AOBPM Preventive Medicine cheat sheet

Boyle's law (P1V1 = P2V2 at constant T) explains barotrauma and trapped-gas expansion: gas volume doubles ascending from 2 ATA (10 m seawater) to 1 ATA at the surface.

Dalton's law of partial pressures: alveolar PO2 = FiO2 × (Pb − 47 mmHg) − (PaCO2 / R); at altitude, reduced Pb lowers PiO2 even at the same FiO2.

Henry's law: dissolved gas content = solubility coefficient × partial pressure; nitrogen loading and unloading in blood and tissues follows this proportionality.

Decompression sickness (DCS) type I is musculoskeletal/cutaneous (pain-only bends, cutis marmorata); type II involves neurologic, pulmonary, or cardiovascular systems and is more urgent.

Arterial gas embolism presents with sudden neurologic deficit within minutes of surfacing after breath-hold ascent or pulmonary barotrauma; treat with hyperbaric recompression.

Hypoxia at altitude: symptoms begin near 10,000 ft cabin altitude; time of useful consciousness falls steeply above FL 350 (e.g., ~30-60 s at FL 430).

Spatial disorientation in aviation is most often somatogyral (leans/somatogravic illusions) from vestibular misinterpretation of sustained acceleration without visual reference.

G-induced loss of consciousness (G-LOC) results from cerebral hypoperfusion during sustained +Gz; A-LOC (almost-LOC) precedes it with tunnel vision and greyout.

Permissible exposure limits: OSHA PELs are legally enforceable; NIOSH RELs and ACGIH TLVs are health-based recommendations, not law.

Noise-induced hearing loss: OSHA action level is 85 dBA TWA; hearing protection required at 90 dBA; standard threshold shift is ≥10 dB average at 2000, 3000, and 4000 Hz.

Heat stress: WBGT (wet bulb globe temperature) integrates dry-bulb, natural wet-bulb, and black-globe temperatures; it is the standard index for work-rest cycles.

Lead exposure: OSHA medical removal at blood lead ≥50 µg/dL (or ≥60 µg/dL averaged); chelation is reserved for symptomatic or very high levels, not routine.

Asbestosis is a diffuse interstitial fibrosis from cumulative asbestos exposure; pleural plaques are a marker of exposure, not of fibrosis severity.

Silicosis: chronic simple form after >10-20 years of silica exposure; accelerated and acute forms follow higher-intensity exposure; risk of tuberculosis is increased.

Carbon monoxide binds hemoglobin with ~200-250× the affinity of oxygen; COHb >20-25% causes headache, nausea, and confusion; treat with 100% O2 and consider hyperbaric O2.

Pesticide poisoning: organophosphates cause cholinergic crisis (SLUDGE/DUMBELS); treat with atropine for muscarinic effects and pralidoxime for nicotinic effects.

Incidence measures new cases over a period (risk or rate); prevalence measures existing cases at a point or over a period; prevalence ≈ incidence × duration for stable disease.

Relative risk (RR) is used in cohort studies; odds ratio (OR) approximates RR when disease is rare (<10%); attributable risk = incidence in exposed − incidence in unexposed.

Sensitivity = TP/(TP+FN); specificity = TN/(TN+FP); positive predictive value depends on prevalence, so a highly specific test is preferred for screening.

Herd immunity threshold ≈ 1 − 1/R0; for R0 = 5 the threshold is 0.80 (80% immune) to interrupt sustained transmission.

Levels of prevention: primordial (risk factor prevention), primary (pre-disease), secondary (early detection), tertiary (disability limitation), quaternary (avoid overmedicalization).

Screening criteria: important disease, accepted treatment, detectable latent stage, suitable test, test acceptable, natural history understood, cost-effective, continuous case finding.

Epidemic curve interpretation: point source shows a single sharp peak within one incubation period; propagated outbreak shows successive peaks one incubation period apart.

Bias: selection bias from non-representative sampling; information/recall bias from differential measurement; confounding is a third variable associated with both exposure and outcome.