Respiratory Mechanics Overview

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Questions and Answers

What happens to the thoracic volume during the start of inspiration?

Thoracic volume increases (correct)

Thoracic volume rapidly fluctuates

Thoracic volume decreases

Thoracic volume remains constant

What does a low compliance in the lungs indicate?

Unchanged lung structure

Over-inflation of lungs

Restrictive pulmonary disease (correct)

Easy lung expansion

What is the role of elastic connective tissue in the lungs?

Promotes lung expansion during inspiration

Facilitates gas exchange in alveoli

Increases lung compliance

Assists in lung recoil during expiration (correct)

What effect does an inflammatory response by macrophages have on the lungs?

Decreases compliance Signup and view all the answers

What happens to the pressures at the end of a single expiration?

Pressures become equalized Signup and view all the answers

What characterizes water's behavior at the alveolar surface?

Water exerts inward forces aiding elastic recoil Signup and view all the answers

What occurs when the transpulmonary pressure gradient is low?

More effort is needed to inspire Signup and view all the answers

How does high compliance affect the lungs?

Lungs expand too easily Signup and view all the answers

What effect does bronchoconstriction have on airway resistance?

Increases airway resistance Signup and view all the answers

Which mechanism primarily stimulates bronchodilation?

Adrenaline acting on B2-receptors Signup and view all the answers

What occurs concurrently when the heart supplies deoxygenated blood to the lungs faster than gaseous exchange can occur?

Decreased airway resistance and vasoconstriction Signup and view all the answers

Which blood gas measurement indicates a normal arterial CO2 level?

40 mmHg Signup and view all the answers

What is the definition of hypoxia?

Too little oxygen Signup and view all the answers

What process involves O2 diffusing from the bloodstream into the cells?

Cellular respiration Signup and view all the answers

Which type of hypoxia is caused by reduced blood flow?

Ischemic hypoxia Signup and view all the answers

What is the normal arterial pH range?

7.35 to 7.45 Signup and view all the answers

What role does surfactant play in the lungs?

Decreases surface tension in smaller alveoli. Signup and view all the answers

According to the Law of LaPlace, how does the pressure relate to the radius of a bubble?

Pressure increases as radius decreases. Signup and view all the answers

Which factor affects airway resistance according to Poiseuille’s Law?

Length of the airways. Signup and view all the answers

What is the relationship between ventilation and perfusion at the apex of the lung?

Ventilation exceeds perfusion. Signup and view all the answers

What role does the diaphragm play in increasing thoracic volume during inspiration?

It contracts and flattens, contributing to 60-75% of volume change. Signup and view all the answers

Which muscles are primarily responsible for moving the rib cage during the inspiration phase?

Sternocleidomastoids and intercostal muscles. Signup and view all the answers

What happens to the intrapleural pressure at the base of the lung compared to the apex?

It is less negative at the base. Signup and view all the answers

What causes air to flow into the lungs during inspiration?

Intra-alveolar pressure being lower than atmospheric pressure. Signup and view all the answers

How does increased airway resistance affect airflow?

It necessitates more work to maintain airflow. Signup and view all the answers

During expiration, how does the thoracic volume decrease?

By relaxation of the diaphragm and gravity acting on the rib cage. Signup and view all the answers

What contributes to alveolar stability through elastic recoil?

Alveolar interdependence. Signup and view all the answers

What physiological change occurs during forced expiration?

Accessory expiratory muscles contract, increasing the intra-alveolar pressure. Signup and view all the answers

What is true about the compliance of the lungs at rest?

Gravity impacts lung compliance differently at various locations. Signup and view all the answers

What happens to the lungs during a pneumothorax?

The lungs collapse due to equalization of pressure inside and outside. Signup and view all the answers

What is the primary role of the transmural pressure gradient in lung function?

To ensure that lungs expand to their maximum capacity. Signup and view all the answers

How does Boyle's Law relate to the process of breathing?

It states that an increase in volume results in a decrease in pressure. Signup and view all the answers

What is the primary factor affecting gas exchange efficiency in healthy individuals?

Concentration gradient Signup and view all the answers

Which of the following is NOT a factor affecting the adequacy of oxygen reaching the alveoli?

Increased tissue oxygen demand Signup and view all the answers

What percentage of oxygen is carried by hemoglobin in the blood?

98% Signup and view all the answers

Which formula estimates oxygen consumption per blood flow?

Q(O2) = Cardiac output x (Arterial O2 - Venous O2) Signup and view all the answers

What component of hemoglobin allows it to bind oxygen?

Heme group with an iron atom Signup and view all the answers

Which statement is true regarding gas diffusion in the lungs?

Diffusion is most rapid over short distances. Signup and view all the answers

What happens to the oxygen-hemoglobin binding reaction when O2 concentration decreases?

O2 unbinds from hemoglobin. Signup and view all the answers

Which of the following affects the transfer of gases between alveoli and pulmonary capillaries?

Surface area Signup and view all the answers

Study Notes

Respiratory Mechanics: Inspiration

Inspiration is initiated by a momentary pause between breaths.
Thoracic volume increases, causing intra-alveolar pressure (PIAP) to decrease below atmospheric pressure (Patm).
Air flows into the lungs down the pressure gradient.
PIAP reaches its lowest value before equalizing with Patm.
Lung volume is at its maximum.

Respiratory Mechanics: Expiration

Expiration begins at maximum lung volume with PIAP equal to Patm.
Thoracic volume decreases, increasing PIAP above Patm.
Air flows out of the lungs.
Pressures equalize at the end of the respiratory cycle.
Pulmonary elasticity facilitates the recoil of the lungs.

Lung Compliance and Elastic Recoil

Compliance refers to the effort required to stretch the lungs. Low compliance implies difficulty in stretching.
High compliance means the lungs stretch too easily, characteristic of restrictive pulmonary disease.
Elastic recoil is the tendency of the lungs to return to their resting volume after being stretched. It's influenced by connective tissue and alveolar surface tension.
Loss of elastic tissue increases compliance.
Alveolar surface tension, facilitated by water molecules, aids in elastic recoil but reduces compliance.

Respiratory Muscles and Thoracic Volume Change

Approximately 60-75% of volume change during inspiration is due to diaphragm contraction.
The remaining 25-40% is due to rib cage movement by external intercostal muscles.
During quiet expiration, inspiratory muscle relaxation passively decreases thoracic volume.
Active expiration (forced) involves accessory muscles contracting to further increase intra-alveolar pressure.

Pneumothorax

A puncture in the pleural membrane causes air to enter the pleural cavity.
Intra-alveolar pressure and intrapleural pressure equalize with atmospheric pressure.
The transmural pressure gradient is lost, leading to lung collapse and outward expansion of the thoracic wall.

Alveolar Stability: Surfactant and Interdependence

Surfactant lowers surface tension in alveoli, preventing collapse, particularly in smaller alveoli. It's composed of phospholipids and proteins.
Alveolar interdependence, the interconnectedness of alveoli, contributes to elastic recoil and prevents alveolar collapse. The Law of Laplace describes the relationship between pressure, surface tension, and alveolar radius.

Ventilation-Perfusion Ratio (V/Q)

V/Q ratio varies across the lung due to gravity. Apex has higher V/Q, while the base has lower V/Q.
Ventilation exceeds perfusion in the apex.
Perfusion exceeds ventilation in the base.

Gas Exchange and Transport

Gas exchange occurs at the alveolar-capillary interface and between blood and tissues.
Oxygen is transported dissolved in plasma and bound to hemoglobin (Hb).
Carbon dioxide is transported dissolved, bound to Hb, and as bicarbonate (HCO3-).
Optimal gas exchange requires adequate oxygen delivery to alveoli, and efficient diffusion across the alveolar-capillary membrane.

Factors Affecting Alveolar Gas Exchange

Factors influencing alveolar gas exchange include adequate O2 reaching the alveoli (affected by altitude, humidity, ventilation), and effective diffusion across the alveolar-capillary membrane (affected by surface area, diffusion distance, and barrier permeability).

Diffusion

Diffusion rate is proportional to surface area, concentration gradient, and barrier permeability, and inversely proportional to distance.

Oxygen Transport and Hemoglobin

Hemoglobin (Hb) is a protein with four subunits, each capable of binding one oxygen molecule.
Oxygen binding to Hb follows an equilibrium reaction, affected by the partial pressure of oxygen (PO2).
The Fick equation estimates oxygen consumption based on cardiac output and arterial-venous oxygen difference.

Factors Affecting O2-Hb Binding

PO2 in plasma is the primary determinant of Hb saturation.
Other factors influencing O2-Hb binding include pH, temperature, and 2,3-bisphosphoglycerate (2,3-BPG).

Control of Airway Resistance and Perfusion

Airway resistance is determined by airway diameter, viscosity, and length. Poiseuille's Law describes this relationship.
Bronchoconstriction increases resistance, while bronchodilation decreases it.
Changes in airway resistance and perfusion work together to maintain adequate gas exchange. For example, a local decrease in alveolar O2 stimulates vasoconstriction and bronchodilation.

Normal Blood Gas Values

Arterial PO2: ~95 mmHg
Venous PO2: ~40 mmHg
Arterial PCO2: ~40 mmHg
Venous PCO2: ~46 mmHg
Arterial pH: ~7.4
Venous pH: ~7.37

Hypoxia and Hypercapnia

Hypoxia is insufficient oxygen.
Hypercapnia is elevated carbon dioxide levels. Different types of hypoxia include hypoxic, anemic, ischemic, and histotoxic.

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Description

Explore the fundamentals of respiratory mechanics, including the processes of inspiration and expiration. Understand how thoracic volume changes affect intra-alveolar pressure and learn about lung compliance and elastic recoil in respiratory health. This quiz covers key concepts essential for studying respiratory physiology.