A 72-year-old woman is brought to the emergency department due to exertional chest pain. The patient is on vacation with her family and her symptoms began after arriving in the Colorado mountains. She has a history of coronary artery disease but has had no ischemic symptoms over the past several years. The patient is a lifetime nonsmoker and has no history of lung disease. Physical examination shows mild hypoxemia, clear lungs, an S4, and no extremity edema. ECG shows T-wave inversion in the lateral leads. Serum troponin and D-dimer levels are within normal limits. It is determined that decreased oxygen levels at high altitude in combination with age-related pulmonary changes lead to an exacerbation of this patient's preexisting heart condition. Which of the following respiratory changes most likely contributed to this patient's increased susceptibility?

Question

A 72-year-old woman is brought to the emergency department due to exertional chest pain.  The patient is on vacation with her family and her symptoms began after arriving in the Colorado mountains.  She has a history of coronary artery disease but has had no ischemic symptoms over the past several years.  The patient is a lifetime nonsmoker and has no history of lung disease.  Physical examination shows mild hypoxemia, clear lungs, an S4, and no extremity edema.  ECG shows T-wave inversion in the lateral leads.  Serum troponin and D-dimer levels are within normal limits.  It is determined that decreased oxygen levels at high altitude in combination with age-related pulmonary changes lead to an exacerbation of this patient's preexisting heart condition.  Which of the following respiratory changes most likely contributed to this patient's increased susceptibility?

Quizplus · Accepted Answer

The reduced partial pressure of inspired oxygen at high altitude leads to hypoxemia (ie, reduced partial pressure of arterial oxygen [PaO₂]). Hyperventilation is the most immediate and important physiologic adjustment to high altitude; peripheral chemoreceptors stimulate increased minute ventilation (via both increased tidal volume and respiratory rate) to help increase PaO₂ and minimize the symptoms of hypoxemia (eg, headache, dyspnea). In older individuals (eg, age >65), the body is less able to compensate for the hypoxemia at high altitude due to a number of age-related changes to the respiratory system. These changes include the following: Decreased chest wall compliance: Calcification of the intercostal joints and tendon insertion sites, as well as degeneration of the spine (eg, kyphosis), reduces chest wall expansion and limits the potential increase in tidal volume. Decreased alveolar elastic recoil: Degeneration of elastin causes increased alveolar compliance with alveolar enlargement and increased air trapping. This increases residual volume and decreases forced vital capacity, further limiting the achievable increase in tidal volume (Choices D and E). Increased alveolar-arterial O₂ gradient: The alveolar enlargement increases ventilation-perfusion mismatch and decreases the efficiency of O₂ exchange in 2 ways. First, it decreases the percentage of alveolar surface area in contact with alveolar capillaries, effectively increasing dead space (Choice B). Second, the increased air trapping decreases ventilation of highly perfused alveoli at the base of the lungs. In this elderly patient, the body's ability to increase PaO₂ at high altitude has likely been reduced, and, given her underlying coronary artery disease, she is likely experiencing angina (eg, exertional chest pain) due to inadequate O₂ supply to the myocardium. (Choice C) Aging appears to have minimal effect on chemoreceptor responsiveness; therefore, respiratory drive is appropriately increased at high altitude. Age-related changes that reduce the mechanical efficiency of the respiratory system (ie, ability to respond to increased respiratory drive) are primarily responsible for reduced compensation for hypoxemia at high altitude. Educational objective: Age-related changes to the respiratory system include decreased chest wall compliance and decreased alveolar elastic recoil with resulting alveolar enlargement and air trapping. These changes limit the potential increase in tidal volume and also increase the alveolar-arterial O₂gradient (ie, decrease the efficiency of alveolar-capillary gas exchange), reducing the ability to compensate for hypoxemia.

A 72-Year-Old Woman Is Brought to the Emergency Department Due