Respiratory

Respiratory US Medical PG Question 1: A 37-year-old man is presented to the emergency department by paramedics after being involved in a serious 3-car collision on an interstate highway while he was driving his motorcycle. On physical examination, he is responsive only to painful stimuli and his pupils are not reactive to light. His upper extremities are involuntarily flexed with hands clenched into fists. The vital signs include temperature 36.1°C (97.0°F), blood pressure 80/60 mm Hg, and pulse 102/min. A non-contrast computed tomography (CT) scan of the head shows a massive intracerebral hemorrhage with a midline shift. Arterial blood gas (ABG) analysis shows partial pressure of carbon dioxide in arterial blood (PaCO2) of 68 mm Hg, and the patient is put on mechanical ventilation. His condition continues to decline while in the emergency department and it is suspected that this patient is brain dead. Which of the following results can be used to confirm brain death and legally remove this patient from the ventilator?

• A. Electrocardiogram
• B. Apnea test (Correct Answer)
• C. Lumbar puncture and CSF culture
• D. Electromyography with nerve conduction studies
• E. CT scan

Respiratory Explanation: ***Correct: Apnea test*** - The **apnea test** is a **mandatory component** of brain death determination according to American Academy of Neurology (AAN) guidelines - It directly confirms the **irreversible absence of brainstem function** by demonstrating no respiratory drive despite adequate stimulus (PaCO2 ≥60 mm Hg or 20 mm Hg rise from baseline) - This patient already has a PaCO2 of 68 mm Hg, making the apnea test particularly relevant for confirmation - Brain death requires both **clinical examination** (absent brainstem reflexes, coma) and a **positive apnea test** to legally declare death and discontinue mechanical ventilation - The apnea test is performed by disconnecting the ventilator, providing supplemental oxygen, and observing for any respiratory effort while PaCO2 rises to adequate levels *Incorrect: CT scan* - While a **CT scan showing massive intracerebral hemorrhage with midline shift** provides anatomical evidence of severe, irreversible structural brain damage, it is **NOT sufficient to confirm brain death** - CT imaging is used to establish the **etiology** and rule out reversible causes, but does not directly test brainstem function - Brain death is a **clinical and functional diagnosis**, not purely an anatomical one—imaging alone cannot confirm cessation of all brain function - A patient can have devastating structural damage on CT but still retain some brainstem reflexes *Incorrect: Electrocardiogram* - An **electrocardiogram (ECG)** measures cardiac electrical activity and provides no information about brain or brainstem function - Cardiac activity commonly persists after brain death due to the heart's intrinsic automaticity - ECG findings are irrelevant to brain death determination *Incorrect: Lumbar puncture and CSF culture* - **Lumbar puncture and CSF culture** are used to diagnose CNS infections (meningitis, encephalitis) or inflammatory conditions - These tests are **completely irrelevant** for brain death diagnosis, which is based on irreversible cessation of all brain function, not infection - In this trauma case with known intracerebral hemorrhage, LP would be contraindicated due to increased intracranial pressure and risk of herniation *Incorrect: Electromyography with nerve conduction studies* - **EMG and nerve conduction studies** assess peripheral nerve and muscle function, used for diagnosing neuromuscular disorders - These tests provide no information about brain or brainstem function - They are not part of brain death determination protocols

Respiratory US Medical PG Question 2: A 55-year-old man is brought to the emergency department by ambulance from a long term nursing facility complaining of severe shortness of breath. He suffers from amyotrophic lateral sclerosis and lives at the nursing home full time. He has had the disease for 2 years and it has been getting harder to breath over the last month. He is placed on a rebreather mask and responds to questions while gasping for air. He denies cough or any other upper respiratory symptoms and denies a history of cardiovascular or respiratory disease. The blood pressure is 132/70 mm Hg, the heart rate is 98/min, the respiratory rate is 40/min, and the temperature is 37.6°C (99.7°F). During the physical exam, he begs to be placed in a sitting position. After he is repositioned his breathing improves a great deal. On physical examination, his respiratory movements are shallow and labored with paradoxical inward movement of his abdomen during inspiration. Auscultation of the chest reveals a lack of breath sounds in the lower lung bilaterally. At present, which of the following muscles is most important for inspiration in the patient?

• A. Muscles of anterior abdominal wall
• B. Sternocleidomastoid muscles (Correct Answer)
• C. Internal intercostal muscles
• D. Trapezius muscle
• E. External intercostal muscles

Respiratory Explanation: ***Sternocleidomastoid muscles*** - In advanced **amyotrophic lateral sclerosis (ALS)**, progressive motor neuron degeneration affects both the diaphragm and intercostal muscles - The **paradoxical inward movement of the abdomen** during inspiration indicates severe diaphragmatic weakness or paralysis - The **shallow respiratory movements** and **severe respiratory distress** (respiratory rate 40/min) suggest that both primary inspiratory muscle groups (diaphragm and external intercostals) are significantly compromised - At this stage, **accessory muscles of inspiration**, particularly the **sternocleidomastoid muscles**, become critically important for maintaining ventilation by elevating the sternum and upper ribs - The dramatic improvement when sitting upright (orthopnea relief) supports accessory muscle recruitment, as this position optimizes sternocleidomastoid mechanical advantage - **Clinical pearl:** In neuromuscular respiratory failure, neck muscle recruitment (visible SCM contraction) is a key sign of impending respiratory failure requiring ventilatory support *External intercostal muscles* - The **external intercostal muscles** are normally primary muscles of inspiration that elevate the ribs - However, in advanced ALS with **2 years of progressive disease** and worsening dyspnea over the past month, these muscles would also be significantly weakened by the neurodegenerative process - The **lack of breath sounds in the lower lungs bilaterally** suggests poor chest wall expansion, indicating compromised intercostal function - While they continue to contribute, they are insufficient to maintain adequate ventilation alone at this stage of disease *Internal intercostal muscles* - The **internal intercostal muscles** function primarily in **forced expiration** by depressing the ribs - They do not play a significant role in inspiration *Muscles of anterior abdominal wall* - The **anterior abdominal wall muscles** (rectus abdominis, external/internal obliques, transversus abdominis) are **expiratory muscles** used in forced expiration and coughing - The **paradoxical inward movement** of the abdomen during inspiration is a passive phenomenon resulting from diaphragmatic weakness—the negative intrathoracic pressure pulls the weakened diaphragm upward, which in turn draws the abdominal wall inward - These muscles are not contributing to inspiration in this patient *Trapezius muscle* - The **trapezius** primarily functions in scapular movement and neck stabilization - While it provides some mechanical stability for the shoulder girdle during accessory muscle breathing, it is not directly involved in rib cage elevation - It plays a minor supportive role compared to the sternocleidomastoid in respiratory distress

Respiratory US Medical PG Question 3: Which of the following physiologic changes decreases pulmonary vascular resistance (PVR)?

• A. Inhaling the inspiratory reserve volume (IRV)
• B. Exhaling the entire vital capacity (VC)
• C. Exhaling the expiratory reserve volume (ERV)
• D. Breath holding maneuver at functional residual capacity (FRC)
• E. Inhaling the entire vital capacity (VC) (Correct Answer)

Respiratory Explanation: ***Inhaling the entire vital capacity (VC)*** - As lung volume increases from FRC to TLC (which includes inhaling the entire VC), alveolar vessels are **stretched open**, and extra-alveolar vessels are **pulled open** by the increased radial traction, leading to a decrease in PVR. - This **maximizes the cross-sectional area** of the pulmonary vascular bed, lowering resistance. *Inhaling the inspiratory reserve volume (IRV)* - While inhaling IRV increases lung volume, it's not the maximal inspiration of the entire VC where **PVR is typically at its lowest**. - PVR continues to decrease as lung volume approaches total lung capacity (TLC). *Exhaling the entire vital capacity (VC)* - Exhaling the entire vital capacity leads to very low lung volumes, where PVR significantly **increases**. - At low lung volumes, **alveolar vessels become compressed** and extra-alveolar vessels **narrow**, increasing resistance. *Exhaling the expiratory reserve volume (ERV)* - Exhaling the ERV results in a lung volume below FRC, which causes a **marked increase in PVR**. - This is due to the **compression of alveolar vessels** and decreased radial traction on extra-alveolar vessels. *Breath holding maneuver at functional residual capacity (FRC)* - At FRC, the PVR is at an **intermediate level**, not its lowest. - This is the point where the opposing forces affecting alveolar and extra-alveolar vessels are somewhat balanced, but not optimized for minimal resistance.

Respiratory US Medical PG Question 4: A 27-year-old woman is admitted to the emergency room with dyspnea which began after swimming and progressed gradually over the last 3 days. She denies cough, chest pain, or other respiratory symptoms. She reports that for the past 4 months, she has had several dyspneic episodes that occurred after the exercising and progressed at rest, but none of these were as long as the current one. Also, she notes that her tongue becomes ‘wadded’ when she speaks and she tires very quickly during the day. The patient’s vital signs are as follows: blood pressure 125/60 mm Hg, heart rate 92/min, respiratory rate 34/min, and body temperature 36.2℃ (97.2℉). Blood saturation on room air is initially 92% but falls to 90% as she speaks up. On physical examination, the patient is slightly lethargic. Her breathing is rapid and shallow. Lung auscultation, as well as cardiac, and abdominal examinations show no remarkable findings. Neurological examination reveals slight bilateral ptosis increased by repetitive blinking, and easy fatigability of muscles on repeated movement worse on the face and distal muscles of the upper and lower extremities. Which arterial blood gas parameters would you expect to see in this patient?

• A. PaCO2 = 51 mm Hg, PaO2 = 58 mm Hg (Correct Answer)
• B. PaCO2 = 37 mm Hg, PaO2 = 46 mm Hg
• C. PaCO2 = 34 mm Hg, PaO2 = 61 mm Hg
• D. PaCO2 = 31 mm Hg, PaO2 = 67 mm Hg
• E. PaCO2 = 43 mm Hg, PaO2 = 55 mm Hg

Respiratory Explanation: ***PaCO2 = 51 mm Hg, PaO2 = 58 mm Hg*** - The patient presents with symptoms highly suggestive of a **myasthenic crisis**, including progressive dyspnea, worsened by exertion (speaking), ptosis, and generalized muscle fatigability. These symptoms indicate **respiratory muscle weakness**, leading to hypoventilation. - **Hypoventilation** results in **hypercapnia (elevated PaCO2)** and **hypoxemia (decreased PaO2)**. An elevated PaCO2 of 51 mm Hg and decreased PaO2 of 58 mm Hg are consistent with this presentation, reflecting inadequate ventilation. *PaCO2 = 37 mm Hg, PaO2= 46 mm Hg* - A PaCO2 of 37 mm Hg is within the normal range or slightly low, suggesting that the patient is not significantly hypercapnic, which contradicts the clinical picture of **respiratory muscle weakness and hypoventilation**. - While PaO2 is significantly low at 46 mm Hg (indicating hypoxemia), the normal/low PaCO2 would point to a primary **oxygenation defect** (e.g., V/Q mismatch) rather than a ventilatory failure. *PaCO2 = 34 mm Hg, PaO2 = 61 mm Hg* - A PaCO2 of 34 mm Hg indicates **hypocapnia**, which is more consistent with hyperventilation rather than the hypoventilation expected from **respiratory muscle weakness** in myasthenic crisis. - While PaO2 of 61 mm Hg indicates hypoxemia, the accompanying hypocapnia suggests a primary **respiratory drive issue** or conditions causing hyperventilation, not ventilatory failure due to muscle weakness. *PaCO2 = 31 mm Hg, PaO2 = 67 mm Hg* - A PaCO2 of 31 mm Hg reflects significant **hypocapnia**, indicating that the patient is **hyperventilating**. This is contrary to what would be expected in a myasthenic crisis where respiratory muscle weakness leads to hypoventilation. - While PaO2 is decreased, suggesting some respiratory compromise, the ventilatory pattern (hypocapnia) does not match the clinical syndrome of **respiratory muscle fatigue**. *PaCO2 = 43 mm Hg, PaO2 = 55 mm Hg* - A PaCO2 of 43 mm Hg is within the **normal reference range**, which would mean there is no CO2 retention and thus no obvious **alveolar hypoventilation** from respiratory muscle weakness. - While PaO2 of 55 mm Hg indicates hypoxemia, the normal PaCO2 suggests that the hypoxemia is due to other causes like a **V/Q mismatch** rather than inadequate overall ventilation.

Respiratory US Medical PG Question 5: A 24-year-old woman presents to the emergency department after she was found agitated and screaming for help in the middle of the street. She says she also has dizziness and tingling in the lips and hands. Her past medical history is relevant for general anxiety disorder, managed medically with paroxetine. At admission, her pulse is 125/min, respiratory rate is 25/min, and body temperature is 36.5°C (97.7°F). Physical examination is unremarkable. An arterial blood gas sample is taken. Which of the following results would you most likely expect to see in this patient?

• A. pH: increased, HCO3-: increased, Pco2: increased
• B. pH: decreased, HCO3-: decreased, Pco2: decreased
• C. pH: decreased, HCO3-: increased, Pco2: increased
• D. pH: increased, HCO3-: decreased, Pco2: decreased (Correct Answer)
• E. pH: normal, HCO3-: increased, Pco2: increased

Respiratory Explanation: ***pH: increased, HCO3-: decreased, Pco2: decreased*** - The patient's presentation with **agitation**, **dizziness**, **paresthesias** (tingling in lips and hands), and **tachypnea** (respiratory rate 25/min) is highly suggestive of **hyperventilation** due to an anxiety attack. - **Hyperventilation** leads to excessive **CO2 expulsion**, causing a decrease in Pco2, which results in respiratory alkalosis (increased pH) and a compensatory decrease in HCO3-. *pH: increased, HCO3-: increased, Pco2: increased* - An **increased pH** coupled with **increased HCO3-** and **increased Pco2** would suggest a **metabolic alkalosis with respiratory compensation**, which is not consistent with the patient's acute hyperventilation. - While pH is increased, the other values contradict the primary respiratory cause suggested by the symptoms. *pH: decreased, HCO3-: decreased, Pco2: decreased* - This profile describes **metabolic acidosis with respiratory compensation**, which would typically present with **Kussmaul breathing** and other signs of acidosis, not acute hyperventilation and agitation. - Symptoms such as dizziness and tingling are associated with alkalosis, not acidosis. *pH: decreased, HCO3-: increased, Pco2: increased* - This pattern is characteristic of **respiratory acidosis with metabolic compensation**, often seen in conditions like **COPD exacerbation** or **opioid overdose** with hypoventilation. - The patient's rapid breathing and clinical picture are not consistent with respiratory acidosis. *pH: normal, HCO3-: increased, Pco2: increased* - A **normal pH** with **increased HCO3-** and **increased Pco2** would indicate a **compensated metabolic alkalosis**. - Her acute symptoms point to an uncompensated or acutely compensated respiratory disorder, not a compensated metabolic issue.

Respiratory Flashcard 1 of 5

Question: In response to high altitude, there is a chronic _____ in ventilation

Answer: increase

Respiratory Flashcard 2 of 5

Question: Peripheral chemoreceptors are stimulated by increased _____

Answer: Paco2

Respiratory Flashcard 3 of 5

Question: The _____ zone of the lung is responsible for warming, humidifying, and filtering the air

Answer: conducting

Respiratory Flashcard 4 of 5

Question: _____ receptors are mechanoreceptors located in the smooth muscle of the airways

Answer: Lung stretch

Respiratory Flashcard 5 of 5

Question: The dorsal respiratory group receives sensory input from lung stretch receptors via the _____ nerve

Answer: vagus (CN X)