A retrospective review of sleep-disordered breathing, hypertenstion and cardiovascular diseases in spinal cord injury patients

We read with great interest the article by Goh _et al._1 on ambulatory blood pressure (BP) monitoring and diurnal urine production in 44 tetraplegic and 10 paraplegic spinal cord injury

(SCI) patients. Data were obtained retrospectively to quantify diurnal BP patterns including nocturnal hypertension and to measure diurnal urine production. The authors concluded that

‘ambulatory BP monitoring in patients with SCI and clinically significant BP disorders detected a high incidence of reversed dipping and nocturnal hypertension.’ In addition, the authors

speculated that ‘elevated nocturnal BP may contribute to nocturnal diuresis that might cause relative volume depletion and thereby contribute to daytime orthostatic hypotension.’ After

reading these conclusions and on the basis of available evidence of very high prevalence of sleep-disordered breathing (SDB) and cardiovascular morbidities in SCI patients, we felt compelled

to write this letter. Our major concern is that the authors do not report information on sleep-related disorders as contributors to the mechanism of nocturnal hypertension in SCI patients.

Further, new data (summarized below) suggest that under-recognition of SDB could contribute to the increased prevalence of hypertension and cardiovascular disorders in this population of

patients. In fact, more than half of patients with SCI are obese or overweight, leading to an increased risk for both SDB and cardiac diseases.2 Our group has been studying SDB among SCI

patients, and, we have found that SDB, defined by the apnea–hypopnea index ⩾5 events per hour, was present in 77% of chronic SCI patients, with rates higher among those with cervical

compared with thoracic injuries (93% vs 55%, respectively, _P_<0.05).3 One in four cervical SCI had Cheyne–Stokes respiration pattern during their overnight laboratory sleep study, and

one in five had hypertension or cardiac disease. Furthermore, nearly all patients had poor sleep quality and daytime sleepiness or fatigue as measured by the Pittsburgh Sleep Quality Index,

the Fatigue Severity Scale and the Epworth Sleepiness Scale. In the manuscript, the authors did not report information on whether or not patients had SDB or whether other cardiovascular

comorbidities were present. We also are interested in the rates of diagnosis of SDB (obstructive sleep apnea and/or central sleep apnea) in SCI patients receiving usual clinical care, and,

to that end, we reviewed medical records of patients who were included in the local Spinal Cord Injury and Disorders Outcomes database at the John D Dingell VA Medical Center. We identified

a total of 168 veterans with SCI/or disorder. We found that only 37 patients (22%) were evaluated for SDB and 34 (20%) had SDB diagnosis confirmed by the sleep study, of whom only 6 patients

(18%) were using the positive airway pressure (PAP) therapy. Moreover, 89 (53%) of SCI veterans had hypertension and 26 (16%) had cardiovascular disease (including one or more of the

following diagnoses: myocardial infarction, coronary artery disease and/or chronic heart failure), which may be caused or exacerbated by untreated SDB. The strong relationship between

untreated SDB and nocturnal hypertension had been repeatedly confirmed in able-bodied individuals with SDB. Ambulatory BP monitoring allows accurate assessment of circadian BP changes, which

can identify a blunted nocturnal decline in BP and indicate the possible secondary cause of hypertension, such as sleep apnea. Specifically, the non-dipping BP phenomenon measured by

ambulatory BP monitoring was found in untreated patients with SDB and was associated with poor outcome. Therefore, on the basis of above findings, it is unfortunate that in this manuscript

the authors did not assess the presence of SDB in these patients. We thank Goh _et al._ for their efforts to address these important problems in SCI patients. However, awareness of sleep

disorders as potentially treatable risk factors for nocturnal hypertension and altered diurnal ambulatory BP is critical to achieving the best outcomes for SCI patients. In this vulnerable

population, the lack of awareness and treatment of SDB among SCI patients may represent a form of healthcare disparity for the disabled. The consequences of untreated SDB and associated

cardiovascular disorders are severe and could contribute to the higher mortality rate in this population. We therefore recommend consideration of SDB as a possible underlying variable

explaining the findings reported in this paper. REFERENCES * Goh MY, Wong ECK, Millard MS, Brown DJ, O'Callaghan CJ . A retrospective review of the ambulatory blood pressure patterns

and diurnal urine production in subgroups of spinal cord injured patients. _Spinal Cord_ 2015; 53: 49–53. Article  CAS  Google Scholar  * Weaver FM, Collins EG, Kurichi J, Miskevics S, Smith

B, Rajan S _et al_. Prevalence of obesity and high blood pressure in veterans with spinal cord injuries and disorders: a retrospective review. _Am J Phys Med Rehabil_ 2007; 86: 22–29.

Article  Google Scholar  * Sankari A, Bascom A, Oomman S, Badr MS . Sleep disordered breathing in chronic spinal cord injury. _J Clin Sleep Med_ 2014; 10: 65–72. PubMed  PubMed Central 

Google Scholar  Download references ACKNOWLEDGEMENTS Research mentioned in this letter was supported by the United States Department of Veterans Affairs Merit Review Award 1I01CX001040 and

Career Development Award 1IK2CX000547 from the Clinical Science Research & Development Service of the VA Office of Research and Development. AUTHOR INFORMATION AUTHORS AND AFFILIATIONS *

Department of Medicine, John D Dingell VA Medical Center, Detroit, MI, USA A Sankari & M Badr * School of Medicine, Wayne State University, Detroit, MI, USA A Sankari & M Badr *

Geriatric Research Education and Clinical Center, VA Greater Los Angeles Healthcare System, North Hills, CA, USA J L Martin * David Geffen School of Medicine at the University of California,

Los Angeles, CA, USA J L Martin Authors * A Sankari View author publications You can also search for this author inPubMed Google Scholar * J L Martin View author publications You can also

search for this author inPubMed Google Scholar * M Badr View author publications You can also search for this author inPubMed Google Scholar CORRESPONDING AUTHOR Correspondence to A Sankari.

ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no conflict of interest. ADDITIONAL INFORMATION Parts of these findings were presented at the American Professional Sleep Society

meeting in Minnesota on June 2014 and reported in abstract form. DISCLAIMER The opinions expressed in this article reflect those of the authors and do not necessarily reflect official views

of the VA. RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Sankari, A., Martin, J. & Badr, M. A retrospective review of sleep-disordered breathing,

hypertenstion and cardiovascular diseases in spinal cord injury patients. _Spinal Cord_ 53, 496–497 (2015). https://doi.org/10.1038/sc.2015.16 Download citation * Published: 10 February 2015

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