Chapter 8 Ventilation-Perfusion Relationships

Flashcards covering the concepts of ventilation-perfusion ratios, gas exchange balances, and the effects of various respiratory disorders as presented in Chapter 8 of Des Jardins' Cardiopulmonary Anatomy & Physiology.

Ventilation-Perfusion Ratio ($\dot{V}/\dot{Q}$ ratio)

The ratio of alveolar ventilation ($\dot{V}$) to pulmonary capillary blood flow ($\dot{Q}$); ideally, each alveolus should receive the same amount of both.

Normal Alveolar Ventilation

The normal volume of air reaching the alveoli per minute, which is approximately $4\,L/min$.

Normal Pulmonary Capillary Blood Flow

The normal volume of blood flow through the pulmonary capillaries per minute, which is approximately $5\,L/min$.

Average Overall $\dot{V}/\dot{Q}$ Ratio

The normal average ratio of ventilation to blood flow is calculated as $4:5$, or approximately $0.8$.

$\dot{V}/\dot{Q}$ Ratio in Upright Lung Apices

In the upper portions of the lungs, alveoli receive a moderate amount of ventilation and little blood flow, resulting in a ratio higher than $0.8$.

$\dot{V}/\dot{Q}$ Ratio in Lower Lung Regions

In the base of the lung, ventilation is moderately increased but blood flow is greatly increased due to gravity, resulting in a ratio lower than $0.8$.

Alveolar Oxygen Pressure ($P_AO_2$)

Determined by the balance between the amount of oxygen entering the alveoli and its removal by capillary blood flow; the normal average is approximately $100\,torr$.

Alveolar Carbon Dioxide Pressure ($P_ACO_2$)

Determined by the balance between the amount of carbon dioxide that diffuses into the alveoli from capillary blood and its removal by ventilation; the normal average is approximately $40\,torr$.

Vascular Obstructions affecting $\dot{V}/\dot{Q}$

Disorders like pulmonary emboli, atherosclerosis, or collagen disease that increase the ratio by obstructing the pulmonary artery or arterioles.

Extrinsic Pressure sources

Factors that increase the $\dot{V}/\dot{Q}$ ratio by compressing pulmonary vessels, such as pneumothorax, hydrothorax, or the presence of a tumor.

Destruction of Pulmonary Vessels

A condition such as emphysema that leads to an increased $\dot{V}/\dot{Q}$ ratio by reducing the available vascular bed.

Obstructive Lung Disorders

Conditions like emphysema, bronchitis, and asthma that are categorized as pulmonary disorders affecting the $\dot{V}/\dot{Q}$ ratio.

Restrictive Lung Disorders

Conditions such as pneumonia, silicosis, and pulmonary fibrosis that result in $\dot{V}/\dot{Q}$ ratio changes.

Shunt Unit

An alveolar unit classification associated with specific $\dot{V}/\dot{Q}$ ratio changes caused by respiratory disorders.

Dead Space Unit

An alveolar unit classification associated with specific $\dot{V}/\dot{Q}$ ratio changes where ventilation occurs without adequate perfusion.

Respiratory Quotient (RQ)

A metric defined as the ratio of metabolic carbon dioxide production to oxygen consumption.

Respiratory Exchange Ratio (R)

A metric defined as the ratio of carbon dioxide elimination to oxygen uptake.