Acute Lunar Orthostatic Hypotension
Earth designation: Acute Orthostatic Hypotension
Acute presentation of Orthostatic Hypotension in lunar residents. A sudden drop in blood pressure when standing, severely exacerbated by the cardiovascular deconditioning that occurs in low-gravity environments. In 1/6 gravity, blood pools less in the legs, causing the cardiovascular system to partially lose its Earth-adapted reflexes. On return from a lunar EVA o...
Lunar Risk Factors
Prolonged microgravity exposure causes cephalad fluid shifts and reduced plasma volume. The cardiovascular system loses its Earth-adapted baroreceptor reflexes within weeks. Risk is highest on return to full lunar gravity after extended EVA in microgravity conditions, during illness, and in residents with more than 6 months habitation.
Symptoms
Dizziness, lightheadedness, blurred vision, weakness, nausea, fainting (syncope) upon standing.
Lunar Presentation
In lunar gravity, symptoms are often milder than on Earth but persist longer. Greying of vision ("tunneling") is common. Some residents report chronic mild symptoms that become background noise — a dangerous normalization.
Diagnosis
Postural blood pressure measurement: drop of ≥20 mmHg systolic or ≥10 mmHg diastolic within 3 minutes of standing. Tilt-table testing in the medical bay.
Treatment
Hydration, compression garments, increased dietary salt, fludrocortisone if chronic.
Lunar Medical Bay Protocol
First line: 500mL oral rehydration solution. Compression garments from suit components. Have patient sit or recline. If syncope occurs, elevate legs (requires strapping in 1/6 g). Fludrocortisone from lunar pharmacy if recurring. Telemedicine consult if not resolving within 30 minutes.
Evacuation Criteria
Repeated syncopal episodes unresponsive to treatment. New-onset severe hypertension following hypotensive episode. Associated chest pain or arrhythmia.
Prevention
Daily cardiovascular exercise (minimum 90 min/day on resistance treadmill), maintaining adequate hydration, gradual postural changes, compression garments during EVA.