Diurnal blood pressure and urine production in acute spinal cord injury compared with controls.

STUDY

DESIGN

This is a prospective observational study.

OBJECTIVES

The objective of this study was to determine time-dependent changes in diurnal blood pressure (BP) and urine production in acute spinal cord injury (SCI).

SETTING

This study was conducted in a specialist, state-based spinal cord service in Victoria, Australia.

METHODS

Consenting patients admitted consecutively with acute SCI were compared with patients confined to bed rest while awaiting surgery and with mobilising able-bodied controls. Participants underwent ambulatory BP monitoring (ABPM), measurement of diurnal urine production and rated orthostatic symptoms over 1 year. Participants with night:day systolic BP (SBP) <90% were classified as dippers, 90-100% as non-dippers and >100% as reverse dippers.

RESULTS

Participants comprised tetraplegics (n=47, 40.0±17.3 years), paraplegics (n=35, 34.4±13.9 years), immobilised (n=18, 30.9±11.3 years) and mobilising (n=44, 33.1±13.5 years) controls. At baseline, 24-h BP was significantly lower in tetraplegics (111.8±1.9/62.1±1.1 mm Hg) but not in paraplegics (116.7± 1.4/66.0±1.1 mm Hg), compared with controls (117.1 ±1.3/69.1±1.1 mm Hg), adjusting for gender. This difference was not observed at 1 year. The average night:day SBP in mobilising controls was 86.1±0.7%, differing from paraplegics (94.0±1.5%, P<0.001) and tetraplegics (101.5±1.5%, P<0.001). Urine production in tetraplegics and paraplegics did not fall at night compared with the day. Abnormal diurnal BP and orthostatic symptoms in tetraplegics persisted throughout the study. Nocturnal hypertension was observed in 27% (n=9) of tetraplegics, of whom only 2 had day hypertension. All mobilising controls with nocturnal hypertension (n=6, 14%) had day hypertension.

CONCLUSION

People with SCI have a high prevalence of isolated nocturnal hypertension, reverse dipping, orthostatic intolerance and nocturnal polyuria. Cardiovascular risk management and assessment of orthostatic symptoms should include ABPM.