ATTENUATED HR AND BLOOD PRESSURE RESPONSE TO ISOMETRIC EXERCISE IN MULTIPLE SCLEROSIS (MS) 472

Abstract

Our previous investigation of 104 MS patients revealed an attenuated pressor response to isometric handgrip exercise at 30% of maximal voluntary contraction (MVC) sustained to fatigue (IHE). Increase in heart rate (HR) was identical to control subjects, and clinical indices of symptom severity (EDSS and ISS scores) did not predict abnormal pressor response in regression analysis. The distribution of the pressor response, however, showed a wide range and was distinctly bimodal, suggesting two subgroups within the cohort. Therefore we retrospectively compared patients with attenuated pressor responses (A) to similar patients with nonattenuated responses (NA). A patients (n = 27), defined by an increase in mean arterial pressure (MAP) of< 20mmHg at end-IHE, were matched with NA patients (n = 22) (peak MAP = 46± 6mmHg). Groups were similar in MVC (37.3 ± 2.6 vs. 38.5± 3.1N, mean ± SEM), time to fatigue (206.8 ± 11.7 vs. 232.0 ± 15.3s) and resting MAP (94.3 ± 2.5 vs. 97.6 ± 2.2mmHg). By definition, change in MAP was lower in A at all time points during IHE (peak Δ: 12.8 ± 1.1 vs. 44.2 ± 1.1 mmHg; P<.0001). Resting HR was higher in A (79.6 ± 2.1 vs. 71.7 ± 2.4 bpm; P =.015) and the change in HR was less in A at all time points during IHE (peak Δ: 14.4 ± 2.3 vs. 26.7 ± 2.3 bpm; P =.0005). Indices of MS-related neurologic symptoms were higher in A (EDSS: 4.5 ± 0.4 vs. 3.1 ± 0.3; P=.009; ISS: 14.9 ± 1.4 vs. 9.5 ± 1.0; P =.003). These data suggest that, contrary to previous reports, certain MS patients have a blunted heart rate response to IHE which may in part underlie the attenuated pressor response seen in these individuals. Moreover, greater overall symptom severity may increase the likelihood of cardiovascular/autonomic involvement in MS patients.