Comparison of diurnal blood pressure and urine production between people with and without chronic spinal cord injury

Abstract

Study design: Observational study. Objectives: To quantify diurnal blood pressure (BP) patterns and nocturnal hypertension and to measure diurnal urine production in people with chronic spinal cord injury (SCI), compared with controls without SCI. Setting: Chronic SCI population in the community in Victoria, Australia. Methods: Participants were recruited by advertisement, and sustained SCI at least a year prior or were healthy able-bodied volunteers. Participants underwent ambulatory BP monitoring (ABPM), measurement of urine production, and completed questionnaires regarding orthostatic symptoms. Comparisons were made between participants with tetraplegia or paraplegia and able-bodied controls. Participants with night:day systolic BP < 90% were classified as dippers, 90–100% as nondippers, and >100% as reverse dippers. Results: Groups with tetraplegia (n = 51) and paraplegia (n = 33) were older (42.1 ± 15 and 41.1 ± 15 vs. 32.4 ± 13 years, mean ± s.d.) and had a higher prevalence of males (88 and 85% vs. 60%) than controls (n = 52). The average BP was 110.8 ± 1.5/64.4 ± 1.2 mmHg, 119.4 ± 2.1/69.8 ± 1.5 mmHg, and 118.1 ± 1.4/69.8 ± 1.0 mmHg in tetraplegia, paraplegia, and controls, respectively. Of participants with tetraplegia, paraplegia and controls, reverse dipping was observed in 45, 13, and 2% (p < 0.001), while nocturnal hypertension was observed in 13, 23, and 18%, respectively (p = 0.48). A reduction in nocturnal urine flow rate compared with the day was observed in paraplegia and controls, but not tetraplegia. Conclusions: Similar to the effects of acute SCI, chronic SCI, specifically tetraplegia, also causes isolated nocturnal hypertension, reverse dipping, orthostatic intolerance, and nocturnal polyuria. Cardiovascular risk management and assessment of orthostatic symptoms should include ABPM.