Estimation of beat-to-beat changes in stroke volume from arterial pressure: A comparison of two pressure wave analysis techniques during head- up tilt testing in young, healthy men

Objective: The aim of this study was to compare beat-to-beat changes in stroke volume (SV) estimated by two different pressure wave analysis techniques during orthostatic stress testing: pulse contour analysis and Modelflow, ie, simulation of a three-element model of aortic input impedance. Methods: A reduction in SV was introduced in eight...

Continuous stroke volume monitoring by modelling flow from non-invasive measurement of arterial pressure in humans under orthostatic stress

The relationship between aortic flow and pressure is described by a three-element model of the arterial input impedance, including continuous correction for variations in the diameter and the compliance of the aorta (Modelflow). We computed the aortic flow from arterial pressure by this model, and evaluated whether, under orthostatic stress,...

Hyperoxia and local organ blood flow in the developing chick embryo

1. Hyperoxia can cause local vasoconstriction in adult animal organs as a protective mechanism against hyperoxia-induced toxicity. It is not known at what time during development this vasoconstrictor capacity is present. Therefore, we measured the cardiac output (GO) distribution in different organs during a period of acute hyperoxia (100% O2)...

The Valsalva manoeuvre as a cardiovascular reflex test in healthy children and teenagers

The objective of this study was to determine whether the Valsalva manoeuvre is applicable as a test for neurocardiovascular control in healthy children and teenagers. Sixty-eight 6- to 16-year-old children and teenagers performed two Valsalva manoeuvres in the sitting position. They were instructed to maintain airway pressure (strain) for 15 s...

Models of brachial to finger pulse wave distortion and pressure decrement

Objective: To model the pulse wave distortion and pressure decrement occurring between brachial and finger arteries. Distortion reversion and decrement correction were also our aims. Methods: Brachial artery pressure was recorded intra-arterially and finger pressure was recorded non-invasively by the Finapres technique in 53 adult human subjects...

Computation of aortic flow from pressure in humans using a nonlinear, three-element model

We computed aortic flow pulsations from arterial pressure by simulating a nonlinear, time-varying three-element model of aortic input impedance. The model elements represent aortic characteristic impedance, arterial compliance, and systemic vascular resistance. Parameter values for the first two elements were computed from a published, age...

Physiological responses of the human extremities to cold water immersion

Five subjects immersed their hands and feet twice during 1 hour sessions in a calorimeter bath, filled with water at 25 degrees C. Before immersion the hand (33.0 +/- 2.2 degrees C) was warmer than the foot (30.6 +/- 2.1 degrees C) and so was the blood flow: respectively 5.8 +/- 5.2 versus 0.7 +/- 0.3 ml.min-1.100 mo tissue-1 as determined by...

The relative influence of physical fitness, acclimatization state, anthropometric measures and gender on the individual reaction to heat stress

An experiment was set up to quantify the relative influence of fitness, acclimatization, gender and anthropometric measures on physiological responses to heat stress. For this purpose, 12 male and 12 female subjects were exposed to a neutral [ambient temperature (T(a)) 21°C, relative humidity (r.h. 50%)], a warm, humid (T(a) 34°C, r.h. 80%) and...

Changes in local cerebral blood flow, local EEG, and flow in the distal stump of the middle cerebral artery in cats with occlusion of the middle cerebral artery

The local EEG, the local cerebral blood flow (lCBF), and the flow in the distal stump of the occluded middle cerebral artery were simultaneously recorded in 28 acute experiments in cats. Nembutal anesthesia was used eleven times, and Halothane anaesthesia 17 times. The recordings were made via platinum electrodes: 12 in the ischaemic hemisphere,...

Features and limitations of the in vivo evaluation of tumour response by optical means

Chemicals/CAS: Oxygen, 7782-44-7

Haemodynamic changes in the cerebral circulation of the cat during occlusion of the middle cerebral artery

In a group of 21 cats, the middle cerebral artery pressure (MCAP) was recorded by means of a catheter introduced into the artery at its origin, just distal to the occlusion. The effects of hypertension, hypercapnia, and hypocapnia were studied. In a group of five cats, both middle cerebral arteries (MCA) were catheterized and the pressure was...