MR-conditional lower body negative pressure chamber: impact of subject position on autonomic response

Non-invasive neuroimaging using fMRI has the potential to identify the brain regions involved in the autonomic nervous system (ANS) and heart-brain interaction. Lower body negative pressure is a potential stressor to elicit the response of the ANS during fMRI studies. This technique is less standardized than traditional stressors such as head-up tilt test. The sealing position on the patient body is a major factor affecting the response to the negative pressure application. This study investigates the effect of two sealing positions (iliac crest - IC and tail bone - TB) on the response to the application of 40 mmHg negative pressure on normal subjects. The cardiovascular and autonomic response was assessed on 10 healthy subjects using beat-to-beat RR intervals (analyzed both in time and frequency domain) and systolic and diastolic pressure. The cardiovascular responses were stronger when the chamber was sealed on the iliac crests, compared to the tail bone sealing. For the IC position, significant differences (p<0.05) were observed in the mean heart rate, blood pressure values and LF/HF ratios. For the TB position, a significant (p<0.05) change was observed only for the mean heart rate.