Respiratory Ventilation & Atmospheric Physics Study Guide

Flashcards covering the mechanics of respiratory ventilation, atmospheric gas laws, pressure conversions, and the phases of the respiratory cycle.

How is ventilation distinguished from respiration in a clinical context?

Ventilation is the mechanical movement of air in and out of the lungs to bring in $O_2$ and remove $CO_2$. Respiration refers to actual gas exchange, occurring externally between alveoli and pulmonary capillaries, and internally between systemic capillaries and tissues.

What is the specific composition of atmospheric air by percentage of Nitrogen, Oxygen, and Carbon dioxide?

Nitrogen makes up $78\%$, Oxygen makes up $20.95\%$ (approximately $21\%$), and Carbon dioxide accounts for $0.03\text{--}0.04\%$.

How does atmospheric pressure and oxygen availability change with an increase in altitude?

Total atmospheric pressure decreases as altitude increases because there is less weight of gas molecules above. While the oxygen percentage remains at $21\%$, the lower total pressure results in less oxygen being available for diffusion.

What is the formula for Dalton's Law of Partial Pressures, and what are the partial pressures for Oxygen and Nitrogen at standard sea level?

The formula is $P_{gas} = F_{gas} \times P_B$. At a standard atmospheric pressure of $760\,mmHg$ ($760\,torr$), $PO_2 = 160\,mmHg$ and $PN_2 = 593\,mmHg$.

What are the conversion values between $mmHg$ and $cmH_2O$?

$1\,mmHg = 1.36\,cmH_2O$ and $1\,cmH_2O = 0.74\,mmHg$. For example, $5\,mmHg = 6.8\,cmH_2O$ and $5\,cmH_2O = 3.7\,mmHg$.

In clinical baseline terms, what is the actual pressure equivalent of a negative pressure of $-8\,mmHg$ and a positive pressure of CPAP 10?

Using the atmospheric baseline of $760\,mmHg$ (0), $-8\,mmHg$ equals an actual pressure of $752\,mmHg$, and CPAP 10 equals $770\,torr$.

State Boyle's Law and explain its relationship to gas flow.

Boyle's Law is $P_1 V_1 = P_2 V_2$. It states that pressure and volume are inversely related. Gas flow occurs as air moves from areas of high pressure to areas of low pressure.

Which nerve innervates the diaphragm and what are its origin levels?

The Phrenic nerve, which originates from spinal levels $C3, C4, \text{ and } C5$. This is often remembered by the phrase "$C3, 4, 5$ keep the diaphragm alive."

Describe the mechanical changes that occur during active inspiration.

The diaphragm contracts downward, causing thoracic volume to increase. This volume increase leads to a decrease in pressure, allowing air to flow into the lungs.

What characterizes the passive phase of expiration?

The diaphragm relaxes upward and lung recoil occurs, which decreases thoracic volume and increases pressure, forcing air out of the lungs.

Why is there no airflow during the end-inspiration and end-expiration phases of the respiratory cycle?

Because the pressures between the atmosphere and the lungs equalize at these points.

What is Functional Residual Capacity (FRC) and what are its two primary functions?

FRC is the volume of air that remains in the lungs after a normal expiration. Its primary functions are to prevent alveolar collapse and to save the energy that would otherwise be required to reopen the lungs.