The effects of beam shape on the ability to predict changes in vessel size from Doppler signal power

Deverson, Stephanie; Evans, David H.

doi:10.1016/s0301-5629(99)00121-0

Cited by 5 publications

(2 citation statements)

References 17 publications

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“…Due to distortion of the TCD's transmitting beam by the skull (Deverson, Evans, & Bouch, ) and the impact of movement of the TCD probe, great care was taken to maximize the received

\overset{P}{true}

signal prior to, and during, the securing of the TCD probe to the participant's head using a snug fitting headband (Multigon Industries). Maximizing the

\overset{P}{true}

signal permits the assumption that the entire cross‐sectional area of the MCA is fully captured within the sample volume of the TCD's transmitted signal and that any changes in the

\overset{P}{true}

signal that ensue represent a change in MCA calibre (Deverson & Evans, ). Though no in vivo validation studies have been performed, changes in the

\overset{P}{true}

signal as an index of changes in cross‐sectional area of the insonated artery has been validated using flow phantoms (Deverson & Evans, ; Hatab et al., ; Saini, Maulik, Nanda, & Rosenzweig, ), which remain the gold standard for validation of non‐invasive techniques used in humans to assess CBF such as duplex ultrasonography (Rominger et al., ) and neuroimaging (Taviani et al., ).…”

Section: Methodsmentioning

confidence: 99%

“…Maximizing theP signal permits the assumption that the entire crosssectional area of the MCA is fully captured within the sample volume of the TCD's transmitted signal and that any changes in theP signal that ensue represent a change in MCA calibre (Deverson & Evans, 2000a). Though no in vivo validation studies have been performed, changes in theP signal as an index of changes in cross-sectional area of the insonated artery has been validated using flow phantoms (Deverson & Evans, 2000b;Hatab et al, 1997;Saini, Maulik, Nanda, & Rosenzweig, 1983), which remain the gold standard for validation of non-invasive techniques used in humans to assess CBF such as duplex ultrasonography (Rominger et al, 2016) and neuroimaging (Taviani et al, 2010).…”

Section: Cbf and Cardiovascular Responses To Hypoxiamentioning

confidence: 99%

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Vascular responses to hypoxia are not impaired in obstructive sleep apnoea patients free of overt cardiovascular disease

Beaudin

Hanly

Raneri

et al. 2019

Experimental Physiology

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New Findings What is the central question of this study?Does treatment of obstructive sleep apnoea (OSA) with nocturnal oxygen or continuous positive airway pressure (CPAP) improve hypoxic vascular responses, which are reportedly impaired in OSA? What is the main finding and its importance?Cerebrovascular and cardiovascular hypoxic responses were not impaired in OSA patients free of overt cardiovascular disease and known risk factors, and were not altered by nocturnal oxygen or CPAP treatment. We conclude that this OSA patient phenotype has normal vascular responses to hypoxia and is unlikely to obtain long term cardiovascular benefits from nocturnal oxygen or CPAP therapy. Abstract Cerebral blood flow (CBF) and cardiovascular responses to hypoxia are reportedly impaired in obstructive sleep apnoea (OSA) patients and corrected by continuous positive airway pressure (CPAP), beneficial effects that are ascribed to correction of OSA‐related intermittent hypoxia (IH). However, CPAP corrects both IH and ancillary OSA features (i.e. intermittent hypercapnia, sympathetic activation, blood pressure surges, negative intrathoracic pressure swings and sleep fragmentation). Whether correction of these ancillary OSA features contribute to CPAP's beneficial effects on vascular hypoxic responses is unknown. Nocturnal oxygen corrects OSA‐induced IH, but apnoeas and ancillary features persist. Thus, we examined the effects of nocturnal oxygen and CPAP on cerebrovascular and cardiovascular hypoxic responses in untreated OSA patients. Responses were assessed in 52 OSA patients free of overt cardiovascular disease and known risk factors at baseline, after 2 weeks of nocturnal oxygen (n = 26) or no treatment (n = 26), and after ∼4 weeks of CPAP treatment (n = 40). Twenty‐two age‐matched controls were assessed at baseline and follow‐up visits. Resting, isocapnic euoxia mean blood pressure was decreased following nocturnal oxygen (−3.6 ± 6.0 mmHg; P = 0.006) and CPAP (−4.5 ± 7.5 mmHg; P < 0.001) while cerebrovascular conductance was increased with CPAP (P = 0.001). However, these changes were not different from controls. Unexpectedly, OSA patients and controls had similar hypoxic vascular responses at baseline that were not changed by either nocturnal oxygen or CPAP. We conclude that OSA patients free of overt cardiovascular disease and known risk factors did not have impaired cerebrovascular or cardiovascular responses to hypoxia and are unlikely to obtain long term cardiovascular benefits from nocturnal oxygen or CPAP therapy.

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“…Due to distortion of the TCD's transmitting beam by the skull (Deverson, Evans, & Bouch, ) and the impact of movement of the TCD probe, great care was taken to maximize the received

\overset{P}{true}

signal prior to, and during, the securing of the TCD probe to the participant's head using a snug fitting headband (Multigon Industries). Maximizing the

\overset{P}{true}

signal permits the assumption that the entire cross‐sectional area of the MCA is fully captured within the sample volume of the TCD's transmitted signal and that any changes in the

\overset{P}{true}

signal that ensue represent a change in MCA calibre (Deverson & Evans, ). Though no in vivo validation studies have been performed, changes in the

\overset{P}{true}

Section: Methodsmentioning

confidence: 99%

Section: Cbf and Cardiovascular Responses To Hypoxiamentioning

confidence: 99%

Vascular responses to hypoxia are not impaired in obstructive sleep apnoea patients free of overt cardiovascular disease

Beaudin

Hanly

Raneri

et al. 2019

Experimental Physiology

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Modelling vascular reactivity to investigate the basis of the relationship between cerebral blood volume and flow under CO2 manipulation

2008

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Relative Blood Flow Changes Measured Using Calibrated Frequency-Weighted Doppler Power at Different Hematocrit Levels

Wallace

Logallo

Faiz

et al. 2014

Ultrasound in Medicine & Biology

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In theory, the power of a trans-cranial Doppler signal may be used to measure changes in blood flow and vessel diameter in addition to velocity. In this study, a flow index (FI) of relative changes in blood flow was derived from frequency-weighted Doppler power signals. The FI, plotted against velocity, was calibrated to the zero intercept with absent flow to reduce the effects of non-uniform vessel insonation. An area index was also calculated. FIs were compared with actual flow in four silicone tubes of different diameter at increasing flow rates and increasing hematocrit (Hct) in a closed-loop phantom model. FI values were strongly correlated with actual flow, at constant Hct, but varied substantially with changes in Hct. Percentage changes in area indexes, relative to the 4-mm tube, were strongly correlated with tube cross-sectional area. The implications of these results for in vivo use are discussed.

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The effects of beam shape on the ability to predict changes in vessel size from Doppler signal power

Cited by 5 publications

References 17 publications

Vascular responses to hypoxia are not impaired in obstructive sleep apnoea patients free of overt cardiovascular disease

Vascular responses to hypoxia are not impaired in obstructive sleep apnoea patients free of overt cardiovascular disease

Modelling vascular reactivity to investigate the basis of the relationship between cerebral blood volume and flow under CO2 manipulation

Relative Blood Flow Changes Measured Using Calibrated Frequency-Weighted Doppler Power at Different Hematocrit Levels

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