TV + IRV
For the lung, elastance is partly due to elastic tissues in the lungs, but mainly due to…
Surface tension produced by the fluid coating the alveoli (surfactant) which tends to release the resist expansion. Surface tension is normally kept at a reduced level by surfactant
It is the total amount if air in the lung after a forceful inspiration.
Total lung capacity.
TLC = VC + RV
VC and rate of expulsion is (high, low) in restrictive lung disease and airway obstructive disease.
What is an important distinction between these two?
RV is low in restrictive lung disease while it is high in airway obstructive disease.
Another difference is the FRC, wherein it is low in restrictive lung disease, and high in airway obstructive disease.
Which is more difficult (inspiration or expiration) in airway obstructive disease (eg. Asthma, bronchitis, emphysema)?
Expiration. The positive pressure of expiration collapses the respiratory passages.
Which is more difficult (inspiration or expiration) in fixed airway obstruction?
Both
Which is more difficult (inspiration or expiration) in upper airway ( extrapulmo) obstruction?
Inspiration. The negative pressure of inspiration is transmitted thru bronchi and trachea to cause constriction of areas higher up
Oxygen therapy (e.g. using an oxygen tent, face mask or nasal cannula) may be useful in hypoxia secondary to poor atmosphere oxygenation or to poor pulmonary gas exchange from lung disease.
Oxygen administration may help, though, in carbon monoxide poisoning. Carbon monoxide (CO) binds more strongly than does O2 to the same site on the hemoglobin molecule, in effect reducing the number of available RBCs.
When the patient cannot breathe or the effort of breathing becomes too much for the patient, it may be necessary to use a mechanical ventilator. Te ventilator is a positive pressure device.
Normally, inspiration occurs because the chest expansion creates a negative pressure in the alveoli, which results in the influx of air from the atmosphere outside the patient, where the pressure is greater.
Normal quiet breathing is accomplished almost entirely by movement of the diaphragm.
During heavy breathing, extra force is needed achieved mainly by contraction of abdominal muscles, which pushes the abdominal contents upward against the diaphragm, thereby compressing the lungs.
Muscles for inspiration
Diaphragm Scalene muscles Sternocleidomastoid External intercostalis Serrated anterior
Muscles of expiration
Internal intercostalis
Rectus a dominos
It is the pressure of the fluid in the thin space between the lung pleura and the chest wall pleura.
Pleural pressure.
Pleural pressure at the beginning of inspiration
-5 cm H2O
Pleural pressure during inspiration
-7.5cm H2O
