Cardiovascular and cognitive consequences of steep head-down tilt in awake older men

This study investigated cerebral hemodynamics, intracranial pressure, and cognitive function in eighteen older men (median 72 years, IQR 68-75, 94% with ≥1 comorbidity) during a 15-minute 30-degree head-down tilt (HDT). Participants were monitored with continuous non-invasive hemodynamic measurements, transcranial and carotid Doppler ultrasound, and optic nerve sheath diameter. Cognitive testing was performed before and after HDT. Hemodynamic changes were compared to data from anesthetized positive pressure ventilated patients undergoing surgery with pneumoperitoneum during steep HDT. During HDT, mean arterial pressure at ear level increased (6.0 mmHg (95%CI 4.25, 7.8) while mean arterial blood pressure at heart level (MAPheart) decreased (-10.2 mmHg (-12.4, 8.0)). Heart rate, stroke volume, and cardiac index (CI) were unchanged. Despite increased estimated ICP, internal carotid artery and middle cerebral artery blood velocities and flow remained unchanged throughout HDT, suggesting preserved cerebral autoregulation. CI was the strongest predictor of moment-to-moment internal carotid blood flow (β=0.3), a 1 L⸱min-1⸱m2 increase predicting an 84 mL/min cerebral blood flow increase. Cognitive testing was mainly unaffected by HDT. Comparison with anesthetized patients revealed different hemodynamic responses to HDT. MAPheart increased in anesthetized patients (14.1 mmHg (8.9, 19.3), p<0.0001) but decreased in awake participants (-6.2 mmHg (-11.8, -0.6), p<0.0001). CI declined after HDT in anesthetized patients (-0.39 L⸱min-1⸱m2 (-0.59, -0.18), p<0.001) but was unchanged in awake participants. Cerebral blood flow remained unaltered in both groups, suggesting effective autoregulation. These findings suggest that short-duration steep HDT in older individuals does not compromise cerebral blood flow or cognitive function.