Plethysmography
- blood flow in the forearm ©
Department of Physiology, FM MU, Jan Novák, 2016
Blood flow measurement I
• Radionuclide method
– patient is injected with radioactive solution (= radiopharmaceutical) with short
half-life (= fast elimination from the body = low toxicity)
– higher the blood flow in the organ, higher the up-take of the
radiopharmaceutical and higher is the radiation (emitted by the
radiopharmaceutical) detected on the special detector
Obrázek 1: http://web.carteret.edu/keoughp/LFreshwater/CPAP/V-Q%20Relationships/VQClassNotes_files/image006.jpg
Obrázek 2: http://img.medscapestatic.com/pi/meds/ckb/39/26839tn.jpg
• Clinical use:
• Lung scintigraphy
• used in the diagnostics of the pulmonary embolism
(clinical condition when embolus blocks part of the
pulmonary circulation and the area ahead of this
obstruction shows no blood flow and is ischemic)
• Myocardial scintigraphy (Cardiac-SPECT)
• used in the diagnostics of ischemic heart disease if the
ECG and laboratory results are unclear
• After administration, radiopharmaceutical is distributed
over the myocardium and areas with low
radiopharmaceuticals concentration corresponds to the
badly-perfused areas („hibernating myocardium“,
locations after coronary artery stenosis) or to areas after
myocardial infarction (myocardial scar is less perfused
compared to healthy myocardium)
Normal lung Arrows = flow defect = embolism
Normal heart Arrow = flow defect = ischemia
Blood flow measurement II
• Doppler measurements
– based on Doppler effect (changes in
the frequency and wavelength of the
emitted and received signal based on
the mutual movement of the
transmission device and receiver)
• Clinical use:
• vessel ultrasound of extremities (thrombosis, ischemia and blood flow assessment in limbs)
• echocardiography (blood flow over valves, valves diseases – stenosis, regurgitations…)
• Transcranial Doppler (blood flow in the brain circulation)
http://thequantumtunnel.com/wp-content/uploads/2013/06/Sheldon-
as-Doppler-Effect.png
Obrázek tepen DKK: http://pacificvascular.com/wp-content/uploads/2014/02/PAEvaluations2.png
Obrázek echokardioagrafie: https://web.stanford.edu/group/ccm_echocardio/wikiupload/thumb/f/f9/A4C_MR_moderate.jpg/480px-A4C_MR_moderate.jpg
Obrázek TCD: http://www.swedish.org/~/media/Images/Swedish/I/Image3CircleofWillis.JPG
Blood flow measurement III
• Plethysmography
– evaluation of the volume changes in the limbs (higher the blood flow, faster the
volume increase if the blood outflow from the limb is closed)
– venous occlusive plethysmography uses two cuffs:
• occlusive cuff (OC) is used to close (=occlude) blood outflow through veins
• measuring cuff (MC) is used to detect volume changes
• Clinical use:
• Evaluation of endothelial function
and dysfunction (within research, so
called FMD = flow-mediated dilation
of brachial artery reflects the function
of endothelial NO-synthasis)
• Evaluation of the ischemic limb
disease (USA, especially in research or
in clinical practice using segmental
measurement of blood pressure,
which informs us about the location of
the arterial occlusion) https://www.perimed-instruments.com/upl/images/377677_464_333_2_0_thumb/segmental-pressures-perimed.jpg
Vascular tone regulation
• Various vasoactive compounds are affecting the vessel at one time including
both vasodilatory (nitric oxide, adenosine, histamine, low pH = acidosis…) and
vasoconstrictive compounds (angiotensin II, adrenaline through α-receptors,
vasopressin, serotonin, caffeine…) = whether vasodilation or vasoconstriction
occurs, depends on their ratio
• Neural regulation
– Vessels are innervated via sympathetic nervous system:
• α-receptors causing vasoconstriction
• β-receptors causing vasodilation (coronary, muscle and lung circulation)
• Myogenic regulation
– increased vessel wall tension causes vasoconstriction (we can image this as an „defense against
too big vessel extension if the blood pressure is too high“)
– myogenic regulation is mediated via stretch-receptors, that are connected to cationic channels
(Na+, Ca2+) = cation influx into cell leads to depolarization and smooth muscle cells contraction
• Metabolic regulation
– under ischemic conditions, variety of metabolic degradation products originates (e.g. lactate,
ADP, AMP) and pH decreases (acidosis), all of which results in vasodilation („the aim is to
remove the degradation products from circulation“)
– this is called reactive hyperemia
– metabolic regulation is tightly connected with functional hyperemia that occurs during physical
exercise (exercise causes the series of contractions and relaxations which affects blood flow in
vessels; after every contraction blood flow increases during the relaxation period and this
hyperemia lasts even after the exercise is over)
Endothelial function and dysfunction
• Endothelial functions:
– Barrier function (endothelium is a part of hematoencephalic barrier, glomerular filtration
membrane, it participates on the creation of the lymph, etc.)
– Blood clotting and coagulation (thrombocyte adhesion, tissue factor, tPA,…)
– Immune and inflammatory reaction (endothelial selectins, VCAM, ICAM…)
– Endocrine functions (e.g. nitric oxide, angiotensin-converting enzyme production, many
various receptors for various hormones and signaling molecules)
• Endothelial dysfunction
– Endothelial dysfunction is a complex pathological phenomenon characterized by:
• disruption of the vasodilation/vasoconstriction ratio (based mainly on the deficiency of nitric oxide)
• pro-trombogenic state (higher risk of thrombi creation consequently causing vessel wall inflammation)
• transition from quiescent to proliferative stage (disrupted endothelium produces various growth factors and
cytokines leading to endothelial and vascular smooth muscle cells proliferation resulting in the vascular
remodeling)
– Endothelial dysfunction represents the initial stage of the atherosclerosis which in the end
of the day leads to ischemic heart disease (including myocardial infarction), ischemic limb
diseases (causing various ulcers and leading to limb amputations) or to brain vessels
atherosclerosis (including ischemic strokes)
ENDOTHELIAL
DYSFUNCTION
DEVELOPED ATHEROSCLEROTIC PLAQUE
(+ ISCHEMIA)