Relationship between central pulsatile aortic and intracranial pressure in humans

Logical management of hypertension and its neurological complications requires understanding of the mechanisms determining pulsatile cerebral blood flow, their disturbance in disease, and their amelioration with therapy. To date, emphasis has been directed to compliance of arterial and arteriolar vessels within the skull. This approach differs with approaches addressing pulsatile function in vascular beds elsewhere. In 10 patients with normal pressure hydrocephalus (NPH), the relationships between central aortic pressure (AP) and intracranial pressure (ICP) waves were studied prior to establishment of a required cerebrospinal fluid shunt to the pleural cavity. Pressures were measured from within the radial artery and cerebral ventricle with matched, fluid-filled, high-frequency manometers. Radial pressure waves were converted to aortic waves using SphygmoCor®. Simultaneously recorded AP and ICP waves were ensemble-averaged and compared in the time and frequency domains. Basic characteristics of patients were: diagnosed NPH with typical clinical features; age 76±4 years, 6 males, systolic 149±19 mmHg, diastolic 62±13 mmHg, mean AP 90±8 mmHg, mean ICP 0.5±3.7 mmHg, pulse AP 60±13 mmHg, pulse ICP 6±2 mmHg. ICP and AP pressure waves were similar and ratio of ICP/ AP amplitude was 0.08±0.01. Similarity in the time domain was confirmed by similarity of ICP/ AP of the first 3 harmonics (which contained 98% of waveform energy) and mean phase delay close to or not significantly different from zero. Close correspondence of ICP and AP pressure waveforms in both time and frequency domains indicates ICP pulsations are due to pulsations of pressure in cerebral arteries without any appreciable effect of venous pressure. Since aortic pressure pulsations are markedly effected by wave reflection from the lower body, one must consider effects of drugs on systemic wave reflection when attempting to reduce fluctuations of ICP.