The one of the following diseases in which examination of the bone marrow is least likely to be helpful in establishment the diagnosis is:

Correct Answer: D

Rationale: Hypersplenism (D) splenomegaly with pancytopenia relies on spleen size, CBC (e.g., platelets <100,000/μL), not marrow, which is hyperplastic, not diagnostic. Aplastic anemia (A), leukemia (B), Hodgkin's (C), myeloma show marrow changes (e.g., blasts, Reed-Sternberg). Hypersplenism's peripheral focus is key, guiding nursing for spleen assessment over marrow biopsy.

Correct Answer: B

Rationale: Functional residual capacity (FRC) is the volume of air remaining in the lungs after a normal expiration, representing a balance point where the opposing forces of the lung and chest wall are equal. The elastic recoil of the lung is inward, tending to collapse the lung, while the elastic recoil of the chest wall is outward, tending to expand it. At FRC, these forces cancel each other out, and the lung-thorax system is indeed at rest with no active muscle contraction. However, FRC is not about 75% of total lung capacity (TLC). In a healthy adult, FRC is typically around 2.5-3 liters, while TLC is about 6 liters, making FRC approximately 40-50% of TLC, not 75%. The claim that FRC is about 75% of TLC is significantly overstated and does not reflect physiological norms, making it the statement that is not true at FRC. This misunderstanding could arise from confusing FRC with other lung volumes, but the standard values clearly indicate a lower percentage relative to TLC.

Correct Answer: D

Rationale: In a severe asthmatic attack, bronchoconstriction obstructs airways, reducing airflow, particularly during expiration, leading to wheezing. Forced expiratory volume in 1 second (FEV1) drops more than forced vital capacity (FVC), decreasing the FEV1/FVC ratio (normal >80%) due to obstruction, not increasing it. The ventilation/perfusion (V/Q) ratio in affected areas decreases, as ventilation is impaired more than perfusion, causing mismatching and hypoxemia (PaO2 60 mmHg, normal 75-100 mmHg). Arterial PCO2 (30 mmHg, normal 35-45 mmHg) is lower than normal, not higher, because hypoxemia stimulates hyperventilation via peripheral chemoreceptors, increasing respiratory rate to compensate for low oxygen. This overbreathing expels CO2 faster than it accumulates, despite uneven ventilation, contrasting with conditions like COPD where CO2 retention occurs. The lower PCO2 reflects this compensatory mechanism, aligning with asthma's acute physiology where gas exchange inefficiency drives respiratory effort, not CO2 trapping.

Correct Answer: D

Rationale: Vital capacity (VC) is the maximum volume of air a person can exhale after a maximal inhalation, measured via spirometry as the sum of inspiratory reserve volume (IRV, ~2-3 L), tidal volume (VT, ~0.5 L), and expiratory reserve volume (ERV, ~1-1.5 L), totaling ~4-5 L in adults. It excludes residual volume (RV), which remains after maximal exhalation. Sum of all lung volumes' describes total lung capacity (TLC, ~6 L), including RV, not VC. Tidal volume plus residual volume' (~2 L) is far less than VC, missing IRV and ERV. IRV plus ERV' omits VT, underestimating VC (~3-4 L). The correct definition IRV + VT + ERV captures the full expirable volume, reflecting the lung's functional capacity for deep breathing, a key metric in assessing respiratory health, distinguishing it from TLC or partial volume sums.

Correct Answer: C

Rationale: Lung compliance (C) is the change in lung volume per change in transpulmonary pressure (C = ΔV / ΔP), correctly defined. It's not maximal during quiet breathing (tidal volume ~500 ml); it's tested across a range, peaking at moderate volumes but decreasing at high volumes (e.g., near TLC) due to stiffness. In quiet breathing, compliance operates efficiently but isn't at its maximum. Crucially, compliance is inversely related to surface tension higher tension (e.g., no surfactant) stiffens alveoli, reducing compliance, as in RDS, not increasing it. This statement is incorrect, contradicting Laplace's law (P = 2T/r), where high tension raises collapse pressure, lowering compliance. Fibrosis decreases compliance by stiffening lungs with collagen, and emphysema increases it by destroying elastic fibers both correct. The surface tension error misrepresents surfactant's role, making it the exception among these statements, as compliance falls with rising tension.