Blood Pressure and Sound FYS 4250 Kap.7 Blood Pressure and Sound

The circulatory system Determining blood pressure = standard clinical measurement Sound = fluctuations in pressure recorded over the frequency range of hearing Blood function = carry oxygen/carbon dioxide + nutrition/metabolic waste Oxygen diffuses from lung alvoeli io the blood, CO2 diffuseds to the lung

Typical blood pressures

Invasive blood pressure measurement Direct measurements Catheter -> three-way stopcock-> pressure sensor Saline-heparine solution -> flushed regularly -> avoid clotting

Pressure sensor, fiberoptic model 1 Advantage: hydraulic connection via catheter is eliminated = high frequency response and no time delay Fiber optic sensors adv = lower cost than strain-gages, electrically safe, some may be used in MRI Fiber disadv = unable to measure relative pressure.

Pressure sensor, fiberoptic. Model 2 Intracranial pressure sensor for newborn Pressure is applied with the sensor such that the curvature of the skin surface is flattened on the anterior fontanelle. Applanation occures = equal pressure both sides

Harmonic analysis, Fourier Use Fourier analysis to characterize the oscillatory components of circulatory & respiratory system Any periodic structure can be modelled by a set of sine waves Fourier analysis => two basic postulates (periodicity & linearity) are usually satisfied More faithful reproduction of the original waveform by adding higher harmonic components

Analogous electric system - catheter sensor system Dynamic properties Increased pressure at input -> flow of liquid to the right -> cause a deflection of the sensor diaphragm Inertial properties - Inductance (compliance) Frictional - Resistance Elastic - Capacitance

Simplified analogous circuit Liquid inertance Lc is mainly due to the mass of the liquid

Frequency response catheter-transducer system

Measurement of transient-response Apply a step input, the pop technique Catheter sealed in tube by screw adaptor Squizing sphygmanometer bulb

Transient response Equation 1.38 yields the damping ratio The undamped natural frequency can be determined

Test-system for pressure transducer-system, sinus waveform

Pressure waveform distortion c) Significant time delay and an attenuated amplitude response In the underdamped case, amplitude of higher-frequency components of the pressure wave are amplified, Overdamped => higher frequency components are attenuated

Pressure waveform distortion Catheter whip. Low frequency oscillations due to bending and whipping of the ventricular catheter in a region of high pulsatile flow

Heart sounds Auscultation of the heart = valuable information Relationship between heart sounds and mechanical and electric events of the cardiac cycle = phonocardiography We don’t know exactly the origin of heart sounds Movement of blood during ventricular systole. Oscillations of blood between the descending root of aorta and ventricle and blood turbulence at the aortic and pulmonary valves Low frequency vibration associated with the deceleration and reversal of flow in the aorta and pulmonary artery and closure of semilunar valves Sudden termination of the rapid filling phase of the ventricles from the atria and the associated vibration of the ventricular muscle walls which are relaxed Not audible, atria contraction Murmurs, abnormal = stenoses and insufficiences (leaks) at the valves

Auscultation techniques Fat and lungs attenuate sounds, best transmitted through solid tissue Murmurs = 0.1 - 2000Hz Audible treshold = 20 Hz

Stethoscopes, spectrogram Transmit heart sounds from the chest wall to the human ear Amplifies sound due to a standing-vawe phenomenon that occurs every quarter wavelengths of the sound. Uneven frequency response curve with many resonance peaks Critical sounds may be lost by an attenuation as little as 3dB Electronic stethoscopes have flopped => physicians are unfamiliar with the sounds

Cardiac catheterization Stenotic aortic valve before and after operation

Estimation of heart valve orifice Poiseuille

Non-invasive blood pressure Measure intra-arterial pressure noninvasively

Måles blodtrykk? Målefeil Eksempel: Non-invasiv måling av blodtrykk: I en medisinsk målesituasjon opptrer en rekke målefeil som er spesielle for fagområdet medisin. I naturvitenskapene måles det på objekter, i medisinen på subjekter. Hver målemetode har sine karakteristiske feilkilder. Metrolog-parametre Trykkutslipps-hastighet sifferpreferanse hørsel/trening Fysiologiske parametre romtemp./bekledning anstrengelse/forhistorie kroppsposisjon målested angst, avslappethet, stress avstegningstid mansjett Tekniske parametre Feilfritt kommunikasjonsrør Avlesningsskala (f.eks. temp.avhengighet) skala i lodd nullpunkt Vevsparametre Mansjettbredde klær under mansjett trykkforplanting kompressibilitet

Blodtrykk, normalverdier

Ultrasound measurement Difference in frequency between transmitted and received signal = wall motion and blood velocity Advantage: Can be used with infants and hypotensive individuals and in high noise environments Disadvantage: Body movements change ultrasonic path between sensor and blood vessel

Bloodpressure, oscillometric Measure amplitude of oscillations created by expansion of the arterial wall Maximum at the mean pressure Disadv: No clear transition to identify the diastolic pressure => algorithms to estimate diastolic Adv: Precise measurement of mean pressure

Blodtrykksmåler

Non-contact tonometry Principler: When a pressureized vessel is partly collapsed by an external object, circumferential stresses in the vessel wall are removed and the internal and external pressures are equal. Air pulse deforms and flattens central cornea Collimator A Linear relationship between intra-ocular pressure and the time interval to applanation Perfect for detection of Glaucoma

Contact tonometry Internal pressure can be calculated by measuring the necessary force F that can flatten a certain area (A) of the sphere p=F/A Best correction if the flattened area has a diameter of 3.06 mm

Schiøtz tonometer 1905

Tonometer, idealized model Similar to ocular pressure, measure dynamic arterial blood pressure

Tonometer, multiple element modell

Arterial tonometry