Spectral characteristics of B-waves and other low-frequency activity.
Low frequency oscillations of intracranial pressure (ICP) between 0.5 to 2.0 cycles/min have been termed B-waves. While such low frequency activity may be generated by cerebral vasomotor activity, activity in the B-wave band may also be related to other causes. The objective of this study is to: 1) describe the low frequency characteristics of ICP and arterial blood pressure (ABP) recordings with a mathematical model based on ventilator-induced intrathoracic pressure (ITP) modulation of arterial blood pressure; and 2) use the model to eliminate low frequency activity within the B-wave range unrelated to vasomotor activity. The model describes the frequency locations of spectra associated with ventilation about both the principal and first harmonic cardiac frequency to within 1% error. Spectra within the B-wave range harmonically related to the ventilator frequency were classified as caused by patient-ventilator interaction. Of 11 patients with severe head-injury, 64% (7/11) demonstrated B-wave activity, and 4 patients demonstrated the activity solely in the ICP recording. Variation of heart rate did not correspond to the occurrence of B-waves. The proposed model describes the low frequency spectra found within ABP and ICP recordings and can be used to eliminate spectra with the B-wave range related to ventilation.
Daley
M L
ML
Department of Electrical and Computer Engineering, University of Memphis, Memphis, TN, USA.
Pasley
R L
RL
Connolly
M
M
Timmons
S D
SD
Angel
J
J
Stidham
G
G
Leffler
C W
CW
D000293:Adolescent; D000328:Adult; D016477:Artifacts; D001794:Blood Pressure / Q000502:physiology*; D002648:Child; D002675:Child, Preschool; D006259:Craniocerebral Trauma / Q000503:physiopathology*; D005260:Female; D015600:Glasgow Coma Scale; D006801:Humans; D007427:Intracranial Pressure / Q000502:physiology*; D007700:Kinetics; D008297:Male; D008433:Mathematics; D008955:Models, Cardiovascular; D009991:Oscillometry