Ventilation and Perfusion Flashcards

A set of 100 flashcards covering ventilation, perfusion, VQ ratios, shunt, dead space, capnography, and clinical respiratory physiology.

Q

A reference to cardiac output or pulmonary capillary blood flow.

Heterogeneous

Characteristics of lungs where different sections may be closed up, anoretic, more ventilated, or more perfused than others.

Alveolar ventilation

The amount of ventilation that takes part in gas exchange, taking into account anatomical and alveolar dead space.

Normal Alveolar Ventilation (V) value

Approximately $4\,\text{liters per minute}$.

Normal Pulmonary Capillary Blood Flow (Q)

Approximately $5\,\text{liters per minute}$.

Normal VQ Ratio

A ratio of $0.8$, calculated by dividing four liters of ventilation by five liters of blood flow ($4/5$).

$$PAO_2$$

Determined by the balance of oxygen added to the alveoli via breathing and oxygen removed by arterial blood.

Shunt

Perfusion without ventilation; a state where blood flows past the alveoli but no air enters for gas exchange.

Decreased VQ Ratio

Occurs when there is more perfusion ($Q$) than ventilation ($V$), often seen in shunt units.

Dead Space

Ventilation without perfusion; air enters the alveoli but there is no blood flow to pick up oxygen or drop off $CO_2$.

Increased VQ Ratio

Occurs when there is more ventilation ($V$) than perfusion ($Q$), as seen in dead space units.

$$2.0$$

A sample calculation of an increased VQ ratio where ventilation is $4$ and perfusion is decreased to $2$.

Effect of Shunt on $PAO_2$

In a shunted alveolar unit, the pressure of alveolar oxygen will decrease as blood continues to remove remaining oxygen.

Effect of Shunt on $PACO_2$

In a shunted alveolar unit, the pressure of alveolar carbon dioxide will increase, potentially equilibrating with venous blood at $46\,\text{mmHg}$.

Effect of Dead Space on $PAO_2$

The pressure of alveolar oxygen increases because it cannot transfer through the AC membrane and there is less occupant $CO_2$.

Effect of Dead Space on $PACO_2$

The pressure of alveolar carbon dioxide decreases toward zero because it is washed out by ventilation but not replenished by blood flow.

Pulmonary Embolism

A blood clot in the pulmonary system that causes a dead space unit (ventilation without perfusion).

Atherosclerosis

A condition that can cause partial or complete obstruction of pulmonary artery or arterioles, leading to increased VQ.

Extrinsic Pressure

Pressure on pulmonary vessels from mechanical ventilation or pleural effusion that can compress capillaries and stop blood flow.

Emphysema

A disease that destroys the lung parenchyma and supports structures, causing pulmonary capillaries to disintegrate.

Hypovolemia

A condition like profuse bleeding that leads to decreased cardiac output and a shift toward dead space ventilation.

Wasted Ventilation

Another name for dead space ventilation, where air does not participate in gas exchange due to lack of perfusion.

Systemic Blood in Shunt Units

Characterized by low oxygen ($PO_2$), high $CO_2$, and a low pH (acidosis).

Absolute Shunt

An extreme case where there is perfusion but zero or very low ventilation.

Restrictive Lung Disorders

Examples of disorders that can lead to a decrease in the VQ ratio.

Hypoventilation

A decrease in respiratory rate (e.g., from $12$ to $3$ breaths per minute) that reduces the introduction of new air into the alveoli.

Zone 1

The upper part of the lung characterized by a high VQ ratio ($3.0$), more ventilation, and less perfusion.

Zone 2

The middle part of the lung where ventilation and perfusion are relatively equal and the VQ ratio is around $0.8$.

Zone 3

The base of the lung characterized by a decreased VQ ratio ($0.6$), more perfusion, and less ventilation.

Mixed End-Capillary Oxygen Content

The result of blood from all lung zones mixing together to produce normal arterial blood gas values.

Internal Respiration

Gas exchange between the systemic capillaries and the cells.

Respiratory Quotient (RQ)

The ratio of the volume of $O_2$ consumed to the volume of $CO_2$ produced internally.

$$250\,\text{mils}$$

The normal amount of oxygen consumed per minute under resting conditions.

$$200\,\text{mils}$$

The normal amount of carbon dioxide produced per minute under resting conditions.

Normal RQ Value

Calculated as $200/250$, resulting in $0.8$.

Respiratory Exchange Ratio (RR or RER)

The ratio of gas exchange between the pulmonary capillaries and the alveoli (external respiration).

Nonsteady State Conditions

Situations like heavy exercise or hyperventilation where RR/RER may differ from RQ.

Capnography

The rapid and continuous noninvasive monitoring of a patient's exhaled carbon dioxide levels.

Capnogram

The graphic display or waveform of a patient's exhaled carbon dioxide levels.

End-Tidal $CO_2$ ($ETCO_2$)

The level of carbon dioxide at the end of an exhaled breath, normally $35-45\,\text{mmHg}$.

$$5\%$$

The normal percentage of carbon dioxide found in end-tidal air.

$ETCO_2$ to $PaCO_2$ Gap

The normal difference between end-tidal and arterial carbon dioxide, typically $2-3\,\text{mmHg}$.

ACLS

Advanced Cardiac Life Support, where end-tidal $CO_2$ is used to monitor ET tube placement and CPR quality.

Phase 1 (Capnogram)

The baseline phase representing inspiration where carbon dioxide is zero.

Phase 2 (Capnogram)

The expiratory upstroke representing anatomical dead space mixing with alveolar air.

Phase 3 (Capnogram)

The alveolar plateau representing gas that has fully participated in gas exchange.

Sharp Downstroke

A feature of the capnogram indicating the beginning of inspiration.

Chronic Bronchitis

A pulmonary disorder that decreases the VQ ratio and increases end-tidal $CO_2$.

Cardiac Arrest Effect on $ETCO_2$

Causes an increase in VQ and a decrease in end-tidal $CO_2$ due to lack of perfusion.

Hyperventilation Effect on $ETCO_2$

Decreases end-tidal $CO_2$ because carbon dioxide is 'washed off' rapidly.

Hypoventilation Effect on $ETCO_2$

Increases end-tidal $CO_2$ because gas is not being cleared effectively from the lungs.

Shark Fin Waveform

A capnogram shape characteristic of a bronchospasm.

ROSC

Return of Spontaneous Circulation, indicated by a sudden rise in end-tidal $CO_2$ from $15$ to $50\,\text{mmHg}$.

Refractory Hypoxemia

Hypoxemia that does not improve significantly with increases in $FiO_2$.

Intrapulmonary Shunt Treatment

Requires adding pressure (like CPAP or PEEP) to pop open collapsed alveoli.

VQ Mismatch

The most common cause of hypoxemia and chronic hypercapnia; the value is between $0$ and $1$.

Hypercapnia in VQ Mismatch

Requires an extensive mismatch before occurring because $CO_2$ diffuses very easily.

Body Position and VQ Matching

The practice of using gravity to align perfusion with the best-ventilated portions of the lung.

Dependent Region

The lowest region of the body where blood tends to aggregate due to gravity.

'Good Lung Down'

The clinical rule for positioning a patient with unilateral lung disease to optimize VQ matching.

Left Extensive Pneumonia Positioning

Positioning the patient with the right lung down (good lung down) and left lung up (bad lung up).

Supine Position Risks

Includes gravitational pressure of the heart and abdominal organs compressing the lungs, leading to alveolar collapse.

Prone Position

Lying on the stomach; used in the ICU to improve VQ matching by decreasing compressive effects on the lungs.

Anatomical Dead Space Calculation

Estimated as $1\,\text{mil per pound}$ of ideal body weight.

Auto-PEEP

A phenomenon that happens on a ventilator that can lead to increased dead space.

Hypoxic Pulmonary Vasoconstriction (HPV)

A homeostatic mechanism where pulmonary vessels constrict around low-oxygen alveoli to shunt blood to better-aerated areas.

Alveolar Duct Constriction

A compensatory response to low $PACO_2$ in dead space units to redirect ventilation.

$A-a$ Gradient

The difference between alveolar and arterial oxygen levels; normal room air value is $7-14\,\text{mmHg}$.

$A-a$ Gradient on $100\%$ Oxygen

Normal values can range from $50-60\,\text{mmHg}$.

$a/A$ Ratio

The percentage of alveolar oxygen that successfully transfers to the arterial blood; lower limit of normal is $75\%$.

$P/F$ Ratio

A measure of oxygen efficiency calculated as $PaO_2$ divided by $FiO_2$.

ARDS Indicator

A $P/F$ ratio lower than $250$, suggesting significant lung damage.

Clinical Shunt Equation

An equation used to calculate the percentage of shunt that specifically accounts for diffusion deficits.

$< 10\%$ Shunt Fraction

A shunt percentage compatible with normal lung function.

$20-29\%$ Shunt Fraction

A significant abnormality requiring ventilatory support and PEEP.

$> 30\%$ Shunt Fraction

A life-threatening condition signifying major oxygenation failure.

Venous Admixture

The mixing of under-oxygenated blood with arterial blood, often seen in VQ mismatches.

Thebesian Veins

Veins that drain into the left atrium, contributing to a normal anatomical right-to-left shunt.

CPAP

Continuous Positive Airway Pressure; used to provide pressure to treat intrapulmonary shunts.

Ventricular Septal Defect (VSD)

An abnormal hole in the wall between the heart's ventricles causing an anatomical shunt.

Atrial Septal Defect (ASD)

An abnormal hole in the wall between the heart's atria causing an anatomical shunt.

Parenchyma

The functional tissue of the lung, which is destroyed in conditions like emphysema.

Capillary Blood Flow in Zones

Blood flow is highest in the bases (Zone 3) due to gravity's effect on blood weight.

Ventilation in Zones

Ventilation is relatively higher in the upper lungs (Zone 1) because the alveoli are already stretched open.

$PACO_2$ in Zone 1

Approximately $30\,\text{mmHg}$, lower than the arterial average.

$PAO_2$ in Zone 1

Approximately $130\,\text{mmHg}$, higher than the arterial average.

$PAO_2$ in Zone 3

Approximately $80\,\text{mmHg}$, lower than the arterial average.

$PACO_2$ in Zone 3

Approximately $46\,\text{mmHg}$, higher than the arterial average.

Inspiratory $CO2$ baseline

The measurement in capnography during inspiration which should be effectively zero.

$ETCO_2$ during sedation

Monitoring used to detect respiratory depression from pain medications or opioids.

Sudden loss of $ETCO_2$

Indicates a total loss of circulatory function (coding) or a disconnected ET tube.

Bronchospasm Capnogram

Often presents as a 'shark fin' shape due to slowed expiration.

CPR Quality Target

The goal is to keep end-tidal $CO_2$ above $10\,\text{mmHg}$ during compressions.

Confirmed Tracheal Intubation

Indicated by a sudden rise in $ETCO_2$ and a consistent waveform.

Esophageal Intubation Indicator

The absence of a CO2 waveform during capnography after placing an ET tube.

Hyperthermia monitoring

Using $CO_2$ levels to detect increased metabolism from fever or infection.

Refractory Hypoxemia Treatment

Requires pressure (CPAP/BiPAP) to increase alveolar surface area or pop open units.

VQ Ratio Limit

In a VQ mismatch, the ratio is typically less than $1.0$ but greater than $0$.

Mixed Venous $CO_2$

Typically $46\,\text{mmHg}$; the pressure $CO_2$ reaches in a shunted alveolar unit.