Respiratory Flashcards
Define the following volumes:
- Tidal volume
- Inspiratory reserve volume
- Expiratory reserve volume
- Residual volume
- TIDAL VOLUME = Amount of air that enters and exits the lung with each normal breath. Normal value = 500mL
- INSPIRATORY RESERVE VOLUME = Amount of air that can be inspired with maximal effort after a normal tidal inspiration. Normal value = 3000 mL
- EXPIRATORY RESERVE VOLUME = Amount of air that can be expired with maximal effort after a normal tidal expiration. Normal value = 1100 mL
- RESIDUAL VOLUME = Amount of air that remains in the lungs after a maximal expiration. Normal value = 1200 mL
Define the following capacities:
- Inspiratory capacity
- Functional residual capacity
- Vital capacity
- Total lung capacity
- INSPIRATORY CAPACITY = Tidal volume + inspiratory reserve volume. Normal value = 3500 mL
- FUNCTIONAL RESIDUAL CAPACITY = Residual volume + expiratory reserve volume. Normal value = 2300 mL
- VITAL CAPACITY = Tidal volume + inspiratory reserve volume + expiratory reserve volume. Normal value = 4600 mL
- TOTAL LUNG CAPACITY = Vital capacity + Residual volume. Normal value = 5800 mL
What muscle are used in inspiration?
What muscles are used in expiration?
Inspiratory muscles = diaphragm, external intercostals
Expiratory muscles = with normal quiet breathing elastic recoil is sufficient for expiration, but with heavy breathing extra force can be achieved by contraction of the internal intercostals and rectus abdominis.
What are the accessory muscles of respiration?
Scalene muscles
Sternocleidomastoic muscle
The long has a tendency to recoil inwards. What causes this elastic recoil?
Elastic recoil is caused by:
- ELASTIC FIBERS in the lung. When the lungs expand, the fibers are stretched, but they have a tendency to return to their resting length.
- SURFACE TENSION. The water lining the alveoli has surface tension, which leads to their inward collapse.
Explain surface tension and Laplace’s law.
What is surfactant and what effect does it have on surface tension?
Surface tension is the force that pulls a liquid’s surface molecules together at an air-fluid interface.
Laplace’s law states that surface tension is greater as the radius of the alveolus decreases - this means that the smaller an alveolus is, the greater the drive to collapse.
Surfactant decreases this surface tension.
In the lungs, the most important surfactant is dipalmitoyl phosphatidylcholine.
Outline the steps of the breathing cycle.
INSPIRATION:
1. Brain initiates a respiratory effort.
2. Nerves carry this command to respiratory muscles.
3. Diaphragm and external intercostals contract.
4. Thoracic volume increases due to chest expansion.
5. Intrapleural pressure becomes more negative.
6. Alveolar transmural pressure difference increases.
7. Alveoli expand in response to increased transmural pressure difference.
8. Alveolar pressure falls below the atmostpheric pressure as a result
9. A pressure difference is created that causes air to flow into the alveoli until the alveolar pressure equals the atmospheric pressure.
EXPIRATION:
1. Brain ceases inspiratory command
2. Inspiratory muscles relax
3. Thoracic volume passively decreases due to recoil
4. Intrapleural pressure becomes more positive as a result
5. This decreases the alveolar transmural pressure difference
6. Causes the alveoli to decrease in volume
7. Causes pressure within the alveoli to increase
8. Establishes a pressure difference for airflow that causes air to leave the alveoli until alveolar pressure equals atmospheric pressure
List and explain the roles of the groups in the brainstem that are responsible for the control of breathing.
The respiratory centre is composed of several groups of neurons:
1. DORSAL respiratory group (in the NTS of the dorsal medulla) - generates action potentials that cause INSPIRATION.
2 PNEUMOTAXIC centre (in the nucleus parabrachialis of the pons) - controls DURATION OF INSPIRATION. When the signal from this centre is strong, inspiration is short; when the signal is weak, inspiration is longer.
3. VENTRAL respiratory group (in the nucleus ambiguus and nucleus retroambiguus of the medulla) - is inactive during normal respiratory, but causes POWERFUL EXPIRATION.
Explain how the levels of chemicals and gases in the body affect respiration.
Excess CO2 or H+ act directly on the respiratory centre, stimulating increased strength of the respiratory commands to respiratory muscles.
Oxygen does not have a significant direct effect, but it acts on peripheral chemoreceptors in the carotid body and aortic body which in turn transmit the signal to the respiratory centre. A decrease in PaO2 stimulates respiration.
The most important factor is CO2. It has a greater effect that O2 and H+.
Describe the structure of haemoglobin.
Hb is a tetramer, with 4 monomers that each consist of a heme and a globin. The heme contains an iron atom. In normal adult Hb, there are 2 alpha globin chains and 2 beta globin chains.
What factors shift the oxygen dissociation curve?
In what direction do they shift the curve?
The oxygen-dissociation curve describe how strongly oxygen is bound to Hb and how much is is unloaded from the Hb.
The 4 factors that affect this curve are:
1. Temperature
2. pCO2
3. 2,3-diphosphoglycerate
4. pH
An increase in temperature and pCO2 occurs in metabolically active tissues. This causes the curve to shift to the right so that more oxygen is supplied when needed.
Metabolically active tissues also have a lowered pH. When the pH is lowered the curve moves to the right so that more oxygen is supplied. This is known as the Bohr effect.
2,3-DPG is produced as byproduct of glycolysis (occurs in hypoxia, anemia and elevated altitude). Increased 2,3-DPG also shifts the curve to the right. This increases the unloading of oxygen to tissues in hypoxic conditions.
How is CO2 transported in the blood?
CO2 is transported from tissues back to the lungs for excretion as:
5% bound to protein
5% dissolved in the blood
90% present as bicarbonate.
For CO2 to be converted into bicarbonate efficiently, carbonic anhydrase is required. This enzyme is present at high concentrations in RBCs.
On general inspection in a respiratory exam, what would you look for?
Does the patient look unwell? Distressed? Obvious cyanosis? Obvious breathlessnes? Breathing that is rapid or laboured? Use of accessory muscles of respiration? Tripod position? Pursed lip breathing? Coughing? Obvious noise - stridor? wheeze? rattling? Hoarse voice? On oxygen? Requiring puffer?
Explain what you would look for in the patients hands/wrists during a respiratory examination.
- NAILS -
- Clubbing. 80% of clubbing has a respiratory cause.
- Nicotine stains
- Peripheral cyanosis - FINGERS/PALMS
- Wasting of the small muscles of the hand can occur with an apical lung tumour invading the T1 root - WRISTS
- Pulse
- Respiratory rate
- Hypertrophic pulmonary osteoarthropathy
- Asterixis (caused by CO2 retention)
What are the respiratory causes of clubbing?
Common respiratory causes of clubbing are:
- Lung cancer
- Bronchiectasis
- Lung abscess
- Empyema
- Idiopathic pulmonary fibrosis
What would you look for in the face of a patient in a respiratory examination? (6)
- FACE
- Plethora of SVC obstruction
- Red/leathery appearance of a long-term smoker - EYES
- Conjunctival pallor
- Horner’s syndrome (pancoast’s tumour) - MOUTH
- Central cyanosis
- Signs of URTI: erythema, tonsillar enlargement, pus
Explain the essential parts of examining the neck in a respiratory exam. (4)
Inspect for use of accessory muscles.
Assess the position of the trachea.
Feel for a tracheal tug - rest a finger on the trachea during inspiration (a tug causes the finger to move inferiorly)
Palpate cervical and supraclavicular lymph nodes
What would you inspect for in the chest during a respiratory examination? (5)
Inspect from the front, back and both sides. SHAPE - Barrel shaped - Pectus carinatum (pigeon chest) - Pectus excavatum (funnel chest) - Kyphosis (forward curvature) - Scoliosis (lateral curvature) SYMMETRY OF CHEST EXPANSION SCARS RADIATION THERAPY SIGNS - Erythema - Skin thickening - Tattoo PROMINENT VEINS from SVC obstruction
Explain your approach to a frontal CXR.
- check the DETAILS
- Patient details: name, DOB, sex
- Film details: PA, AP, erect, supine, date and time - check the film QUALITY
PIR - Penetration, Inspiration, Rotation - AIRWAY AND MEDIASTINUM
- Trachea
- Widened mediastinum - BREATHING
- Lungs
- Pleura - CORONARY AND CIRCULATION
- Heart
- Aorta - DIAPHRAGM
- Costophrenic angle
- Subdiaphragmatic air
- Shape: flattened?
- Height of hemidiaphragms - EXTRAs
- Tubes, ECG electrodes, pacemaker, defibrillator - SOFT TISSUE and BONE
List the features of pulmonary interstitial oedema on CXR.
- Pleural effusion
- Fluid in fissures
- Kerley B lines
- Peribronchial cuffing
What are the common causes of pleural effusions? Differentiate the causes of transudates and exudates.
Common causes of TRANSUDATES. - Congestive heart failure - Hypoalbuminemia - Cirrhosis - Nephrotic syndrome Common cause of EXUDATES. - Malignancy
What causes an exudate?
What causes a transudate?
Exudates are usually caused by inflammation.
Transudates are caused by increased capillary hydrostatic pressure or decreased colloid osmotic pressure.
What does COPD look like on CXR?
- Hyperinflation
- Flattened diaphragm
- Hyperlucency with reduced lung markings
What are the normal values during ABG of:
- pH
- PaCO2
- HCO3
- Anion gap
pH = 7.35-7.45
PaCO2 = 35-45
HCO3 = 22-26
Anion gap = 8-16
During spirometry, what must be present for the obstruction to be considered reversible?
The obstruction is reversible if:
Increase of FEV1 of > 12% AND
Increase of > 200mL
What FEV1/FVC ratio defines obstructive airway disease?
FEV1/FVC of less than 0.7
How is dyspnoea caused by respiratory disease?
How is dyspnoea caused by cardiovascular disease?
What are other common causes of dyspnoea?
Dyspnoea can result from:
RESPIRATORY DISEASE -
1. Any cause of hypercapnia and hypoxia stimulates the respiratory centre in the medulla causes the sensation of air hunger and dyspnoea
2. Disease that affects the respiratory muscles increases the work of breathing and causes the sensation of dyspnoea.
CARDIOVASCULAR DISEASE -
1. Decreased cardiac output (as with CHF) causes a build-up of blood behind the lungs and this increases the pulmonary venous pressure. Increased pressure stimulates receptors in the pulmonary vessels, which produces the sensation of dypsnoea.
OTHER -
1. Anaemia
2. Deconditioning
List 6 respiratory DDX for dyspnoea.
Upper airway obstruction - 1. Foreign object 2. Angioedema 3. Anaphylaxis 4. Infection - epiglottitis 5. Airway trauma 6. Airway burns Lower airway causes - 1. Pulmonary embolism 2. COPD - severe COPD or COPD exacerbation 3. Asthma 4. Infection - pneumonia 5. ARDS 6. Pneumothorax 7. Pleural effusion 8. Lung cancer
Give DDX for dyspnoea other than respiratory causes.
Consider - cardiac (give at least 2), neurologic (at least 2), toxins (1), metabolic (1) and other (at least 3).
CARDIAC - Acute coronary syndrome - Acute decompensated CHF - Flash pulmonary oedema - Valvular dysfunction NEUROLOGICAL - Guillain-Barre syndrome - Myasthenia gravis - Multiple sclerosis - Motor neuron disease METABOLIC/TOXINS - DKA - Poisons - CO, aspirin OTHER - Anaemia - Hypervention - Anxiety - Obesity - Deconditioning - Pregnancy - Sepsis
List investigations that you would consider ordering in a patient presenting with dyspnoea. Also give the disease/s that you are checking for.
FBC (anaemia, infection)
Spirometry (reversibility, obstructive vs restrictive disease)
Pulse oximetry (respiratory disease affecting oxygen saturations)
CXR, Chest CT (respiratory disease)
CTPA, V/Q (Pulmonary embolism)
D-Dimer (PE)
Echocardiogram (cardiac causes)
ECG (cardiac causes)
BNP (congestive heart failure)
DLCO (ability of gas to diffuse from lungs into blood)
Venous or arterial blood gas (respiratory causes, acid-base imbalances)
Give your diagnosis of a cough according to the following time course:
- Acute cough of < 3 weeks
- Subacute cough of 3-8 weeks
- Chronic cough of > 8 weeks
- Common causes of acute cough are:
- Infection: URTI, pneumonia, COPD exacerbation
- Asthma exacerbation
- Aspiration - Common causes of subacute cough are:
- Post-URTI - Common causes of chronic cough are:
- Chronic infection - e.g. TB
- Lung cancer
- GORD
- Medications - e.g ACE-inhibitor
- Congestive heart failure
Give your DDX for haemoptysis. (4)
Acute bronchitis
Bronchiectasis
Lung cancer - primary or metastatic
Lung infections
