Transcranial Doppler Study of the Cerebral Hemodynamic Changes During Breath-Holding and Hyperventilation Tests

BACKGROUND AND PURPOSE: The aim of the present study was to assess the time course of hyperventilation (HV) and breath-holding (BH) tests in healthy volunteers. SUBJECTS AND METHODS: Young healthy volunteers (n = 29) underwent continuous registration of the middle cerebral artery mean blood flow velocity (MCAV) during and after 30 seconds of BH and 60 seconds of HV. Absolute values as well as percentage changes of the MCAV are reported. In 13 subjects, determination of capillary blood gas parameters (pH, pCO2, pO2, and O2 saturation) was performed before tests, after BH and after HV. RESULTS: MCAV during 30 seconds of breath-holding starts to increase after 10 seconds and reaches its highest level at 30 seconds. After breathing normally, MCAV normalizes within 30 seconds. Hyper-ventilation results in a decrease in MCAV, which reaches a plateau at 20 to 30 seconds after starting to hyperventilate, and blood flow velocity did not change significantly any further until the end of the procedure. The normalization of the MCAV is incomplete at 30 seconds after finishing hyperventilation. None of the capillary blood gases changed significantly after breath-holding, whereas capillary pH, pO2, and oxygen saturation increased and pCO2 decreased after hyperventilation. No relationship was found between capillary blood gas parameters and MCAV values. CONCLUSIONS: The authors concluded that breath-holding and hyperventilation tests seem to be a practical alternative to acetazolamide and the CO2 inhalation method in the assessment of cerebral hemodynamics.