Carotid Doppler Ultrasound for the Measurement of Intravascular Volume Status
| Status: | Recruiting |
|---|---|
| Conditions: | Cardiology, Hospital |
| Therapuetic Areas: | Cardiology / Vascular Diseases, Other |
| Healthy: | No |
| Age Range: | 18 - 60 |
| Updated: | 6/30/2018 |
| Start Date: | September 2016 |
| End Date: | July 2018 |
| Contact: | Jill C Crosby, MD |
| Email: | jcrosby059@gmail.com |
Carotid Doppler Ultrasound for the Measurement of Intravascular Volume Status During Lower Body Negative Pressure Simulation
Ultrasound represents an attractive non-invasive method to assess hemodynamic status.
Understanding dynamic changes in hemodynamics in situations such as hypovolemia, sepsis, and
cardiogenic shock can potentially help improve patient care. However, the inter-rater
reliability and accuracy of how various ultrasound measurements reflect dynamic changes in
physiology remains incompletely understood. Overall our aims are to investigate the use of
ultrasound in a controlled setting, specifically using lower body negative pressure (LBNP),
which can simulate hypovolemia at varied levels in human volunteers.
Aim 1: To determine the change in carotid blood flow (measured by velocity time integral,
VTI) in subjects undergoing simulated hypovolemia at LBNP levels that precede vital sign
changes.
Hypothesis: Carotid VTI will demonstrate significant changes that precede vital sign changes
in simulated hypovolemia.
Aim 2: To compare transcranial color Doppler indices of cerebral blood flow with carotid
blood flow, as assessed by VTI of the common carotid artery.
Hypothesis: Changes in transcranial color Doppler indices of cerebral blood flow will be
mirrored by changes in carotid blood flow, indicating carotid VTI is an adequate surrogate
for measuring cerebral blood flow in variable states of central hypovolemia. However, if
cerebral blood flow remains more constant than carotid blood flow throughout varying levels
of hypovolemia, our assumption is that cerebral autoregulation alters the relationship
between carotid and cerebral blood flow. The more complex procedure of Transcranial Doppler
ultrasound (TCD) must be performed to obtain valid assessments of cerebral blood flow.
Understanding dynamic changes in hemodynamics in situations such as hypovolemia, sepsis, and
cardiogenic shock can potentially help improve patient care. However, the inter-rater
reliability and accuracy of how various ultrasound measurements reflect dynamic changes in
physiology remains incompletely understood. Overall our aims are to investigate the use of
ultrasound in a controlled setting, specifically using lower body negative pressure (LBNP),
which can simulate hypovolemia at varied levels in human volunteers.
Aim 1: To determine the change in carotid blood flow (measured by velocity time integral,
VTI) in subjects undergoing simulated hypovolemia at LBNP levels that precede vital sign
changes.
Hypothesis: Carotid VTI will demonstrate significant changes that precede vital sign changes
in simulated hypovolemia.
Aim 2: To compare transcranial color Doppler indices of cerebral blood flow with carotid
blood flow, as assessed by VTI of the common carotid artery.
Hypothesis: Changes in transcranial color Doppler indices of cerebral blood flow will be
mirrored by changes in carotid blood flow, indicating carotid VTI is an adequate surrogate
for measuring cerebral blood flow in variable states of central hypovolemia. However, if
cerebral blood flow remains more constant than carotid blood flow throughout varying levels
of hypovolemia, our assumption is that cerebral autoregulation alters the relationship
between carotid and cerebral blood flow. The more complex procedure of Transcranial Doppler
ultrasound (TCD) must be performed to obtain valid assessments of cerebral blood flow.
Study Design: This is a prospective laboratory study using human volunteers.
Study Setting and Subjects: The study will take place in The John B. Pierce Laboratory where
volunteers will be subjected to lower body negative pressure using the on-site LBNP chamber.
Protocol: Study subjects will be instructed to refrain from caffeine, alcohol, or cigarettes
within 12 hours of the protocol, but will otherwise be allowed their routine oral intake
prior to enrollment. The chamber is constructed of a sealed wood and acrylic box that is
connected to a vacuum. Subjects will be placed into the chamber, which is sealed to the level
of their pelvis by a neoprene skirt. Chamber pressure is transduced to an electronic digital
manometer. The pressure in the chamber will reduced rapidly and held for 15-minute intervals
at -5, -10, -15, and -20 mm Hg. If the subject becomes lightheaded, nauseated, or does not
tolerate the test run in any way; negative pressure will be stopped.
Subjects will be monitored with continuous electrocardiogram monitoring, a standard automated
blood pressure cuff, and a noninvasive beat-to-beat hemodynamic monitor (Finometer, Finapres
Medical Systems, Amsterdam, The Netherlands). All carotid ultrasound measurements will be
performed by specifically trained emergency physicians, using a Philips ultrasound machine
(Philips Medical Systems, Andover, MA) equipped with phased and linear array probes
programmed with Doppler capability. For transcranial Doppler imaging, we will use a 5- to
1-MHz sector array transducer and an Iu-22 ultrasound system (Philips Healthcare, Best, the
Netherlands). Duplex sonography will be performed at the lower end of the frequency range
(1-2 MHz) for better sound wave penetration of selected bone windows. For both the common
carotid artery and transcranial portion of this study, we will obtain spectral Doppler
waveform tracings and record measurements of corresponding vessel diameters. We will use data
generated from software analysis of these spectral tracings to calculate hemodynamic
parameters of interest to our study. Calculations are based on Bernoulli's principles of
fluid dynamics.
Study Setting and Subjects: The study will take place in The John B. Pierce Laboratory where
volunteers will be subjected to lower body negative pressure using the on-site LBNP chamber.
Protocol: Study subjects will be instructed to refrain from caffeine, alcohol, or cigarettes
within 12 hours of the protocol, but will otherwise be allowed their routine oral intake
prior to enrollment. The chamber is constructed of a sealed wood and acrylic box that is
connected to a vacuum. Subjects will be placed into the chamber, which is sealed to the level
of their pelvis by a neoprene skirt. Chamber pressure is transduced to an electronic digital
manometer. The pressure in the chamber will reduced rapidly and held for 15-minute intervals
at -5, -10, -15, and -20 mm Hg. If the subject becomes lightheaded, nauseated, or does not
tolerate the test run in any way; negative pressure will be stopped.
Subjects will be monitored with continuous electrocardiogram monitoring, a standard automated
blood pressure cuff, and a noninvasive beat-to-beat hemodynamic monitor (Finometer, Finapres
Medical Systems, Amsterdam, The Netherlands). All carotid ultrasound measurements will be
performed by specifically trained emergency physicians, using a Philips ultrasound machine
(Philips Medical Systems, Andover, MA) equipped with phased and linear array probes
programmed with Doppler capability. For transcranial Doppler imaging, we will use a 5- to
1-MHz sector array transducer and an Iu-22 ultrasound system (Philips Healthcare, Best, the
Netherlands). Duplex sonography will be performed at the lower end of the frequency range
(1-2 MHz) for better sound wave penetration of selected bone windows. For both the common
carotid artery and transcranial portion of this study, we will obtain spectral Doppler
waveform tracings and record measurements of corresponding vessel diameters. We will use data
generated from software analysis of these spectral tracings to calculate hemodynamic
parameters of interest to our study. Calculations are based on Bernoulli's principles of
fluid dynamics.
Inclusion criteria:
1. Generally healthy
2. Able to provide informed consent
3. Over 18 years of age
Exclusion criteria:
1. Non-English speaking or decisionaly impaired
2. Significant medical illness (as determined by the study physician, JC)
3. Taking vasoactive medications
4. Older than 60 years of age
5. Inability to lie flat for prolonged period
6. Severe claustrophobia
7. Pregnant
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