Tourniquet-induced hypertension correlates with autonomic nervous system changes detected by power spectral heart rate analysis.

STUDY OBJECTIVE

To determine the autonomic changes associated with pneumatic tourniquet-induced hypertension as measured by power spectral heart rate analysis (PSHR).

DESIGN

Prospective study.

SETTING

Tertiary teaching hospital.

PATIENTS

21 healthy-patients scheduled for lower extremity surgery, during which pneumatic tourniquet inflation was expected to exceed 90 minutes.

INTERVENTIONS

Hemodynamic and PSHR data collected at 5 minute intervals during inflation of the pneumatic tourniquet. Tourniquet-induced hypertension (T-HTN) defined at 30% increase above baseline.

MEASUREMENTS AND MAIN RESULTS

Blood pressure, heart rate, maximum changes in low frequency variability (LFa), high frequency variability (HFa), and their ratio (LFa/HFa) were measured. Of the 21 patients, 11 had T-HTN. A significantly greater increase in LFa and LFa/HFa ratio was seen in the T-HTN group, where patients were greater in age. LFa, HFa, and ratio were not significantly different with T-HTN until 60 minutes or greater. Best correlation with T-HTN occurred with maximum increase in LFa/HFa ratio compared with increase in LFa or decrease in HFa.

CONCLUSION

Tourniquet hypertension correlated with activation of the sympathetic nervous systems, as measured by PSHR variables.