Conventional pulse transit times as markers of blood pressure changes in humans

Abstract

Pulse transit time (PTT) represents a potential approach for cuff-less blood pressure (BP) monitoring. Conventionally, PTT is determined by (1) measuring (a) ECG and ear, finger, or toe PPG waveforms or (b) two of these PPG waveforms and (2) detecting the time delay between the waveforms. The conventional PTTs (cPTTs) were compared in terms of correlation with BP in humans. Thirty-two volunteers [50% female; 52 (17) (mean (SD)) years; 25% hypertensive] were studied. The four waveforms and manual cuff BP were recorded before and after slow breathing, mental arithmetic, cold pressor, and sublingual nitroglycerin. Six cPTTs were detected as the time delays between the ECG R-wave and ear PPG foot, R-wave and finger PPG foot [finger pulse arrival time (PAT)], R-wave and toe PPG foot (toe PAT), ear and finger PPG feet, ear and toe PPG feet, and finger and toe PPG feet. These time delays were also detected via PPG peaks. The best correlation by a substantial extent was between toe PAT via the PPG foot and systolic BP [− 0.63 ± 0.05 (mean ± SE); p < 0.001 via one-way ANOVA]. Toe PAT is superior to other cPTTs including the popular finger PAT as a marker of changes in BP and systolic BP in particular.

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“…Third, the long blood pressure acquisition time could not send hypertension notification to the caretaker on time. We hence used the concept of pulse transit time to acquire arterial blood pressure in real time [ 23 , 24 , 25 , 26 , 27 ].…”

“…The onset of the R-peak is the time when the heart pumps blood from the left ventricle to extremities, where the onset of plethysmogram peak determines the time arterial blood arriving at the fingertip. Many factors affect pulse transit time, including vessel length, blood density, inner radius of the vessel, vessel wall thickness and elastic modulus of vascular wall [ 24 ]. Most factors are constant parameters, except for blood pressure.…”

“…In our research, we opted to use the logarithm model, due to the minimum-error estimation [ 28 ]. In the model, the relation between blood pressure ( BP ) and pulse transit time (PTT) can be written as follows [ 24 ]: where L is the vessel length, PTT is the time that a pressure pulse spends in transmitting through that length, ρ is the blood density, r is the inner radius of the vessel, h is the vessel wall thickness, α is constant term related of elasticity and E 0 is the elastic modulus of vascular wall. Constant parameters in Equation (8) are unique for each individual and can be estimated by fitting to the known n dataset of blood pressure and PTT .…”

“…The constant-parameter vector A can then be estimated by using the minimized mean square error [ 24 ], as follows: A = ( X T X ) −1 ( X T Y ) …”

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“…En concreto, el dispositivo que se propone es capaz de medir el tiempo transcurrido desde que se produce la onda R del electrocardiograma hasta que la onda de pulso captada por el sensor de fotopletismografía (situado en el dedo índice de la mano izquierda) llega a su valor máximo. El parámetro PTT es usado como un indicador de cambio de la presión arterial [3]. Dicho parámetro es inversamente proporcional a la presión sanguínea, debido a que un aumento en la presión arterial provoca que la onda de pulso viaje antes al lugar de la periferia de medida (dedo índice) reduciéndose de esta manera el tiempo de transito de pulso.…”