Respiratory Physiology

Mechanics of Breathing

4 distinct events Pulmonary ventilation: air is moved in and out of the lungs External respiration: gas exchange between blood and alveoli Respiratory gas transport: CV system transports oxygen and carbon dioxide between lungs & tissues Internal respiration: gas exchange between blood & tissue cells

Cellular respiration: actual use of oxygen & production of carbon dioxide in the cells to make energy: C6H12O6 + 9O2  6CO2 + 6H2O

Pulmonary ventilation: Depends on pressure changes Breathing Inspiration = moving air into the lungs Expiration = moving air out of lungs Breathing Mechanism Animation

Pressure Relationships Intrapulmonary pressure Pressure within the alveoli (lungs) Changes with phases of breathing Always equalizes itself with atmospheric pressure Intrapleural pressure Pressure within intrapleural space Always 4 mmHg less than intrapulmonary pressure

Lung Pressure Atelectasis – term for lung collapse pneumothorax – air in the intrapleural space due to trauma causing lung collapse Pneumothorax

Atelectasis

Inspiration Main inspiratory muscles Diaphragm & external intercostals Thoracic dimensions change to increase volume of thoracic cavity by 0.5 liters Intrapulmonary pressure drops 1-3 mmHg and air rushes in for normal quiet inspiration A deep forced inspiration requires activation of accessory muscles

Expiration A passive process dependent on natural lung elasticity The lungs recoil, alveoli compress, volume decreases,, intrapulmonary pressure rises, gas outflows to equalize the pressure with atmospheric pressure Forced expiration requires contraction of abdominal muscles

Respiratory Sounds Bronchial sounds: produced by air rushing through trachea & bronchi Vesicular sounds: produced by air filling lungs Bronchial vs. Vesicular

Respiratory Sounds Wheezing: whistling sound Rales: rasping sound Wheezing vs rales

Physical factors influencing Pulmonary ventilation can be influenced by 4 physical factors Respiratory passage resistance Lung compliance Lung elasticity Alveolar surface tension forces

Respiratory passage resistance Friction as air moves through passages Smooth muscle bronchoconstriction Disorders such as asthma Local accumulations of mucus, infectious material, and tumors will also cause the air flow to be reduced

Asthma

Lung compliance The ease with which lungs can readily expand Affected by the elasticity of the lungs and the thoracic cage Diminished by 2 main factors: Fibrosis of the lung tissue Ossification and/or muscle paralysis impairs flexibility of the thoracic cage

Lung fibrosis

Lung Elasticity Essential for normal expiration Emphysema: tissue becomes less elastic and more fibrous (alveolar walls break down and surface area is lost)

Alveolar Surface Tension Forces Surface tension – molecules of liquid hold together with hydrogen bonds Surfactant – substance which interferes with cohesion of water molecules so less energy is needed to expand the lungs IRDS – Infant Respiratory Distress Syndrome

Gas Exchanges in the Body

Gas exchanges occur: Between the blood and the alveoli AND Between the blood and the tissue cells Takes place by simple diffusion Depends on pressures of oxygen & carbon dioxide that exist on opposite sides of the exchange membrane Always move from high to low pressures

Factors influencing internal & external respiration

Factors that Influence: Ratio Relationships Partial pressure gradients and gas solubilities Oxygen = has low solubility but steep partial pressure gradient Carbon dioxide = has solubility ~20x greater than oxygen but very low partial pressure gradient

Factors influencing internal & external respiration Thickness of respiratory membranes 0.5 to 1.0 micrometers edematous (swollen) tissue can be caused by congestion and pneumonia - hinders diffusion Hypoxia = oxygen deprivation

Edematous lung tissue

Factors influencing internal & external respiration Surface Area 50-70 square meters for gas exchange

Factors influencing internal & external respiration Surface Area Emphysema Walls of alveoli break down Less surface area to volume ratio

Control of Respiration

Nerves The two nerves that transmit to the respiratory muscles are the phrenic and intercostal nerves The neural centers that control respiration rate & depth are located in the medulla & pons Irritation to phrenic nerve is responsible for hiccups (spasm of diaphragm muscle)

Breathing Terms Eupnea = normal respiration rate Approx 12-15 breaths per min Hyperpnea = higher than normal rate Apnea = No rate Dyspnea = general term for abnormal rate Physical factors, conscious control, emotional factors, and chemical factors all influence rate & depth

Hyperventilation Respiratory alkalosis results Deep & rapid respiration Too much CO2 is vented out of the body Respiratory alkalosis results

Hyperventilation treatment Trap CO2 and rebreathe it – building back up the levels of CO2 until they are normal again.

Hypoventilation Slow & shallow respiration (usually caused by a disease process) Not adequate expiration so CO2 is not vented out of the body

Disorders of Respiratory System

COPD Chronic Obstructive Pulmonary Disorder A group of disorders that block airflow & make breathing difficult

Chronic Bronchitis chronic mucus production Impairs ventilation and gas exchange Reduction of airway diameter Causative factors: cigarette smoking

Emphysema Alveolar walls collapse = loss of surface area so less gas diffusion Causative factor: cigarette smoking

4 features in common Both emphysema and chronic bronchitis have: Smoking history Dyspnea Coughing & pulmonary infections Will develop respiratory failure, hypoxia, acidosis

Lung Cancer Basic Info 1/3 of all cancer deaths are due to lung cancers 90% have a smoking history Metastasizes very rapidly due to vascularity of lungs

Metastasis

3 types of lung cancer Squamous cell carcinoma Adenocarcinoma Small cell carcinoma

Squamous cell carcinoma Begins in larger bronchi & bronchioles Forms masses that have bleeding cavities within them

Adenocarcinoma Nodules that develop in peripheral areas of lung Develop from alveolar cells & bronchial glands

Small cell carcinoma Originate in primary bronchi Grow into small grape like clusters in mediastinum Very aggressive cancer

Treatments Resection of diseased portion of lung (thoracotomy) Radiation therapy Chemotherapy

Lung Resection

Cystic Fibrosis Genetic disorder – recessive Causes oversecretion of thick mucus that clogs respiratory passages & other organs Impairs food digestion by clogging ducts that secrete enzymes

Cystic Fibrosis

SIDS - Sudden Infant Death Syndrome Sudden, unexplained death of an infant less than 1 year old Possibly caused by brain abnormalities that control respiration, heart rate, or consciousness Environmental factors to reduce risks – sleep on back not on stomach, firm crib with no blankets or stuffed animals or pillows Sudden infant death syndrome (SIDS): Risk factors - MayoClinic.com

Asthma Bronchoconstriction of passageways in response to allergen, temperature changes, & exercise Can be managed with medication