Difference between revisions of "Physiological impact of continuous positive airway pressure (CPAP) on total cerebral blood flow in healthy awake volunteers (ultrasound study)"

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==Preliminary results==
 
==Preliminary results==
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==References==
 
==References==

Revision as of 10:15, 13 November 2009

Personel

The problem

Continuous positive airway pressure (CPAP) is used for the treatment of sleep apnea patients, acting as a pneumatic splint to prevent collapse of the pharyngeal airway by increasing intrathoracic pressure1. Communication between intrathoracic and intracranial pressure (ICP) through the venous system has been established4,6,10,11 (Figure 1), which are linked with changes in intracranial compliance2 and cardiac output2,12. However, the influence CPAP has on cerebral blood flow (CBF) dynamics is not well understood.

Some studies have quantified CBF velocity using transcranial Doppler ultrasound in the cerebral middle cerebral artery during CPAP1,3,7,9. However, TCD measurements do not take into account changes in artery diameter which can occur, however minute, resulting from CBF autoregulation. Thus, the precise blood flow rate (ml/s) in the vessels of interest was not obtained, and total CBF was not measured. The proposed study investigates the influence of CPAP on total CBF by measuring velocity, rate, and lumen diameter in the internal carotid and vertebral arteries, and velocity in the middle cerebral arteries using duplex Doppler ultrasound with and without CPAP.


Hypothesis and research objectives

We hypothesize that an increase in CPAP will decrease CBF rate in healthy volunteers. The goal of this research is thus to determine the influence of CPAP on CBF dynamics in healthy individuals.

Methods and study outline

in vivo Ultrasound measurements. Our approach is to obtain CBF rate measurements during CPAP using duplex color Doppler ultrasound on 20 male age matched healthy volunteers (20-30 yrs.). Each subject will have blood velocity and lumen diameter in the internal carotid and vertebral arteries, and velocity in the middle cerebral arteries, measured with duplex Doppler ultrasound 8. These measurements will be obtained with subjects in the supine position at atmospheric pressure and after CPAP has been administered for 10 minutes at various pressures (e.g. +5, +10 and +15 cm H2O). Transcutaneous carbon dioxide tension, PCO2, will be monitored during the entire testing period for each subject. Pressure test order will be randomized for each subject. Measurement reproducibility will be examined by performing the same measurements three times on three subjects.

Expected results and potential impact

The proposed work will improve understanding of how CBF in healthy volunteers is influenced by CPAP. The test could be further explored to investigate how CPAP influences CBF in patients with sleep apnea and various types of cerebrovascular and craniospinal disorders such as stroke and hydrocephalus.

Preliminary results

File:Data cpap-us.xls

References

1. Bowie RA, O'Connor PJ, Hardman JG, Mahajan RP: The effect of continuous positive airway pressure on cerebral blood flow velocity in awake volunteers. Anesth Analg 92:415-417, 2001

2. Feldman Z, Robertson CS, Contant CF, Gopinath SP, Grossman RG: Positive end expiratory pressure reduces intracranial compliance in the rabbit. J Neurosurg Anesthesiol 9:175-179, 1997

3. Haring HP, Hormann C, Schalow S, Benzer A: Continuous positive airway pressure breathing increases cerebral blood flow velocity in humans. Anesth Analg 79:883-885, 1994

4. Heiss JD, Patronas N, DeVroom HL, Shawker T, Ennis R, Kammerer W, et al: Elucidating the pathophysiology of syringomyelia. J Neurosurg 91:553-562, 1999

5. Lockey P, Poots G, Williams B: Theoretical aspects of the attenuation of pressure pulses within cerebrospinal-fluid pathways. Med Biol Eng 13:861-869, 1975

6. Sansur CA, Heiss JD, DeVroom HL, Eskioglu E, Ennis R, Oldfield EH: Pathophysiology of headache associated with cough in patients with Chiari I malformation. J Neurosurg 98:453-458, 2003

7. Scala R, Turkington PM, Wanklyn P, Bamford J, Elliott MW: Effects of incremental levels of continuous positive airway pressure on cerebral blood flow velocity in healthy adult humans. Clin Sci (Lond) 104:633-639, 2003

8. Soustiel JF, Glenn TC, Shik V, Boscardin J, Mahamid E, Zaaroor M: Monitoring of cerebral blood flow and metabolism in traumatic brain injury. J Neurotrauma 22:955-965, 2005

9. Werner C, Kochs E, Dietz R, Schulte am Esch J: [The effect of positive end expiratory pressure on the blood flow velocity in the basal cerebral arteries during general anesthesia]. Anasth Intensivther Notfallmed 25:331-334, 1990

10. Williams B: Simultaneous cerebral and spinal fluid pressure recordings. 2. Cerebrospinal dissociation with lesions at the foramen magnum. Acta Neurochir (Wien) 59:123-142, 1981

11. Williams B: Simultaneous cerebral and spinal fluid pressure recordings. I. Technique, physiology, and normal results. Acta Neurochir (Wien) 58:167-185, 1981

12. Zaramella P, Freato F, Grazzina N, Saraceni E, Vianello A, Chiandetti L: Does helmet CPAP reduce cerebral blood flow and volume by comparison with Infant Flow driver CPAP in preterm neonates? Intensive Care Med 32:1613-1619, 2006