medwireNews: Deconditioning is present in almost all patients with orthostatic intolerance, report US researchers.
"Our findings support the approach of initiation of a vigorous reconditioning program in all patients with this condition, although further studies are necessary to document long-term outcome," say Paola Sandroni and team from the Mayo Clinic in Rochester, Minnesota.
They report in Neurology that 93% of the 184 patients in their study had evidence of deconditioning, having a maximum oxygen uptake during exercise that was less than 85% of that predicted. Deconditioning was present in 95% of the 84 patients who had orthostatic tachycardia and 91% of the 100 patients who did not.
The severity of deconditioning was mild in about half of the patients (maximum oxygen uptake 85‑65% of predicted), and severe in the others.
Sandroni et al say this "intriguing" finding of near universal deconditioning in their patients "supports the argument that deconditioning plays a role in the pathophysiology" of orthostatic intolerance. However, they note that the condition can often be debilitating; 98% of the patients in the study had a reduced work capacity as a result of their symptoms.
"Whether deconditioning is a primary or secondary phenomenon remains therefore unclear, although a major pathophysiologic role of this finding has to be postulated in most of the patients with this condition."
The patients' orthostatic intolerance had lasted a median of 4 years at the time of the exercise testing, but deconditioning did not correlate with symptom duration, or with age or gender.
The researchers found correlations between the extent of deconditioning and a few autonomic parameters. These included 24-hour urine volume and blood pressure changes during various stages of the Valsalva maneuver. However, all correlations were generally weak and none of the parameters significantly predicted deconditioning.
"Therefore, deconditioning cannot be predicted by laboratory and autonomic parameters, so that exercise evaluation is necessary to define the presence and severity of deconditioning," concludes the team.
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