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

This study investigated cerebral hemodynamics, intracranial pressure (ICP), and cognitive function in 18 older men (median 72 yr, interquartile range 68-75, 94% with ≥1 comorbidity) during a 15-min, 30° head-down tilt (HDT). Participants were monitored with continuous noninvasive hemodynamic measurements, transcranial and carotid Doppler ultrasound, and optic nerve sheath diameter. Cognitive testing was performed before and after HDT. Hemodynamic changes were compared with 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% confidence interval 4.25, 7.8)], whereas systolic arterial blood pressure at heart level (SBP_heart) 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 internal carotid blood flow (β = 0.3), with a 1 L·min^-1·m^-2 increase predicting an 84 mL·min^-1 increase in cerebral blood flow. Cognitive testing was mainly unaffected by HDT. Comparison with anesthetized patients revealed different hemodynamic responses to HDT. Mean arterial blood pressure at heart level 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·m^-2 (-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.NEW & NOTEWORTHY In awake older men, self-reporting as healthy but with prevalent well-controlled comorbidities, 15 min of 30° head-down tilt did not affect cerebral blood flow or induce cognitive decline despite significantly increasing noninvasively measured intracranial pressure. Mean arterial pressure at heart level decreased during tilt, ensuring only a marginal increase in mean arterial pressure at ear level. These hemodynamic effects differed considerably from those in anesthetized laparoscopy patients.