LPN exams respiratory practice questions set 13

Correct answer:

Step-by-step rationale for choice A being correct: 1. Myoglobin is composed of a single polypeptide chain with 153 amino acids, making it monomeric. 2. Being monomeric, myoglobin does not exhibit cooperative binding, leading to a hyperbolic oxygen dissociation curve. 3. The lack of multiple subunits in myoglobin results in non-cooperative binding and a hyperbolic curve. 4. The monomeric nature allows myoglobin to have a simple structure, enhancing its affinity for oxygen. Summary of why other choices are incorrect: B: High concentration in the muscle does not directly explain the hyperbolic curve. C: Being a muscle protein does not inherently determine the hyperbolic nature of the oxygen dissociation curve. D: Quaternary structure would involve multiple subunits, leading to cooperative binding and a sigmoidal oxygen dissociation curve.

Correct answer:

Physiological dead space (VDphys) includes anatomic dead space (~150 ml) and alveolar dead space (ventilated, non-perfused alveoli). Pulmonary embolism (PE) blocks pulmonary arteries, cutting perfusion to ventilated alveoli, vastly increasing alveolar dead space (e.g., from near 0 to 150+ ml), raising VDphys significantly. Atelectasis collapses alveoli, reducing ventilation and thus dead space, as unventilated areas don't count. Pneumothorax collapses lung, lowering ventilated volume, not increasing dead space. Bronchoconstriction narrows airways, possibly reducing anatomic dead space slightly, with minimal alveolar effect unless severe. PE's perfusion loss creates the greatest VDphys rise, measurable via Bohr (PaCO2-PECO2), reflecting high V/Q mismatch, a critical gas exchange inefficiency distinguishing it from ventilation-focused conditions.

Correct answer:

At sea level (760 mmHg), inspired air's pO₂ is inconsistent at 130 mmHg (choice D). Inspired air's pO₂ is calculated as 0.21 × (760 - 47) = 149.7 mmHg, where 47 mmHg is water vapor pressure. Choice A (alveolar pCO₂ = 40 mmHg) is consistent with normal alveolar values, reflecting CO₂ production and ventilation balance. Choice B (alveolar pO₂ = 100 mmHg) aligns with the alveolar gas equation: pO₂ = FiO₂ × (P_atm - PH₂O) - (pCO₂/R), approximately 100 mmHg with R ≈ 0.8. Choice C (PH₂O = 47 mmHg) is correct for saturated air at 37°C. Choice E's 573 mmHg for PN₂ is reasonable (760 - 47 - 100 - 40 ≈ 573). The stated 130 mmHg for inspired pO₂ underestimates the true value (≈150 mmHg), making D inconsistent with standard sea-level conditions.

Correct answer:

Air enters the lungs during inspiration per Boyle's law: thoracic expansion lowers intrapulmonary pressure below atmospheric (e.g., 760 to 758 mmHg), creating a pressure gradient driving airflow. Increasing this gradient via stronger diaphragm and intercostal contraction directly boosts inspired volume (e.g., from 500 ml to 600 ml), the primary factor. Increase in action potential' likely means neural impulses to respiratory muscles; more impulses enhance contraction, but this is secondary to the gradient they produce. Combining both overcomplicates pressure is the direct mechanism. Decreasing the gradient reduces flow, opposing the goal. The pressure gradient is the key driver, quantifiable (e.g., 1-2 mmHg for tidal breathing), linking muscle action to volume via physics, distinguishing it as the most impactful factor in ventilation mechanics.

Correct answer:

Physiological dead space (VDphys) includes anatomic dead space (~150 ml) and alveolar dead space (ventilated, non-perfused alveoli). Pulmonary embolism (PE) blocks pulmonary arteries, cutting perfusion to ventilated alveoli, vastly increasing alveolar dead space (e.g., from near 0 to 150+ ml), raising VDphys significantly. Atelectasis collapses alveoli, reducing ventilation and thus dead space, as unventilated areas don't count. Pneumothorax collapses lung, lowering ventilated volume, not increasing dead space. Bronchoconstriction narrows airways, possibly reducing anatomic dead space slightly, with minimal alveolar effect unless severe. PE's perfusion loss creates the greatest VDphys rise, measurable via Bohr (PaCO2-PECO2), reflecting high V/Q mismatch, a critical gas exchange inefficiency distinguishing it from ventilation-focused conditions.

Correct answer:

The correct answer is D: Diaphragm and intercostal muscles. The diaphragm is the primary muscle responsible for inhalation and exhalation by contracting and relaxing, respectively. Intercostal muscles aid in expanding and contracting the rib cage to assist in breathing. The combination of the diaphragm and intercostal muscles working together ensures efficient ventilation of the lungs in mammals. Choices A and B are incorrect because the muscular wall of the lungs and intercostal muscles alone are not solely responsible for regulating ventilation. Choice C is incorrect because the diaphragm alone does not govern ventilation movements without the assistance of the intercostal muscles. Therefore, the correct answer is D as it accurately reflects the coordinated effort of both the diaphragm and intercostal muscles in regulating lung ventilation.

Correct answer:

In anemia (Hb = 5 g/100 ml), choice D (PₙO₂ decreased) is incorrect. PₙO₂ (assumed PaO₂, arterial pO₂) remains normal (≈100 mmHg) because lung function isn't impaired; only O₂-carrying capacity drops. Choice A (decreased TPR) is correct; reduced blood viscosity lowers total peripheral resistance. Choice B (increased cardiac output) is true; the heart compensates for lower O₂ content by pumping more blood. Choice C (increased 2,3-DPG) is accurate; RBCs produce more 2,3-DPG to shift the O₂ dissociation curve rightward, enhancing O₂ unloading to tissues. Choice E (curve shifts right) supports this adaptation. PaO₂ reflects dissolved O₂, not Hb-bound O₂, so it's unaffected by anemia unless hypoxemia coexists. The body's compensatory mechanisms focus on delivery, not arterial pO₂, making D the false statement here.

Correct answer:

The correct answer is B: Egophony. Egophony is a lung sound in which the spoken "E" sound changes to a loud, nasal "A" sound when auscultated, indicating consolidation in the lungs, such as in pneumonia. This finding should be documented as egophony because it specifically describes the distortion of voice sounds during auscultation related to lung pathology. A: Bronchophony refers to increased clarity and loudness of spoken sounds during auscultation and is not specific to the distortion of the voice sounds as in the given scenario. C: Whispered pectoriloquy describes whispered sounds being heard clearly during auscultation, which is different from the scenario presented. D: Sonorous wheezes are continuous low-pitched wheezing sounds heard with inspiration or expiration, not related to the distortion of voice sounds as in egophony.

Correct answer:

The arytenoid cartilages are paired, pyramid-shaped structures in the larynx, pivotal for vocal cord movement. They sit atop the cricoid cartilage, articulating via a synovial joint, not the thyroid cartilage's inferior horn (A), which connects to the cricoid via the cricothyroid ligament. Their apex supports the corniculate cartilage (C), and their vocal process anchors the vocal ligaments. B states they have two surfaces, but anatomically, they have three (medial, posterior, anterolateral); however, this phrasing is often simplified in questions, making B debatably true. A is unequivocally false no facet exists for the thyroid's inferior horn, which is structurally unrelated to arytenoid articulation. The superior horn of the thyroid connects to the hyoid, further clarifying A's inaccuracy. Thus, A is the exception among the statements.

Correct answer:

The arytenoid cartilages are paired, pyramid-shaped structures in the larynx, pivotal for vocal cord movement. They sit atop the cricoid cartilage, articulating via a synovial joint, not the thyroid cartilage's inferior horn (A), which connects to the cricoid via the cricothyroid ligament. Their apex supports the corniculate cartilage (C), and their vocal process anchors the vocal ligaments. B states they have two surfaces, but anatomically, they have three (medial, posterior, anterolateral); however, this phrasing is often simplified in questions, making B debatably true. A is unequivocally false no facet exists for the thyroid's inferior horn, which is structurally unrelated to arytenoid articulation. The superior horn of the thyroid connects to the hyoid, further clarifying A's inaccuracy. Thus, A is the exception among the statements.