Altitude and Diving Physiology

Altitude and Diving Physiology Indian Medical PG Question 1: Which of the following statements are correct regarding primary survey/management of traumatic head injury patient? I. Ensure adequate oxygenation and circulation II. Exclude hypoglycaemia III. Check for mechanism of injury IV. Check pupil size and response Select the answer using the code given below :

• A. II, III and IV
• B. I, III and IV
• C. I, II and III
• D. I, II and IV (Correct Answer)

Altitude and Diving Physiology Explanation: ***I, II and IV*** - **Primary survey** in trauma management, including head injury, focuses on immediately life-threatening conditions (Airway, Breathing, Circulation, Disability, Exposure). Ensuring adequate **oxygenation and circulation** (Statement I) is paramount to prevent secondary brain injury. - Exclude **hypoglycemia** (Statement II) is critical because altered mental status due to low blood sugar can mimic head injury and delay appropriate treatment, making it an essential part of the 'D' (disability) assessment. Checking **pupil size and response** (Statement IV) is also part of the 'D' assessment, providing vital information about potential brain stem compromise or intracranial pressure changes. *II, III and IV* - While excluding hypoglycemia and checking pupil response are crucial parts of the primary survey, Statement III, "Check for mechanism of injury," is typically part of the **secondary survey** or initial assessment but not immediately life-saving like ABCD. - The primary survey prioritizes immediate threats to life, and while understanding the mechanism of injury informs subsequent care, it does not directly address a patient's immediate physiologic stability. *I, III and IV* - This option includes checking the mechanism of injury (Statement III) as part of the primary survey, which is generally conducted after the **life-threatening conditions** are addressed. - It omits the critical step of excluding **hypoglycemia** (Statement II), which is an immediate reversible cause of altered mental status that must be ruled out during the primary assessment. *I, II and III* - This option correctly includes ensuring adequate **oxygenation and circulation** (Statement I) and excluding **hypoglycemia** (Statement II) as part of the primary survey. - However, it incorrectly includes checking for the **mechanism of injury** (Statement III) as a primary survey component and omits checking **pupil size and response** (Statement IV), which is an essential part of the 'Disability' assessment in the primary survey for head injury.

Altitude and Diving Physiology Indian Medical PG Question 2: A 45-year-old woman presents with shortness of breath and cyanosis. Arterial blood gas shows a low oxygen saturation despite a normal PaO2. What is the most likely diagnosis?

• A. Pulmonary embolism
• B. Carbon monoxide poisoning (Correct Answer)
• C. Asthma
• D. Pneumonia

Altitude and Diving Physiology Explanation: ***Carbon monoxide poisoning*** - **Carbon monoxide** binds to **hemoglobin** with a much higher affinity than oxygen, forming **carboxyhemoglobin (COHb)**, which prevents oxygen transport [1]. - This leads to a low-oxygen saturation reading by pulse oximetry, even when the **partial pressure of oxygen (PaO2)** in the blood is normal, because the PaO2 measures dissolved oxygen, not oxygen bound to hemoglobin [1], [2]. - Furthermore, CO causes a leftward shift of the oxyhemoglobin dissociation curve affecting the offloading of oxygen from hemoglobin to the tissue [1], [2]. *Pulmonary embolism* - A **pulmonary embolism** typically causes **hypoxemia** and a low **PaO2** due to ventilation-perfusion mismatch, which contradicts the normal PaO2 in this case. - While it can cause shortness of breath and cyanosis, the **ABG** findings of **normal PaO2** despite **low oxygen saturation** are not characteristic. *Asthma* - **Asthma** involves **bronchoconstriction** and airflow obstruction, leading to **hypoxemia** and a **low PaO2** in severe cases. - It would not typically present with a normal PaO2 alongside a significantly desaturated pulse oximeter reading, as the PaO2 directly reflects the amount of dissolved oxygen in the blood. *Pneumonia* - **Pneumonia** causes impaired gas exchange due to inflammation and fluid in the alveoli, resulting in **hypoxemia** and a **low PaO2**. - The coexistence of **normal PaO2** with **low oxygen saturation** points away from pneumonia, as the primary issue in pneumonia is usually a failure to oxygenate the blood effectively, thus lowering PaO2.

Altitude and Diving Physiology Indian Medical PG Question 3: In an accident case, after the arrival of medical team, all should be done in early management except;

• A. Glasgow coma scale
• B. Check BP (Correct Answer)
• C. Stabilization of cervical vertebrae
• D. Check Respiration

Altitude and Diving Physiology Explanation: ***Check BP*** - In the **immediate/early management** of trauma (primary survey), while circulation assessment is crucial, the **initial assessment of circulation** focuses on: - **Pulse rate and quality** (radial, carotid) - **Capillary refill time** - **Skin color and temperature** - **Active hemorrhage control** - **Formal blood pressure measurement** with a cuff, while important, is typically recorded during or after these rapid initial assessments, as it takes more time to obtain an accurate reading. - In the context of this question, among the four options listed, BP measurement is relatively less immediate compared to the other life-saving priorities (airway protection, breathing assessment, C-spine stabilization, and GCS). - **Note:** This is a nuanced distinction - BP is assessed during primary survey, but the other three options have more immediate life-threatening implications if not addressed. *Glasgow coma scale* - **GCS assessment** is part of the **"D" (Disability)** step in the ATLS primary survey. - It is performed early to assess neurological status and level of consciousness. - GCS <8 indicates need for **definitive airway protection** (intubation). - This is a critical early assessment that guides immediate management decisions. *Stabilization of cervical vertebrae* - **C-spine immobilization** is part of the **"A" (Airway)** step - "Airway with cervical spine protection." - It is performed **simultaneously** with airway assessment using a **rigid cervical collar**. - This is the **first priority** in trauma management to prevent secondary spinal cord injury. - All trauma patients should be assumed to have C-spine injury until proven otherwise. *Check Respiration* - **Respiratory assessment** is part of the **"B" (Breathing)** step in the ATLS primary survey. - This involves checking: - **Respiratory rate and pattern** - **Chest wall movement** - **Air entry bilaterally** - **Signs of tension pneumothorax or flail chest** - This is an immediate life-saving priority and must be assessed early.

Altitude and Diving Physiology Indian Medical PG Question 4: Compensating mechanism involved in acclimatization to altitude is:

• A. Respiratory depression
• B. Hypoventilation
• C. Hyperventilation (Correct Answer)
• D. Respiratory acidosis

Altitude and Diving Physiology Explanation: ***Hyperventilation*** - **Hyperventilation** is the primary immediate compensatory mechanism at altitude, increasing alveolar ventilation to improve **oxygen uptake** despite lower partial pressures of oxygen. - This response is mediated by the **carotid bodies**, which sense the reduced arterial PO2 and stimulate the respiratory center. *Respiratory depression* - **Respiratory depression** would worsen hypoxia at high altitude by further reducing **oxygen intake**. - This is not a compensatory, but rather a detrimental, response in this setting. *Hypoventilation* - **Hypoventilation** decreases the amount of air reaching the alveoli, exacerbating the **hypoxia** present at high altitudes. - This would further reduce the **partial pressure of oxygen** in the blood, which is counterproductive for acclimatization. *Respiratory acidosis* - **Respiratory acidosis** results from **hypoventilation** and CO2 retention. - Acclimatization leads to **respiratory alkalosis** due to increased CO2 excretion from hyperventilation, which is then partially compensated by renal mechanisms.

Altitude and Diving Physiology Indian Medical PG Question 5: Which drug is given to prevent acute mountain sickness?

• A. Acetazolamide (Correct Answer)
• B. Diltiazem
• C. Digoxin
• D. Dexamethasone

Altitude and Diving Physiology Explanation: ***Acetazolamide*** - This drug is a **carbonic anhydrase inhibitor** that acidifies the blood and causes compensatory hyperventilation, increasing oxygenation. - It is the **first-line prophylactic agent** for acute mountain sickness (AMS) and is best started 24-48 hours before ascent. - Most effective and widely recommended for AMS prevention. *Digoxin* - This is a **cardiac glycoside** used to treat heart failure and irregular heartbeats. - Its mechanism of action is unrelated to the physiological changes that cause acute mountain sickness. *Diltiazem* - This is a **calcium channel blocker** primarily used for hypertension, angina, and certain arrhythmias. - It has no known role in the prevention or treatment of acute mountain sickness. *Dexamethasone* - While **dexamethasone** can be used for AMS prophylaxis, it is typically reserved as an **alternative agent** when acetazolamide is contraindicated or not tolerated. - It is more commonly used for **treatment** of severe altitude illness including **High Altitude Cerebral Edema (HACE)** and **High Altitude Pulmonary Edema (HAPE)**. - **Acetazolamide remains the preferred first-line prophylactic agent** due to its mechanism of action that directly addresses the underlying pathophysiology of AMS.

Altitude and Diving Physiology Indian Medical PG Question 6: Which of the following is seen in high altitude climbers?

• A. Hyperventilation
• B. Pulmonary edema
• C. Decreased PaCO2
• D. All of the options (Correct Answer)

Altitude and Diving Physiology Explanation: ***All of the options*** - High altitude climbers experience **hypoxia**, which triggers several physiological responses as the body tries to compensate. - **Hyperventilation**, **pulmonary edema**, and **decreased PaCO2** are all common occurrences in individuals exposed to high altitudes. *Hyperventilation* - **Hypoxia** at high altitudes stimulates the peripheral chemoreceptors, leading to an increased respiratory rate and depth. - This increased ventilation is a compensatory mechanism to try and increase **oxygen intake**. *Pulmonary edema* - **High-altitude pulmonary edema (HAPE)** is a potentially life-threatening condition caused by exaggerated hypoxic pulmonary vasoconstriction. - This leads to increased pulmonary arterial pressure, capillary leakage, and **fluid accumulation in the lungs**. *Decreased PaCO2* - The increased respiratory rate due to **hyperventilation** causes an excessive exhalation of carbon dioxide. - This results in a **decreased partial pressure of arterial carbon dioxide (PaCO2)**, leading to respiratory alkalosis.

Altitude and Diving Physiology Indian Medical PG Question 7: What is the primary physiological effect of increased 2,3-DPG on hemoglobin?

• A. Increased affinity of hemoglobin to oxygen
• B. Decreased affinity of hemoglobin to oxygen (Correct Answer)
• C. Left shift of oxygen-hemoglobin dissociation curve
• D. Right shift of oxygen-hemoglobin dissociation curve

Altitude and Diving Physiology Explanation: ***Decreased affinity of hemoglobin to oxygen*** - **2,3-Diphosphoglycerate (2,3-DPG)** binds to the beta subunits of deoxyhemoglobin, stabilizing the **deoxygenated state** and thus **reducing hemoglobin's affinity for oxygen**. - This is the **primary molecular mechanism** by which 2,3-DPG exerts its effect, facilitating **oxygen unloading** in peripheral tissues. - This decreased affinity manifests graphically as a **right shift** in the oxygen-hemoglobin dissociation curve. *Increased affinity of hemoglobin to oxygen* - This is incorrect because 2,3-DPG specifically works to **decrease hemoglobin's affinity** for oxygen, promoting oxygen release. - Increased affinity would mean oxygen is held more tightly, which is counterproductive for **oxygen delivery** to tissues. *Left shift of oxygen-hemoglobin dissociation curve* - A **left shift** indicates **increased affinity** of hemoglobin for oxygen, meaning oxygen is held more tightly. - Since 2,3-DPG decreases affinity, it causes a **right shift**, not a left shift. *Right shift of oxygen-hemoglobin dissociation curve* - While this is the **graphical representation** of 2,3-DPG's effect, it is a **consequence** of the primary molecular mechanism (decreased affinity). - A right shift signifies that for any given partial pressure of oxygen, hemoglobin is **less saturated** with oxygen, reflecting the decreased affinity caused by 2,3-DPG binding.

Altitude and Diving Physiology Indian Medical PG Question 8: Which of the following is the most important clinical principle regarding acute high-altitude pulmonary edema (HAPE)?

• A. HAPE is more common at altitudes above 2500 meters but can occur at lower altitudes.
• B. Elevated ESR is the most specific diagnostic marker for HAPE
• C. The primary treatment for HAPE is immediate descent to a lower altitude. (Correct Answer)
• D. HAPE only occurs at altitudes above 4000 meters

Altitude and Diving Physiology Explanation: The primary treatment for HAPE is immediate descent to a lower altitude [1]. - **Immediate descent** is crucial as it reverses the hypoxic vasoconstriction and reduces pulmonary artery pressure, which are central to HAPE pathophysiology [1], [2]. - This intervention directly addresses the underlying cause and significantly improves outcomes, making it the most important clinical principle. *Elevated ESR is the most specific diagnostic marker for HAPE* - **Elevated ESR** (Erythrocyte Sedimentation Rate) is a non-specific inflammatory marker and is not used as a diagnostic marker for HAPE. - Diagnosis of HAPE relies primarily on clinical symptoms, signs, and imaging findings. *HAPE is more common at altitudes above 2500 meters but can occur at lower altitudes.* - While it is true that HAPE most commonly occurs at altitudes above 2500 meters [2], this statement describes an epidemiological fact rather than the most important **clinical principle** for management. - The most crucial clinical principle focuses on the immediate action required for patient safety, which is descent [1]. *HAPE only occurs at altitudes above 4000 meters* - HAPE can occur at **altitudes much lower than 4000 meters**, typically starting around 2500 meters, especially in susceptible individuals or with rapid ascent [2]. - This statement is factually incorrect and misrepresents the altitude range for HAPE development.

Altitude and Diving Physiology Indian Medical PG Question 9: What is the most immediate hematological adaptation that occurs during high-altitude exposure to improve oxygen delivery to tissues?

• A. Increased red blood cell mass
• B. Reduced erythropoietin production
• C. Increased white blood cell count
• D. Increased 2,3-BPG levels (Correct Answer)

Altitude and Diving Physiology Explanation: ***Increased 2,3-BPG levels*** - **2,3-Bisphosphoglycerate (2,3-BPG)** is an organic phosphate that binds to hemoglobin, reducing its affinity for oxygen and thereby facilitating oxygen release to tissues. - This is a **rapid adaptation** in response to hypoxia at high altitudes, occurring within hours to days, providing an immediate improvement in oxygen delivery. *Increased red blood cell mass* - An increase in **red blood cell mass (polycythemia)** is a more chronic adaptation, typically taking weeks to months to develop in response to sustained hypoxia. - While it ultimately improves oxygen-carrying capacity, it is not the most immediate hematological adaptation. *Reduced erythropoietin production* - High-altitude exposure actually leads to **increased erythropoietin (EPO) production** by the kidneys due to tissue hypoxia. - This increased EPO stimulates erythropoiesis, leading to the delayed increase in red blood cell mass. *Increased white blood cell count* - An **increased white blood cell count (leukocytosis)** is primarily associated with infection, inflammation, or stress, not with the physiological response to high-altitude hypoxia for improving oxygen delivery. - It does not directly contribute to the oxygen-carrying capacity of the blood.

Altitude and Diving Physiology Indian Medical PG Question 10: All are examples of negative feedback except

• A. Regulation of blood CO2 level
• B. Regulation of pituitary hormones
• C. Regulation of blood pressure
• D. Coagulation of the blood (Correct Answer)

Altitude and Diving Physiology Explanation: ***Coagulation of the blood*** - **Blood coagulation** is a classic example of **positive feedback**, where the initial clotting process amplifies itself until bleeding stops - Platelets aggregate and release factors that promote further platelet aggregation and activation of the clotting cascade, thereby **accelerating the response** rather than diminishing it - This is the exception among the options, as it represents positive feedback while all others are negative feedback *Regulation of blood CO2 level* - The regulation of **blood CO2 levels** is a vital example of **negative feedback**, where an increase in CO2 stimulates breathing to expel excess CO2 - This mechanism works to return the blood CO2 concentration to its homeostatic set point, thus **counteracting the initial stimulus** - Central and peripheral chemoreceptors detect elevated CO2 and trigger increased ventilation *Regulation of pituitary hormones* - The regulation of **pituitary hormones** involves **negative feedback loops**, where high levels of target gland hormones inhibit the release of stimulating hormones from the pituitary and hypothalamus - For example, high thyroid hormone levels inhibit TSH release from the pituitary and TRH from the hypothalamus - This effectively **reduces the initial stimulus** and maintains hormonal balance *Regulation of blood pressure* - The regulation of **blood pressure** is primarily controlled by **negative feedback mechanisms** involving baroreceptors, which detect changes in pressure - If blood pressure rises, baroreceptors in the carotid sinus and aortic arch signal the medulla to reduce heart rate and dilate blood vessels - This response **lowers the pressure back to the set point**, maintaining cardiovascular homeostasis

Altitude and Diving Physiology Flashcard 1 of 7

Question: Gas emboli occur due to bubbling of _____ out of blood, due to rapid ascent by a diver

Answer: nitrogen gas

Altitude and Diving Physiology Flashcard 2 of 7

Question: Exercise adaptation at high altitudes:_____ pH inhibits brain stem and reduces maximal exercise effort

Answer: Increased

Altitude and Diving Physiology Flashcard 3 of 7

Question: Exercise adaptation at high altitudes:To make up for the respiratory alkalosis, kidneys _____ hydrogen ion secretion and increase bicarbonate excretion.

Answer: reduce

Altitude and Diving Physiology Flashcard 4 of 7

Question: In response to high altitude, there is chronic hypoxic pulmonary vasoconstriction which results in pulmonary _____ and RV hypertrophy

Answer: hypertension

Altitude and Diving Physiology Flashcard 5 of 7

Question: ascent should not be > _____ meters/minute to avoid mountain sickness

Answer: 300

Extra Information: 

Altitude and Diving Physiology Flashcard 6 of 7

Question: mountain sickness is seen in altitudes of >_____ meters

Answer: 2500

Extra Information: 

Altitude and Diving Physiology Flashcard 7 of 7

Question: Exercise adaptation at high altitudes:_____ in pulmonary ventilation upon rising to a high altitude* blows off large quantities of CO2, reducing the PCO2

Answer: Increase